Effects of an Avidin-Biotin Binding System on Chondrocyte Adhesion and Growth on Biodegradable Polymers

Development and Evaluation of an Expedited System for Creation of Single Walled Carbon Nanotube Platforms

Single-walled carbon nanotubes (SWNT) have a strong and stable near-infrared (nIR) fluorescence that can be used to selectively detect target analytes, even at the single molecule level, through changes in either their fluorescence intensity or emission peak wavelength. SWNTs have been employed as NIR optical sensors for detecting a variety of analytes. However, high costs, long fabrication times, and poor distributions limit the current methods for immobilizing SWNT sensors on solid substrates. Recently, our group reported a protocol for SWNT immobilization with high fluorescence yield, longevity, fluorescence distribution, and sensor response, unfortunately this process takes 5 days to complete. Herein we report an improved method to immobilize SWNT sensors that only takes 2 days and results in higher fluorescence intensity while maintaining a high level of SWNT distribution. We performed surface morphology and chemical composition tests on the original and new synthesis methods and compared the sensor response rates. The development of this new method of attaching SWNT sensors to a platform allows for creation of a sensing system in just 2 days without sacrificing the advantageous characteristics of the original, 5-day platforms.

Progress of polysaccharide-based tissue adhesives

Recently, polymer-based tissue adhesives (TAs) have gained the attention of scientists and industries as alternatives to sutures for sealing and closing wounds or incisions because of their ease of use, low cost, minimal tissue damage, and short application time. However, poor mechanical properties and weak adhesion strength limit the application of TAs, although numerous studies have attempted to develop new TAs with enhanced performance. Therefore, next-generation TAs with improved multifunctional properties are required. In this review, we address the requirements of polymeric TAs, adhesive characteristics, adhesion strength assessment methods, adhesion mechanisms, applications, advantages and disadvantages, and commercial products of polysaccharide (PS)-based TAs, including chitosan (CS), alginate (AL), dextran (DE), and hyaluronic acid (HA). Additionally, future perspectives are discussed.

Effects of Various Cell Surface Engineering Reactions on the Biological Behavior of Mammalian Cells

Cell surface engineering technologies can regulate cell function and behavior by modifying the cell surface. Previous studies have mainly focused on investigating the effects of cell surface engineering reactions and materials on cell activity. However, they do not comprehensively analyze other cellular processes. This study exploits covalent bonding, hydrophobic interactions, and electrostatic interactions to modify the macromolecules succinimide ester-methoxy polyethylene glycol (NHS-mPEG), distearoyl phosphoethanolamine-methoxy polyethylene glycol (DSPE-mPEG), and poly-L-lysine (PLL), respectively, on the cell surface. This work systematically investigates the effects of the three surface engineering reactions on the behavior of human umbilical vein endothelial cells (HUVECs) and human skin fibroblasts, including viability, growth, proliferation, cell cycle, adhesion, and migration. The results reveals that the PLL modification method notably affects cell viability and G2/M arrest and has a short modification duration. However, the DSPE-mPEG and NHS-mPEG modification methods have little effect on cell viability and proliferation but have a prolonged modification duration. Moreover, the DSPE-mPEG modification method highly affects cell adherence. Further, the NHS-mPEG modification method can significantly improve the migration ability of HUVECs by reducing the area of focal adhesions. The findings of this study will contribute to the application of cell surface engineering technology in the biomedical field.

Biomimetic Strategies to Develop Bioactive Scaffolds for Myocardial Tissue Engineering

The aim of this paper is to provide an overview of the results of the research activity carried out in our laboratories, over the last 10 years, in relation to the development of strategies for the production of biomimetic and bioactive scaffolds for myocardial tissue engineering. Biomimetic and bioactive polymeric scaffolds for cardiac regeneration were designed and manufactured in our laboratories and their morphological, physicochemical, mechanical and biological properties were investigated by different techniques, such as scanning electron microscopy, infrared chemical imaging, swelling test, in vitro degradation assessment, dynamic mechanical analysis, in vitro and in vivo biological tests. Biomimetic scaffolds, able to favor tissue regeneration by mimicking nature, were engineered by different strategies, comprising: (i) the imitation of the composition and interactions among components of the natural extracellular matrix (ECM), by mixing of proteins and polysaccharides; (ii) the material surface modification, using both traditional and innovative techniques, such as molecular imprinting; (iii) the incorporation and release of specific active agents and (iv) the production of scaffolds with a microarchitecture similar to that of native ECM. All the developed strategies were found to be effective in creating materials able to influence cellular behavior and therefore to favor the process of new tissue formation. In particular, the approach based on the combination of different strategies aimed at creating a system capable of communicating with the cells and promoting specific cellular responses, as the ECM does, has appeared particularly promising, in view to favor the formation of a tissue equivalent to the cardiac one.

Hydrogel Containing Anti-CD44-Labeled Microparticles, Guide Bone Tissue Formation in Osteochondral Defects in Rabbits

Hydrogels are suitable for osteochondral defect regeneration as they mimic the viscoelastic environment of cartilage. However, their biomechanical properties are not sufficient to withstand high mechanical forces. Therefore, we have prepared electrospun poly-ε-caprolactone-chitosan (PCL-chit) and poly(ethylene oxide)-chitosan (PEO-chit) nanofibers, and FTIR analysis confirmed successful blending of chitosan with other polymers. The biocompatibility of PCL-chit and PEO-chit scaffolds was tested; fibrochondrocytes and chondrocytes seeded on PCL-chit showed superior metabolic activity. The PCL-chit nanofibers were cryogenically grinded into microparticles (mean size of about 500 µm) and further modified by polyethylene glycol-biotin in order to bind the anti-CD44 antibody, a glycoprotein interacting with hyaluronic acid (PCL-chit-PEGb-antiCD44). The PCL-chit or PCL-chit-PEGb-antiCD44 microparticles were mixed with a composite gel (collagen/fibrin/platelet rich plasma) to improve its biomechanical properties. The storage modulus was higher in the composite gel with microparticles compared to fibrin. The Eloss of the composite gel and fibrin was higher than that of the composite gel with microparticles. The composite gel either with or without microparticles was further tested in vivo in a model of osteochondral defects in rabbits. PCL-chit-PEGb-antiCD44 significantly enhanced osteogenic regeneration, mainly by desmogenous ossification, but decreased chondrogenic differentiation in the defects. PCL-chit-PEGb showed a more homogeneous distribution of hyaline cartilage and enhanced hyaline cartilage differentiation.

Bioadhesives for internal medical applications: A review

Bioadhesives such as tissue adhesives, hemostatic agents, and tissue sealants have gained increasing popularity in different areas of clinical operations during the last three decades. Bioadhesives can be categorized into internal and external ones according to their application conditions. External bioadhesives are generally applied in topical medications such as wound closure and epidermal grafting. Internal bioadhesives are mainly used in intracorporal conditions with direct contact to internal environment including tissues, organs and body fluids, such as chronic organ leak repair and bleeding complication reduction. This review focuses on internal bioadhesives that, in contrast with external bioadhesives, emphasize much more on biocompatibility and adhesive ability to wet surfaces rather than on gluing time and intensity. The crosslinking mechanisms of present internal bioadhesives can be generally classified as follows: 1) chemical conjugation between reactive groups; 2) free radical polymerization by light or redox initiation; 3) biological or biochemical coupling with specificity; and 4) biomimetic adhesion inspired from natural phenomena. In this review, bioadhesive products of each class are summarized and discussed by comparing their designs, features, and applications as well as their prospects for future development.

STATEMENT OF SIGNIFICANCE

Despite the emergence of numerous novel bioadhesive formulations in recent years, thus far, the classification of internal and external bioadhesives has not been well defined and universally acknowledged. Many of the formulations have been proposed for treatment of several diseases even though they are not applicable for such conditions. This is because of the lack of a systematic standard or evaluation protocol during the development of a new adhesive product. In this review, the definition of internal and external bioadhesives is given for the first time, and with a focus on internal bioadhesives, the criteria of an ideal internal bioadhesive are adequately discussed; this is followed by the review of recently developed internal bioadhesives based on different gluing mechanisms.

Biotin-avidin mediates the binding of adipose-derived stem cells to a porous β-tricalcium phosphate scaffold: Mandibular regeneration

The present study aimed to investigate the properties of a promising bone scaffold for bone repair, which consisted of a novel composite of adipose-derived stem cells (ADSCs) attached to a porous β-tricalcium phosphate (β-TCP) scaffold with platelet-rich plasma (PRP). The β-TCP powder was synthesized and its composition was determined using X-ray diffraction and Fourier transform infrared spectroscopy. The surface morphology and microstructure of the fabricated porous β-TCP scaffold samples were analyzed using light and scanning electron microscopy, and their porosity and compressive strength were also evaluated. In addition, the viability of rabbit ADSCs incubated with various concentrations of the β-TCP extraction fluid was analyzed. The rate of attachment and the morphology of biotinylated ADSCs (Bio-ADSCs) on avidin-coated β-TCP (Avi-β-TCP), and untreated ADSCs on β-TCP, were compared. Furthermore, in vivo bone-forming abilities were determined following the implantation of group 1 (Bio-ADSCs/Avi-β-TCP) and group 2 (Bio-ADSCs/Avi-β-TCP/PRP) constructs using computed tomography, and histological osteocalcin (OCN) and alkaline phosphatase (ALP) expression analyses in a rabbit model of mandibulofacial defects. The β-TCP scaffold exhibited a high porosity (71.26±0.28%), suitable pore size, and good mechanical strength (7.93±0.06 MPa). Following incubation with β-TCP for 72 h, 100% of viable ADSCs remained. The avidin-biotin binding system significantly increased the initial attachment rate of Bio-ADSCs to Avi-β-TCP in the first hour (P<0.01). Following the addition of PRP, group 2 exhibited a bony-union and mandibular body shape, newly formed bone and increased expression levels of OCN and ALP in the mandibulofacial defect area, as compared with group 1 (P<0.05). The results of the present study suggested that the novel Bio-ADSCs/Avi-β-TCP/PRP composite may have potential application in bone repair and bone tissue engineering.

Biotin-Avidin Based Universal Cell-Matrix Interaction for Promoting Three-Dimensional Cell Adhesion

To promote cell adhesion in three-dimensional (3D) extracellular matrix (ECM) is crucial for avoiding cell anoikis, which is one of the most important issues for fundamental cell biology. Herein, a biotin-avidin based universal cell-matrix interaction for different types of cells is developed in order to achieve the promoted adhesion in 3D ECM. For the purpose, biotinylated nanofibrous hydrogels are constructed by coassembling 1,4-benzyldicarboxamide (C2) based non-biotinylated and biotinylated supramolecular gelators. The used cells are modified by avidin (AV-cells) through biotinylating cells and then interacting with avidin. After in situ encapsulating AV-cells in the hydrogels, the adhered amount can be increased by tens of percent even with adding several percentages of the biotinylated C2 gelators in the coassembly due to the specific biotin-avidin interaction. Reverse transcription polymerase chain reaction (RT-PCR) confirms that AV-cells can proliferate without varying gene expression and denaturation. Compared with the interaction between RGD and cells, this avidin-biotin interaction should be much more universal and it is feasible to be employed to promote cell adhesion for most types of cells in 3D matrix.

Strategies for the chemical and biological functionalization of scaffolds for cardiac tissue engineering: a review

The development of biomaterials for cardiac tissue engineering (CTE) is challenging, primarily owing to the requirement of achieving a surface with favourable characteristics that enhances cell attachment and maturation. The biomaterial surface plays a crucial role as it forms the interface between the scaffold (or cardiac patch) and the cells. In the field of CTE, synthetic polymers (polyglycerol sebacate, polyethylene glycol, polyglycolic acid, poly-l-lactide, polyvinyl alcohol, polycaprolactone, polyurethanes and poly(N-isopropylacrylamide)) have been proven to exhibit suitable biodegradable and mechanical properties. Despite the fact that they show the required biocompatible behaviour, most synthetic polymers exhibit poor cell attachment capability. These synthetic polymers are mostly hydrophobic and lack cell recognition sites, limiting their application. Therefore, biofunctionalization of these biomaterials to enhance cell attachment and cell material interaction is being widely investigated. There are numerous approaches for functionalizing a material, which can be classified as mechanical, physical, chemical and biological. In this review, recent studies reported in the literature to functionalize scaffolds in the context of CTE, are discussed. Surface, morphological, chemical and biological modifications are introduced and the results of novel promising strategies and techniques are discussed.

Application of avidin-biotin technology to improve cell adhesion on nanofibrous matrices

BACKGROUND

Electrospinning is an easy and effective technique to produce submicron fibers possessing a range of attractive characteristics such as interconnected porous structures similar to natural ECM and good resilience to movement. Rapid and efficient cell attachment to nanofibrous matrices is a necessary prerequisite in tissue engineering. Thus, the aim of this study is to evaluate poly(ε-caprolactone-co-lactide)/Pluronic (PLCL/Pluronic) nanofibrous matrices with avidin-biotin technology for improving cell adhesion for the first time.

RESULTS

PLCL/Pluronic nanofibers had relatively homogeneous fibers and interconnected porous structures. Pluronic significantly modified the hydrophilicity of nanofibrous matrices and PLCL/Pluronic nanofibrous matrices had better performance on maintaining cell proliferation. Avidin-biotin technology had no negative effect on the hydrophilic property, mechanical property and cell proliferation. Meanwhile, the attachment and spreading of adipose-derived stem cells (ADSCs) onto PLCL/Pluronic nanofibrous matrices with avidin-biotin technology was promoted obviously.

CONCLUSIONS

PLCL/Pluronic nanofibrous matrices inheriting the excellent characteristics of both PLCL and Pluronic have the better cell adhesion ability through avidin-biotin technology, implying a promising application in skin care, tissue regeneration and other related area.

Poly(dopamine) coating to biodegradable polymers for bone tissue engineering

In this study, a technique based on poly(dopamine) deposition to promote cell adhesion was investigated for the application in bone tissue engineering. The adhesion and proliferation of rat osteoblasts were evaluated on poly(dopamine)-coated biodegradable polymer films, such as polycaprolactone, poly(l-lactide) and poly(lactic- co-glycolic acid), which are commonly used biodegradable polymers in tissue engineering. Cell adhesion was significantly increased to a plateau by merely 15 s of dopamine incubation, 2.2–4.0-folds of increase compared to the corresponding untreated substrates. Cell proliferation was also greatly enhanced by poly(dopamine) deposition, indicated by shortened cell doubling time. Mineralization was also increased on the poly(dopamine)-deposited surfaces. The potential of poly(dopamine) deposition in bone tissue engineering is demonstrated in this study.

Modulation of the proliferation and matrix synthesis of chondrocytes by dynamic compression on genipin-crosslinked chitosan/collagen scaffolds

Dynamic compression is an important physical stimulus for the physiology of chondrocyte and articular cartilage tissue engineering. In this study, modulation of chondrocyte behaviors in chitosan/collagen scaffolds with different mechanical properties under free-swelling or dynamic compression conditions was investigated. Rabbit chondrocytes were seeded in chitosan/collagen scaffolds crosslinked by genipin (GP) with different concentrations, and then cultured for 3 days prior to cyclic compression of 40% strain, 0.1 Hz, and 30 min/day for 2 weeks. The results showed that the cell proliferation was increased with increasing genipin concentrations and dynamic compression. On the other hand, although total glycosaminoglycans (GAGs) deposition was enhanced by dynamic compression under certain conditions, e.g. the GP0.5 chitosan/collagen scaffolds for 1 week of compression culture, normalized GAGs deposition per cell was decreased by dynamic compression. Our results suggest that while several studies suggest that dynamic compression benefits articular cartilage tissue engineering, many factors including scaffold types and compression conditions determine the outcome of dynamic compression culture.

Development of channeled nanofibrous scaffolds for oriented tissue engineering

A tissue-engineering scaffold resembling the structure of the natural extracellular matrix can often facilitate tissue regeneration. Nerve and tendon are oriented micro-scale tissue bundles. In this study, a method combining injection molding and thermally induced phase separation techniques is developed to create single- and multiple-channeled nanofibrous poly(L-lactic acid) scaffolds. The overall shape, the number and spatial arrangement of channels, the channel wall matrix architecture, the porosity and mechanical properties of the scaffolds are all tunable. The porous NF channel wall matrix provides an excellent microenvironment for protein adsorption and the attachment of PC12 neuronal cells and tendon fibroblast cells, showing potential for neural and tendon tissue regeneration.

Poly(dopamine) coating of scaffolds for articular cartilage tissue engineering

A surface modification technique based on poly(dopamine) deposition developed from oxidative polymerization of dopamine is known to promote cell adhesion to several cell-resistant substrates. In this study this technique was applied to articular cartilage tissue engineering. The adhesion and proliferation of rabbit chondrocytes were evaluated on poly(dopamine)-coated polymer films, such as polycaprolactone, poly(L-lactide), poly(lactic-co-glycolic acid) and polyurethane, biodegradable polymers that are commonly used in tissue engineering. Cell adhesion was significantly increased by merely 15 s of dopamine incubation, and 4 min incubation was enough to reach maximal cell adhesion, a 1.35-2.69-fold increase compared with that on the untreated substrates. Cells also grew much faster on the poly(dopamine)-coated substrates than on untreated substrates. The increase in cell affinity for poly(dopamine)-coated substrates was demonstrated via enhancement of the immobilization of serum adhesive proteins such as fibronectin. When the poly(dopamine)-coating technique was applied to three-dimensional (3-D) polyurethane scaffolds, the proliferation of chondrocytes and the secretion of glycosaminoglycans were increased compared with untreated scaffolds. Our results show that the deposition of a poly(dopamine) layer on 3-D porous scaffolds is a simple and promising strategy for articular cartilage tissue engineering, and may be applied to other types of tissue engineering.

Modulation of the functions of osteoblast-like cells on poly(allylamine hydrochloride) and poly(acrylic acid) multilayer films

Deposition of layer-by-layer polyelectrolyte multilayer (PEM) films has been a widely applied surface modification technique to improve the biocompatibility of biomaterials. The objective of this study was to investigate the impact of the deposition of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) multilayer films on adhesion, growth and differentiation of osteoblasts-like MG63 cells. PAH and PAA were deposited sequentially onto tissue culture polystyrene at either pH 2.0 or pH 6.5 with 4-21 layers. While the MG63 cells attached poorly on the PAH/PAA multilayer films deposited at pH 2.0, while the cells adhered to the PEM films deposited at pH 6.5, depending on layer numbers. Cell adhesion, proliferation and osteogenic activities (alkaline phosphatase activity, expression of osteogenic marker genes and mineralization) were highest on the 4-layer PAH/PAA film and decreased with increasing layer numbers. On the other hand, the behavior of MG63 cells did not show any difference on the adjacent even and odd layers, except PEM4 and PEM5, i.e. the surface charges of the PAH/PAA multilayer films with over ten layers seem indifferent to osteoblastic functions. The results in this study suggested that the mechanical properties of PEM films may play a critical role in modulating the behavior of osteoblasts, providing guidance for application of PEM films to osteopaedic implants.

Dopamine-assisted immobilization of poly(ethylene imine) based polymers for control of cell-surface interactions

Non-fouling coatings play a critical role in many biomedical applications, such as diagnostic assay materials, biosensors, blood contacting devices and other implants. In the present work we have developed a facile, one step deposition method based on dopamine polymerization for preparation of non-fouling and biotinylated surfaces for biomedical applications. Poly(ethylene imine)-graft-poly(ethylene glycol) co-polymer (PEI-g-PEG) was mixed with an alkaline dopamine solution and then deposited onto different substrates. The dopamine coatings formed by this method were characterized by X-ray photoelectron spectroscopy (XPS), and the results indicated successful deposition of PEG. The resultant dopamine coatings formed on tissue culture polystyrene by this method revealed successful deposition of PEG, as shown by XPS. PEI-g-PEG/dopamine deposition for 2h inhibited the adsorption of serum proteins and the attachment of fibroblasts, suggesting that PEG molecules were immobilized in a sufficient density on the surface of the coating. Furthermore, co-deposition of PEI-g-PEG and PEI-g-biotin in alkaline dopamine solutions provided a cell-resisting background surface, at the same time providing accessible biotin molecules. We have demonstrated that the surface can be used for the selective binding of avidin, followed by the binding of Arg-Gly-Asp-Ser-biotin and enhanced cell attachment by specific cell-ligand interactions. In conclusion, our one step immobilization method provides a simple tool to fabricate surfaces with controllable cell affinity.

Effect of seeding using an avidin-biotin binding system on the attachment of periodontal ligament fibroblasts to nanohydroxyapatite scaffolds: three-dimensional culture

Purpose

For periodontal tissue engineering, it is a primary requisite and a challenge to select the optimum types of cells, properties of scaffold, and growth factor combination to reconstruct a specific tissue in its natural form and with the appropriate function. Owing to fundamental disadvantages associated with using a two-dimensional substrate, several methods of seeding cells into three-dimensional scaffolds have been reported and the authors have asserted its usefulness and effectiveness. In this study, we explore the cell attachment of periodontal ligament fibroblasts on nanohydroxyapatite (n-HA) scaffold using avidin biotin binding system (ABBS).

Methods

Human periodontal ligament fibroblasts were isolated from the health tooth extracted for the purpose of orthodontic procedure. HA nanoparticles were prepared and Ca(NO₃)₂-4H₂O and (OC₂H₅)₃P were selected as precursors of HA sol. The final scaffold was 8 mm in diameter and 3 mm in height disk with porosity value of 81.55%. 1×10⁵ periodontal ligament fibroblasts were applied to each scaffold. The cells were seeded into scaffolds by static, agitating and ABBS seeding method.

Results

The number of periodontal ligament fibroblasts attached was greater for ABBS seeding method than for static or agitating method (P<0.05). No meaningful difference has been observed among seeding methods with scanning electron microscopy images. However, increased strength of cell attachment of ABBS could be deduced from the high affinity between avidin and biotin (Kd=10^-15 M).

Conclusions

The high-affinity ABBS enhances the ability of periodontal ligament fibroblasts to attach to three-dimensionally constructed n-HA scaffolds.

Chitosan/poly(epsilon-caprolactone) blend scaffolds for cartilage repair

Chitosan (CHT)/poly(ɛ-caprolactone) (PCL) blend 3D fiber-mesh scaffolds were studied as possible support structures for articular cartilage tissue (ACT) repair. Micro-fibers were obtained by wet-spinning of three different polymeric solutions: 100:0 (100CHT), 75:25 (75CHT) and 50:50 (50CHT) wt.% CHT/PCL, using a common solvent solution of 100 vol.% of formic acid. Scanning electron microscopy (SEM) analysis showed a homogeneous surface distribution of PCL. PCL was well dispersed throughout the CHT phase as analyzed by differential scanning calorimetry and Fourier transform infrared spectroscopy. The fibers were folded into cylindrical moulds and underwent a thermal treatment to obtain the scaffolds. μCT analysis revealed an adequate porosity, pore size and interconnectivity for tissue engineering applications. The PCL component led to a higher fiber surface roughness, decreased the scaffolds swelling ratio and increased their compressive mechanical properties. Biological assays were performed after culturing bovine articular chondrocytes up to 21 days. SEM analysis, live-dead and metabolic activity assays showed that cells attached, proliferated, and were metabolically active over all scaffolds formulations. Cartilaginous extracellular matrix (ECM) formation was observed in all formulations. The 75CHT scaffolds supported the most neo-cartilage formation, as demonstrated by an increase in glycosaminoglycan production. In contrast to 100CHT scaffolds, ECM was homogenously deposited on the 75CHT and 50CHT scaffolds. Although mechanical properties of the 50CHT scaffold were better, the 75CHT scaffold facilitated better neo-cartilage formation.

Rapid and Direct Cell-to-Cell Adherence Using Avidin-Biotin Binding System: Large Aggregate Formation in Suspension Culture and Small Tissue Element Formation Having a Precise Microstructure Using Optical Tweezers

Effectively organizing isolated cells to tissue elements having an appropriate microstructure is a fundamental issue in future tissue engineering, but biological cell-to-cell adhesion is too weak to assemble single cells directly. In order to overcome the difficulty, we applied an Avidin-Biotin Binding System (ABBS) to cell surfaces, and avidinylated and biotinylated cells could mutually bind in the short time they were mixed together. Unlike conventional intact cells, ABBS helped make larger spheroids. Interestingly, avidinylated and biotinylated cell adherence occurred within 1 sec using laser trapping, enabling single cell manipulation. We showed precise, direct single-cell-based tissue assembly using ABBS and optical tweezers, followed by damage-free tissue culture. The combination of ABBS and single cell manipulation has considerable potential for use in application such as tissue engineering, regenerative medicine, and drug screening system.

Preparation of porous collagen/hyaluronic acid hybrid scaffolds for biomimetic functionalization through biochemical binding affinity

This study demonstrated the feasibility of introducing an avidin-biotin system to three-dimensional and highly porous scaffolds for the purpose of designing scaffolds that have binding affinity with bioactive molecules for various biomimetic modifications. Porous hybrid scaffolds composed of collagen and hyaluronic acid (HA) were prepared by a novel overrun process. The overrun-processed scaffolds showed a uniform dual-pore structure because of the injection of gas bubbles and ice recrystallization during the fabrication process and had a higher porosity than scaffolds prepared by a conventional freeze-drying method. The mechanical strength and biodegradation kinetics were controlled by the method of preparation and the composition of collagen/HA. Collagen/HA scaffolds did not show any significant adverse effects on cell viability even after 10 days of incubation. The fibroblasts cultured in the overrun-processed scaffolds were widely distributed and had proliferated on the surfaces of the macropores in the scaffolds, whereas the cells that were seeded in the freeze-dried scaffolds had attached mainly on the dense surface of the scaffolds. As the collagen content in the scaffolds increased, the cellular ingrowth into the inner pores of the scaffolds decreased because of the high affinity between the collagen and the cells. Measurements obtained via confocal microscopy revealed that the porous collagen/HA scaffolds could be functionalized with the biotin by incorporating avidin. Therefore, the present biotinylation approach may allow the incorporation of various bioactive molecules (DNA, growth factors, drug, peptide, etc) into the three-dimensional porous scaffolds.

Fibronectin and culture temperature modulate the efficacy of an avidin–biotin binding system for chondrocyte adhesion and growth on biodegradable polymers

Cell adhesion to a scaffold is a prerequisite for tissue engineering. Many studies have been focused on enhancing cell adhesion to synthetic materials that are used for scaffold fabrication. Previously, we showed that immobilization of biotin molecules to chondrocyte surfaces enhanced cell adhesion to avidin-coated biodegradable polymers such as poly-L-lactic acid, poly-D,L-lactic acid and polycaprolactone. However, the endocytosis of cell membrane biotin molecules decreases binding strength between biotinylated-chondrocytes (B-chondrocytes) and avidin-coated substrata, and therefore decreases cell spreading and discourages long-term chondrocytes culture. In this study, we proposed two strategies to solve the shortcoming of the avidin-biotin binding system. First, the avidin-biotin binding system is combined with the intrinsic integrin-dependent adhesion systems in order to enhance long-term cell culture. Second, the incubation temperature is lowered in order to slow down the endocytosis process. We found that the avidin-biotin binding system in combination with FN-integrin binding system enhanced cell adhesion, cell spreading and cell growth. Decrease of cell culture temperature to 4 degrees C enhanced the adhesion of B-chondrocytes to the avidin-coated surfaces, but decreased cell viability and proliferation, compared to culture temperature of 37 degrees C. Whether there is an optimal seeding temperature between 4 and 37 degrees C for both adhesion and proliferation of B-chondrocytes needs further investigation. Our results indicated that modulation of the adhesion conditions could further enhance the efficacy of the avidin-biotin binding system in mediating cell adhesion, and subsequent tissue culture.

The effect of electrochemical functionalization of Ti-alloy surfaces by aptamer-based capture molecules on cell adhesion

To improve cell seeding efficiency and cytocompatibility, we designed a new coating material for scaffolds. We used aptamers, highly specific cell binding nucleic acids generated by combinatorial chemistry with an in vitro selection called systematic evolution of exponential enrichment (SELEX). In this study, we functionalized Ti-alloy surfaces to enhance cell adhesion. By coating the material with a cell specific aptamer, working as a capture molecule, we could improve the attachment of cells effectively and avoid the limitations of the currently available materials. Aptamers, immobilized by partial electrochemical entrapment in oxide layers on Ti-alloy surfaces were able to capture cells out of a flowing suspension rapidly. This model proves that surface immobilized aptamers can greatly enhance the attachment of seeded cells. This technology opens new perspectives towards clinical application of stem cell and tissue engineering strategies.

Rapid hepatic cell attachment onto biodegradable polymer surfaces without toxicity using an avidin–biotin binding system

Efficient cell attachment to biodegradable polymer scaffolds is a necessary prerequisite in tissue engineering. However, it is difficult to evenly cover scaffold surfaces with cells because scaffolds are generally highly porous, with complex three-dimensional (3D) surfaces. In this article, we demonstrate the efficiency of avidin-biotin binding systems (ABBS) for the initial attachment of biotinylated Hep G2 cells to avidin adsorbed flat, two-dimensional (2D) and highly porous 3D poly L-lactic acid (PLLA) surfaces. The potential toxicity of biotinylation and/or strong ABBS binding forces was also investigated. ABBS assisted Hep G2 cells to adhere to a flat PLLA surface within 10min; the proliferation of these attached cells was comparable with control intact cells cultured on collagen. Hepatic functions of the attached cells, such as albumin secretion, induction of CYP1A1 and CYP1A2 genes, and metabolic capacity of CYP1A1/2 as measured by the ethoxyresorufin O-deethylase assay, were not significantly changed. Also, a stimulus of a cytokine: oncostatin M (OSM) phosphorylated an intracellular signaling molecule, extracellular signal-related kinase 1 (ERK1) via transmembrane receptor complex, at 24h after inoculation by ABBS. In addition, efficient attachment of Hep G2 cells to a highly porous PLLA 3D scaffold was demonstrated. These results clearly show that ABBS is useful for rapidly trapping cells in both biodegradable, polymer-based, flat 2D surfaces, and in highly porous 3D scaffolds. Furthermore, binding hepatic cells by this technique has only small effects on liver-specific functions, or on signal transfer ability of transmembrane receptor complexes.

The Chondrocyte: Biology and Clinical Application

Chondrocyte is a unique cell type in articular cartilage tissue and is essential for cartilage formation and functionality. It arises from mesenchymal stem cells (MSCs) and is regulated by a series of cytokine and transcription factor interactions, including the transforming growth factor-beta super family, fibroblast growth factors, and insulin-like growth factor-1. To understand the biomechanisms of the chondrocyte differentiation process, various cellular model systems have been employed, such as primary chondrocyte culture, clonal normal cell lines (HCS-2/8, Ch-1, ATDC5, CFK-2, and RCJ3.1C5.18), and transformed clonal cell lines (T/C-28a2, T/C-28a4, C-28/I2, tsT/AC62, and HPV-16 E6/E7). Additionally, cell culture methods, including conventional monolayer culture, three-dimensional scaffold culture, bioreactor culture, pellet culture, and organ culture, have been established to create stable environments for the expansion, phenotypic maintenance, and subsequent biological study of chondrocytes for clinical application. Knowledge gained through these study systems has allowed for the use of chondrocytes in orthopedics for the treatment of cartilage injury and epiphyseal growth plate defects using tissue-engineering approaches. Furthermore, the potential of chondrocyte implantation for facial reconstruction, the treatment of long segmental tracheal defects, and urinary incontinence and vesicoureteral reflux are being investigated. This review summarizes the present study of chondrocyte biology and the potential uses of this cell in orthopedics and other disciplines.