Surface modification of poly (D,L-lactic acid) with chitosan and its effects on the culture of osteoblasts in vitro

Advances in Functionalization of Bioresorbable Nanomembranes and Nanoparticles for Their Use in Biomedicine

Bioresorbable nanomembranes (NMs) and nanoparticles (NPs) are powerful polymeric materials playing an important role in biomedicine, as they can effectively reduce infections and inflammatory clinical patient conditions due to their high biocompatibility, ability to physically interact with biomolecules, large surface area, and low toxicity. In this review, the most common bioabsorbable materials such as those belonging to natural polymers and proteins for the manufacture of NMs and NPs are reviewed. In addition to biocompatibility and bioresorption, current methodology on surface functionalization is also revisited and the most recent applications are highlighted. Considering the most recent use in the field of biosensors, tethered lipid bilayers, drug delivery, wound dressing, skin regeneration, targeted chemotherapy and imaging/diagnostics, functionalized NMs and NPs have become one of the main pillars of modern biomedical applications.

Development and Characterization of Functional Polylactic Acid/Chitosan Porous Scaffolds for Bone Tissue Engineering

In this study, we developed and characterized various open-cell composite scaffolds for bone regeneration. These scaffolds were made from Polylactic acid (PLA) as the scaffold matrix biopolymeric phase, and chitosan (CS) and chitosan-grafted-PLA (CS-g-PLA) copolymer as the dispersed biopolymeric phase. As a first step, successful grafting of PLA onto CS backbone was executed and confirmed by both FTIR and XPS. Mechanical characterization confirmed that adding CS or CS-g-PLA to the intrinsically rigid PLA made their corresponding PLA/CS and PLA/CS-g-PLA composite scaffolds more flexible under compression. This flexibility was higher for the latter due to the improved compatibility between PLA and CS-g-PLA copolymer. The hydrolytic stability of both PLA/CS and PLA/CS-g-PLA composite scaffolds inside phosphate-buffered saline (PBS) solution, as well as MG-63 osteoblast cell adhesion and proliferation inside both scaffolds, were characterized. The corresponding results revealed that PLA/CS composite scaffolds showed hydrolytic degradation due to the cationic properties of CS. However, modified PLA/CS-g-PLA scaffolds were hydrolytically stable due to the improved interfacial adhesion between the PLA matrix and CS-g-PLA copolymer. Finally, biological characterization was done for both PLA/CS and PLA/CS-g-PLA composite scaffolds. Contrarily to what was observed for uncompatibilized PLA/CS scaffolds, compatibilized PLA/CS-g-PLA scaffolds showed a high MG-63 osteoblast cell proliferation after three and five days of cell culture. Moreover, it was observed that cell proliferation increased with CS-g-PLA content. This suggests that the PLA/CS-g-PLA composite scaffolds could be a potential solution for bone regeneration.

Novel 3D-printed methacrylated chitosan-laponite nanosilicate composite scaffolds enhance cell growth and biomineral formation in MC3T3 pre-osteoblasts

This study compared the effect of gelatin- and chitosan-based scaffolds on osteoblast biomineralization. These scaffolds have been modified using methacrylate and laponite nanosilicates to improve their mechanical strength and support osteoblast function. Scaffold materials were prepared to have the same compressive strength (14-15 MPa) such that differences in cell response would be isolated to differences in biopolymer chemistry. The materials were tested for rheological properties to optimize the bio-ink for successful 3D printing using a robocast-assisted deposition system. Osteoblasts were cultured on the surface of 3D-printed methacrylated chitosan-laponite (MAC-Lp), methacrylated gelatin-laponite (MAG-Lp), MAC, and MAG scaffolds. MAC-Lp scaffolds showed increased cell viability, cell growth, and biomineral formation as compared to MAG-Lp scaffolds. FTIR results showed the presence of higher biomineral phosphate and extracellular matrix (ECM) collagen-like amide formation on MAC-Lp scaffolds as compared to MAG-Lp scaffolds. MAC-Lp scaffolds showed increased density of ECM-like tissue from SEM analysis, stained mineral nodules from Alizarin staining, and the existence of Ca─P species evident by X-ray absorbance near edge structure analysis. In conclusion, MAC-Lp scaffolds enhanced osteoblast growth and biomineral formation as compared to MAG-Lp scaffolds.

The Production Possibility of the Antimicrobial Filaments by Co-Extrusion of the PLA Pellet with Chitosan Powder for FDM 3D Printing Technology

The last decades have witnessed a major advancement and development in three-dimensional (3D) printing technology. In the future, the trend’s utilization of 3D printing is expected to play an important role in the biomedical field. This work presents co-extrusion of the polylactic acid (PLA), its derivatives (sPLA), and chitosan with the aim of achieving filaments for printing 3D objects, such as biomedical tools or implants. The physicochemical and antimicrobial properties were evaluated using SEM, FT-IR, DSC, instrumental mechanical test, and based on the ASTM E2149 standard, respectively. The addition of chitosan in the PLA and sPLA filaments increased their porosity and decreased density. The FT-IR analysis showed that PLA and chitosan only formed a physical mixture after extrusion. The addition of chitosan caused deterioration of the mechanical properties of filaments, especially elongation at break and Young’s modulus. The addition of chitosan to the filaments improved their ability to crystallize and provide their antimicrobial properties against Escherichia coli and Staphylococcus aureus.

Polydopamine-Assisted Anchor of Chitosan onto Porous Composite Scaffolds for Accelerating Bone Regeneration

Surface function has an importance for the bioactivity of porous polymeric scaffolds. The goal of the present study is to immobilize highly bioactive chitosan (CS) onto the surface of porous composite scaffolds to accelerate bone regeneration. Porous poly(ε-caprolactone) (PCL)/bioactive glass (BG) composite scaffolds with strong anchor of CS were fabricated via mussel-inspired polydopamine (PDA) coating as a bridging layer. In vitro cell culture showed that firm immobilization of CS onto the composite scaffolds significantly enhanced protein adsorption, cell adhesion, and osteogenic differentiation compared to CS-decorated scaffolds via physical adsorption. In vivo assessments demonstrated that covalent immobilization of CS onto the surface of scaffolds obviously promoted cranial bone regeneration in comparison with the counterparts with physical adsorption of CS. The proposed method offers a feasible and effective means to fabricate artificial bioactive scaffolds for bone tissue engineering application.

Surface Modification of 3D Printed PLA Objects by Fused Deposition Modeling: A Review

Polylactic acid (PLA) filaments are very popular as a thermoplastic source used in the 3D printing field by the “Fused Deposition Modeling” method in the last decade. The PLA market is expected to reach 5.2 billion US dollars in 2020 for all of its industrial uses. On the other hand, 3D printing is an expanding technology that has a large economic potential in many industries where PLA is one of the main choices as the source polymer due to its ease of printing, environmentally friendly nature, glossiness and multicolor appearance properties. In this review, we first reported the chemical structure, production methods, general properties, and present market of the PLA. Then, the chemical modification possibilities of PLA and its use in 3D printers, present drawbacks, and the surface modification methods of PLA polymers in many different fields were discussed. Specifically, the 3D printing method where the PLA filaments are used in the extrusion-based 3D printing technologies is reviewed in this article. Many methods have been proposed for the permanent surface modifications of the PLA where covalent attachments were formed such as alkaline surface hydrolysis, atom transfer polymerization, photografting by UV light, plasma treatment, and chemical reactions after plasma treatment. Some of these methods can be applied for surface modifications of PLA objects obtained by 3D printing for better performance in biomedical uses and other fields. Some recent publications reporting the surface modification of 3D printed PLA objects were also discussed.

Biological Compatibility of a Polylactic Acid Composite Reinforced with Natural Chitosan Obtained from Shrimp Waste

The aim of this work is to evaluate the effect of chitosan content (1, 3 and 5 wt %) dispersed in polylactic acid (PLA) on the structure and properties of composites. Also, the hydrolytic degradation, and the cell viability and adhesion of human MG-63 osteoblasts are analyzed to determine the composites’ suitability for use in tissue engineering. For the manufacture of the materials, natural chitosan was extracted chemically from shrimp exoskeleton. The composites were fabricated by extrusion, because it is a low-cost process, it is reproducible, and it does not compromise the biocompatibility of the materials. FT-IR and XRD show that the chitosan does not change the polymer structure, and interactions between the composite components are discarded. In vitro degradation tests show that the composites do not induce significant pH changes in phosphate buffer solution due to their low susceptibility to hydrolytic degradation. The adhesion and morphological characteristics of the osteoblasts are evaluated using confocal microscopy and scanning electron microscopy. The cell viability is determined by the MTT assay. Osteoblasts adhesion is observed on the surface of PLA and composites. A higher amount of chitosan, higher number of cells with osteoblastic morphology, and mineralized nodules are observed on the composite surface. The highest metabolic activity is evidenced at 21 days. The results suggest that the Polylactic acid/chitosan composites are potentially suitable for use as a biomaterial.

The fabrication of biomineralized fiber-aligned PLGA scaffolds and their effect on enhancing osteogenic differentiation of UCMSC cells

The key factor of scaffold design for bone tissue engineering is to mimic the microenvironment of natural bone extracellular matrix (ECM) and guide cell osteogenic differentiation. The biomineralized fiber-aligned PLGA scaffolds (a-PLGA/CaPs) was developed in this study by mimicking the structure and composition of native bone ECM. The aligned PLGA fibers was prepared by wet spinning and then biomineralized via an alternate immersion method. Introduction of a bioceramic component CaP onto the PLGA fibers led to changes in surface roughness and hydrophilicity, which showed to modulate cell adhesion and cell morphology of umbilical cord mesenchymal stem cells (UCMSCs). It was found that organized actin filaments of UCMSCs cultured on both a-PLGA and a-PLGA/CaP scaffolds appeared to follow contact guidance along the aligned fibers, and those cells grown on a-PLGA/CaP scaffolds exhibited a more polarized cellular morphology. The a-PLGA/CaP scaffold with multicycles of mineralization facilitated the cell attachment on the fiber surfaces and then supported better cell adhesion and contact guidance, leading to enhancement in following proliferation and osteogenic differentiation of UCMSCs. Our results give some insights into the regulation of cell behaviors through design of ECM-mimicking structure and composition and provide an alternative wet-spun fiber-aligned scaffold with HA-mineralized layer for bone tissue engineering application.

Tissue engineering; strategies, tissues, and biomaterials

Current tissue regenerative strategies rely mainly on tissue repair by transplantation of the synthetic/natural implants. However, limitations of the existing strategies have increased the demand for tissue engineering approaches. Appropriate cell source, effective cell modification, and proper supportive matrices are three bases of tissue engineering. Selection of appropriate methods for cell stimulation, scaffold synthesis, and tissue transplantation play a definitive role in successful tissue engineering. Although the variety of the players are available, but proper combination and functional synergism determine the practical efficacy. Hence, in this review, a comprehensive view of tissue engineering and its different aspects are investigated.

Development of bioabsorbable polylactide membrane with controllable hydrophilicity for adjustment of cell behaviours

Cell functions can be mediated through their interactions with the microenvironments, which highly depend on the surface state of the substrate. However, how to finely adjust the surface of biomaterials is still very challenging. In this study, poly(d,l-lactide) (PDLLA) with high molecular weight was synthesized via ring opening polymerization, which was hot-pressed into PDLLA membrane. In order to modify the hydrophobicity of the membrane (a limiting factor for its biomedical application), an amphiphilic monomethoxyl poly(ethylene glycol)-b-poly(d,l-lactide) (PEG-PDLLA) was selected to improve its surface hydrophilicity through a simple self-assembly approach. It was found that the contact angles of the modified membrane can be well controlled by variation of PEG-PDLLA concentrations. In vitro cell biological study indicates that optimized cell adhesion can be achieved on the modified membrane with a contact angle of around 50° via its self-assembly with an ethanol/water solution of PEG-PDLA (35 mg ml-1). The surface modification of the membrane also changed its biodegradation property in the process of its incubation period up to 240 days. The surface modification method may afford an effective way for adjustment of the surface (interface) of membrane (scaffolds) of different biomaterials, beyond polylactide.

Preparation and Characterization of Extruded Composites Based on Polypropylene and Chitosan Compatibilized with Polypropylene-Graft-Maleic Anhydride

The preparation of composites of synthetic and natural polymers represent an interesting option to combine properties; in this manner, polypropylene and chitosan extruded films using a different proportion of components and polypropylene-graft-maleic anhydride (PPgMA) as compatibilizer were prepared. The effect of the content of the biopolymer in the polypropylene (PP) matrix, the addition of compatibilizer, and the particle size on the properties of the composites was analyzed using characterization by fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), tensile strength, and contact angle, finding that in general, the addition of the compatibilizer and reducing the particle size of the chitosan, favored the physicochemical and morphological properties of the films.

Hydrogel Layers on the Surface of Polyester-Based Materials for Improvement of Their Biointeractions and Controlled Release of Proteins

The modification of bioresorbable polyester surfaces in order to alter their biointeractions presents an important problem in biomedical polymer science. In this study, the covalent modification of the surface of poly(lactic acid)-based (PLA-based) films with poly(acryl amide) and sodium alginate hydrogels was performed to change the non-specific polyester interaction with proteins and cells, as well as to make possible the covalent attachment of low-molecular weight ligands and to control protein release. The effect of such modification on the film surface properties was studied. Parameters such as swelling, water contact angle, surface area, and binding capacity of low-molecular weight substances were evaluated and compared. The comparative study of adsorption of model protein (BSA) on the surface of non-modified and modified films was investigated and the protein release was evaluated. Cell viability on the surface of hydrogel-coated films was also tested. The developed approach could be applied for the modification of PLA-based scaffolds for tissue engineering and will be further studied for molecular-imprinting of biomolecules on the surface of polyester-based materials for control of biointeractions.

Myocardial tissue engineering using electrospun nanofiber composites

Emerging trends for cardiac tissue engineering are focused on increasing the biocompatibility and tissue regeneration ability of artificial heart tissue by incorporating various cell sources and bioactive molecules. Although primary cardiomyocytes can be successfully implanted, clinical applications are restricted due to their low survival rates and poor proliferation. To develop successful cardiovascular tissue regeneration systems, new technologies must be introduced to improve myocardial regeneration. Electrospinning is a simple, versatile technique for fabricating nanofibers. Here, we discuss various biodegradable polymers (natural, synthetic, and combinatorial polymers) that can be used for fiber fabrication. We also describe a series of fiber modification methods that can increase cell survival, proliferation, and migration and provide supporting mechanical properties by mimicking micro-environment structures, such as the extracellular matrix (ECM). In addition, the applications and types of nanofiber-based scaffolds for myocardial regeneration are described. Finally, fusion research methods combined with stem cells and scaffolds to improve biocompatibility are discussed. [BMB Reports 2016; 49(1): 26-36]

Biocompatibility of Poly(ε-caprolactone) Scaffold Modified by Chitosan—The Fibroblasts Proliferation in vitro

In this study, the surface of poly("-caprolactone) (PCL) scaffold was modified by chitosan (CS) in order to enhance its cell affinity and biocompatibility. It is demonstrated by scanning electronic microscopy (SEM) that when 0.5-2.0 wt% chitosan solutions are used to modify the PCL scaffold, the amount of adhesion of the fibroblasts on the chitosan-modified PCL scaffolds dramatically increase when compared to the control after 7 days cell culture. The results indicate that the chitosan-modified PCL scaffolds are more favorable for cell proliferation by improving the scaffold biocompatibility. The improvement may be helpful for the extensive applications of PCL scaffold in heart valve and blood vessel tissue engineering.

Preparation and Characterization of Films Extruded of Polyethylene/Chitosan Modified with Poly(lactic acid)

The use of mixtures of synthetic and natural polymers is a potential option to reduce the pollution by plastic waste. In this work, the method for the chemical modification of chitosan with poly(lactic acid) was developed; then, the preparation of films of blends of polyethylene and chitosan-poly(lactic acid) produced by an extrusion method using polyethylene-graft maleic anhydride as a compatibilizer. It was possible to obtain films with a maximum content of 20 wt% and 30 wt%, chitosan, with and without compatibilizer, respectively. Scanning electron microscope (SEM) analysis showed a homogeneous surface on all films. The addition of the compatibilizer had a significant effect on the mechanical properties of the films, such as an increase in Young’s modulus and a decrease in the elongation at break; additionally, the compatibilizer promotes thermal degradation in a single step and gives the film a slight increase in thermal resistance. These results are attributed to an improved interaction in the interface of polyethylene and chitosan-poly(lactic acid), promoted by the compatibilizer.

Synthesis and surface modification of polyurethanes with chitosan for antibacterial properties

Surface modification and providing antibacterial properties to the materials or devices are getting great attention especially in the last decades. In this study, polyurethane (PU) films were prepared by synthesizing them in medical purity from toluene diisocyanate and polypropylene ethylene glycol without using any other ingredients and then the film surfaces were modified by covalent immobilization of chitosan (CH) which has antibacterial activity. CH immobilized PU films (PU-CH) were found to be more hydrophilic than control PU films. Electron Spectroscopy for Chemical Analysis (ESCA) and Atomic Force Microscopy (AFM) analyses showed higher nitrogen contents and rougher surface topography for PU-CH compared to PU films. Modification with CH significantly increased antibacterial activity against Gram positive (Staphylococcus aureus) and Gram negative (Pseudomonas aeruginosa) bacteria. It was observed that the number of bacteria colonies were less about 10(2)-10(5) CFU/mL and number of attached viable bacteria decreased significantly after CH modification of PU films.

Effect of cellulose nanowhiskers on surface morphology, mechanical properties, and cell adhesion of melt-drawn polylactic Acid fibers

Polylactic acid (PLA) fibers were produced with an average diameter of 11.2 (± 0.9) μm via a melt-drawing process. The surface of the PLA fibers was coated with blends of cellulose nanowhiskers (CNWs) (65 to 95 wt %) and polyvinyl acetate (PVAc). The CNWs bound to the smooth PLA fiber surface imparted roughness, with the degree of roughness depending on the coating blend used. The fiber tensile modulus increased 45% to 7 GPa after coating with 75 wt % CNWs compared with the uncoated PLA fibers, and a significant increase in the fiber moisture absorption properties at different humidity levels was also determined. Cytocompatibility studies using NIH-3T3 mouse fibroblast cells cultured onto CNWs-coated PLA surface revealed improved cell adhesion compared with the PLA control, making this CNW surface treatment applicable for biomedical and tissue engineering applications. Initial studies also showed complete cell coverage within 2 days.

Construction of microenvironment onto titanium substrates to regulate the osteoblastic differentiation of bone marrow stromal cells in vitro and osteogenesis in vivo

To mimic the extracellular matrix of natural bone, apatite/gelatin composite was deposited onto nanostructured titanium substrates via a coprecipitation method, which was pretreated by potassium hydroxide and heat treatment to generate an anticorrosive nanostructured layer. The successful formation of the apatite/gelatin nanocomposite onto titanium surfaces was revealed by Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, atomic force microscopy (AFM), and thin film X-ray diffraction (TF-XRD) measurements, respectively. The immunofluorescence staining of vinculin revealed that the apatite/gelatin nanocomposite deposited titanium substrate was favorable for cell adhesion. More importantly, bone marrow stromal cells cultured onto the apatite/gelatin nanocomposite deposited titanium substrates displayed significantly higher (p < 0.05 or p < 0.01) proliferation and differentiation levels of alkaline phosphatase, mRNA expressions of osteocalcin (OC), osteopontin (OPN), and collagen type I (Col I), and OC content after culture for 7, 14, and 21 days, respectively, which was also revealed by the immunofluorescence analysis of OC and OPN expression. The deposition of apatite/gelatin nanocomposite improved bone density (p < 0.05) and bone-implant contact rate (p < 0.05), which was reflected by microcomputed tomography analysis and histological evaluation in vivo using a rabbit model. This work provides an approach to fabricate high-performance titanium-based implants with enhanced bone osseointegration.

Engineering biomaterials to integrate and heal: the biocompatibility paradigm shifts

This article focuses on one of the major failure routes of implanted medical devices, the foreign body reaction (FBR)--that is, the phagocytic attack and encapsulation by the body of the so-called "biocompatible" biomaterials comprising the devices. We then review strategies currently under development that might lead to biomaterial constructs that will harmoniously heal and integrate into the body. We discuss in detail emerging strategies to inhibit the FBR by engineering biomaterials that elicit more biologically pertinent responses.

Regulation of the behaviors of mesenchymal stem cells by surface nanostructured titanium

The study describes the influence of surface nanostructured titanium substrates on the growth behaviors of mesenchymal stem cells. Surface nanostructures of titanium were produced with surface mechanical attrition treatment (SMAT) technique. The morphologies of native titanium and surface nanostructured titanium substrates were characterized by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and contact-angle measurements, respectively. A thin nanostructured layer was formed onto the surfaces of titanium substrates after SMAT treatment. The effects of the surface nanostructured titanium substrates on the adhesion, spreading, proliferation and differentiation of mesenchymal stem cells (MSCs) was examined at cellular and molecular levels in vitro. The results suggest that the surface nanostructured substrates were beneficial for the growth of MSCs, including adhesion, filament orientation, proliferation and gene expression. This approach for the fabrication of surface nanostructured titanium may be exploited in the development of high performance titanium-based implants.

CHITOSAN/GELATIN NETWORK BASED BIOMATERIALS IN TISSUE ENGINEERING

Tissue can be looked upon as a cell composite, where cell expresses its functions, while extra cellular matrixes (ECMs) secreted provide cell information and do its matrix functions. Here ECMs are, physical and chemical networks consisted of proteins (e.g. collagen, fibronectin, laminin and vitronectin etc.) and glycosaminoglycans (GAGs, e.g. hyaluronic acid, chodroitin 4-sulfate, chodroitin 6-sulfate etc.). The idea cell-carrier should be the one, which most mimics the ECM. Therefore, chitosan in which the N-acetylglucosamine moiety is a structural feature also found in the GAGs, and gelatin, the partially denatured derivative of collagen were used to develop hiomaterials. They will exhibit related bioactivities, as their analogue and precursor, respectively.

Chitosan gelatin network based biomaterials can be applied as membrane, scaffold, surface modifier and non-viral vectorfor. DNA delivery in tissue engineering. Some of our activities were reported. These biomaterials have promising perspectives.

Functionalized synthetic biodegradable polymer scaffolds for tissue engineering

Scaffolds (artificial ECMs) play a pivotal role in the process of regenerating tissues in 3D. Biodegradable synthetic polymers are the most widely used scaffolding materials. However, synthetic polymers usually lack the biological cues found in the natural extracellular matrix. Significant efforts have been made to synthesize biodegradable polymers with functional groups that are used to couple bioactive agents. Presenting bioactive agents on scaffolding surfaces is the most efficient way to elicit desired cell/material interactions. This paper reviews recent advancements in the development of functionalized biodegradable polymer scaffolds for tissue engineering, emphasizing the syntheses of functional biodegradable polymers, and surface modification of polymeric scaffolds.

Scaffolds based bone tissue engineering: the role of chitosan

As life expectancy increases, malfunction or loss of tissue caused by injury or disease leads to reduced quality of life in many patients at significant socioeconomic cost. Even though major progress has been made in the field of bone tissue engineering, present therapies, such as bone grafts, still have limitations. Current research on biodegradable polymers is emerging, combining these structures with osteogenic cells, as an alternative to autologous bone grafts. Different types of biodegradable materials have been proposed for the preparation of three-dimensional porous scaffolds for bone tissue engineering. Among them, natural polymers are one of the most attractive options, mainly due to their similarities with extracellular matrix, chemical versatility, good biological performance, and inherent cellular interactions. In this review, special attention is given to chitosan as a biomaterial for bone tissue engineering applications. An extensive literature survey was performed on the preparation of chitosan scaffolds and their in vitro biological performance as well as their potential to facilitate in vivo bone regeneration. The present review also aims to offer the reader a general overview of all components needed to engineer new bone tissue. It gives a brief background on bone biology, followed by an explanation of all components in bone tissue engineering, as well as describing different tissue engineering strategies. Moreover, also discussed are the typical models used to evaluate in vitro functionality of a tissue-engineered construct and in vivo models to assess the potential to regenerate bone tissue are discussed.

Addition of chitosan to silicate cross-linked PEO for tuning osteoblast cell adhesion and mineralization

The addition of chitosan to silicate (Laponite) cross-linked poly(ethylene oxide) (PEO) is used for tuning nanocomposite material properties and tailoring cellular adhesion and bioactivity. By combining the characteristics of chitosan (which promotes cell adhesion and growth, antimicrobial) with properties of PEO (prevents protein and cell adhesion) and those of Laponite (bioactive), the resulting material properties can be used to tune cellular adhesion and control biomineralization. Here, we present the hydration, dissolution, degradation, and mechanical properties of multiphase bio-nanocomposites and relate these to the cell growth of MC3T3-E1 mouse preosteoblast cells. We find that the structural integrity of these bio-nanocomposites is improved by the addition of chitosan, but the release of entrapped proteins is suppressed. Overall, this study shows how chitosan can be used to tune properties in Laponite cross-linked PEO for creating bioactive scaffolds to be considered for bone repair.

Directional differentiation of chicken spermatogonial stem cells in vitro

BACKGROUND

Mammalian spermatogonial stem cells (SSC) are able to differentiate into different cell types in vitro, which are valuable sources for regenerative medicine and gene transfer studies. We investigated the differentiation potential of chicken SSC into osteoblasts, neuron-like cells and adipocytes in vitro.

METHODS

Chicken SSC from the testes of 18- and 20-day-old chicken embryos were cultured in different induction media for three passages in vitro. For differentiation into osteoblasts, SSC were cultured in Dulbecco's modified Eagle medium (DMEM) supplemented with 1 x 10(-4) micromol/mL desamethasone, 10 micromol/mL (beta-sodium glycerophosphate and 0.05 mg/mL vitamin C, and examined by microscopy after Von Kossa's, cytochemical and immunohistochemical staining. For differentiation into neuron-like cells, SSC were cultured in DMEM supplemented with 1 x 10(-3) micromol/mL retinoic acid (RA), 5.0 micromol/mL 3-isobutyl-1-methylxanthine (IBMX) and examined by microscopy after toluidine blue or immunohistochemical staining. For differentiation into adipocytes, SSC were cultured in DMEM supplemented with 1 x 10(-3) micromol/mL dexamethasone, 0.01 mg/mL insulin, 0.5 micromol/mL IBMX and examined by microscopy after Oil red O staining and reverse transcriptase-polymerase chain reaction (RT-PCR) for gene expression of peroxisome proliferation activation receptor-gamma (PPAR-gamma).

RESULTS

After 15 and 21 days of culture in the induction medium for osteoblast differentiation, 75% and 80% chicken SSC differentiated into osteoblasts, as confirmed by Von Kossa's, calcium-cobalt and collagen I antibody staining. After 3 and 7 days of culture in the induction medium for neuron-like cell differentiation, 78% and 85% SSC became neuron-like cells, as confirmed by staining with toluidine blue and the monoclonal antibody against neuron-specific enolase, nestin and glial fibrillary acidic protein. After 7 days of culture in the induction for adipocyte differentiation, 85% SSC differentiated into adipocytes, as confirmed by Oil red O staining and RT-PCT for PPAR-gamma gene expression.

DISCUSSION

Our results show that chicken SSC can differentiate into osteoblasts, neuron-like cells and adipocytes under similar conditions as for directional differentiation of mammalian SSC in vitro. The findings show the feasibility of using SSC-derived cells for developmental biology and gene transfer studies in chickens.

Surface engineering of titanium with potassium hydroxide and its effects on the growth behavior of mesenchymal stem cells

To improve the corrosion resistance and biological performance of commercially pure titanium (cp-Ti) substrates, potassium hydroxide was employed to modify the surfaces of titanium substrates, followed by biomimetic deposition of apatite on the substrates in a simulated body fluid. The morphologies of native and treated titanium substrates were characterized by field emission scanning electron microscopy (FE-SEM). Treatment with potassium hydroxide led to the formation of intermediate layers of potassium titanate on the surfaces of titanium substrates, while apatite was subsequently deposited onto the intermediate layer. The formation of potassium titanate and apatite was confirmed by thin-film X-ray diffraction and FE-SEM equipped with energy dispersive spectroscopy, respectively. Electrochemical impedance spectroscopy showed that the formed potassium titanate layer improved the corrosion-resistance properties of titanium substrates. The influence of modified titanium substrates on the biological behavior of mesenchymal stem cells (MSCs), including osteogenic differentiation, was investigated in vitro. Compared with cp-Ti substrates, MSCs cultured onto alkali- and heat-treated titanium substrates and apatite-deposited titanium substrates displayed significantly higher (P<0.05 or P<0.01) proliferation and differentiation levels of alkaline phosphatase and osteocalcin in 7 and 14day cultures, respectively. More importantly, our results suggest that the modified titanium substrates have great potential for inducing MSCs to differentiate into osteoblasts. The approach presented here may be exploited to fabricate titanium-based implants.

Multilayer composite scaffolds with mechanical properties similar to small intestinal submucosa

Use of biodegradable scaffolds to engineer new tissues has become an attractive option in various transplantation protocols. In particular, small intestinal submucosa (SIS) has generated immense interest in various tissue engineering applications because of its diverse favorable properties. However, it is a natural matrix, which leads to problems in large-scale preparations and contains sample to sample heterogeneity. In this study, we explored the formation of synthetic matrix mimicking the characteristics of the SIS. Three-dimensional composite structures were developed by sandwiching 50:50 PLGA film between porous chitosan matrices. The outer chitosan layers provide biological activity while the inner PLGA layer provides mechanical strength. PLGA films were initially perforated at 1 cm distance, and the porous chitosan matrix was formed sequentially on each side by controlled rate freezing and lyophilization technique at -80 degrees C. Scanning electron microscopy analysis showed a layered microarchitecture with chitosan filling the perforations of PLGA membrane. Urea permeability studies confirmed that the perforations were filled (negligible urea transfer across composite over 8 h). Tensile strength analysis showed that the matrices formed using 160 kDa PLGA had sufficient break stress ( approximately 4.5 MPa). Degradation analysis over 8 weeks in the presence of 10 mg/L lysozyme showed a 50% decrease in total weight and an 80% decrease in PLGA molecular weight. When cellular adhesion and actin distribution of mouse embryonic fibroblasts were evaluated, for 7 days, cells showed their typical spindle shape and redistribution of actin fibers on composite matrices. Viability studies and MMP-2/MMP-9 activity showed that the cells were viable and functional, similar to tissue culture plastic. Further, canine bladder smooth muscle cells also showed similar cell adhesion and spreading on the composite matrix. In summary, composite structures mimicking SIS were constructed and show potential as a tissue engineering material.

Surface modification of titanium thin film with chitosan via electrostatic self-assembly technique and its influence on osteoblast growth behavior

Chitosan (Chi) and poly (styrene sulfonate) (PSS) were employed to surface modify titanium thin film via electrostatic self-assembly (ESA) technique in order to improve its biocompatibility. The surface chemistry, wettability and surface topography of the coated films with different number of deposited layers were investigated by using X-ray photoelectron spectroscopy (XPS), water contact angle measurement and atomic force microscopy (AFM), respectively. The results indicated that a full surface coverage for the outmost layer was achieved at least after deposition of five layers, i.e., PEI/(PSS/Chi)2 on the titanium films. The formed multi-layered structure of PEI(PSS/Chi)x (x > or = 2) on the titanium film was stable in air at room temperature and in phosphate buffered solution (PBS) for at least 3 weeks. Cell proliferation, cell viability, DNA synthesis as well as differentiation function (alkaline phosphatase) of osteoblasts on chitosan-modified titanium film (PEI/(PSS/Chi)6) and control sample were investigated, respectively. Osteoblasts cultured on chitosan-modified titanium film displayed a higher proliferation tendency than that of control (p < 0.01). Cell viability, alkaline phosphatase as well as DNA synthesis measurements indicated that osteoblasts on chitosan-modified titanium films were greater (p < 0.01) than those for the control, respectively. These results suggest that surface modification of titanium film was successfully achieved via deposition of PEI/(PSS/Chi)x layers, which is useful to enhance the biocompatibility of the titanium film.

Surface functionalization of titanium with hyaluronic acid/chitosan polyelectrolyte multilayers and RGD for promoting osteoblast functions and inhibiting bacterial adhesion

Titanium (Ti) and its alloys are used extensively in orthopedic implants due to their excellent biocompatibility and mechanical properties. However, titanium-based implant materials have specific complications associated with their applications, such as the loosening of implant-host interface owing to unsatisfactory cell adhesion and the susceptibility of the implants to bacterial infections. Hence, a surface which displays selective biointeractivity, i.e. enhancing beneficial host cell responses but inhibiting pathogenic microbial adhesion, would be highly desirable. This present study aims to improve biocompatibility and confer long-lasting antibacterial properties on Ti via polyelectrolyte multilayers (PEMs) of hyaluronic acid (HA) and chitosan (CH), coupled with surface-immobilized cell-adhesive arginine-glycine-aspartic acid (RGD) peptide. The HA/CH PEM-functionalized Ti is highly effective as an antibacterial surface but the adhesion of bone cells (osteoblasts) is poorer than on pristine Ti. With additional immobilized RGD moieties, the osteoblast adhesion can be significantly improved. The density of the surface-immobilized RGD peptide has a significant effect on osteoblast proliferation and alkaline phosphatase (ALP) activity, and both functions can be increased by 100-200% over that of pristine Ti substrates while retaining high antibacterial efficacy. Such substrates can be expected to have good potential in orthopedic applications.