Bioactive glass/polymer composite scaffolds mimicking bone tissue

The aim of this work was the preparation and characterization of scaffolds with mechanical and functional properties able to regenerate bone. Porous scaffolds made of chitosan/gelatin (POL) blends containing different amounts of a bioactive glass (CEL2), as inorganic material stimulating biomineralization, were fabricated by freeze-drying. Foams with different compositions (CEL2/POL 0/100; 40/60; 70/30 wt %/wt) were prepared. Samples were crosslinked using genipin (GP) to improve mechanical strength and thermal stability. The scaffolds were characterized in terms of their stability in water, chemical structure, morphology, bioactivity, and mechanical behavior. Moreover, MG63 osteoblast-like cells and periosteal-derived stem cells were used to assess their biocompatibility. CEL2/POL samples showed interconnected pores having an average diameter ranging from 179 ± 5 μm for CEL2/POL 0/100 to 136 ± 5 μm for CEL2/POL 70/30. GP-crosslinking and the increase of CEL2 amount stabilized the composites to water solution (shown by swelling tests). In addition, the SBF soaking experiment showed a good bioactivity of the scaffold with 30 and 70 wt % CEL2. The compressive modulus increased by increasing CEL2 amount up to 2.1 ± 0.1 MPa for CEL2/POL 70/30. Dynamical mechanical analysis has evidenced that composite scaffolds at low frequencies showed an increase of storage and loss modulus with increasing frequency; furthermore, a drop of E' and E″ at 1 Hz was observed, and for higher frequencies both moduli increased again. Cells displayed a good ability to interact with the different tested scaffolds which did not modify cell metabolic activity at the analyzed points. MTT test proved only a slight difference between the two cytotypes analyzed. ? 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A 100A:2654-2667, 2012.     

Bioactive glass surface for fiber reinforced composite implants via surface etching by Excimer laser

Biostable fiber-reinforced composites (FRC) prepared from bisphenol-A-glycidyldimethacrylate (BisGMA)-based thermosets reinforced with E-glass fibers are promising alternatives to metallic implants due to the excellent fatigue resistance and the mechanical properties matching those of bone. Bioactive glass (BG) granules can be incorporated within the polymer matrix to improve the osteointegration of the FRC implants. However, the creation of a viable surface layer using BG granules is technically challenging. In this study, we investigated the potential of Excimer laser ablation to achieve the selective removal of the matrix to expose the surface of BG granules. A UV–vis spectroscopic study was carried out to investigate the differences in the penetration of light in the thermoset matrix and BG. Thereafter, optimal Excimer laser ablation parameters were established. The formation of a calcium phosphate (CaP) layer on the surface of the laser-ablated specimens was verified in simulated body fluid (SBF). In addition, the proliferation of MG63 cells on the surfaces of the laser-ablated specimens was investigated. For the laser-ablated specimens, the pattern of proliferation of MG63 cells was comparable to that in the positive control group (Ti6Al4V). We concluded that Excimer laser ablation has potential for the creation of a bioactive surface on FRC-implants.     

组织工程化人工角膜的临床应用：距离还有多远？

背景：人工角膜是取代混浊角膜组织而用异质成形材料制成的一种特殊屈光装置,通过手术植入患眼,以取得一定视力。 目的：介绍近年来人工角膜研究进展。 方法：由第一作者用计算机检索万方医学网和Medline database数据库,检索词分别为“人工角膜、角膜移植、生物相容性、组织工程”和“keratoprosthesis, corneal transplantation, biocompatibility, tissue engineering”,对人工角膜移植的动物实验、临床进展、植入方式及生物相容性、并发症等方面进行探讨。 结果与结论：共检索到204篇文章,按纳入和排除标准对文献进行筛选,共纳入50篇文章。人工角膜的研制在近年来有了较大的进步,非组织工程化人工角膜在材料选择,处理和设计方式上有所创新,同时具有活性的组织工程化人工角膜的出现为人工角膜的研制开辟了一条新途径。 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程全文链接：     

Bioactive glass/polymer composite materials with mechanical properties matching those of cortical bone

Stress shielding resulting from mismatch in dynamic mechanical properties contributes to the reduced stability of osseous implants. Our objective was to develop biocompatible composites having mechanical properties similar to those of cortical bone. Polymers of urethane dimethacrylate (UDMA) and 2-hydroxyethyl methacrylate (HEMA, 0-20%) and composites containing bioactive glass particles (70% SiO(2), 25% CaO, and 5% P(2)O(5)), with or without silane treatment were prepared. Young's moduli of composites containing silane-treated glass (16 GPa) were significantly greater than those of composites containing untreated glass (12-13 GPa) or of unfilled polymers (5-6 GPa). Bioactive glass reduced water sorption by the composites and incorporation of silane-treated glass prevented HEMA-induced increases in water sorption. Osteoblast-like cells attached equally well to UDMA polymer and composite containing silane-treated bioactive glass. Thus, silane treatment improved the mechanical properties of bioactive glass composites without compromising biocompatibility. This material has a Young's modulus comparable to that of cortical bone. Therefore, silane-treated bioactive glass composites, when used as implant or cement materials, would reduce stress shielding and improve implant stability.     

Functionally adapted surfaces on a silicone keratoprosthesis.

BACKGROUND: Silicone intraocular lenses as well as silicone sponges and encircling bands on the bulbar surface are widely used and are well tolerated. The aim of this project is a new one-piece silicone keratoprosthesis with enhanced cell adhesion in the haptic region to optimize the keratoprosthesis stability. These investigations show how enhanced profileration of conjunctival fibroblasts and, therefore, improved tissue compatibility can be achieved by hydrophilizing and by protein immobilisation on a hydrophobic silicone surface. This allows a combination of desired chemical and mechanical properties of the silicone bulk material with surfaces of improved tissue compatibility. METHODS: Silicone foils with surface modifications of different kinds were tested. Experiments were done using cell cultures with murine fibroblasts L-929 and human conjuctival fibroblasts. Cytotoxicity assays were carried out with cells grown on the material in direct contact, as well as in indirect contact, with extracts (EN 30993-5). Viability stains by means of fluoresceindiacetate and ethidiumbromide together with morphology analyses by hemalaun-staining were performed. RESULTS: For the unmodified and modified foils themselves and their extracts any negative influence on cell cultures of murine and human cells could be excluded. There was a gradual improvement of cell morphology, spreading and proliferation dependent on the degree of surface modification. Covalently immobilised fibronectin showed the best results in contrast to adsorptive binding. CONCLUSIONS: Silicone surfaces can be modified chemically with bioactive proteins. These modifications are cell compatible and do not result in toxic reactions. The degree and type of silicone hydrophilization results in improved development of cell morphology, spreading and proliferation. Even better results are obtained after covalent binding of bioactive proteins like fibronectin. Improved biocompatibility with enhanced cellular overgrowth has been demonstrated in vitro for the modified silicone of the haptic region. We believe that this type of modification will help in reducing extrusion problems observed with former keratoprostheses.     

Bioactive and mechanically strong Bioglass-poly(D,L-lactic acid) composite coatings on surgical sutures

New coating processes have been investigated for degradable (Vicryl) and nondegradable (Mersilk) sutures with the aim to develop Bioglass coated polymer fibers for wound healing and tissue engineering scaffold applications. First, the aqueous phase of a Bioglass particle slurry was replaced with a poly(D,L-lactic acid) (PDLLA) polymer dissolved in solvent dimethyle carbonate (DMC) to act as third phase. SEM observations indicated that this alteration significantly improved the homogeneity of the coatings. Second, a new coating strategy involving two steps was developed: the sutures were first coated with a Bioglass-PDLLA composite film followed by a second PDLLA coating. This two-step process of coating has addressed the problem of poor adherence of Bioglass particles on suture surfaces. The coated sutures were knotted to determine qualitatively the mechanical integrity of the coatings. The results indicated that adhesion strength of coatings obtained by the two-step method was remarkably enhanced. A comparative assessment of the bioactivity of one-step and two-step produced coatings was carried out in vitro using acellular simulated body fluid (SBF) for up to 28 days. Coatings produced by the two-step process were found to have similar bioactivity as the one-step produced coatings. The novel Bioglass/PDLLA/Vicryl and Bioglass/PDLLA/Mersilk composite sutures are promising bioactive materials for wound healing and tissue engineering applications.     

Bioactive films on metallic surfaces for osteoconduction

A fast and effective electrochemical method was developed to make a dense calcium phosphate films on titanium and stainless steel for hard tissue replacement. The surfaces of titanium and stainless steel were cathodically treated in an electrochemical cell. By controlling the treatment parameters, a film of 100-nm thickness was deposited on the metal surface in several minutes. The thin film was amorphous calcium phosphate containing octacalcium phosphate nuclei, and also dense and ductile. The treated metals were able to induce bioactive calcium phosphate deposition after immersion in simulated body fluid (SBF) for only 1 and 2 days. In vivo study was conducted by implanting the treated specimens of titanium and stainless steel in dog's femur cavity. The treated metallic surfaces showed good ability of osteoconduction. This surface treatment method can be potentially used to enhance bioactivity of any type of metallic surfaces.     

Bioactive glasses for in situ tissue regeneration

Historically the function of biomaterials has been to replace diseased or damaged tissues. Recent findings show that controlled release of the ionic dissolution products of bioactive glasses results in regeneration of tissues. The mechanism for in situ tissue regeneration involves upregulation of seven families of genes that control the osteoblast cell cycle, mitosis and differentiation. In the presence of critical concentrations of Si and Ca ions, within 48 h osteoblasts that are capable of differentiating into a mature osteocyte phenotype begin to proliferate and regenerate new bone. Osteoblasts that are not in the correct phase of the cell cycle and unable to proceed towards differentiation are switched into apoptosis by the ionic dissolution products. A controlled release of soluble Ca and Si from bioactive glass--resorbable polymer composites leads to vascularised soft tissue regeneration. Gene activation by controlled ion release provides the conceptual basis for molecular design of a third generation of biomaterials optimised for in situ tissue regeneration.     

Bioactive glasses for in situ tissue regeneration

Historically the function of biomaterials has been to replace diseased or damaged tissues. Recent findings show that controlled release of the ionic dissolution products of bioactive glasses results in regeneration of tissues. The mechanism for in situ tissue regeneration involves upregulation of seven families of genes that control the osteoblast cell cycle, mitosis and differentiation. In the presence of critical concentrations of Si and Ca ions, within 48 h osteoblasts that are capable of differentiating into a mature osteocyte phenotype begin to proliferate and regenerate new bone. Osteoblasts that are not in the correct phase of the cell cycle and unable to proceed towards differentiation are switched into apoptosis by the ionic dissolution products. A controlled release of soluble Ca and Si from bioactive glass - resorbable polymer composites leads to vascularised soft tissue regeneration. Gene activation by controlled ion release provides the conceptual basis for molecular design of a third generation of biomaterials optimised for in situ tissue regeneration.     

组织工程角膜材料研究进展

1　人工角膜材料人工角膜的发展经历了一个曲折漫长的过程 ,早在 1 789年 ,法国医生ＰｅｌｌｉｅｒｄｅＱｕｅｎｓｅｙ就提出了人工角膜的设想 ,继之而来各国的学者展开了研究 ,使用了不同的光学材料 ,如水晶、玻璃、赛璐珞、石英等 ,目前的人工角膜由二部分组成 :(1 )光柱 :一个光学透明的中心 ;(2 )支架 :周边部既具有支持光柱的功能 ,同时又能与角膜组织形成永久的固定[1] 。1 .1　光柱材料　光柱材料要求首先必须具有较好的光学性能 ,并且具有无化学毒性和良好的生物相容性。早期使用过无机玻璃 ,但因其耐受性较差而基本上被其他材料取…     

复合水凝胶人工角膜裙边支架材料的生物相容性评价

背景：β-磷酸三钙/聚乙烯醇复合水凝胶具有高含水量、良好柔软性优点,有利于成纤细胞生长及胶原沉积,适用于做人工角膜裙边支架材料。 目的：评价β-磷酸三钙/聚乙烯醇复合水凝胶人工角膜裙边支架材料的生物相容性。 方法：①迟发型超敏反应：在豚鼠脊柱两侧皮内由头到尾分别注射A液(完全弗氏佐剂与生理盐水等体积混合液)、B液(β-磷酸三钙/聚乙烯醇复合水凝胶浸提液或生理盐水或2-巯基苯并噻唑)、C液(A液与B液等体积混合稳定性乳化剂),并进行局部诱导及激发。②急性全身性毒性实验：由昆明小鼠尾静脉分别注射生理盐水与β-磷酸三钙/聚乙烯醇复合水凝胶浸提液。③体外细胞毒性实验：分别以β-磷酸三 钙/聚乙烯醇复合水凝胶浸提液、细胞培养液及含苯酚的细胞培养液培养MRC-5细胞。④皮内反应：在兔脊柱皮内分别注射β-磷酸三钙/聚乙烯醇复合水凝胶生理盐水(或芝麻油)浸提液、生理盐水及芝麻油。 结果与结论：β-磷酸三钙/聚乙烯醇复合水凝胶人工角膜裙边支架材料的迟发型超敏反应分级为0-1级,急性全身毒性实验结果为正常无症状,体外细胞毒性均为0级或1级,皮内反应为极轻微。表明β-磷酸三钙/聚乙烯醇复合水凝胶人工角膜裙边支架材料生物相容性指标达到生物植入医用材料的要求。     

Bioactive anti-inflammatory coating for chronic neural electrodes

Chronic electrodes are widely used for brain degenerative and psychiatric daises such as Parkinson's diseases, major depression, and obsessive-compulsive disorder, and for neuronal prosthesis. Brain immune reaction to electrodes in the form of glial scar encapsulates the electrode and reduces the efficacy of deep brain stimulation and neuronal prosthesis. State-of-the-art strategies for improving brain-electrode interface use passive protein coating to "camouflage" the electrode from the immune system. In this study, we actively reduced the brain immune reaction to the chronic electrodes using immune suppressing protein, that is, interleukin (IL)-1 receptor antagonist. IL-1 receptor antagonist-coated electrodes and noncoated electrodes were chronically implanted in rats. An additional group of rats was chronically implanted with IL-1 receptor antagonist- and laminin-coated electrodes (as passive protein). Examination of glial scaring 1ne and 4 weeks after implantation indicated a significant reduction in the amount of glial scar in the vicinity of the IL-1 receptor antagonist-coated electrode in comparison to both noncoated electrode and laminin-coated electrodes. The results strongly suggest that active immune suppressing protein reduces the level of immune reaction to chronic electrodes already after 1 week after implantation and generates less immune reaction then passive protein coating.     

Designing Bioactive Delivery Systems for Tissue Regeneration

The direct infusion of macromolecules into defect sites generally does not impart adequate physiological responses. Without the protection of delivery systems, inductive molecules may likely redistribute away from their desired locale and are vulnerable to degradation. In order to achieve efficacy, large doses supplied at interval time periods are necessary, often at great expense and ensuing detrimental side effects. The selection of a delivery system plays an important role in the rate of re-growth and functionality of regenerating tissue: not only do the release kinetics of inductive molecules and their consequent bioactivities need to be considered, but also how the delivery system interacts and integrates with its surrounding host environment. In the current review, we describe the means of release of macromolecules from hydrogels, polymeric microspheres, and porous scaffolds along with the selection and utilization of bioactive delivery systems in a variety of tissue-engineering strategies.     

Bioactive sol-gel foams for tissue repair.

Bioactive glasses are known to have the ability to regenerate bone, but their use has been restricted mainly to powder, granules, or small monoliths. This work reports on the development of sol-gel foams with potential applications as bone graft implants or as templates for the in vitro synthesis of bone tissue for transplantation. These bioactive foams exhibit a hierarchical structure with interconnected macropores (10-500 microm) and a mesoporous framework typical of gel-glasses (pores of 2-50 nm). The macroporous matrixes were produced through a novel route that comprises foaming of sol-gel systems. Three glass systems were tested to verify the applicability of this manufacturing route, namely SiO(2), SiO(2)-CaO, and SiO(2)-CaO-P(2)O(5). This new class of material combines large pores to support vascularization and 3-D tissue growth with the ability that bioactive materials have to provide bone-bonding and controlled release of ionic biologic stimuli to promote bone cell proliferation by gene activation.     

Bioactive self-assembled peptide nanofibers for corneal stroma regeneration

Defects in the corneal stroma caused by trauma or diseases such as macular corneal dystrophy and keratoconus can be detrimental for vision. Development of therapeutic methods to enhance corneal regeneration is essential for treatment of these defects. This paper describes a bioactive peptide nanofiber scaffold system for corneal tissue regeneration. These nanofibers are formed by self-assembling peptide amphiphile molecules containing laminin and fibronectin inspired sequences. Human corneal keratocyte cells cultured on laminin-mimetic peptide nanofibers retained their characteristic morphology, and their proliferation was enhanced compared with cells cultured on fibronectin-mimetic nanofibers. When these nanofibers were used for damaged rabbit corneas, laminin-mimetic peptide nanofibers increased keratocyte migration and supported stroma regeneration. These results suggest that laminin-mimetic peptide nanofibers provide a promising injectable, synthetic scaffold system for cornea stroma regeneration.     

Bioactive hydrogel-filament scaffolds for nerve repair and regeneration

The design of novel biomaterials is crucial for the advancement of tissue engineering in nerve regeneration. In this study we developed and evaluated novel biosynthetic scaffolds comprising collagen crosslinked with a terpolymer of poly(N-isopropylacrylamide) (PNiPAAm) as conduits for nerve growth. These collagen-terpolymer (collagen-TERP) scaffolds grafted with the laminin pentapeptide YIGSR were previously used as corneal substitutes in pigs and demonstrated enhanced nerve regeneration compared to allografts. The purpose of this project was to enhance neuronal growth on the collagen-TERP scaffolds through the incorporation of supporting fibers. Neuronal growth on these matrices was assessed in vitro using isolated dorsal root ganglia as a nerve source. Statistical significance was assessed using a one-way ANOVA. The incorporation of fibers into the collagen-TERP scaffolds produced a significant increase in neurite extension (p<0.05). The growth habit of the nerves varied with the type of fiber and included directional growth of the neurites along the surface of certain fiber types. Furthermore, the presence of fibers in the collagen-TERP scaffolds appeared to influence neurite morphology and function; neurites grown on fibers-incorporated collagen-TERP scaffolds expressed higher levels of Na channels compared to the scaffolds without fiber. Overall, our results suggest that incorporation of supporting fibers enhanced neurite outgrowth and that surface properties of the scaffold play an important role in promoting and guiding nerve regeneration. More importantly, this study demonstrates the potential value of tissue engineered collagen-TERP hybrid scaffolds as conduits in peripheral nerve repair.     

Bioactive glass-polymer materials for controlled release of ibuprofen

The ibuprofen (IB) release from samples composed by SiO2-CaO-P2O5 bioactive glass, poly-L-lactic acid (PLA), and polymethylmethacrylate (PMMA) has been studied. Data showed a fast anti-inflammatory drug release during the first 8h when these polyphasic materials are soaked in simulated body fluid (SBF). The analysis of the samples before and after different soaking periods in SBF demonstrates the growth of an apatite-like layer on the materials surface. The IB release rate is related with the growth kinetics of this layer, that is slower when the materials do not contain the biodegradable polymer PLA. On the other hand, different IB and/or glass contents do not affect the in vitro behavior of these materials.     

Bioactive hydroxyapatite coatings on polymer composites for orthopedic implants

Hydroxyapatite [HA, Ca10(PO4)6(OH)2] coatings on polymer composite substrates were investigated for their bioactivity and their physicochemical and mechanical characteristics. HA holds key characteristics for use in orthopedic applications, such as for coating of the femoral stem in a hip replacement device. The plasma-spray technique was used to project HA onto a carbon fiber/polyamide 12 composite substrate. The resulting HA coatings exhibited mechanical adhesion as high as 23 MPa, depending on the surface treatment of the composite substrate. The purpose of this investigation was to evaluate the bioactivity of an HA-coated composite substrate. HA- coated samples have been immersed in simulated body fluid (SBF) and maintained within a shaker bath for periods of 1, 7, 14, 21, and 28 days at 37 degrees C. Scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction techniques were performed on the samples before and after immersion into SBF. SBF was analyzed using inductively coupled plasma atomic emission spectrometry for element concentration and evaluation of the solution's purity. SBF conditioning led to the deposition of crystalline HA onto the surface of the coatings. The calcium-to-phosphorous ratios of initial HA coating and of newly deposited HA were respectively 1.72 and 1.65, close to the HA theoretical calcium/phosphorous value of 1.67. Results demonstrated that bioactive HA coatings were produced by plasma spraying, because SBF conditioning induced newly formed HA with high crystallinity. Mechanical adhesion of the HA coatings was not significantly affected upon SBF conditioning.     

Bioactive Stratified Polymer Ceramic-Hydrogel Scaffold for Integrative Osteochondral Repair

Due to the intrinsically poor repair potential of articular cartilage, injuries to this soft tissue do not heal and require clinical intervention. Tissue engineered osteochondral grafts offer a promising alternative for cartilage repair. The functionality and integration potential of these grafts can be further improved by the regeneration of a stable calcified cartilage interface. This study focuses on the design and optimization of a stratified osteochondral graft with biomimetic multi-tissue regions, including a pre-designed and pre-integrated interface region. Specifically, the scaffold based on agarose hydrogel and composite microspheres of polylactide-co-glycolide (PLGA) and 45S5 bioactive glass (BG) was fabricated and optimized for chondrocyte density and microsphere composition. It was observed that the stratified scaffold supported the region-specific co-culture of chondrocytes and osteoblasts which can lead to the production of three distinct yet continuous regions of cartilage, calcified cartilage and bone-like matrices. Moreover, higher cell density enhanced chondrogenesis and improved graft mechanical property over time. The PLGA-BG phase promoted chondrocyte mineralization potential and is required for the formation of a calcified interface and bone regions on the osteochondral graft. These results demonstrate the potential of the stratified scaffold for integrative cartilage repair and future studies will focus on scaffold optimization and in vivo evaluations.     

Bioactive polymer scaffold for fabrication of vascularized engineering tissue

Tissue engineering seeks strategies to design polymeric scaffolds that allow high-cell-density cultures with signaling molecules and suitable vascular supply. One major obstacle in tissue engineering is the inability to create thick engineered-tissue constructs. A pre-vascularized tissue scaffold appears to be the most favorable approach to avoid nutrient and oxygen supply limitations as well as to allow waste removal, factors that are often hurdles in developing thick engineered tissues. Vascularization can be achieved using strategies in which cells are cultured in bioactive polymer scaffolds that can mimic extracellular matrix environments. This review addresses recent advances and future challenges in developing and using bioactive polymer scaffolds to promote tissue construct vascularization.