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Biomaterials (v.27, #21)

Editorial board (pp. co2).
Calendar (pp. i).

The integrity of welded interfaces in ultra-high molecular weight polyethylene: Part 2—Interface toughness by David W. Haughie; C. Paul Buckley; Junjie Wu (pp. 3875-3881).
In Part 2 of a study of welding of ultra-high molecular weight polyethylene (UHMWPE), experiments were conducted to measure the interfacial fracture energy of butt welds, for various welding times and temperatures above the melting point. Their toughness was investigated at 37°C in terms of their fracture energy, obtained by adapting the essential work of fracture (EWF) method. However, a proportion of the welded samples (generally decreasing with increasing welding time or temperature) failed in dual ductile/brittle mode, hence invalidating the EWF test. Even those failing in purely ductile mode showed a measurable interface work of fracture only for the highest weld temperature and time: 188°C and 90min. Results from the model presented in Part 1 show that this corresponds to the maximum reptated molecular weight reaching close to the peak in the molar mass distribution. Hence this work provides the first experimental evidence that the slow rate of self-diffusion in UHMWPE leads to welded interfaces acting as low-toughness crack paths. Since such interfaces exist around every powder particle in processed UHMWPE this problem cannot be avoided, and it must be accommodated in design of hip and knee bearing surfaces made from this polymer.

Keywords: Adhesion; Fracture toughness; Interface; Joint replacement; Polyethylene

Comparison of VEGF-producing cells in periprosthetic osteolysis by J.P. Spanogle; K. Miyanishi; T. Ma; N.J. Epstein; R.L. Smith; S.B. Goodman (pp. 3882-3887).
The pro-angiogenic cytokine vascular endothelial growth factor (VEGF) has been implicated in periprosthetic osteolysis and subsequent aseptic loosening of implants following total hip arthroplasty (THA). The goal of this study was to investigate whether increased VEGF at the bone–implant interface is secondary to a greater number of VEGF-producing cells or to increased VEGF production by individual cells. Real time polymerase chain reaction (RT-PCR) techniques were used to assess the expression of VEGF mRNA (isoforms 121, 165, 189) in periprosthetic tissues from revision THAs. Immunofluorescence was used to determine both differences in overall cellularity and in VEGF-producing cell type (macrophages, fibroblasts, endothelial cells) between patients with periprosthetic osteolysis (OL) and a control group undergoing primary THA for osteoarthritis (OA). Quantitative analysis of VEGF release in periprosthetic membranes via RT-PCR demonstrated no significant difference in the per-cell mRNA production of VEGF isoforms 121 165, or 189 between OL and OA patient groups. Immunofluorescence showed both higher cellularity and higher overall VEGF expression in the OL group. Immunofluorescence also showed a significant increase in macrophages in the OL group, but no significant difference in the proportion of fibroblasts or endothelial cells between the OL and OA groups. Co-localization of CD68+ and CD11b+ macrophage fluorescent signals with VEGF signal was greater in the OL group than in the OA group. Our results demonstrate that increased VEGF in OL periprosthetic tissue compared to OA synovium is correlated to increased numbers of VEGF-producing CD68+ and CD11b+ macrophages. Impact statement: Aseptic loosening, caused in large part by OL, remains the major cause of failed THAs leading to revision surgery. At the bone–implant interface, we found increased numbers of macrophages—cellular mediators of OL—and increased VEGF expression. VEGF may be a possible target for therapeutic intervention in mitigating OL.

Keywords: Osteolysis; Macrophage; VEGF (Vascular endothelial growth factor); Fibroblast; Endothelium; Fluroscence

The effect of particulate material on the regulation of chemokine receptor expression in leukocytes by Keiko Fujiyoshi; John Alan Hunt (pp. 3888-3896).
Cellular chemotaxis is one of the most significant components of the host response to implanted materials. However, the effect of materials and their particulates on the regulation of chemokine receptor expression is not well known. This study investigated the effects of alloy particulates on the regulation of CXCR1 and CXCR2 expression on leukocytes from whole blood and purified leukocyte cultures. The volumetric particle concentration and opsonisation dependent manner of CXCR1 and CXCR2 expression on neutrophils and CCR1 and CCR2 expression on monocytes/macrophages was analysed using both flow cytometry (FACS) and real time-PCR. Variation in volumetric concentrations of particulates demonstrated that cell:particulate ratios of 1:1 of non-opsonised NiCr alloy induced the down regulation of CXCR1, and 1:0.25 of opsonised NiCr induced the up regulation of CXCR2. CoCr alloy particulates had no effect on CXCR expression. This study demonstrated that the regulation of chemokine receptor expression could be effected by the properties of materials and the expression of these receptors may contribute to host cellular reactions such as chemotaxis. This study also demonstrated that the response of leukocytes can be demonstrated using a whole blood assay for the study of chemokine receptor expression after direct contact with materials.

Keywords: Neutrophil; Chemokine receptors; Particulate material

Mechanical and histological evaluation of a PMMA-based bone cement modified with γ-methacryloxypropyltrimethoxysilane and calcium acetate by Tadashi Tsukeoka; Masahiko Suzuki; Chikara Ohtsuki; Atsushi Sugino; Yoshikazu Tsuneizumi; Jin Miyagi; Kouichi Kuramoto; Hideshige Moriya (pp. 3897-3903).
Polymethylmethacrylate (PMMA) bone cement is widely used for prosthetic fixation in orthopaedic surgery; however, the interface between bone and cement is a weak zone. We developed a bioactive PMMA cement through modification with γ-methacryloxypropyltrimethoxysilane (MPS) and calcium acetate. The purpose of this study was to compare the handling, mechanical and histological properties of the modified bone cement with those of the conventional cement. The modified specimens exhibited higher bonding strength between bone and implant. Histological observation and micro-focus X-ray computed tomogram (micro-CT) images showed that the modified cement exhibited osteoconduction, which the conventional PMMA bone cement lacked. The modification was found to be effective in enabling osteoconduction with PMMA bone cement, thus providing stable fixation for a long period after implantation.

Keywords: Bioactivity; Bone cement; Mechanical property; In vitro test; In vivo test

Bioactivity and cytocompatibility of zirconia (ZrO2) films fabricated by cathodic arc deposition by Xuanyong Liu; Anping Huang; Chuanxian Ding; Paul K. Chu (pp. 3904-3911).
Zirconium oxide thin films were fabricated on silicon wafers using a filtered cathodic arc system in concert with oxygen plasma. The structure and phase composition of the zirconium oxide thin films were characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), and transmission electron microscopy (TEM). The bioactivity was assessed by investigating the formation of apatite on the film surface after soaking in simulated body fluids. Bone marrow mesenchymal stem cells (BMMSC) were used to further evaluate the cytocompatibility of the materials. The results indicate that the films are composed of stoichiometric ZrO2 and the composition is quite uniform throughout the thickness. Bone-like apatite can be formed on the surface of the ZrO2 thin film in our SBF immersion experiments, suggesting that the surface is bioactive. The outermost layer of the ZrO2 thin film comprises nano-sized particles that can be identified by AFM images taken on the thin film surface and TEM micrographs obtained from the interface between the ZrO2 thin film and apatite layer. The nanostructured surface is believed to be the key factor that apatite is induced to precipitate on the surface. Bone marrow mesenchymal stem cells are observed to grow and proliferate in good states on the film surface. Our results show that ZrO2 thin films fabricated by cathodic arc deposition exhibit favorable bioactivity and cytocompatibility.

Keywords: ZrO; 2; thin film; Cathodic arc deposition; Bioactivity; Apatite

Osteoblast functions on functionalized PMMA-based polymers exhibiting Staphylococcus aureus adhesion inhibition by Fani Anagnostou; Aurore Debet; Graciela Pavon-Djavid; Zakaryia Goudaby; G. Helary Gérard Hélary; V. Véronique Migonney (pp. 3912-3919).
Staphylococcus aureus adhesion and osteoblast functions were assessed on functionalized poly(methyl methacrylate)-based terpolymers bearing randomly distributed carboxylate and sulfonate groups. These terpolymers were synthesized by radical polymerization, characterized by nuclear resonance spectroscopy and classified by the ratio R=[COO/COO+SO3] in the range 0.5–0.8. Bacterial adhesion study showed that fibronectin-coated terpolymers with R varying from 0.5 to 0.8 exhibited inhibition rate of S. aureus adhesion from 90% to 98% as compared to the adhesion on unfunctionalized poly(methyl methacrylate). In contrast, the adhesion of osteoblasts onto the same functionalized terpolymers was decreased by 20% when compared to the results obtained on poly(methyl methacrylate). While the amount of attached osteoblasts are similar onto all the functionalized terpolymers whatever its R value, the cell proliferation was different and was found to vary with R in the range 0.5–0.8. Osteoblast proliferation, alkaline phosphatase activity and accumulation of calcium in the extracellular matrix of these cells, cultured on the functionalized terpolymers with R equal to 0.7–0.8 were similar to that observed onto non-functionalized poly(methyl methacrylate). In contrast, osteoblast proliferation was inhibited on terpolymers with an R value around 0.6. These results provide evidence that functionalized poly(methyl methacrylate)-based terpolymers with R ratio equaling 0.7–0.8 simultaneously inhibit bacteria adhesion and support osteoblast functions pertinent to new bone formation. These functionalized polymers could, therefore, be used as coating or grafted on orthopedic and dental implants to render them both bone compatible and able to prevent bacterial infection.

Keywords: Functionalized PMMA-based polymers; Osteoblast proliferation; Osteoblast phenotype; Bacterial adhesion; S. aureus

Enzymatic degradation of poly(ether urethane) and poly(carbonate urethane) by cholesterol esterase by Elizabeth M. Christenson; Sachin Patel; James M. Anderson; Anne Hiltner (pp. 3920-3926).
This study examined the effect of cholesterol esterase (CE) on the degradation of commercial poly(ether urethane) (PEU) and poly(carbonate urethane) (PCU). Unstrained PEU and PCU films were incubated in 400U/mL CE solution or a buffer control for 36 days. The study used a concentration of cholesterol esterase that was considerably higher than the estimated physiological level in order to accelerate degradation. However, characterization of treated polyurethane films with SEM, attenuated total reflectance Fourier transform infrared (ATR-FTIR) and GPC analysis revealed only a small loss in surface soft segment content. Comparison with implanted PEU and PCU films led to the conclusion that any effect of enzymatic hydrolysis was confined to the immediate surface, and the magnitude of the effect was too small to contribute significantly to in vivo degradation. The study confirmed that oxidation, rather than enzymatic hydrolysis, is the primary mechanism responsible for the observed biodegradation of PEU and PCU. The oxidative H2O2/CoCl2 treatment continues to accurately predict the long-term biostability of polyurethanes.

Keywords: Poly(carbonate urethane); Poly(ether urethane); Biodegradation; Cholesterol esterase; In vivo; In vitro

Ectopic bone formation in mice associated with a lactic acid/dioxanone/ethylene glycol copolymer–tricalcium phosphate composite with added recombinant human bone morphogenetic protein-2 by Minori Kato; Takashi Namikawa; Hidetomi Terai; Masatoshi Hoshino; Shimpei Miyamoto; Kunio Takaoka (pp. 3927-3933).
A new putty-like material with bone-inducing capacity was made by combining a block copolymer of polyd,l-lactic acid with randomly inserted p-dioxanone and polyethylene glycol (PLA-DX-PEG) and beta-tricalcium phosphate ( β-TCP) powder with added recombinant human bone morphogenetic protein-2 (rhBMP-2). To optimize the material's efficacy for bone formation, we formulated the optimal composition ratio of the respective constituent that gives the greatest osteoinductive efficacy in a mouse model of ectopic bone formation.In this series of studies, we investigated the size of ectopic bone mass induced 3 and 6 weeks after implantation of the materials composed of 30mg of PLA-DX-PEG with 2μg of rhBMP-2 and 0, 15, 30, or 60mg of β-TCP powder. An additional experiment was designed to investigate how content ratios of β-TCP powder in 30mg-putty implants (0%, 16.7%, 33.3%, 50%, 66.7%, 83.3%, or 100%) for a fixed dose (5μg) of the rhBMP-2 altered the size of the induced ossicle.The results from the first experiment indicated that the bone yields were linearly dependent on the amount of additional β-TCP powder. In the second experiment, the largest ossicles induced by 5μg of rhBMP-2 were obtained when the polymer/ β-TCP ratio was 1/2 in mice. The data provide important insights into the fabrication of implants that provide efficacious delivery of rhBMP-2. The new putty-like material may be valuable for repairing or regenerating bone in a clinical setting.

Keywords: Bone morphogenetic protein (BMP); Biodegradation; Bone; Bone repair; Drug delivery

Electrospinning of chitin nanofibers: Degradation behavior and cellular response to normal human keratinocytes and fibroblasts by Hyung Kil Noh; Sung Won Lee; J.-M. Jin-Man Kim; J.-E. Ju-Eun Oh; K.-H. Kyung-Hwa Kim; C.-P. Chong-Pyoung Chung; S.-C. Soon-Chul Choi; Won Ho Park; B.-M. Byung-Moo Min (pp. 3934-3944).
An electrospinning method was used to fabricate chitin nanofibrous matrices for biodegradability and cell behavior tests. The morphology of as-spun chitin nanofibers (Chi-N) and commercial chitin microfibers (Beschitin W®; Chi-M) was investigated by scanning electron microscopy. From the image analysis, the average diameters of Chi-N and Chi-M were 163nm and 8.77μm, respectively. During in vitro degradation for 15 days, the degradation rate of Chi-N was faster than that of Chi-M, likely due to higher surface area of Chi-N. Chi-N that was grafted into rat subcutaneous tissue had almost degraded within 28 days, and no inflammation could be seen on the nanofiber surfaces or in the surrounding tissues (except in the early stage wound). To assay and compare the cytocompatibility and cell behavior with Chi-N and Chi-M, cell attachment and spreading of normal human keratinocytes and fibroblasts seeded on chitin matrices and the interaction between cells and chitin fibers were studied. Relatively high cell attachment and spreading of all the cells tested were observed on Chi-N in comparison to Chi-M, and Chi-N treated with type I collagen significantly promoted the cellular response. Our results indicate that the Chi-N, alone or with extracellular matrix proteins (particularly type I collagen), could be potential candidates for the cell attachment and spreading of normal human keratinocytes and fibroblasts. This property of Chi-N might be particularly useful for wound healing and regeneration of oral mucosa and skin.

Keywords: Electrospinning; Chitin nanofibers; Degradation; Extracellular matrix protein; Cell behavior

The effect of environmental factors on the response of human corneal epithelial cells to nanoscale substrate topography by Ana I. Teixeira; George A. McKie; John D. Foley; Paul J. Bertics; Paul F. Nealey; Christopher J. Murphy (pp. 3945-3954).
We have previously shown that human corneal epithelial cells sense and react to nanoscale substrate topographic stimuli [Teixeira AI, Abrams GA, Bertics PJ, Murphy CJ, Nealey PF. Epithelial contact guidance on well-defined micro- and nanostructured substrates. J Cell Sci 2003;116(10):1881–92; Karuri NW, Liliensiek S, Teixeira AI, Abrams G, Campbell S, Nealey PF, et al. Biological length scale topography enhances cell-substratum adhesion of human corneal epithelial cells. J Cell Sci 2004;117(15):3153–64]. Here we demonstrate that cellular responses to nanoscale substrate topographies are modulated by the context in which these stimuli are presented to cells. In Epilife medium, cells aligned preferentially in the direction perpendicular to nanoscale grooves and ridges. This is in contrast to a previous study where cells cultured in DMEM/F12 medium aligned in the direction parallel to nanoscale topographic features [Teixeira AI, Abrams GA, Bertics PJ, Murphy CJ, Nealey PF. Epithelial contact guidance on well-defined micro- and nanostructured substrates. J Cell Sci 2003;116(10):1881–92]. Additionally, cell alignment in Epilife medium was dependent on pattern pitch. Cells switched from perpendicular to parallel alignment when the pitch was increased from 400 to 4000nm. There was a transition region (between 800 and 1600nm pitch) where both parallel and perpendicular alignments were favored compared to all other cellular orientations. Cells formed focal adhesions parallel to the substrate topographies in this transition region. On the nano- and microscale patterns, 400 and 4000nm pitch, focal adhesions were almost exclusively oriented obliquely to the topographic patterns.

Keywords: Nanotopography; Grooves and ridges; Alignment; Focal adhesions; Corneal epithelial cells

Cellulose-based scaffold materials for cartilage tissue engineering by Muller Frank A. Müller; Muller Lenka Müller; Ingo Hofmann; Peter Greil; Magdalene M. Wenzel; Rainer Staudenmaier (pp. 3955-3963).
Non-woven cellulose II fabrics were used as scaffolds for in vitro cartilage tissue engineering. The scaffolds were activated in a saturated Ca(OH)2 solution and subsequently coated with a calcium phosphate layer precipitated from a supersaturated physiological solution. Chondrocyte cell response and cartilage development were investigated. The cell adherence was significantly improved compared to untreated cellulose fabrics, and the proliferation and vitality of the adhered chondrocytes were excellent, indicating the biocompatibility of these materials. A homogeneous distribution of the seeded cells was possible and the development of cartilageous tissue could be proved. In contact with a physiological chondrocyte solution, calcium is expected to be leached out from the precipitated layer, which might lead to a microenvironment that triggers the development of cartilage in a way similar to cartilage repair in the vicinity of subchondral bone.

Keywords: Cellulose; Calcium phosphate; Biomimetic apatite; Chondrocytes; Tissue engineering; Cartilage

Framework for optimal design of porous scaffold microstructure by computational simulation of bone regeneration by Taiji Adachi; Yuki Osako; Mototsugu Tanaka; Masaki Hojo; Scott J. Hollister (pp. 3964-3972).
In bone tissue engineering using a biodegradable scaffold, geometry of the porous scaffold microstructure is a key factor for controlling mechanical function of the bone–scaffold system in the regeneration process as well as after the regeneration. In this study, we propose a framework for the optimal design of the porous scaffold microstructure by three-dimensional computational simulation of bone tissue regeneration that consists of scaffold degradation and new bone formation. The rate of scaffold degradation due to hydrolysis, that leads to decrease in mechanical properties, was simply assumed to relate to the water content diffused from the surface to the bulk material. For the new bone formation on both bone and scaffold surfaces, the rate equation of trabecular surface remodeling driven by mechanical stimulation was applied. Solving these two phenomena in the same time frame, the bone regeneration process in the bone–scaffold system was predicted by computational simulation using a voxel finite element method. The change in the mechanical function of the bone–scaffold system during the regeneration process was quantitatively evaluated by measuring the change in total strain energy, and this was used for the evaluation function to optimize the scaffold microstructure that provides the desired mechanical function during and after the bone regeneration process. A case study conducted for the scaffold with a simple microstructure demonstrated that the proposed simulation method could be applied to the design of a porous scaffold microstructure. In addition, the regeneration process was found to be very complex even though the simple rate equations for scaffold regeneration and new bone formation were used because of the coupling effects of these phenomena.

Keywords: Bone tissue engineering; Porous scaffold; Optimal design; Computational biomechanics

Bone regeneration on computer-designed nano-fibrous scaffolds by Victor J. Chen; Laura A. Smith; Peter X. Ma (pp. 3973-3979).
The ability to control architectural features in tissue engineering scaffolds is critical to the success of neo-tissue regeneration. In this work, reverse solid freeform fabrication and thermal phase separation of poly(l-lactic acid) (PLLA) solutions were used to create three-dimensional nano-fibrous (NF) scaffolds with complex geometries on the macro- and micro-scales. This approach allows for the fabrication of NF matrices while having precise control of internal pore size and structure, as well as external scaffold shape including architectures generated from computed-tomography scans and histological sections. In vitro cell cultivation experiments with MC3T3-E1 preosteoblasts were performed on NF scaffolds and on similarly designed solid-walled (SW) scaffolds that did not have nano-fibers. Proliferation studies showed significantly more cells on NF scaffolds after 7 d. In differentiation studies, the NF scaffolds displayed more uniform matrix and mineral production throughout. Real-time PCR also showed significantly higher expression of osteocalcin and bone sialoprotein mRNAs after 2 and 6 weeks in the NF scaffolds. Expression of type I collagen mRNA was lower in NF scaffolds which possibly indicates quicker differentiation on the NF substrate. In summary, we controlled the geometry of NF PLLA scaffolds at multiple size scales, and the in vitro results showed that these NF scaffolds were advantageous to control scaffolds for bone tissue engineering.

Keywords: Polylactic acid; Rapid prototyping; Tissue engineering; 3-D printing; Nano fiber; Osteoblast

Porogen-induced surface modification of nano-fibrous poly(l-lactic acid) scaffolds for tissue engineering by Xiaohua Liu; Youngjun Won; Peter X. Ma (pp. 3980-3987).
In addition to suitable pore architecture of a tissue-engineering scaffold, surface modification after scaffolding fabrication is often needed to enhance the interactions between cells and the synthetic material. In this study, a novel one-step process was developed to fabricate surface-modified nano-fibrous poly(l-lactic acid) (NF-PLLA) scaffolds. First, gelatin spheres with smooth surface were prepared by non-surfactant emulsification, solvent extraction, and freeze-drying. A three-dimensional NF-PLLA scaffold was then fabricated by using gelatin spheres as porogen. Gelatin molecules were entrapped onto the scaffold surface during the fabrication process. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy analysis demonstrated the existence of gelatin molecules on the surface of the polymer scaffold. The amount of gelatin on the scaffold surface was controlled by the composition of the solvent mixture of gelatin solution. The compressive modulus of scaffold prepared with gelatin spheres was more than three times higher than that prepared with irregular gelatin particles of the same size range. The surface modification significantly improved initial cell adhesion and proliferation over a 2-week culture. SEM images indicated that cells spread on the gelatin-entrapped scaffolds in contrast to spherical or spindle morphology on the control 1 day after cell seeding. Furthermore, more matrix secretion was observed on the surface-modified scaffolds than on the control after 2 weeks of in vitro cultivation. In conclusion, this approach provides a simple one-step process to fabricate surface-modified collagen-like NF-PLLA scaffolds, which have improved cell adhesion and proliferation.

Keywords: Gelatin; Nano fiber; Surface modification; Scaffold; Bone regeneration; Polymer

The influence of surface coatings of dicalcium phosphate (DCPD) and growth and differentiation factor-5 (GDF-5) on the stability of titanium implants in vivo by H.-G. Hans-Georg Simank; Marco Stuber; Ronny Frahm; Lars Helbig; Harry van Lenthe; Müller Ralph Müller (pp. 3988-3994).
Mechanical stability of implants is usually tested by pull out or push out tests which destroy the interface between the implant and bone. Pull out tests do not ideally reflect the clinical situation. In contrast, applying submaximal load leads to more physiologic micro-displacement between implant and bone. The aim of this study was to evaluate a new non-destructive mechanical testing device on different modifications of titanium implants. In 18 rabbits we investigated the influence of a dicalcium phosphate(DCPD) coating, or of a growth and differentiation factor-5 (GDF-5) coating, or a combination of both on the stability of titanium implants. The stability of implant was assessed by a non-destructive micro-measurement. In the same specimens the interface was investigated by micro-CT and histological evaluation. Surface modifications had a positive effect on the implant stability regarding displacement (p=0.001). Mechanical stability correlated with the quality of peri-implant tissue. Micro-displacement correlated negatively with the bone formation around the implants in histomorphometric evaluation (p=0.02). Amount of peri-prosthetic soft tissue showed a positive correlation with micro-displacement (p=0.01). Our findings indicate the positive effect of DCPD and GDF-5 coatings on stability of titanium implants. Results demonstrate the non-destructive testing to be an effective method to evaluate mechanical stability of implants.

Keywords: Bone ingrowth; Histomorphometry; Mechanical test; Micromotion; Titanium

Antibacterial activity of dental composites containing quaternary ammonium polyethylenimine nanoparticles against Streptococcus mutans by Nurit Beyth; Ira Yudovin-Farber; Ran Bahir; Abraham J. Domb; Ervin I. Weiss (pp. 3995-4002).
The antibacterial activity of quaternary ammonium polyethylenimine (PEI) nanoparticles embedded at 1%w/w with clinically used bonding, flowable and hybrid dental composite resins and cured by light polymerization was studied. The antibacterial activity was tested with Streptoccocus mutans by: (i) the agar diffusion test (ADT); (ii) the direct contact test; (iii) bacterial growth in the materials elute; (iv) and scanning electron microscope (SEM). Using the direct contact test, antibacterial activity ( p<0.001) was found in all three types of composite resins incorporated with the synthesized nanoparticles. The effect lasted for at least 1 month. SEM demonstrated bacterial debris and no streptococcal chains at 24h of bacterial contact. The addition of 1%w/w of nanoparticles did not affect the flexural modulus and the flexural strength of the dental composite materials.The results indicate that quaternary ammonium PEI nanoparticles immobilized in resin-based materials have a strong antibacterial activity upon contact without leach-out of the nanoparticles and without compromise in mechanical properties.

Keywords: Quaternary ammonium; Nanoparticles; Antibacterial; Dental composite; Polyethylenimine

Biomimetic modification of titanium dental implant model surfaces using the RGDSP-peptide sequence: A cell morphology study by Martin Schuler; Gethin Rh. Owen; Douglas W. Hamilton; Michael de Wild; Marcus Textor; Donald M. Brunette; Samuele G.P. Tosatti (pp. 4003-4015).
Surface topography and (bio)chemistry are key factors in determining cell response to an implant. We investigated cell adhesion and spreading patterns of epithelial cells, fibroblasts and osteoblasts on biomimetically modified, smooth and rough titanium surfaces. The RGD bioactive peptide sequence was immobilized via a non-fouling poly(l-lysine)- graft-poly(ethylene glycol) (PLL- g-PEG) molecular assembly system, which allowed exploitation of specific cell–peptide interactions even in the presence of serum. As control surfaces, bare titanium and bio-inactive surfaces (scrambled RDG and unfunctionalized PLL- g-PEG) were used. Our findings demonstrated that surface topography and chemistry directly influenced the attachment and morphology of all cell types tested. In general, an increase in cell number and more spread cells were observed on bioactive substrates (containing RGD) compared to bio-inactive surfaces. More fibroblasts were present on smooth than on rough topographies, whereas for osteoblasts the opposite tendency was observed. Epithelial cell attachment did not follow any regular pattern. Footprint areas for all cell types were significantly reduced on rough compared to smooth surfaces. Osteoblast attachment and footprint areas increased with increasing RGD-peptide surface density. However, no synergy (interaction) between RGD-peptide surface density and surface topography was observed for osteoblasts neither in terms of attachment nor footprint area.

Keywords: Titanium oxide; Surface topography; Surface modification; Biomimetic material; Peptide; Cell morphology

Preparation, properties and controlled release behaviors of pH-induced thermosensitive amphiphilic gels by Y.-Y. Yu-Yang Liu; Y.-H. Ying-Hui Shao; Lu Jian Lü (pp. 4016-4024).
Two pH-induced thermosensitive amphiphilic gels for controlled drug release were constructed with thermosensitive poly( N-isopropylacrylamide) (PNIPAm) and hydrophobic poly(ethyl acrylate) (PEA) by interpenetrating polymer network (IPN) technology. To obtain pH-induced thermosensitive functionality at physiological temperature, 5mol% of acrylic acid (AAc) and N, N-dimethyl aminoethyl methacrylate (DMA) were incorporated into PNIPAm chain by their copolymerization. It is found that the IPN hydrogels show pH-induced thermosensitivity at physiological temperature. When the amphiphilic gels with IPN structure were immersed in water, the hydrophobic moieties formed by PEA have the potential to act as reservoirs for hydrophobic drugs, from which drug may be released slowly. Using drug daidzein (DAI) as a model molecule, controlled release behaviors of the IPNs were investigated. It is found that the presence of permanently hydrophobic PEA network can indeed slow the release rate of DAI and to some extent overcome disadvantageous burst effect of PNIPAm-based networks in hydration state. The release kinetics of DAI from the IPNs seems to follow pseudo-zero-order release character, regardless of the hydrogels in swollen or shrunken state.

Keywords: pH-induced thermosensitivity; Amphiphilic hydrogel; Interpenetrating polymer networks; Controlled release

The drug encapsulation efficiency, in vitro drug release, cellular uptake and cytotoxicity of paclitaxel-loaded poly(lactide)–tocopheryl polyethylene glycol succinate nanoparticles by Zhiping Zhang; S.-S. Si-Shen Feng (pp. 4025-4033).
Paclitaxel is one of the most effective antineoplastic drugs. Its current clinical administration is formulated in Cremophor EL, which causes serious side effects. Nanoparticle (NP) technology may provide a solution for such poisonous adjuvant problems and promote a sustained chemotherapy, in which biodegradable polymers play a key role. Our group has successfully synthesized novel poly(lactide)–tocopheryl polyethylene glycol succinate (TPGS) (PLA–TPGS) copolymers of desired hydrophobic–hydrophilic balance for NP formulation of anticancer drugs. The present work is focused on effects of the PLA:TPGS composition ratio on drug encapsulation efficiency, in vitro drug release, in vitro cellular uptake and viability of the PLA–TPGS NP formulation of paclitaxel. The PLA–TPGS copolymers of various PLA:TPGS ratios were synthesized by the ring-opening polymerization method and characterized by GPC and1H NMR for their molecular structure. Paclitaxel-loaded PLA–TPGS NPs were prepared by a modified solvent extraction/evaporation method and characterized by laser light scattering for size and size distribution, scanning electron microscopy for surface morphology and zeta potential for surface charge. High performance liquid chromatography was used to measure the drug encapsulation efficiency and in vitro drug release profile. Cancer cell lines HT-29 and Caco-2 were used to image and measure the cellular uptake of fluorescent PLA–TPGS NPs. Cancer cell viability of the drug-loaded PLA–TPGS was measured by MTT assay. It was found that the PLA:TPGS composition ratio has little effects on the particle size and size distribution. However, the PLA–TPGS NPs of 89:11 PLA:TPGS ratio achieved the best effects on the drug encapsulation efficiency, the cellular uptake and the cancer cell mortality of the drug-loaded PLA–TPGS NPs. This research was also carried out in close comparison with the drug-loaded PLGA NPs.

Keywords: Biodegradable polymers; Cancer; Cancer nanotechnology; Chemotherapy; Taxol; ®

Fabrication of polymeric microparticles for drug delivery by soft lithography by Jingjiao Guan; Nicholas Ferrell; L. James Lee; Derek J. Hansford (pp. 4034-4041).
Soft lithographic techniques were used to fabricate polymeric microparticles for drug delivery applications. The microparticles were made of thermoplastics and thermosets from different types of precursors including reactive resin and polymer solutions in organic solvents or water. The microparticles produced using these methods were made of widely used polymers for drug delivery with highly uniform sizes, plate-like morphology, and well-defined lateral sizes and shapes, making them potentially useful for drug delivery applications and as platform for the construction of multi-functional drug delivery devices.

Keywords: Drug delivery; Soft lithography; Microfabrication; Microparticle

Multilayered construction of glucose oxidase and silica nanoparticles on Au electrodes based on layer-by-layer covalent attachment by Yingying Sun; Feng Yan; Wensheng Yang; Changqing Sun (pp. 4042-4049).
A feasible approach to construct multilayer films of aminated silica nanoparticles/glucose oxidase (ASNPs/GOx) on the Au electrode surface using a glutaraldehyde as a covalent attachment cross-linker is described. The covalent attachment processes were followed and confirmed by electrochemical impedance spectroscopy (EIS), which demonstrated that the ASNPs/GOx multilayer films are formed in a progressive and uniform manner. The gold electrodes modified with the ASNPs/GOx multilayer films were studied by cyclic voltammetry (CV) and showed excellent electrocatalytical response to the oxidation of glucose when ferrocenemethanol was used as an artificial redox mediator. From the analysis of voltammetric signals, the coverage of active enzyme on the electrode was estimated, which showed a linear relationship with the number of ASNPs/GOx bilayers. This suggests that the analytical performance such as sensitivity, detection limit is tunable by controlling the number of attached bilayers. The linear response range of the biosensor constructed with four bilayers of ASNPs/GOx to the concentration of glucose can extend at least to 8mm and reached 95% of the steady-state current in less than 4s with the sensitivity of 5.11μA/mmcm2 and the detection limit of 9μm. In addition, the sensor exhibited good stability and long-term life.

Keywords: Glucose oxidase; Aminated silica nanoparticles; Layer-by-layer covalent attachment; Multilayered enzyme construction; Biosensors

A hypothetical mechanism of bone remodeling and modeling under electromagnetic loads by Chuanyong Qu; Q.-H. Qing-Hua Qin; Yilan Kang (pp. 4050-4057).
A hypothetical regulation mechanism for bone modeling and remodeling under electromagnetic field is proposed. In this hypothesis, the bone modeling and remodeling mechanism is described as follows: the circular loads that we bear during ordinary daily activities generate micro-damage in cortical bone and these micro-cracks are removed by osteoclasts. Then growth factors, which are in latent forms in osteocytes, are activated by osteoclasts and released into bone fluid. These growth factors stimulate osteoblasts to refill the cavities. An electromagnetic field can stimulate the multiplication of growth factors and accelerate the bone remodeling process indirectly. It can be seen that many features reported in adaptive bone modeling and remodeling are explained by the proposed hypothesis. Further, a computational model is established based on the hypothesis, which can simulate the bone modeling and remodeling process under multi-field loads.

Keywords: Bone modeling and remodeling; Electromagnetic field; Biomaterial; Biomechanics

Erratum to “Attenuated alloreactivity of dendritic cells engineered with surface-modified microspheres carrying a plasmid encoding interleukin-10? by Liang Jia; Jeffrey R. Kovacs; Ying Zheng; Ellen S. Gawalt; Hongmei Shen; Wilson S. Meng (pp. 4058-4058).
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