Biomaterials (v.30, #28)
Tissue assembly and organization: Developmental mechanisms in microfabricated tissues
by Nicolas C. Rivron; Jeroen Rouwkema; Roman Truckenmüller; Marcel Karperien; Jan De Boer; Clemens A. Van Blitterswijk (pp. 4851-4858).
In vitro-generated tissues hold significant promise in modern biology since they can potentially mimic physiological and pathological tissues. However, these are currently structurally and functionally of limited complexity and necessitate self-organization and recapitulation of tissue development mechanisms in vitro. Tools derived from nano- and microfabrications along with bottom-up strategies are emerging to allow the fabrication of primitive tissues structures that can remodel overtime. Subsequently, clues are accumulating to show that, beyond genetic material, both intrinsic tissue architectures and microenvironmental cues can lead to morphogenesis related mechanisms in vitro. The question arises, however, as how we may design and assemble structures prone to adequate tissue remodeling, predict and manipulate those developmental mechanisms in vitro? Systems integrating architectural, physical and molecular cues will allow more systematic investigation of basic principles of tissue morphogenesis, differentiation or maintenance and will feedback to reproduce the dynamic of tissue development in vitro and form more complex tissues.
Keywords: Self-organization; Morphogenesis; Microscale tissue engineering
Conformational recovery and preservation of protein nature from heat-induced denaturation by water-soluble phospholipid polymer conjugation
by Ji-Hun Seo; Ryosuke Matsuno; Yan Lee; Madoka Takai; Kazuhiko Ishihara (pp. 4859-4867).
The effect of water-soluble phospholipid polymer conjugated to a protein on conformational change during heat-quenched stress was investigated in this study. Well-defined pyridine disulfide end-functional poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) was synthesized by well controlled atom transfer radical polymerization method. Synthesized PMPC was the site specifically conjugated to a protein, and the effect on conformational change during heat-quenched stress was estimated by circular dichroism and fluorescence study. As a result, a single phospholipid polymer chain conjugated to a protein give a great effect on conformational preservation in both secondary and tertiary structures even after the heat-quenced process. Moreover, even the conformational recovery which gave the completely reversible conformational preservation was observed in circular dichroism study. The resulting protein activity was also confirmed, and no significant decline was induced by heat-quenched stress.
Keywords: Phospholipid polymer; Bioconjugation; Conformation change; Protein; Enzyme
Physical approaches for fabrication of organized nanostructure of resilin-mimetic elastic protein rec1-resilin
by Naba K. Dutta; Namita R. Choudhury; My Y. Truong; Misook Kim; Christopher M. Elvin; Anita J. Hill (pp. 4868-4876).
Protein adsorption on surfaces is a fundamental step in many applications. While various methods such as lithography, self assembly using nanoparticles, layer-by-layer attachment, etc. have been employed, here we report fabrication of controlled nanostructure of a new resilin-mimetic elastic protein rec1-resilin using physical approaches. We investigate the assembly, morphology and tunability of the nanostructure of adsorbed rec1-resilin architectures by atomic force microscopy (AFM) and scanning thermal microscopy (SThm) demonstrating that the protein conformation and structure during assembly can be controlled by tuning the physical conditions at the surface. Our findings show distinct morphology and height of monomolecular rec1-resilin film, dependent on substrate surface energy. We also show that these heights, a function of molecular orientation, can be maintained on swelling and drying.
Keywords: Biomimetic; Rec1-resilin; Adsorption; Hydrophobicity; Scanning thermal microscopy; Nanostructure
pH-triggered injectable hydrogels prepared from aqueous N-palmitoyl chitosan: In vitro characteristics and in vivo biocompatibility
by Ya-Ling Chiu; Sung-Ching Chen; Chun-Jen Su; Chun-Wen Hsiao; Yu-Ming Chen; Hsin-Lung Chen; Hsing-Wen Sung (pp. 4877-4888).
In-situ forming hydrogels triggered by environmental stimuli have emerged as a promising injectable strategy targeted for various biomedical applications. However, several drawbacks associated with temperature-stimulated hydrogels have been reported. Employing a hydrophobically-modified chitosan ( N-palmitoyl chitosan, NPCS), we developed a pH-triggered hydrogel system which showed a rapid nanostructure transformation within a narrow pH range (pH 6.5–7.0). NPCS in an aqueous environment was found to be a shear-thinning fluid and exhibited an instant recovery of its elastic properties after shear thinning, thereby making it an injectable material. Additionally, aqueous NPCS, an associating polyelectrolyte, can be rapidly transformed into hydrogel triggered simply by its environmental pH through a proper balance between charge repulsion and hydrophobic interaction. This in-situ hydrogel system was shown to be nontoxic. Subcutaneous injection of aqueous NPCS (pH 6.5) into a rat model resulted in rapid formation of a massive hydrogel at the location of injection. The implanted hydrogel was found to be degradable and was associated with an initial macrophage response which decreased with time as the degradation proceeded. These results suggested that the developed NPCS hydrogel may be used as an injectable drug/cell delivery system.
Keywords: pH-sensitive hydrogel; N; -Palmitoyl chitosan; Viscoelastic property; Biocompatibility
Simultaneous release of multiple molecules from poly(lactide- co-glycolide) nanoparticles assembled onto medical devices
by Catherine T. Lo; Paul R. Van Tassel; W. Mark Saltzman (pp. 4889-4897).
Cell and tissue responses to implanted biomaterials often limit their effectiveness and lifetime. This is particularly true for materials implanted into the brain. We present here a new approach for the modification of materials to enable release of multiple agents, which might be useful in modulating tissue responses, without changing the properties of the underlying material, in this case, a silicon probe. Poly(lactide- co-glycolide) nanoparticles (NPs) were assembled onto silicon probe surfaces by electrostatic interactions. Charged NPs were fabricated by altering the properties of the surfactant. NPs formed with poly(ethylene- alt-maleic anhydride) (PEMA) were strongly negatively charged; these NPs assembled onto probes best when suspended at nearly physiological conditions (surface density∼83,600±3000 particles/mm2). The percentage of surface area coverage by the NPs was estimated to be ∼13% and was maintained over two weeks during constant exposure to PBS. Multiple fluorescent NP populations were attached to the same probe to allow visualization of simultaneous delivery of multiple agents by fluorescence microscopy. Release from NP coatings was reproducible and controllable. The distinct release profiles of each agent from the coatings were preserved upon attachment to the surfaces. The unique feature of this new system is that NPs encapsulating various molecules (i.e. drugs, proteins, or DNA) can be fabricated separately, in advance, and simply mixed prior to attachment. The versatility of this delivery system, therefore, makes it suitable for many applications.
Keywords: Nanoparticle; Self assembly; Drug delivery; Biocompatibility
The modulation of platelet and endothelial cell adhesion to vascular graft materials by perlecan
by Megan S. Lord; Weiyun Yu; Bill Cheng; Anne Simmons; Laura Poole-Warren; John M. Whitelock (pp. 4898-4906).
Controlled neo-endothelialisation is critical to the patency of small diameter vascular grafts. Endothelialisation and platelet adhesion to purified endothelial cell-derived perlecan, the major heparan sulfate (HS) proteoglycan in basement membranes, were investigated using in vivo and in vitro assays. Expanded polytetrafluoroethylene (ePTFE) vascular grafts were coated with perlecan and tested in an ovine carotid interposition model for a period of 6 weeks and assessed using light and scanning microscopy. Enhanced endothelial cell growth and reduced platelet adhesion were observed on the perlecan coated grafts when compared to uncoated controls implanted in the same sheep ( n=5). Perlecan was also found to stimulate endothelial cell proliferation in vitro over a period of 6 days in the presence of plasma proteins and fibroblastic growth factor 2 (FGF-2), however in the absence of FGF-2 endothelial cell growth could not be maintained during this period. Perlecan was found to be anti-adhesive for platelets, however after removal of the HS chains attached to perlecan, platelet adhesion and aggregation were supported. These results suggest a role for HS chains of perlecan in improving graft patency by selectively promoting endothelial cell proliferation while modulating platelet adhesion.
Keywords: Perlecan; Vascular graft; Polytetrafluoroethylene; Platelet adhesion; Endothelialisation; Heparan sulfate
Functional PEG–peptide hydrogels to modulate local inflammation inducedby the pro-inflammatory cytokine TNFα
by Chien-Chi Lin; Andrew T. Metters; Kristi S. Anseth (pp. 4907-4914).
Hydrogels are an important class of biomaterials for cell encapsulation and delivery, providing a physical barrier or “immuno-isolation” between the host tissue and encapsulated cells. The semi-permeable gel protects the encapsulated cells from host immune cells and/or antibody recognition while allowing facile diffusion of nutrients. However, a previously un-addressed problem is that highly permissive hydrogels cannot exclude the infiltration of soluble immune-mediators, such as pro-inflammatory cytokines that are highly expressed in wounded environments in vivo. When encountered with pro-inflammatory cytokines, encapsulated cells fail to perform their desired functions. Here, we report the synthesis, characterization, and application of peptide-functionalized, cytokine-antagonizing poly(ethylene glycol) (PEG) hydrogels capable of sequestering the pro-inflammatory cytokine, tumor necrosis factor α (TNFα). Results demonstrate that the survival, function, and differentiation of encapsulated cells (e.g., rat adrenal pheochromocytoma cells – PC12s, mouse pancreatic islets, and human mesenchymal stem cells or hMSCs) are significantly hindered in un-modified PEG hydrogels under in vitro TNFα treatments. In contrast, cells encapsulated in TNFα-antagonizing hydrogels are un-affected by the infiltrated TNFα. This study demonstrates the importance of controlling the availability of pro-inflammatory cytokines in highly permissive hydrogels.
Keywords: Hydrogel; Inflammation; Cytokine; Apoptosis; Mesenchymal stem cells
Moderation of prekallkrein–factor XII interactions in surface activation of coagulation by protein-adsorption competition
by Kaushik Chatterjee; Jennifer L. Thornton; James W. Bauer; Erwin A. Vogler; Christopher A. Siedlecki (pp. 4915-4920).
Traditional biochemistry of contact activation of blood coagulation suggesting that anionic hydrophilic surfaces are specific activators of the cascade is inconsistent with known trends in protein adsorption. To investigate contact activation reactions, a chromogenic assay was used to measure prekallkrein (PK) hydrolysis to kallikrein (Kal) by activated factor XII (FXIIa) at test hydrophilic (clean glass) and hydrophobic (silanized glass) surfaces in the presence of bovine serum albumin (BSA). Hydrolysis of PK by FXIIa is detected after contact of the zymogen FXII with a test hydrophobic surface only if putatively-adsorbed FXIIa is competitively displaced by BSA. By contrast, FXIIa activity is detected spontaneously following FXII activation by a hydrophilic surface and requires no adsorption displacement. These results (i) show that an anionic hydrophilic surface is not a necessary cofactor for FXIIa-mediated hydrolysis of PK, (ii) indicate that PK hydrolysis does not need to occur by an activation complex assembled directly on an anionic, activating surface, (iii) confirms that contact activation of FXII (autoactivation) is not specific to anionic hydrophilic surfaces, and (iv) demonstrates that protein-adsorption competition is an essential feature that must be included in any comprehensive mechanism of surface-induced blood coagulation.
Keywords: Coagulation; Blood compatibility; Protein adsorption
Influences of protein films on antibacterial or bacteria-repellent surface coatings in a model system using silicon wafers
by Rainer Müller; Andreas Eidt; Karl-Anton Hiller; Verena Katzur; Michael Subat; Helmut Schweikl; Satoshi Imazato; Stefan Ruhl; Gottfried Schmalz (pp. 4921-4929).
Immobilization of defined chemical functionalities to biomaterial surfaces is employed to optimize them not only for tissue compatibility but also for prevention of bacterial infection. Grafting surfaces with chains of poly(ethylene glycol) (PEG) results in bacterial repellence whereas modification with cationic groups conveys them with bactericidal properties. Since biomaterials in situ will become exposed to a protein-rich environment, it is necessary to investigate the influence of prior protein adsorption on the antibacterial activity of this type of chemical surface modification. In the present study, we immobilized short-chain PEG and two pyridinium group-containing methacrylate monomers, 12-methacryloyloxydodecylpyridinium bromide (MDPB) and 6-methacryloyloxyhexylpyridinium chloride (MHPC), to silicon wafer model surfaces to investigate the influence of prior protein adsorption on the bactericidal activity of the surface coating towards subsequently attached bacteria. Adsorbed amounts of human serum albumin and salivary proteins were found to be two times higher on cationic compared to PEG-modified surfaces. An analogous tendency was found for attachment of Streptococcus gordonii and Streptococcus mutans to the same surfaces without prior protein exposure. However, most bacteria attached to cationic surfaces were found to be dead. Prior exposure of cationic surfaces to protein solutions drastically altered bacterial attachment dependent on the type of protein solution and bacterial species employed. Significantly, the original bactericidal activity of pyridinium-coated surfaces was found greatly reduced upon adsorption of a protein film. As a conclusion we propose that future approaches should combine the protein- and bacteria-repellent properties of PEG-coatings with the bactericidal function of charged cationic groups.
Keywords: Antibacterial activity; Cationic charges; MDPB; Silicon wafers; Saliva; Oral streptococci
Protein adsorption and cell adhesion on cationic, neutral, and anionic 2-methacryloyloxyethyl phosphorylcholine copolymer surfaces
by Yan Xu; Madoka Takai; Kazuhiko Ishihara (pp. 4930-4938).
Protein adsorption and cell adhesion on cationic, neutral, and anionic water-soluble 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymer surfaces were compared. These model MPC copolymers coated SiO2 surfaces exhibited comparable surface ζ-potentials of 26.1mV, near 0mV, and −24.2mV, respectively. X-ray photoelectron spectroscopy analyses indicated the similarities and the differences in the surface composition between the sample surfaces. Atomic force microscopy analyses revealed that the type of the charged moiety did not affect the surface roughness. Static contact angle measurements and dynamic contact angle analyses not only indicated that the surfaces were very hydrophilic in general, but also provided information on the surface mobility and the dominant role of MPC at the surface in aqueous conditions. Comparing with the SiO2 substrates on which protein seriously adsorbed and cell heavily adhered, three MPC copolymers coated surfaces, despite their different charge properties, exhibited significantly low adsorbed amounts of different proteins having various electrical natures and totally no cell adhesion. This suggested that the incorporation of charged moieties in the MPC copolymers did not significantly inspire both the protein adsorption and cell adhesion. The MPC moieties were predominant at the surface when in contact with aqueous conditions and thereby dominated the bio-adsorptions, while the possible effect from electrostatic interactions would be too small and too limited to influence the overall situation. Therefore, these MPC copolymer surfaces can satisfy those biological applications requiring not only electrical but also non-biofouling properties.
Keywords: 2-Methacryloyloxyethyl phosphorylcholine polymer; Coating; Surface charge; Protein adsorption; Cell adhesion
pH-dependent modulation of fibroblast adhesion on multilayers composed of poly(ethylene imine) and heparin
by Marcus S. Niepel; Dieter Peschel; Xavier Sisquella; Josep A. Planell; Thomas Groth (pp. 4939-4947).
Adhesion of tissue cells is a prerequisite for their growth and differentiation but prevents also apoptosis. Here the layer-by-layer technique (LbL) was used to design multilayer structures of poly(ethylene imine) (PEI) and heparin (HEP) on glass as model biomaterial to control the adhesion of primary human dermal fibroblasts. Distinct surface features like wettability, charge and lateral structures were controlled by changing the pH value of the HEP solution during multilayer assembly to acidic, neutral or alkaline values. While plain terminal layers were rather cytophobic, the pre-adsorption of serum or fibronectin (FN) caused a distinct change in cell morphology in dependence on the pH setup. The effect of serum was more prominent on PEI layers probably due to their positive surface charge, whereas the effect of FN was more pronounced on HEP terminated multilayers possibly due to its ability to bind FN specifically. Those layers which hampered cell adhesion also inhibited growth of human fibroblasts under serum conditions. Conversely, on layers where cell adhesion was increased also an elevated growth and, thus, metabolic activity was observed.
Keywords: Surface modification; Layer-by-layer; Poly(ethylene imine); Heparin; Serum; Fibronectin
The effect of quantum dots on synaptic transmission and plasticity in the hippocampal dentate gyrus area of anesthetized rats
by Mingliang Tang; Zhifeng Li; Liang Chen; Tairan Xing; Yong Hu; Bo Yang; Di-Yun Ruan; Fei Sun; Ming Wang (pp. 4948-4955).
Recently, quantum dots (QDs) have attracted widespread interest in biology and medicine. They are rapidly being used as new tools for both diagnostic and therapeutic purposes. Critical issues for further applications of QDs include the assessment of biocompatibility and biosafety of QDs. Most of previous researches concerning QD cytotoxicity focused on in vitro studies. In the present study, the impairments of acute exposure to well-modified and unmodified QDs (streptavidin-CdSe/ZnS and CdSe QDs, respectively) on synaptic transmission and plasticity were examined in adult rat hippocampal dentate gyrus (DG) area in vivo. The input/output (I/O) functions, paired-pulse ratio (PPR), field excitatory postsynaptic potential (fEPSP) and population spike (PS) amplitude were measured. The results showed that PPR and long-term potentiation (LTP) were all significantly decreased in these two types of QD-exposed rats compared to those in control rats. While the I/O functions and the amplitudes of fEPSP slope and PS amplitude of the baseline were significantly increased under QD exposure. These findings suggest that exposure to QDs, no matter whether they are well modified or not, could impair synaptic transmission and plasticity in the rat DG area in vivo and reveal the potential risks of QD applications in biology and medicine, especially in the toxin-susceptible central nervous system (CNS).
Keywords: Biocompatibility; Nanoparticles; Long-term potentiation; Quantum dots
The use of platelet-rich plasma in bone reconstruction therapy
by Giuseppe Intini (pp. 4956-4966).
The use of platelet-rich plasma (PRP) in bone reconstruction therapy was introduced in the late 1990s. Since then, many scientists and clinicians have employed it in orthopaedic and oral surgeries. Unfortunately, studies that analyze the use of PRP are somewhat controversial as some conclude that the use of PRP may favor bone regeneration and others conclude that the use of PRP is irrelevant. By listing and analyzing the biological effect that each factor released by the activated platelets can have in bone regeneration, the present review answers the question of why PRP may be useful in bone reconstruction therapy. Subsequently, by examining the studies that have both successfully and unsuccessfully utilized PRP, it suggests how PRP might be used in order to achieve successful results in orthopaedic and dental bone reconstruction surgeries.
Keywords: Platelet-rich plasma; Dental surgery; Bone regeneration; Bone reconstruction therapy; Growth factors; Orthopaedic surgery
Anterior cruciate ligament regeneration using mesenchymal stem cells and silk scaffold in large animal model
by Hongbin Fan; Haifeng Liu; Siew L. Toh; James C.H. Goh (pp. 4967-4977).
Although in vivo studies in small animal model show the ligament regeneration by implanting mesenchymal stem cells (MSCs) and silk scaffold, large animal studies are still needed to evaluate the silk scaffold before starting a clinical trial. The aim of this study is to regenerate anterior cruciate ligament (ACL) in pig model. The micro-porous silk mesh was fabricated by incorporating silk sponges into knitted silk mesh with lyophilization. Then the scaffold was prepared by rolling the micro-porous silk mesh around a braided silk cord to produce a tightly wound shaft. In vitro study indicated that MSCs proliferated profusely on scaffold and differentiated into fibroblast-like cells by expressing collagen I, collagen III and tenascin-C genes in mRNA level. Then the MSCs-seeded scaffold was implanted in pig model to regenerate ACL. At 24 weeks postoperatively, the MSCs in regenerated ligament exhibited fibroblast morphology. The key ligament-specific extracellular matrix components were produced prominently and indirect ligament–bone insertion with three zones (bone, Sharpey's fibers and ligament) was observed. Although there was remarkable scaffold degradation, the maximum tensile load of regenerated ligament could be maintained after 24 weeks of implantation. In conclusion, the results imply that silk-based material has great potentials for clinical applications.
Keywords: Silk; Mesenchymal stem cell; Tissue engineering; Ligament
The effect of neurotrophin-3/chitosan carriers on the proliferation and differentiation of neural stem cells
by Xiaoguang Li; Zhaoyang Yang; Aifeng Zhang (pp. 4978-4985).
In this study, the behavior of neural stem cells from the newborn rat spinal cord was compared at neurosphere level after the addition of neurotrophin-3 (NT-3) once or daily, blank chitosan carriers, or NT-3-chitosan carriers respectively. We found that NT-3 enhanced the viability and differentiation of neural stem cells, but as NT-3 has an extremely short half-life at 37°C, in order to maintain the NT-3-mediated proliferation and differentiation effects on neural stem cells, NT-3 needed to be added to the medium every 24h. However, NT-3-chitosan carriers dramatically increase the differentiation percentage of neural stem cells into neurons, which includes GABAergic and as cholinergic neurons. Although blank chitosan carriers also showed good biocompatibility to the neural stem cells, they induced the differentiation of these cells into neurons at a much lower percentage than the daily addition of NT-3 or the NT-3-chitosan carriers. Our results suggest that NT-3-chitosan carriers may not only maintain the viability of neural stem cells and increase their differentiation percentage into neurons, but also reduce the amount of NT-3 required for the survival and differentiation of these cells. These results may provide an experimental basis for the maximum replacement of dead neurons by neural stem cell transplant after spinal cord injury (SCI).
Keywords: Chitosan; NT-3; Neural stem cells; Neuron; Cell differentiation
Dual luciferase labelling for non-invasive bioluminescence imaging of mesenchymal stromal cell chondrogenic differentiation in demineralized bone matrix scaffolds
by Marta Vilalta; Christian Jorgensen; Irene R. Dégano; Yuti Chernajovsky; David Gould; Danièle Noël; José A. Andrades; José Becerra; Nuria Rubio; Jerónimo Blanco (pp. 4986-4995).
Non-invasive bioluminescence imaging (BLI) to monitor changes in gene expression of cells implanted in live animals should facilitate the development of biomaterial scaffolds for tissue regeneration. We show that, in vitro, induction of chondrogenic differentiation in mouse bone marrow stromal cell line (CL1) and human adipose tissue derived mesenchymal stromal cells (hAMSCs), permanently transduced with a procollagen II (COL2A1) promoter driving a firefly luciferase gene reporter (PLuc) (COL2A1p·PLuc), induces PLuc expression in correlation with increases in COL2A1 and Sox9 mRNA expression and acquisition of chondrocytic phenotype. To be able to simultaneously monitor in vivo cell differentiation and proliferation, COL2A1p·PLuc labelled cells were also genetically labelled with a renilla luciferase (RLuc) gene driven by a constitutively active cytomegalovirus promoter, and then seeded in demineralized bone matrix (DBM) subcutaneously implanted in SCID mice. Non-invasive BLI monitoring of the implanted mice showed that the PLuc/RLuc ratio reports on gene expression changes indicative of cell differentiation. Large (CL1) and moderated (hAMSCs) changes in the PLuc/RLuc ratio over a 6 week period, revealed different patterns of in vivo chondrogenic differentiation for the CL1 cell line and primary MSCs, in agreement with in vitro published data and our results from histological analysis of DBM sections. This double bioluminescence labelling strategy together with BLI imaging to analyze behaviour of cells implanted in live animals should facilitate the development of progenitor cell/scaffold combinations for tissue repair.
Keywords: Bioluminescence imaging (BLI); Collagen type II (COL2A1); Demineralized bone matrix (DBM); Human adipose tissue derived mesenchymal stromal cells (hAMSCs); Murine cell line (CL1)
Mesenchymal stem cell differentiation to neuronal cells on electrospun nanofibrous substrates for nerve tissue engineering
by Molamma P. Prabhakaran; Jayarama Reddy Venugopal; Seeram Ramakrishna (pp. 4996-5003).
Bone marrow Mesenchymal stem cells capable of differentiating into neuronal cells on engineered nanofibrous scaffolds have great potential for bionanomaterial–cell transplantation therapy of neurodegenerative diseases and injuries of the nervous system. MSCs have been the highlight of many tissue engineering studies mainly because of their multipotential properties. We investigated the potential of human bone marrow derived Mesenchymal stem cells (MSCs) for neuronal differentiation in vitro on poly(l-lactic acid)-co-poly-(3-caprolactone)/Collagen (PLCL/Coll) nanofibrous scaffolds. PLCL and PLCL/Coll nanofibrous scaffolds were fabricated by electrospinning process and their chemical and mechanical characterizations were carried out using SEM, contact angle, FTIR, and tensile instrument. The differentiation of MSCs was carried out using neuronal inducing factors including β-mercaptoethanol, epidermal growth factor, nerve growth factor and brain derived growth factor in DMEM/F12 media. The proliferations of MSCs evaluated by MTS assay showed that the cells grown on PLCL/Coll nanofibrous scaffolds were comparatively higher (80%) than those on PLCL. Scanning electron microscopy results showed that MSCs differentiated on PLCL/Coll nanofibrous scaffolds showed neuronal morphology, with multipolar elongations and expressed neurofilament and nestin protein by immuno-fluorescent microscopy. Our studies on the differentiation of MSCs to neuronal cells on nanofibrous scaffolds suggest their potential application towards nerve regeneration.
Keywords: Mesenchymal stem cells; Neuronal cells; Nerve tissue engineering; Electrospun nanofibers; Inducing factors; Differentiation
Chitosan/polyglycolic acid nerve grafts for axon regeneration from prolonged axotomized neurons to chronically denervated segments
by Haishan Jiao; Jian Yao; Yumin Yang; Xue Chen; Weiwei Lin; Yi Li; Xiaosong Gu; Xiaodong Wang (pp. 5004-5018).
Peripheral nerve regeneration for long-term delayed injuries is usually unsatisfied. Here we attempted to use a chitosan/polyglycolic acid (PGA) artificial nerve graft to bridge a long-term delayed 10-mm defect in SD rats based on the previous studies on the graft used for immediate repair of 30-mm-long dog sciatic nerve defects and for clinical treatment of a 35-mm-long median nerve defect at elbow of a human patient. In this study, for experimental groups, the rat sciatic nerve had been transected leaving a 10-mm defect, which was maintained for 3 or 6 months before implantation with the chitosan/PGA artificial nerve graft. The animals non-grafted or grafted with autograft served as negative or positive control group. In experiment groups, nerve regeneration with functional recovery was achieved as measured by electrophysiological and histological techniques, although differences in the quantity and the quality of the regenerated nerve were observed between the 3- and 6-month delayed subgroups. The results showed that: (1) a few denervated Schwann cells survived and sustained their ability to myelinate axons at least 6 months, and (2) the atrophic denervated muscle could be reinnervated by regenerated axons through new muscle-nerve connections. These observations provide the possibility of guiding regenerated axons from survived axotomized neurons to distal nerve stump by the chitosan/PGA artificial nerve graft.
Keywords: Nerve tissue engineering; Nerve regeneration; Long-term axotomy; Chronic denervation; Artificial nerve graft; Reinnervation
Osteogenic and adipogenic differentiation of rat bone marrow cells on non-mulberry and mulberry silk gland fibroin 3D scaffolds
by Biman B. Mandal; Subhas C. Kundu (pp. 5019-5030).
This study investigates the potential of 3D silk scaffolds fabricated using tropical tasar non-mulberry, Antheraea mylitta and mulberry, Bombyx mori silk gland fibroin proteins as substrate for osteogenic and adipogenic differentiation of rat bone marrow cells (BMCs). The scaffolds are mechanically robust and show homogenous pore distribution with high porosity and interconnected pore walls. Low immunogenicity of fabricated silk scaffolds as estimated through TNF α release indicates its potential as future biopolymeric graft material. Rat bone marrow cells cultured on scaffolds for 28 days under static conditions in osteogenic and adipogenic media respectively led to induction of differentiation. Proliferation and spreading of fibroblasts and bone marrow cells on silk scaffolds were observed to be dependent on scaffold porosity as revealed through confocal microscopic observations. Histological analysis shows osteogenic differentiation within silk scaffolds resulting in extensive mineralization in the form of deposited nodules as observed through intense Alizarin Red S staining. Similarly, adipogenesis was marked by the presence of lipid droplets within scaffolds on staining with Oil Red O. Real-time PCR studies reveal higher transcript levels for osteopontin ( Spp1), osteocalcin ( Bglap2) and osteonectin ( Sparc) genes under osteogenic conditions. Similarly, upregulated adipogenic gene expression was observed within A. mylitta and B. mori scaffolds under adipogenic conditions for Peroxisome proliferator activated receptor gamma ( PPARγ2), lipoprotein lipase ( LPL) and adipocyte binding protein ( aP2) genes. The results suggest suitability of silk fibroin protein 3D scaffolds as natural biopolymer for potential bone and adipose tissue engineering applications.
Keywords: Silk fibroin; Osteogenesis; Adipogenesis; Biomaterial; Tissue engineering
The enhancement of dermal papilla cell aggregation by extracellular matrix proteins through effects on cell–substratum adhesivity and cell motility
by Tai-Horng Young; Hui-Ru Tu; Chih-Chieh Chan; Yi-Ching Huang; Meng-Hua Yen; Nai-Chen Cheng; Hsien-Ching Chiu; Sung-Jan Lin (pp. 5031-5040).
Generally, cells tend to aggregate on a substratum with lower cell adhesivity. However, it also leads to compromised cell growth and higher cell loss after seeding. This study is aimed at tackling this dilemma by extracellular matrix (ECM) protein coating of a lower adhesive substratum poly(ethylene-co-vinyl alcohol) (EVAL) that has been shown to facilitate hair follicle dermal papilla (DP) spheroid formation. We found that coating with either fibronectin (Fn), collagen I, or collagen IV yields higher adhesivity and cell growth than that with laminin. However, cells can only aggregate on uncoated or Fn-coated EVAL. Quantitatively, Fn coating increases the number of spheroids by 67%. Analysis of cell migration reveals that collagen I, collagen IV and laminin coatings reduce cell motility, while Fn coating keeps cells highly motile. Inhibition of cell migration hinders spheroid formation. In addition, disruption of Fn function does not significantly compromise intercellular adhesion. Hence, Fn enhances cell aggregation by enhancing cell attachment, cell growth and cell motility. Our study demonstrates that intercellular organization as spheroids or flat monolayers is switchable by specific ECM protein coating and preserving cell motility is vital to cell aggregation. In addition to generation of spheroidal DP microtissues for hair follicle regeneration and large-scale production of aggregates of other cells, this strategy can help to regulate the tissue–substrate adhesivity and tissue spreadibility on the surface of implantable materials.
Keywords: Hair follicle regeneration; Bioreactor; Spheroid; Extracellular matrix protein; Tissue spreadibility
In vitro and in vivo evaluation of akermanite bioceramics for bone regeneration
by Yan Huang; Xiaogang Jin; Xiaoling Zhang; Hongli Sun; Jinwen Tu; Tingting Tang; Jiang Chang; Kerong Dai (pp. 5041-5048).
This study investigated the effects of a calcium magnesium silicate bioceramic (akermanite) for bone regeneration in vitro and in vivo, with β-tricalcium phosphate (β-TCP) as a control. In vitro, the human bone marrow-derived mesenchymal stromal cells (hBMSCs) were cultured in an osteogenic medium supplemented with a certain concentration of two bioceramics' extracts for 20 days. An MTT assay showed that akermanite extract promoted proliferation of hBMSC significantly more than did β-TCP extract. The results of alkaline phosphatase (ALP) activity test and the expression of osteogenic marker genes such as ALP, osteopontin (OPN), osteocalcin (OCN) and bone sialoprotein (BSP) demonstrated that the osteogenic differentiation of hBMSC was enhanced more by akermanite extract than by β-TCP extract. In vivo, a histomorphology analysis and histomorphometry of the two porous bioceramics implants in rabbit femur defect models indicated that both in early- and late-stage implantations, akermanite promoted more osteogenesis and biodegradation than did β-TCP; and in late-stage implantations, the rate of new bone formation was faster in akermanite than in β-TCP. These results suggest that akermanite might be a potential and attractive bioceramic for tissue engineering.
Keywords: Akermanite; β-Tricalcium phosphate; Extract; Mesenchymal stem cell; Rabbit femur defect models
A star-PEG–heparin hydrogel platform to aid cell replacement therapies for neurodegenerative diseases
by Uwe Freudenberg; Andreas Hermann; Petra B. Welzel; Katja Stirl; Sigrid C. Schwarz; Milauscha Grimmer; Andrea Zieris; Woranan Panyanuwat; Stefan Zschoche; Dorit Meinhold; Alexander Storch; Carsten Werner (pp. 5049-5060).
Biofunctional matrices for in vivo tissue engineering strategies must be modifiable in both biomolecular composition and mechanical characteristics. To address this challenge, we present a modular system of biohybrid hydrogels based on covalently cross-linked heparin and star-shaped poly(ethylene glycols) (star-PEG) in which network characteristics can be gradually varied while heparin contents remain constant. Mesh size, swelling and elastic moduli were shown to correlate well with the degree of gel component cross-linking. Additionally, secondary conversion of heparin within the biohybrid gels allowed the covalent attachment of cell adhesion mediating RGD peptides and the non-covalent binding of soluble mitogens such as FGF-2. We applied the biohybrid gels to demonstrate the impact of mechanical and biomolecular cues on primary nerve cells and neural stem cells. The results demonstrate the cell type-specific interplay of synergistic signaling events and the potential of biohybrid materials to selectively stimulate cell fate decisions. These findings suggest important future uses for this material in cell replacement based-therapies for neurodegenerative diseases.
Keywords: Biohybrid material; Cell replacement/implantation; Neural stem cells
Chondrogenic and osteogenic differentiations of human bone marrow-derived mesenchymal stem cells on a nanofibrous scaffold with designed pore network
by Jiang Hu; Kai Feng; Xiaohua Liu; Peter X. Ma (pp. 5061-5067).
The utilization of 3D scaffolds and stem cells is a promising approach to solve the problem of bone and cartilage tissue shortage and to construct osteochondral (cartilage/bone composite) tissues. In this study, 3D highly porous nanofibrous (NF) poly(l-lactic acid) (PLLA) scaffolds fabricated using a phase separation technique were seeded with multi-potent human bone marrow-derived mesenchymal stem cells (hMSCs) and the constructs were induced along osteogenic and chondrogenic development routes in vitro. Histological analysis and calcium content quantification showed that NF scaffolds supported in vitro bone differentiation. SEM observation showed an altered shape for cells cultured on an NF matrix compared with those on smooth films. Consistent with the morphological change, the gene expression of early chondrogenic commitment marker Sox-9 was enhanced on the NF matrix. NF scaffolds were then used to support long-term in vitro 3D cartilaginous development. It was found that in the presence of TGF-β1, cartilage tissue developed on PLLA NF scaffolds, with the cartilage-specific gene expressed, glycosaminoglycan and type II collagen accumulated, and typical cartilage morphology formed. These findings suggest that NF scaffolds can support both bone and cartilage development and are excellent candidate scaffolds for osteochondral defect repair.
Keywords: Mesenchymal stem cell; Cartilage; Bone; Nanofiber; Poly(; l; -lactic acid) scaffold; Tissue engineering
Silk fibroin/hyaluronan scaffolds for human mesenchymal stem cell culture in tissue engineering
by Marcos Garcia-Fuentes; Anne J. Meinel; Monika Hilbe; Lorenz Meinel; Hans P. Merkle (pp. 5068-5076).
The design of new bioactive scaffolds mimicking the physiologic environment present during tissue formation is an important frontier in biomaterials research. Herein, we evaluated scaffolds prepared from blends of two biopolymers: silk fibroin and hyaluronan. Our rationale was that such blends would allow the combination of silk fibroin's superior mechanical properties with the biological characteristics of hyaluronan. We prepared scaffolds with porous microstructures by freeze-drying aqueous solutions of silk fibroin and hyaluronan and subsequent incubation in methanol to induce water insolubility of silk fibroin. Hyaluronan acted as an efficient porogenic excipient for the silk fibroin scaffolding process, allowing the formation of microporous structures within the scaffolds under mild processing conditions. Mesenchymal stem cells were seeded on silk fibroin/hyaluronan scaffolds and cultured for three weeks. Histology of the constructs after cell culture showed enhanced cellular ingrowth into silk fibroin/hyaluronan scaffolds as compared to plain silk fibroin scaffolds. In the presence of tissue-inductive stimuli, in vitro stem cell culture on silk fibroin/hyaluronan scaffolds resulted in more efficient tissue formation when measured by glycosaminoglycan and type-I and type-III collagen gene expression, as compared to plain silk fibroin scaffolds. In conclusion, our data encourages further exploration of silk fibroin/hyaluronan scaffolds as biomimetic platform for mesenchymal stem cells in tissue engineering.
Keywords: Silk fibroin; Hyaluronan; Scaffolds; Mesenchymal stem cells; Tissue engineering
Hemoglobin conjugated micelles based on triblock biodegradable polymers as artificial oxygen carriers
by Quan Shi; Yubin Huang; Xuesi Chen; Meng Wu; Jing Sun; Xiabin Jing (pp. 5077-5085).
An artificial oxygen carrier is constructed by conjugating hemoglobin molecules to biodegradable micelles. Firstly a series of triblock copolymers (PEG–PMPC–PLA) in which the middle block contains pendant propargyl groups were synthesized and characterized. After the amphiphilic copolymer was self-assembled into core-shell micelles in aqueous solution, azidized hemoglobin molecules protected by carbon monoxide (CO) were conjugated to the micelles via click reaction between the propargyl and azido groups. The conjugation causes an increase of the micelle's mean diameter. Maximum conjugation ratio is 250wt% in the hemoglobin-conjugated micelles (HCMs). Oxygen-binding ability of the HCMs was demonstrated by converting the CO-binding state of the HCMs into O2-binding state.
Keywords: Hemoglobin; Artificial oxygen carrier; Red blood cells; Micelles
Biological performance of a polycaprolactone-based scaffold used as fusion cage device in a large animal model of spinal reconstructive surgery
by Sunny A. Abbah; Christopher X.L. Lam; Dietmar W. Hutmacher; James C.H. Goh; Hee-Kit Wong (pp. 5086-5093).
A bioactive and bioresorbable scaffold fabricated from medical grade poly (epsilon-caprolactone) and incorporating 20% beta-tricalcium phosphate (mPCL–TCP) was recently developed for bone regeneration at load bearing sites. In the present study, we aimed to evaluate bone ingrowth into mPCL–TCP in a large animal model of lumbar interbody fusion. Six pigs underwent a 2-level (L3/4; L5/6) anterior lumbar interbody fusion (ALIF) implanted with mPCL–TCP + 0.6 mg rhBMP-2 as treatment group while four other pigs implanted with autogenous bone graft served as control. Computed tomographic scanning and histology revealed complete defect bridging in all (100%) specimen from the treatment group as early as 3 months. Histological evidence of continuing bone remodeling and maturation was observed at 6 months. In the control group, only partial bridging was observed at 3 months and only 50% of segments in this group showed complete defect bridging at 6 months. Furthermore, 25% of segments in the control group showed evidence of graft fracture, resorption and pseudoarthrosis. In contrast, no evidence of graft fractures, pseudoarthrosis or foreign body reaction was observed in the treatment group. These results reveal that mPCL–TCP scaffolds could act as bone graft substitutes by providing a suitable environment for bone regeneration in a dynamic load bearing setting such as in a porcine model of interbody spine fusion.
Keywords: Bone graft substitute; Bone regeneration; Bioresorbable fusion cage devices; Spinal reconstructive surgery; Porcine model
The use of nanoscale topography to modulate the dynamics of adhesion formation in primary osteoblasts and ERK/MAPK signalling in STRO-1+ enriched skeletal stem cells
by Manus J.P. Biggs; R. Geoff Richards; Nikolaj Gadegaard; Chris D.W. Wilkinson; Richard O.C. Oreffo; Matthew J. Dalby (pp. 5094-5103).
The physiochemical characteristics of a material with in vivo applications are critical for the clinical success of the implant and regulate both cellular adhesion and differentiated cellular function. Topographical modification of an orthopaedic implant may be a viable method to guide tissue integration and has been shown in vitro to dramatically influence osteogenesis, inhibit bone resorption and regulate integrin mediated cell adhesion. Integrins function as force dependant mechanotransducers, acting via the actin cytoskeleton to translate tension applied at the tissue level to changes in cellular function via intricate signalling pathways. In particular the ERK/MAPK signalling cascade is a known regulator of osteospecific differentiation and function. Here we investigate the effects of nanoscale pits and grooves on focal adhesion formation in human osteoblasts (HOBs) and the ERK/MAPK signalling pathway in mesenchymal populations. Nanopit arrays disrupted adhesion formation and cellular spreading in HOBs and impaired osteospecific differentiation in skeletal stem cells. HOBs cultured on 10μm wide groove/ridge arrays formed significantly less focal adhesions than cells cultured on planar substrates and displayed negligible differentiation along the osteospecific lineage, undergoing up-regulations in the expression of adipospecific genes. Conversely, osteospecific function was correlated to increased integrin mediated adhesion formation and cellular spreading as noted in HOBS cultured on 100μm wide groove arrays. Here osteospecific differentiation and function was linked to focal adhesion growth and FAK mediated activation of the ERK/MAPK signalling pathway in mesenchymal populations.
Keywords: Osteoblasts; Mesenchymal stem cells; Focal adhesions; Nanotopography; ERK/MAPK
Tracking transplanted cells in live animal using upconversion fluorescent nanoparticles
by Niagara Muhammad Idris; Zhengquan Li; Lei Ye; Eugene Kwang Wei Sim; Ratha Mahendran; Paul Chi-Lui Ho; Yong Zhang (pp. 5104-5113).
With the emergence of cell transplant as an attractive treatment modality for various diseases, there is a parallel need to track the fate of these cells to assess their therapeutic effectiveness. Here, we report the use of upconversion fluorescent nanoparticles, silica/NaYF4:Yb,Er, to dynamically track live myoblast cells in vitro and in a living mouse model of cryoinjured hind limb. Nanoparticles loaded into cells were confirmed for its intracellular uptake by confocal imaging, spectrophotometry and inductively coupled plasma analysis. Loaded nanoparticles demonstrated absolute resistance to photobleaching and were applied for dynamic imaging to real time track in vitro cell migratory activity for a continuous 5h duration using a time-lapse confocal microscope. Direct observation on the direction, speed and cell–cell interaction of migrating cells was clearly visualized. In vivo confocal imaging of nanoparticle-loaded cells intravenously injected into a mouse tail vein showed them flowing in the ear blood vessels. Nanoparticle-loaded cells were also unambiguously identified with superior contrast against a negligible background at least 1300μm deep in a fully vascularized living tissue upon intramuscular injection. Spatiotemporal migratory activity of the transplanted cells within the three-dimensional living tissue was captured for at least 7 days post-delivery. Direct in vivo visualization of cell dynamics in the native tissue was unobtrusively followed over a 4h time course and revealed subtle migratory activity of the transplanted cells. With these unique optical properties, we present silica/NaYF4:Yb,Er nanoparticles as a new fluorescent live cell tracker probe for superior in vitro and in vivo dynamic imaging.
Keywords: Confocal microscopy; Nanoparticle; Stem cell; Transplantation
Folic acid–Pluronic F127 magnetic nanoparticle clusters for combined targeting, diagnosis, and therapy applications
by Jia-Jyun Lin; Jenn-Shing Chen; Shih-Jer Huang; Jyun-Han Ko; Yu-Ming Wang; Ting-Lung Chen; Li-Fang Wang (pp. 5114-5124).
Superparamagnetic iron oxides possess specific magnetic properties in the presence of an external magnetic field, which make them an attractive platform as contrast agents for magnetic resonance imaging (MRI) and as carriers for drug delivery. In this study, we investigate the drug delivery and the MRI properties of folate-mediated water-soluble iron oxide incorporated into micelles. Pluronic® F127 (PF127), which can be self-assembled into micelles upon increasing concentration or raising temperatures, is used to decorate water-soluble polyacrylic acid-bound iron oxides (PAAIO) via a chemical reaction. Next, the hydrophobic dye Nile red is encapsulated into the hydrophobic poly(propylene oxide) compartment of PF127 as a model drug and as a fluorescent agent. Upon encapsulation, PAAIO retains its superparamagnetic characteristics, and thus can be used for MR imaging. A tumor-specific targeting ligand, folic acid (FA), is conjugated onto PF127–PAAIO to produce a multifunctional superparamagnetic iron oxide, FA–PF127–PAAIO. FA–PF127–PAAIO can be simultaneously applied as a diagnostic and therapeutic agent that specifically targets cancer cells that overexpress folate receptors in their cell membranes. PF127–PAAIO is used as a reference group. Based on FTIR and UV–vis absorbance spectra, the successful synthesis of PF127–PAAIO and FA–PF127–PAAIO is realized. The magnetic nanoparticle clusters of PF127–PAAIO and FA–PF127–PAAIO are visualized by transmission electron microscope (TEM). FA–PF127–PAAIO, together with a targeting ligand, displays a higher intracellular uptake into KB cells. This result is confirmed by laser confocal scanning microscopy (CLSM), flow cytometry, and atomic absorption spectroscopy (AAS) studies. The hysteresis curves, generated by using a superconducting quantum interference device (SQUID) magnetometer analysis, demonstrate that the magnetic nanoparticles are superparamagnetic with insignificant hysteresis. The MTT assay explains the negligible cell cytotoxicity of PF127–PAAIO and FA–PF127–PAAIO. In KB cells, the in vitro MRI study indicates the better T2-weighted images in FA–PF127–PAAIO than in PF127–PAAIO.
Keywords: Fe; 3; O; 4; Pluronic F127; Folic acid; Magnetic nanoparticles; Diagnosis; Therapy
Chemical conjugation of urokinase to magnetic nanoparticles for targeted thrombolysis
by Feng Bi; Jing Zhang; Yijing Su; Yan-Chun Tang; Jian-Ning Liu (pp. 5125-5130).
Thrombolytic therapy is an important treatment for thrombosis, a life-threatening condition in cardiovascular diseases. However, the traditional thrombolytic therapies have often been associated with the risk of severe bleeding. By conjugating urokinase with magnetic nanoparticles (MNPs), we have presented a strategy to control thrombolysis within a specific site. The covalent bioconjugate of urokinase and dextran-coated MNPs was synthesized and isolated. Thrombolysis by the conjugate was studied under a magnetic field in a rat arteriovenous shunt thrombosis model. The magnetic field was generated by two AlNiCo permanent magnets around the site of thrombus. The magnetic field enhanced the thrombolytic efficacy of the conjugate by 5-fold over urokinase with no reduction in plasma fibrinogen and little prolonged bleeding time. It suggested that thrombolysis had been specifically directed to the desired site by the magnetic carrier under the magnetic field. Additionally, the conjugate had a longer half-life than urokinase in circulation.
Keywords: Magnetic nanoparticles; Urokinase; Thrombosis; Thrombolysis; Magnetic drug targeting
The simultaneous effect of polymer chemistry and device geometry on the in vitro activation of murine dendritic cells
by Latrisha K. Petersen; Li Xue; Michael J. Wannemuehler; Krishna Rajan; Balaji Narasimhan (pp. 5131-5142).
Polyanhydrides are a promising class of biomaterials for use as vaccine adjuvants and as multi-component implants. Their properties can be tailored for such applications as controlled drug release, drug stability, and/or immune regulation (adjuvant effect). Understanding the induction of immunomodulatory mechanisms of this polymer system is important for the design and development of efficacious vaccines and tissue compatible multi-component implantable devices using this polymer system. This study describes the development of a rapid multiplexed method for the investigation of the adjuvanticity of polyanhydride nanospheres and films using murine dendritic cells (DCs). To assess the immune response, cell surface markers including MHC II, CD86, CD40, and CD209 and cytokines including IL-6, IL-12p40, and IL-10 were measured. The DCs incubated with nanospheres displayed enhanced expression of all the surface markers and the production of IL-12p40 compared to DCs incubated with polymer films in a chemistry-dependent manner. This suggests that polyanhydrides of various chemistries and device geometries can be tailored to achieve desired levels of immune cell activation for specific applications. The observed biocompatibility and activation of DCs by polyanhydride devices supports their inclusion in vaccine delivery devices as well as in multi-component medical implants.
Keywords: Polyanhydrides; Murine dendritic cells; Adjuvants; Vaccine delivery; Nanospheres
Pharmacokinetics and bone formation by BMP-2 entrapped in polyethylenimine-coated albumin nanoparticles
by Sufeng Zhang; Michael R. Doschak; Hasan Uludağ (pp. 5143-5155).
The osteoinductive growth factor, bone morphogenetic protein-2 (BMP-2), is capable of inducing de novo bone formation after implantation. A nanoparticulate (NP) system was developed for BMP-2 delivery based on NPs fabricated from bovine serum albumin (BSA) and stabilized by polyethylenimine (PEI) coating. In this study, the pharmacokinetics and osteoinductivity of BMP-2 delivered with different BSA NP formulations were determined by subcutaneous implantation in rats. A 7-day pharmacokinetics study showed that PEI coating on NPs effectively reduced the initial burst release of BMP-2 and prolonged the BMP-2 retention at implantation site. However, the uncoated BMP-2 NPs (BMP-2 loading of 1.44%w/w) were able to induce a robust ectopic bone formation, while no bone formation was found by the BMP-2 NPs coated with PEI. The toxicity of the PEI used for NP coating was determined to be the reason for lack of osteoinduction. Increasing BMP-2 loading (up to 5.76%w/w) was then employed to formulate NPs with lower PEI content; the higher BMP-2 loading was found to better promote induction of de novo bone. Our findings indicated that PEI coating on BSA NPs was effective for controlling BMP-2 release from NPs, but the toxicity of cationic PEI was a concern for the osteoinductive activity, which should be alleviated by further optimization of NP formulations.
Keywords: Bone morphogenetic protein-2; Polyethylenimine; Bovine serum albumin; Nanoparticle; Pharmacokinetics; Ectopic bone formation
Near-infrared fluorescence tumor imaging using nanocarrier composed of poly(l-lactic acid)- block-poly(sarcosine) amphiphilic polydepsipeptide
by Akira Makino; Shinae Kizaka-Kondoh; Ryo Yamahara; Isao Hara; Tatsuya Kanzaki; Eiichi Ozeki; Masahiro Hiraoka; Shunsaku Kimura (pp. 5156-5160).
A nanocarrier, lactosome, which is composed of poly(l-lactic acid)- block-poly(sarcosine), as a contrast agent for the liver tumor imaging was examined using the near infrared fluorescence (NIRF) optical imaging technique. Lactosome labeled with indocyanine green (ICG) showed a high escape ability from the reticulo-endothelial system (RES). Lactosome was found to be stable in a blood circulation, and gradually accumulated specifically at a model liver tumor site, which was obtained by graft of HepG2/EF-Luc cells at a mouse liver. The high tumor/liver imaging ratio is due to the enhanced permeation and retention (EPR) effect of lactosome. The fluorescence intensity at the tumor site was correlated with the degree of malignancy. Tumor imaging using lactosome as a nanocarrier is therefore a potential candidate for a facile and general tumor imaging technique.
Keywords: Molecular imaging; Drug delivery system; Biodegradation; Biocompatibility; In vivo; test; Fluorescence
Antibody and cytokine-associated immune responses to S. equi antigens entrapped in PLA nanospheres
by Helena F. Florindo; Sreenivas Pandit; Lídia M.D. Gonçalves; Mafalda Videira; Oya Alpar; António J. Almeida (pp. 5161-5169).
Strangles is an infectious disease caused by Streptococcus equi subspecies equi that affects the upper respiratory tract of the Equidae. The control of this disease seems to be dependent on its earlier detection and prevention, but prolonged animal protection without development of strong and severe side effects has not yet been achieved. Convalescent horses exhibit a protective immune response, mainly against SeM (58kDa), an antiphagocytic and opsonogenic S. equi M-like protein, known as the major protective antigen against strangles. Purified recombinant SeM and S. equi protein extract-entrapped poly(lactic acid) (PLA) nanospheres were developed and their adjuvant potential was studied via the intramuscular route. The effect including molecules with adjuvant properties such as spermine, oleic acid, alginate and glycol-chitosan was also evaluated. Spherical nanometric particles <500nm containing the protein antigen were prepared by the solvent evaporation method and protein structure was not affected throughout preparation. The humoral immune response induced by nanospheres was markedly higher than that elicited by soluble antigens, isolated or co-admixed with CpG. The IgG and IgG subtypes, along with cytokine titres, indicated that nanospheres composed by glycolchitosan developed a more balanced Th1/Th2 response for both purified SeM and S. equi enzymatic extract proteins, although those induced by the pure antigen-entrapped particles were higher than the S. equi tested vaccines composed by total antigens entrapped in polymeric nanospheres.
Keywords: Poly(lactic acid); Nanospheres; SeM; Vaccines; Immune responses
Calcium alginate beads embedded in silk fibroin as 3D dual drug releasing scaffolds
by Biman B. Mandal; Subhas C. Kundu (pp. 5170-5177).
3D scaffolds based on embedding drug loaded calcium alginate beads within silk fibroin protein were fabricated for investigating controlled dual drug release. The 3D matrices were evaluated for in vitro release using two different molecular weight model compounds, bovine serum albumin (66kDa) and FITC–Inulin (3.9kDa). The model compound release profiles revealed dependence on molecular weight of encapsulated model drugs for sustained release. Further, silk fibroin protein blended calcium alginate beads resulted in prolonged drug release without initial bursts for 35 days as compared to calcium alginate beads without silk fibroin as control. The release kinetics were further tested as a function of wt% silk content for scaffold fabrication suggesting their possible role in restricting initial burst and leading to sustainable release of compounds for prolong time. Silk coatings on calcium alginate beads provided mechanically stable shells as well as a diffusion barrier to the encapsulated protein drugs thus controlling their release. Scanning electron microscopic observations were carried out to assess cellular viability and biocompatibility of bead embedded-silk 3D scaffolds using fibroblast cells. The results highlight the versatile and tunable properties of calcium alginate embedded fibroin 3D scaffolds making them exciting candidate for the controlled release of a wide spectrum of bioactive molecules from a single delivery vehicle.
Keywords: Silk fibroin; Scaffolds; Drug delivery; Controlled release; Tissue engineering
A paradigm for peptide vaccine delivery using viral epitopes encapsulated in degradable polymer hydrogel capsules
by Siow-Feng Chong; Amy Sexton; Robert De Rose; Stephen J. Kent; Alexander N. Zelikin; Frank Caruso (pp. 5178-5186).
We report on the use of degradable polymer capsules as carriers for the delivery of oligopeptide antigens to professional antigen presenting cells (APCs). To achieve encapsulation, oligopeptide sequences were covalently linked to a negatively charged carrier polymer via biodegradable linkages and the resulting conjugate was then adsorbed onto amine-functionalized silica particles. These peptide-coated particles were then used as templates for the layer-by-layer (LbL) deposition of thiolated poly(methacrylic acid) (PMASH) and poly(vinylpyrrolidone) (PVPON) multilayers. Removal of the silica core and disruption of the hydrogen bonding between PMASH and PVPON by altering the solution pH yielded disulfide-stabilized PMA capsules that retain the encapsulated cargo in an oxidative environment. In the presence of a natural reducing agent, glutathione, cleavage of the disulfide bonds causes release of the peptide from the capsules. The developed strategy provides control over peptide loading into polymer capsules and yields colloidally stable micron- and submicron-sized carriers with uniform size and peptide loading. The conjugation and encapsulation procedures were proven to be non-degrading to the peptide vaccines. The peptide-loaded capsules were successfully used to deliver their cargo to APCs and activate CD8 T lymphocytes in a non-human primate model of SIV infection ex vivo. The reported approach represents a novel paradigm in the delivery of peptide vaccines and other therapeutic agents.
Keywords: Layer-by-layer membrane; Drug delivery; Drug release; Cross-linking
In-situ crosslinking hydrogels for combinatorial delivery of chemokines and siRNA–DNA carrying microparticles to dendritic cells
by Ankur Singh; Shalu Suri; Krishnendu Roy (pp. 5187-5200).
Polymer-based, injectable systems that can simultaneously deliver multiple bioactive agents in a controlled manner could significantly enhance the efficacy of next generation therapeutics. For immunotherapies to be effective, both prophylactically or therapeutically, it is not only critical to drive the antigen (Ag)-specific immune response strongly towards either T helper type 1 (Th1) or Th2 phenotype, but also to promote recruitment of a high number of antigen-presenting cells (APCs) at the site of immunization. We have recently reported a microparticle-based system capable of simultaneously delivering siRNA and DNA to APCs. Here we present an in-situ crosslinkable, injectable formulation containing dendritic cell (DC)-chemo-attractants and dual-mode DNA–siRNA loaded microparticles to attract immature DCs and simultaneously deliver, to the migrated cells, immunomodulatory siRNA and plasmid DNA antigens. These low crosslink density hydrogels were designed to degrade within 2–7 days in vitro and released chemokines in a sustained manner. Chemokine carrying gels attracted 4–6 folds more DCs over a sustained period in vitro, compared to an equivalent bolus dose. Interestingly, migrated DCs were able to infiltrate the hydrogels and efficiently phagocytose the siRNA–DNA carrying microparticles. Hydrogel embedded microparticles co-delivering Interleukin-10 siRNA and plasmid DNA antigens exhibited efficient Interleukin-10 gene knockdown in migrated primary DCs in vitro.
Keywords: In-situ; crosslinking; Hydrogel; Microparticles; siRNA; Chemotaxis; Plasmid DNA
Controlled drug release from multilayered phospholipid polymer hydrogel on titanium alloy surface
by Jiyeon Choi; Tomohiro Konno; Madoka Takai; Kazuhiko Ishihara (pp. 5201-5208).
Here we describe the functionalization of a multilayered hydrogel layer on a Ti alloy with an antineoplastic agent, paclitaxel (PTX). The multilayered hydrogel was synthesized via layer-by-layer self-assembly (LbL) using selective intermolecular reactions between two water-soluble polymers, phospholipid polymer (PMBV) containing a phenylboronic acid unit and poly(vinyl alcohol) (PVA). Reversible covalent bonding between phenylboronic acid and the polyol provided the driving force for self-assembly. Poorly water-soluble PTX dissolves in PMBV aqueous solutions because PMBV is amphiphilic. Therefore, our multilayered hydrogel could be loaded with PTX at different locations to control the release profile and act as a drug reservoir. The amount of PTX incorporated in the hydrogel samples increased with the number of layers but was not directly proportional to the number of layers. However, as the step for making layers was repeated, the concentration of PTX in the PMBV layers increased. The different solubilities of PTX in PMBV and PVA aqueous solutions allow for the production of multilayered hydrogels loaded with PTX at different locations. In vitro experiments demonstrated that the location of PTX in the multilayered hydrogel influences the start and profile of PTX release. We expect that this rapid and facile LbL synthesis of multilayered hydrogels and technique for in situ loading with PTX, where the location of loading controls the release pattern, will find applications in biomedicine and pharmaceutics as a promising new technique.
Keywords: Layer-by-layer self-assembly; Multilayer; Hydrogel; Paclitaxel; Controlled release
The application of poly (glycerol–sebacate) as biodegradable drug carrier
by Zhi-Jie Sun; Chang Chen; Ming-Zhen Sun; Chang-Hong Ai; Xi-Li Lu; Yu-Feng Zheng; Bao-Feng Yang; De-Li Dong (pp. 5209-5214).
Poly (glycerol–sebacate) (PGS) is an elastomeric biodegradable polymer which possesses the ideal properties of drug carriers. In the present study, we prepared a series of PGS implants (5-FU-PGSs) loaded with different weight percent of 5-fluorouracil (2, 5, 7.5 and 10%). We studied the infrared spectrum properties, in vitro degradation and drug release, in vivo degradation and tissue biocompatibility of 5-FU-PGSs, in order to provide detailed information for the application of PGS as biodegradable drug carrier in cancer therapy. Macroscopically, all 5-FU-PGS wafers in phosphate buffer solution (PBS) kept their geometries during the degradation period of 30 days. The in vitro degradation rates of 5-FU-PGSs were accelerated when higher concentration of 5-FU was doped. Scanning electron microscopy observation showed that the surfaces of 5-FU-PGSs with higher concentration of 5-FU had irregular pits. The cumulative drug release profiles of 5-FU-PGSs exhibited a biphasic release with an initial burst release in the first day. After 7 days, almost 100% cumulative release of 5-FU was found for all 5-FU-PGSs.The degradation rate of 5-FU-PGSs in vivo was much quicker than that in vitro. Hematoxylin and eosin staining showed that no remarkable inflammations were observed in the tissue surrounding 5-FU-PGS implants, suggesting 5-FU-PGSs had good biocompatibility and no tissue toxicity. In vitro anti-tumor activity assay suggested that 5-FU-PGSs exhibited anti-tumor activity through sustained-release drug mode. These results demonstrate that PGS is a candidate of biodegradable drug carriers.
Keywords: Poly (glycerol–sebacate); Drug delivery; 5-Fluorouracil; Biodegradation
In vitro cellular responses to scaffolds containing two microencapulated growth factors
by Fa-Ming Chen; Rong Chen; Xiao-Jing Wang; Hai-Hua Sun; Zhi-Fen Wu (pp. 5215-5224).
Growth factors play an important role in the complex cascade of tissue events in periodontal regeneration, although optimal methods of delivery remain to be identified. We hypothesize that multiple delivery of growth factors, particularly via a microparticle-containing scaffold, will enhance cellular events leading to periodontal regeneration. In this study, cellular responses of periodontal ligament fibroblasts (PDLFs) in scaffolds containing microparticles (MPs) loaded with either bone morphogenetic protein (BMP)-2, insulin-like growth factor (IGF)-1, or a mixture of both MPs were evaluated, and the dual-MP-containing scaffold exhibited the release of different proteins in a sustained and independent fashion. When PDLF-seeded scaffolds were cultured in a flow perfusion bioreactor, cell metabolism and proliferation of PDLFs were significantly increased within 3 days in all IGF-1-containing scaffolds compared with those in groups lacking IGF-1 and particulate delivery enhanced these effects between 3 and 7 days. The dual-MP-containing group showed the most positive results. Both the BMP-2-in-MP and IGF-1-in-MP groups showed greater effects of alkaline phosphatase activity, more osteocalcin and osteopontin production, and more calcium deposition compared with matched GF-adsorbed groups. All osteoblastic markers were at their highest in the dual-MP-containing group at all detected time points. The combined results suggest that our dual-MP-containing scaffold can be used as a cell vehicle to positively affect cell behavior, thus exhibiting the potential to be a candidate scaffold for future periodontal tissue engineering.
Keywords: Dual delivery; Periodontal regeneration; Tissue engineering; Periodontal ligament fibroblasts; Cell vehicles; Controlled release
An acid-labile temperature-responsive sol–gel reversible polymer for enhanced gene delivery to the myocardium and skeletal muscle cells
by Ran Namgung; Sujin Nam; Soo Kyung Kim; Sejin Son; Kaushik Singha; Jin-Sook Kwon; Youngkeun Ahn; Myung Ho Jeong; In-Kyu Park; Vivek K. Garripelli; Seongbong Jo; Won Jong Kim (pp. 5225-5233).
The work demonstrates the development of acid-labile temperature-responsive sol–gel reversible polymer for enhanced in vivo myocardium and skeletal muscle gene delivery. In this report, multi-block copolymers (MBCPs) synthesized from pluronic® and di-(ethylene glycol) divinyl ether (DEGDVE) were used as a delivery vehicle for controlled and sustained release of plasmid DNA (pDNA) in in vitro as well as in vivo experiments. The non-ionic MBCP/pDNA complex showed remarkable transfection efficiencies against the myocardium cells as well as muscle cells in vivo, which is otherwise very difficult to achieve by using cationic polymers. In in vitro experimental settings, this intelligent stimuli-responsive polymer is shown to improve the transfection efficiency of branched polyethylenimine (BPEI)/pDNA complex when used together. The effect of MBCP on the surface charge and particle size of its various complexes with pDNA and BPEI was also studied. The release profile of pDNA from the MBCP gel was investigated and pH of the degraded polymer was also monitored to ascertain its non-cytotoxicity arising due to the increased acidity as observed with other PLGA-based polymers. The rapid sol–gel transition of MBCP under thermal stimuli with concomitant release of pDNA under acidic stimulation has potential for site specific, efficient and controlled transfection of therapeutic gene. In short, MBCP provides the silver lining in combat against the hurdles encountered in transfection to myocardial or other muscle cells.
Keywords: Myocardium; Skeletal muscle; Gene delivery; Acid-labile; Non-ionic polymer
Zwitterionic carboxybetaine polymer surfaces and their resistance to long-term biofilm formation
by Gang Cheng; Guozhu Li; Hong Xue; Shengfu Chen; James D. Bryers; Shaoyi Jiang (pp. 5234-5240).
In this work, we report a systematic study of zwitterionic poly(carboxybetaine methacrylate) (pCBMA) grafted from glass surfaces via atom transfer radical polymerization (ATRP) for their resistance to long-term bacterial biofilm formation. Results show that pCBMA-grafted surfaces are highly resistant to non-specific protein adsorption (fibrinogen and undiluted blood plasma) at 25, 30 and 37 °C. Long-term (over 24 h) colonization of two bacterial strains ( Pseudomonas aeruginosa PAO1 and Pseudomonas putida strain 239) on pCBMA surface was studied using a parallel flow cell at 25, 30 and 37 °C. Uncoated glass cover slips were chosen as the positive reference. Results show that pCBMA coatings reduced long-term biofilm formation of P. aeruginosa up to 240 h by 95% at 25 °C and for 64 h by 93% at 37 °C, and suppressed P. putida biofilm accumulation up to 192 h by 95% at 30 °C, with respect to the glass reference. The ability of pCBMA coatings to resist non-specific protein adsorption and significantly retard bacterial biofilm formation makes it a very promising material for biomedical and industrial applications.
Keywords: Biofilm; Carboxybetaine; Non-fouling; Surface; Zwitterionic materials
Integrating polyurethane culture substrates into poly(dimethylsiloxane) microdevices
by Christopher Moraes; Yoan K. Kagoma; Bogdan M. Beca; Rachel L.M. Tonelli-Zasarsky; Yu Sun; Craig A. Simmons (pp. 5241-5250).
Poly(dimethylsiloxane) (PDMS)-based microdevices have enabled rapid, high-throughput assessment of cellular response to precisely controlled microenvironmental stimuli, including chemical, matrix and mechanical factors. However, the use of PDMS as a culture substrate precludes long-term culture and may significantly impact cell response. Here we describe a method to integrate polyurethane (PU), a well-studied and clinically relevant biomaterial, into the PDMS multilayer microfabrication process, enabling the exploration of long-term cellular response on alternative substrates in microdevices. To demonstrate the utility of these hybrid microdevices for cell culture, we compared initial cell adhesion, cell spreading, and maintenance of protein patterns on PU and PDMS substrates. Initial cell adhesion and cell spreading after three days were comparable between collagen-coated PDMS and PU substrates (with or without collagen coating), but significantly lower on native PDMS substrates. However, for longer culture durations (≥6 days), cell spreading and protein adhesion on PU substrates was significantly better than that on PDMS substrates, and comparable to that on tissue culture-treated polystyrene. Thus, the use of a generic polyurethane substrate in microdevices enables longer-term cell culture than is possible with PDMS substrates. More generally, this technique can improve the impact and applicability of microdevice-based research by facilitating the use of alternate, relevant biomaterials while maintaining the advantages of using PDMS for microdevice fabrication.
Keywords: Polyurethane; Polydimethylsiloxane; Cell culture; Microfabrication; Protein patterning