Biomaterials (v.33, #8)

Switchable adhesive substrates: Revealing geometry dependence in collective cell behavior by Claudio G. Rolli; Hidekazu Nakayama; Kazuo Yamaguchi; Joachim P. Spatz; Ralf Kemkemer; Jun Nakanishi (2409-2418).
Collective cell migration plays a major role in cancer metastasis and wound healing, therefore, several in vitro assays for studying such behavior have been developed. Using photoswitchable surfaces, we studied collective cell expansion behavior from initially precisely controlled adhesive patterns. A non-adhesive poly(ethylene glycol) (PEG) layer is conjugated to a glass coverslip via 2-nitrobenzyl groups, which cleave upon exposure to UV light, changing the surface from non-cell-adhesive to cell-adhesive without mechanical interference. Initial cell attaching areas are generated in arbitrary shapes via projection exposure through a photomask. After a growth phase, epithelial cell sheets are released from their confinement by a second illumination allowing for collective cell expansion. Our experiments with epithelial cells show that cluster size and boundary curvature modulate the expansion of the cell sheet and the formation of leader cells. At a certain cluster size, characteristics of the expansion behavior change and cells in the core are hardly affected by the boundary release. With donut-like ring structures, we demonstrate a break in symmetry between the behavior of cells along the outer convex boundary and along the inner concave boundary. Additionally, we observe that collective migration characteristics are modulated by the initial incubation time of the cell sheet.
Keywords: Collective cell migration; Photopatterning; Wound healing; Cell spreading; Passivation; Cell adhesion;

A 3D microfibrous scaffold for long-term human pluripotent stem cell self-renewal under chemically defined conditions by Hong Fang Lu; Karthikeyan Narayanan; Sze-Xian Lim; Shujun Gao; Meng Fatt Leong; Andrew C.A. Wan (2419-2430).
Realizing the potential of human pluripotent stem cell (hPSC)-based therapy requires the development of defined scalable culture systems with efficient expansion, differentiation and isolation protocols. We report an engineered 3D microfiber system that efficiently supports long-term hPSCs self-renewal under chemically defined conditions. The unique feature of this system lies in the application of a 3D ECM-like environment in which cells are embedded, that affords: (i) uniform high cell loading density in individual cell-laden constructs (∼107 cells/ml); (ii) quick recovery of encapsulated cells (<10 min at 37 °C) with excellent preservation of cell viability and 3D multicellular structure; (iii) direct cryopreservation of the encapsulated cells in situ in the microfibers with >17-fold higher cell viability compared to those cultured on Matrigel surface; (iv) long-term hPSC propagation under chemically defined conditions. Four hPSC lines propagated in the microfibrous scaffold for 10 consecutive passages were capable of maintaining an undifferentiated phenotype as demonstrated by the expression of stem cell markers and stable karyotype in vitro and the ability to form derivatives of the three germ layers both in vitro and in vivo. Our 3D microfibrous system has the potential for large-scale cultivation of transplantable hESCs and derivatives for clinical applications.
Keywords: Stem cell; Scaffold; Cell culture; Cell encapsulation; Cell proliferation;

Cell behavior on a CCN1 functionalized elastin-mimetic protein polymer by Swathi Ravi; Carolyn A. Haller; Rory E. Sallach; Elliot L. Chaikof (2431-2438).
We report the design of an elastin-mimetic triblock copolymer with the ability to guide endothelial cell adhesion, spreading, and migration while maintaining the elastomeric properties of the protein polymer. The V2 ligand sequence from matricellular protein CCN1 (cysteine-rich 61, CYR61) was multimerized and cloned into elastin polymer LysB10, creating LysB10.V2. Cell adhesion studies demonstrated that a LysB10.V2 surface density of at least 40 pmol/cm2 was required to elicit cell attachment. Peptide blocking studies confirmed V2 specific engagement with integrin receptor αvβ3 (P < 0.05) and we observed the formation of actin stress fiber networks and vinculin clustering, characteristic of focal adhesion assembly. Haptotatic migration assays demonstrated the ability of LysB10.V2 surfaces to stimulate migration of endothelial cells (P < 0.05). Significantly, we illustrated the ability of LysB10.V2 to support a quiescent endothelium. The CCN1 molecule functions to support many key biological processes necessary for tissue repair and thus presents a promising target for bioengineering applications. Collectively, our results demonstrate the potential to harness CCN1 specific function in the design of new scaffold materials for applications in regenerative medicine.
Keywords: Protein polymer; Elastin-mimetic; Extracellular matrix; Matricellular protein; Endothelial cell;

The use of magnetic resonance cell tracking to monitor endothelial progenitor cells in a rat hindlimb ischemic model by Carlos A. Agudelo; Yoichi Tachibana; Andres F. Hurtado; Takayuki Ose; Hidehiro Iida; Tetsuji Yamaoka (2439-2448).
A water-soluble magnetic resonance imaging (MRI) contrast agent, Dextran mono-N-succinimidyl 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-gadolinium3+ (Dex-DOTA-Gd3+), was shown to enable monitoring of the anatomical migration and the survival period of transplanted stem cells for up to 1 month. Gadolinium molecules in the cells were rapidly eliminated from the site and excreted upon cell death. Endothelial progenitor cells (EPCs) transplanted into the inguinal femoral muscle of rats migrated distally through the knee in rats after hindlimb ischemia but did not migrate in non-ischemic rats. Interestingly, the survival period of transplanted EPCs was notably prolonged in the ischemic limb, indicating that EPCs are required by the ischemic tissues and that the fate of transplanted EPCs was affected by the disease. Compared to the commonly used particle type of MRI contrast agents, the system described in this study is expected to be invaluable to help clarifying the process of stem cell transplantation therapy.
Keywords: Dextran; MRI; Progenitor cell; Transplantation;

Tooth root regeneration using dental follicle cell sheets in combination with a dentin matrix - based scaffold by Bo Yang; Gang Chen; Jie Li; Qing Zou; Dan Xie; Yali Chen; Hang Wang; Xiaohui Zheng; Jie Long; Wei Tang; Weihua Guo; Weidong Tian (2449-2461).
Stem cell mediated tissue engineering has been acknowledged as a prospective strategy for repairing and replacing damaged and lost tissues. However, the low survival rate of implanted stem cells proves to be a major challenge in the management of transplantation failures. While previous studies have indicated the effectiveness of tissue engineered cell sheets in improving the survival rate of implanted cells, we have recently demonstrated the use of treated dentin matrix (TDM) as a biological scaffold and dental follicle cells (DFCs) as the seeding cells for dentinogenesis and tooth root construction. This study proposes a strategy utilizing TDM with human dental follicle cell sheets (DFCSs) for root regeneration. The biological characteristics and changes of human DFCSs under the effect of TDM were studied with scanning electron microscopy, transmission electron microscopy, immunofluorescence microscopy, immunohistochemistry and quantitative real-time PCR. DFCSs combined with TDM were implanted subcutaneously into the dorsum of mice. Histological examination of the harvested grafts revealed a whirlpool-like alignment of the DFCs in multiple layers that were positive for COLI, integrinβ1, fibronectin and alkaline phosphatase (ALP), suggestive of the formation of a rich extracellular matrix. DFCSs, under the effect of TDM, highly expressed DMP-1 and bone sialoprotein (BSP), indicating their potential for odontogenesis and osteogenesis. Importantly, in vivo, TDM could induce and support DFCSs to develop new dentin-pulp like tissues and cementum-periodontal complexes that were positive for markers such as DSP, nestin and VIII factors, COLI and cementum attachment protein (CAP), implying successful root regeneration. Therefore, DFCSs combined with TDM may prove to be a better strategy for the construction of tooth root, and is a prospective approach that could be utilized for the treatment of root or tooth defect or loss in future.
Keywords: Dental follicle cell; Cell sheet technology; Tooth root; Treated dentin matrix; Tooth regeneration;

The role of endothelial cell-bound Jagged1 in Notch3-induced human coronary artery smooth muscle cell differentiation by Ying Xia; Aparna Bhattacharyya; Eric E. Roszell; Martin Sandig; Kibret Mequanint (2462-2472).
Phenotype regulation of vascular smooth muscle cells (VSMC) is an important requirement in both tissue engineering and balloon angioplasty strategies. In recent years, it has become increasingly evident that the Notch signalling pathway plays a critical role in regulating vascular morphogenesis during development and the transcription of differentiated VSMC and its maturation. In arteries, Notch3 is the predominant receptor on VSMC and, signalling is initiated upon binding to its ligand, Jagged1. However, little is known on how ligand presenting strategies affect Notch signalling and subsequently upregulation of smooth muscle cell differentiation. In this study, using human coronary artery smooth muscle cells (HCASMC) and human coronary artery endothelial cells (HCAEC), we show several lines of evidence that direct heterocellular cell-cell contact is necessary for VSMC differentiation via Notch3 signalling. First, neither the addition of soluble Jagged1 nor Jagged1 immobilized to protein G beads induced HCASMC differentiation in culture. Second, despite the upregulation of Notch3 expression, EC-conditioned medium failed to induce HCASMC differentiation. However, when HCASMC and HCAEC were co-cultured either on opposite sides of porous membrane or when these cells were co-cultured directly, both Notch3 and VSMC differentiation marker proteins were upregulated. These upregulations were abrogated by Jagged1-specific siRNA. This study provides the first direct evidence that contact of HCASMC and HCAEC is required for regulating smooth muscle cell differentiation. These findings may have clinical importance and therapeutic potential for modulating vascular SMC phenotype during various cardiovascular disease states and in tissue engineering.
Keywords: Notch3 signalling; Jagged1; Co-culture; siRNA; Differentiation marker proteins; Vascular smooth muscle cell;

In neural tissue engineering, designing materials with the right chemical cues is crucial in providing a permissive microenvironment to encourage and guide neuronal cell attachment and differentiation. Modifying synthetic hydrogels with biologically active molecules has become an increasingly important route in this field to provide a successful biomaterial and cell interaction. This study presents a strategy of using the monomer 2-methacryloxyethyl trimethylammonium chloride (MAETAC) to provide tethered neurotransmitter acetylcholine-like functionality with a complete 2-acetoxy-N,N,N-trimethylethanaminium segment, thereby modifying the properties of commonly used, non-adhesive PEG-based hydrogels. The effect of the functional monomer concentration on the physical properties of the hydrogels was systematically studied, and the resulting hydrogels were also evaluated for mice hippocampal neural cell attachment and growth. Results from this study showed that MAETAC in the hydrogels promotes neuronal cell attachment and differentiation in a concentration-dependent manner, different proportions of MAETAC monomer in the reaction mixture produce hydrogels with different porous structures, swollen states, and mechanical strengths. Growth of mice hippocampal cells cultured on the hydrogels showed differences in number, length of processes and exhibited different survival rates. Our results indicate that chemical composition of the biomaterials is a key factor in neural cell attachment and growth, and integration of the appropriate amount of tethered neurotransmitter functionalities can be a simple and effective way to optimize existing biomaterials for neuronal tissue engineering applications.
Keywords: PEG-based hydrogels; Neurotransmitters; Acetylcholine functionality; Concentration-dependent manner;

Mechanical derivation of functional myotubes from adipose-derived stem cells by Yu Suk Choi; Ludovic G. Vincent; Andrew R. Lee; Marek K. Dobke; Adam J. Engler (2482-2491).
Though reduced serum or myoblast co-culture alone can differentiate adipose-derived stem cells (ASCs) into mesenchymal lineages, efficiency is usually not sufficient to restore function in vivo. Often when injected into fibrotic muscle, their differentiation may be misdirected by the now stiffened tissue. Here ASCs are shown to not just simply reflect the qualitative stiffness sensitivity of bone marrow-derived stem cells (BMSCs) but to exceed BMSC myogenic capacity, expressing the appropriate temporal sequence of muscle transcriptional regulators on muscle-mimicking extracellular matrix in a tension and focal adhesion-dependent manner. ASCs formed multi-nucleated myotubes with a continuous cytoskeleton that was not due to misdirected cell division; microtubule depolymerization severed myotubes, but after washout, ASCs refused at a rate similar to pre-treated values. BMSCs never underwent stiffness-mediated fusion. ASC-derived myotubes, when replated onto non-permissive stiff matrix, maintained their fused state. Together these data imply enhanced mechanosensitivity for ASCs, making them a better therapeutic cell source for fibrotic muscle.
Keywords: Myogenic differentiation; Skeletal muscle; Mechanotransduction; Extracellular matrix; Stiffness;

Liposomal formulations of Etoposide and Docetaxel for p53 mediated enhanced cytotoxicity in lung cancer cell lines by Kaustubh A. Jinturkar; Chakkumkal Anish; Mukesh K. Kumar; Tamishraha Bagchi; Amulya K. Panda; Ambikanandan R. Misra (2492-2507).
The objective of present investigation was to develop and assess comparative enhancement in cytotoxicity of liposomal Etoposide and Docetaxel in non-small cell lung cancer cell lines after pre-treatment and co-administration of p53 tumor suppressor gene and to assess direct lung targeting of optimized formulations by dry powder inhaler technology. Cationic liposomes with and without drug were prepared and allowed to form p53-lipoplex for undertaking cytotoxicity studies in H-1299 (p53 null) and A-549 (p53 wt) cell lines. The optimized lipoplexes showed average size of 200–350 nm, zeta potential of 25–32 mV and sustained drug release up to 16–24 h. The developed liposomes and lipoplexes showed significant intracellular uptake and demonstrated enhanced cytotoxicity of 13–28 % after p53-drug co-administration and 41–63 % after p53 pre-treatment. The p53 mediated enhanced cytotoxicity by increased apoptosis and necrosis was also confirmed using Annexin V – FITC assay. The increased apoptosis suggested restored p53 function and reduced anti-apoptotic drug resistance theirby causing cell sensitization and synergism towards cytotoxicity. The studies conducted above demonstrated significant cell chemo-sensitization after p53 pre-treatment followed by Etoposide/Docetaxel liposomes administration than p53-Etoposide or p53-Docetaxel lipoplex co-administration; more significantly in Docetaxel and in H 1299 cell line. All the formulations when developed as dry powder inhalers showed significant in vitro lung deposition pattern in cascade impactor with fine particle faction of 33–37%. The study opens up a new strategy to treat lung cancer especially in cases of drug resistance. Moreover direct delivery to lung may provide an important role in complete remission of the disease due to target specificity.
Keywords: p53; Chemo-sensitization; Etoposide; Docetaxel; Cytotoxicity;

The efficiency of tumor-specific pH-responsive peptide-modified polymeric micelles containing paclitaxel by Bing-Xiang Zhao; Yang Zhao; Yue Huang; Lin-Min Luo; Ping Song; Xin Wang; Su Chen; Ke-Fu Yu; Xuan Zhang; Qiang Zhang (2508-2520).
The acidic pH in tumor tissues could be used for targeting solid tumors. In the present study, we designed a tumor-specific pH-responsive peptide H7K(R2)2, which could respond to the acidic pH in tumor tissues, and prepared H7K(R2)2-modified polymeric micelles containing paclitaxel (PTX-PM-H7K(R2)2) in order to evaluate their potential targeting of tumor cells and tumor endothelial cells and their anti-tumor activity in mice with tumor cells. PTX-PM-H7K(R2)2 was prepared by a thin-film hydration method. The in vitro release of PTX from PTX-PM-H7K(R2)2 was tested. The in vitro targeting characteristics of H7K(R2)2-modified polymeric micelles on HUVEC (human umbilical vein endothelial cells) and MCF-7 (human breast adenocarcinoma cells) were evaluated. The in vivo targeting activity of H7K(R2)2-modified polymeric micelles and the in vivo anti-tumor activity of PTX-PM-H7K(R2)2 were also investigated in MCF-7 tumor-bearing mice. The released PTX from the PTX-PM-H7K(R2)2 was not affected by the pH. The targeting activity of the H7K(R2)2-modified polymeric micelles was demonstrated by in vitro flow cytometry and confocal microscopy as well as in vivo biodistribution. PTX-PM-H7K(R2)2 produced very marked anti-tumor and anti-angiogenic activity in MCF-7 tumor-bearing mice in vivo.
Keywords: Tumor pH; pH-responsive peptide; Polymeric micelles; Targeting; anti-Tumor efficacy;

We report on a novel type of multifunctional pH-disintegrable micellar nanoparticles fabricated from asymmetrically functionalized β-cyclodextrin (β-CD) based star copolymers covalently conjugated with doxorubicin (DOX), folic acid (FA), and DOTA-Gd moieties for integrated cancer cell-targeted drug delivery and magnetic resonance (MR) imaging contrast enhancement. Asymmetrically functionalized β-CD, (N 3)7-CD-(Br)14, which possesses 7 azide functionalities and 14 α-bromopropionate moieties in the upper and lower rim of rigid toroidal β-CD core, respectively, was synthesized at first. The subsequent atom transfer radical polymerization (ATRP) of N-(2-hydroxypropyl) methacrylamide (HPMA), conjugation with DOX and FA, and click reaction with alkynyl-(DOTA-Gd) complex afforded (DOTA-Gd)7-CD-(PHPMA-FA-DOX)14 star copolymer comprising of 7 DOTA-Gd complex moieties and 14 PHPMA arms covalently anchored with DOX and FA via acid-labile carbamate linkages and ester bonds, respectively. The covalent conjugation with ∼13 DOX molecules onto PHPMA arms per star copolymer (∼14 wt% loading content) endows the initially hydrophilic one with amphiphilicity, leading to the self-assembly into micellar nanoparticles of several tens of nanometers in aqueous solution at pH 7.4. In vitro DOX release profile from micellar nanoparticles is highly pH-dependent, and over a time period of 42 h, cumulative releases of ∼10%, 53%, and 89% conjugated DOX at pH 7.4, 5.0, and 4.0, respectively, were observed. Most importantly, the pH-modulated release of conjugated DOX from micellar nanoparticles is accompanied with the micelle disintegration due to the loss of amphiphilicity of the star copolymer scaffold. In vitro cell viability assays revealed that (DOTA-Gd)7-CD-(PHPMA15)14 star copolymer is almost non-cytotoxic up to a concentration of 0.5 g/L, whereas DOX-conjugated micellar nanoparticles of (DOTA-Gd)7-CD-(PHPMA-FA-DOX)14 can effectively enter and kill HeLa cells at a concentration higher than ∼80 mg/L. In vitro MR imaging experiments indicated a considerably enhanced T 1 relaxivity (r 1 = 11.4 s−1 mM−1) for micellar nanoparticles compared to that for the small molecule counterpart, alkynyl-DOTA-Gd (r 1 = 3.1 s−1 mM−1). In vivo MR imaging assay in rats revealed considerable accumulation of micellar nanoparticles within rat liver and kidney and prominent positive contrast enhancement. The integrated design of diagnostic and therapeutic functions of multifunctional pH-disintegrable micellar nanoparticles augurs well for their practical applications in the field of image-guided cancer chemotherapy.
Keywords: Targeted drug delivery; MR imaging; pH-labile; Intracellular; Theranostic nanocarriers;

Multi-functional graphene as an in vitro and in vivo imaging probe by Ganesh Gollavelli; Yong-Chien Ling (2532-2545).
A strategy has been developed for the synthesis of multi-functional graphene (MFG) using green synthetic approach and explored its biomedical application as a promising fluorescent marker for in vitro and in vivo imaging. In-situ microwave-assisted reduction and magnetization process was adopted to convert the graphene oxide into magnetic graphene within 1 min, which was further covalently modified to build a polyacrylic acid (PAA) bridge for linking the fluorescein o-methacrylate (FMA) to yield MFG with water-dispersibility (∼2.5 g/l) and fluorescence property (emission maximum at 526 nm). The PAA bridges also functions to prevent graphene-induced fluorescence quenching of conjugated FMA. The extent of reduction, magnetization, and functionalization was confirmed with TEM, AFM, Raman, XPS, FT-IR, TGA, and SQUID measurements. In vitro cytotoxicity study of HeLa cells reveal that MFG could stand as a biocompatible imaging probe with an IC50 value of ∼100 μg/ml; whereas in vivo zebrafish study does not induce any significant abnormalities nor affects the survival rate after microinjection of MFG. Confocal laser scanning microscopy images reveals that MFG locates only in the cytoplasm region and exhibits excellent co-localization and biodistribution from the head to tail in the zebrafish. Our results demonstrate the applicability of graphene based fluorescence marker for intracellular imaging and, more significantly, as well as whole-animal imaging. Hence, MFG could preferentially serve as a dual functional probe in biomedical diagnostics.
Keywords: Multi-functional graphene; Zebrafish; Intracellular imaging; Whole-animal imaging and green;

Supramolecular assemblies in functional siRNA delivery: Where do we stand? by Hamidreza M. Aliabadi; Breanne Landry; Chongbo Sun; Tian Tang; Hasan Uludağ (2546-2569).
The discovery of RNA interference (RNAi) has excited the scientific field due to its potential for wide range of therapeutic applications. The pharmacological mediator of RNAi, short interfering RNA (siRNA), however, has faced significant obstacles in reaching its target site and effectively exerting its silencing activity. Effective pharmacological use of siRNA requires ‘carriers’ that can deliver the siRNA to its intended site of action. The carriers assemble the siRNA into supramolecular complexes that display functional properties during the delivery process. This review will summarize non-viral approaches to siRNA delivery, emphasizing the current obstacles to delivery and the mechanisms employed to overcome these obstacles. The carriers successfully pursued in pre-clinical (animal) models will be presented so as to provide a glimpse of possible candidates for clinical testing. Supramolecular assembly of nucleic acids with carriers will be probed from thermodynamics and computational perspectives to understand supramolecular structures and their dynamics. The delivery and trafficking requirements for siRNA are then dissected and engineering approaches to overcoming these barriers will be articulated. The latter has been attempted both at the cellular levels, focusing on intracellular barriers, as well as systemic level, emphasizing macroscopic challenges affecting siRNA delivery. Clinical experience with non-viral siRNA delivery is summarized, highlighting the nature delivery modes attempted in clinical settings. We conclude with a perspective on the future of siRNA therapeutics, specifically concentrating on the possible impact of non-viral carriers in the field.
Keywords: Supramolecules; Short interfering RNA (siRNA); Non-viral delivery; Intracellular trafficking; Targeting; Clinical trials;

Targeting human epidermal growth factor receptor 2 by a cell-penetrating peptide–affibody bioconjugate by Srinath Govindarajan; Jeyarajan Sivakumar; Prathyusha Garimidi; Nandini Rangaraj; Jerald M. Kumar; Nalam M. Rao; Vijaya Gopal (2570-2582).
Cell-penetrating peptide (CPP)-based delivery systems represent a strategy that facilitates DNA import efficiently and non-specifically into cells. To introduce specificity, we devised an approach that combines a cell-penetrating peptide, TAT-Mu (TM) and a targeting ligand, an HER2 antibody mimetic-affibody (AF), designated as TMAF to deliver nucleic acids into the cells. In this study, we synthesized TMAF protein and its truncated versions, i.e. MAF and AF, by expressing the corresponding plasmids in Escherichia coli BL21(DE3)pLysS cells. Purified TMAF binds DNA efficiently and protects plasmid DNA from DNaseI action. Transfection of HER2+ breast cancer cell lines MDA-MB-453, SK-OV-3, SK-BR-3 and an ovarian cancer cell line with plasmid DNA pCMVβ-gal, resulted in enhanced β-galactosidase activity when compared to control MDA-MB-231 cells. Maximal activity observed in MDA-MB-453 cells at DNA:TMAF:Protamine sulphate (PS) corresponding to 1:8:2 charge ratios. Further the observed gene transfection was resistant to serum, sensitive to the presence of free AF and non-toxic. Variants of TMAF although non-toxic, were far less efficient indicating the effective role of the TAT and Mu domains. The observed DNA uptake and reporter gene activity mediated by TMAF in vitro could be linked with the cell-surface density of tyrosine kinase receptor HER2 (ErbB2) levels estimated by Western blot. Further, we confirmed the efficacy of DNA transfer by TMAF protein in xenograft mouse models using MDA-MB-453 cells. Expression of β-galactosidase as the reporter gene, upon intratumoral injection of DNA, in complex with TMAF, lends credence to specific DNA import and distribution within the tumor tissue that was attributed to high HER2 receptor overexpression in MDA-MB-453 cells. Through delivery of anti-TF hshRNA: TMAF: PS complex, we demonstrate specific knockdown of tissue factor (TF) in MDA-MB-453 cells in vitro. Most importantly, in a xenograft mouse model, we observe significant (P  < 0.05) and specific reduction of tumor volume when anti-TF hshRNA: TMAF: PS complex was injected intratumorally. Collectively our data indicate that AF-based chimeric peptides with nucleic acid binding properties may provide an effective tumor specific strategy to deliver therapeutic nucleic acids.
Keywords: Affibody; Epidermal growth factor receptor 2; Cell targeting; Nucleic acid delivery; Gene transfer; CPPs;

pH-responsive drug delivery system based on luminescent CaF2:Ce3+/Tb3+-poly(acrylic acid) hybrid microspheres by Yunlu Dai; Cuimiao Zhang; Ziyong Cheng; Ping’an Ma; Chunxia Li; Xiaojiao Kang; Dongmei Yang; Jun Lin (2583-2592).
In this study, we design a controlled release system based on CaF2:Ce3+/Tb3+-poly(acrylic acid) (PAA) composite microspheres, which were fabricated by filling the pH-responsive PAA inside CaF2:Ce3+/Tb3+ hollow spheres via photopolymerization route. The CaF2:Ce3+/Tb3+ hollow spheres prepared by hydrothermal route possess mesoporous structure and show strong green fluorescence from Tb3+ under UV excitation. Doxorubicin hydrochloride (DOX), a widely used anti-cancer drug, was used as a model drug to evaluate the loading and controlled release behaviors of the composite microspheres due to the good biocompatibility of the samples using MTT assay. The composite carriers provide a strongly pH-dependent drug release behavior owing to the intrinsic property of PAA and its interactions with DOX. The endocytosis process of drug-loaded microspheres was observed using confocal laser scanning microscopy (CLSM) and the in vitro cytotoxic effect against SKOV3 ovarian cancer cells of the DOX-loaded carriers was investigated. In addition, the extent of drug release could be monitored by the altering of photoluminescence (PL) intensity of CaF2:Ce3+/Tb3+. Considering the good biocompatibility, high drug loading content and pH-dependent drug release of the materials, these hybrid luminescent microspheres have potential applications in drug controlled release and disease therapy.
Keywords: Drug carrier; Poly(acrylic acid); Hollow structure; Doxorubicin; Luminescence;