Insoluble elastin reduces collagen scaffold stiffness,improves viscoelastic properties,and induces a contractile phenotype in smooth muscle cells

Biomaterials with the capacity to innately guide cell behaviour while also displaying suitable mechanical properties remain a challenge in tissue engineering. Our approach to this has been to utilise insoluble elastin in combination with collagen as the basis of a biomimetic scaffold for cardiovascular tissue engineering. Elastin was found to markedly alter the mechanical and biological response of these collagen-based scaffolds. Specifically, during extensive mechanical assessment elastin was found to reduce the specific tensile and compressive moduli of the scaffolds in a concentration dependant manner while having minimal effect on scaffold microarchitecture with both scaffold porosity and pore size still within the ideal ranges for tissue engineering applications. However, the viscoelastic properties were significantly improved with elastin addition with a 3.5-fold decrease in induced creep strain, a 6-fold increase in cyclical strain recovery, and with a four-parameter viscoelastic model confirming the ability of elastin to confer resistance to long term deformation/creep. Furthermore, elastin was found to result in the modulation of SMC phenotype towards a contractile state which was determined via reduced proliferation and significantly enhanced expression of early (α-SMA), mid (calponin), and late stage (SM-MHC) contractile proteins. This allows the ability to utilise extracellular matrix proteins alone to modulate SMC phenotype without any exogenous factors added. Taken together, the ability of elastin to alter the mechanical and biological response of collagen scaffolds has led to the development of a biomimetic biomaterial highly suitable for cardiovascular tissue engineering.     

Three-dimensional nanocomposite scaffolds fabricated via selective laser sintering for bone tissue engineering

Bionanocomposites formed by combining biodegradable polymers and nanosized osteoconductive inorganic solids have been regarded as promising biomimetic systems which possess much improved structural and functional properties for bone tissue regeneration. In this study three-dimensional nanocomposite scaffolds based on calcium phosphate (Ca-P)/poly(hydroxybutyrate–co-hydroxyvalerate) (PHBV) and carbonated hydroxyapatite (CHAp)/poly(l-lactic acid) (PLLA) nanocomposite microspheres were successfully fabricated using selective laser sintering, which is a rapid prototyping technology. The sintered scaffolds had controlled material microstructure, totally interconnected porous structure and high porosity. The morphology and mechanical properties of Ca-P/PHBV and CHAp/PLLA nanocomposite scaffolds as well as PHBV and PLLA polymer scaffolds were studied. In vitro biological evaluation showed that SaOS-2 cells had high cell viability and normal morphology and phenotype after 3 and 7 days culture on all scaffolds. The incorporation of Ca-P nanoparticles significantly improved cell proliferation and alkaline phosphatase activity for Ca-P/PHBV scaffolds, whereas CHAp/PLLA nanocomposite scaffolds exhibited a similar level of cell response compared with PLLA polymer scaffolds. The nanocomposite scaffolds provide a biomimetic environment for osteoblastic cell attachment, proliferation and differentiation and have great potential for bone tissue engineering applications.     

Innovative magnetic scaffolds for orthopedic tissue engineering

The use of magnetism in tissue engineering is a very promising approach, in fact magnetic scaffolds are able not only to support tissue regeneration, but they can be activated and work like a magnet attracting functionalized magnetic nanoparticles (MNPs) injected close to the scaffold enhancing tissue regeneration. This study aimed to assess the in vivo biocompatibility and osteointegrative properties of novel magnetic scaffolds. Two hydroxyapatite/collagen (70/30 wt %) magnetic scaffolds were magnetized with two different techniques: direct nucleation of biomimetic phase and superparamagnetic nanoparticles (MNPs) on self-assembling collagen fibers (MAG-A) and scaffold impregnation in ferro-fluid solution (MAG-B). Magnetic scaffolds were implanted in rabbit distal femoral epiphysis and tibial mid-diaphysis. Histopathological screening showed no inflammatory reaction due to MNPs. Significantly higher bone healing rate (ΔBHR) results were observed in MAG-A in comparison to MAG-B. Significant differences were also found between experimental times with an increase in ΔBHR from 2 to 4 weeks for both scaffolds in trabecular bone, while only for MAG-B (23%, p < 0.05) in cortical bone. The proposed magnetic scaffolds seem to be promising for magnetic guiding in orthopedic tissue engineering applications and they will be suitable to treat also several pathologies in regenerative medicine area.     

软骨修复材料种类的比较

背景：软骨修复材料要求具有特定的生化、物理性质,如极强的生物相容性、合适的生物降解性、可控的孔径大小、足够的孔隙率等。 目的：对比分析各种软骨修复材料的特点。 方法：应用计算机检索万方数据库、CNKI数据库2001/2010与软骨修复材料相关的文章,检索关键词为“软骨,修复,支架材料,组织工程,生物材料”。 结果与结论：软骨组织工程支架材料分为天然支架材料、复合支架材料、可注射支架材料、仿生支架材料等。但是各种材料具有各自的优势与不足,目前多采用复合支架材料或利用仿生原理制备仿生支架材料或是可注射型支架材料,以充分发挥材料的优势,克服不足,使其生物力学特性更加接近天然骨组织。尽管骨组织工程研究已经取得了相当快速的进展和成果,但仍有许多问题需要解决：支架的免疫原性即降解转归及对机体的影响;支架是否可与软骨下骨有效结合;支架材料的降解速度是否可与组织形成相匹配;支架的生物力学性能是否与软骨组织相同或接近等。     

组织工程神经支架材料的临床应用

背景：神经损伤后没有自我修复的能力,因此,神经组织工程支架材料应用于神经修复、促进神经再生成为研究的热点。 目的：分析目前常用的神经组织工程支架材料的应用范围及效果。 方法：分别对胶原、壳聚糖、凝胶以及透明质酸与人工合成材料形成的聚合物用于神经损伤修复进行动物模型分析,应用免疫染色、生化检测等方法观察评估再生神经的结构和生理功能,确定不同神经组织工程支架材料的应用效果。 结果与结论：神经组织工程支架材料胶原、壳聚糖、凝胶、透明质酸以及人工合成材料均可以通过不同的方式用于损伤神经的再生修复,既可以联合细胞进行生物聚合,也可以联合神经片段移植形成损伤神经桥状联接导管,应用于动物模型实验均显示较好的治疗效果。     

Designed hybrid scaffolds consisting of polycaprolactone microstrands and electrospun collagen-nanofibers for bone tissue regeneration

Biomedical scaffolds used in bone tissue engineering should have various properties including appropriate bioactivity, mechanical strength, and morphologically optimized pore structures. Collagen has been well known as a good biomaterial for various types of tissue regeneration, but its usage has been limited due to its low mechanical property and rapid degradation. In this work, a new hybrid scaffold consisting of polycaprolactone (PCL) and collagen is proposed for bone tissue regeneration. The PCL enhances the mechanical properties of the hybrid scaffold and controls the pore structure. Layered collagen nanofibers were used to enhance the initial cell attachment and proliferation. The results showed that the hybrid scaffold yielded better mechanical properties of pure PCL scaffold as well as enhanced biological activity than the pure PCL scaffold did. The effect of pore size on bone regeneration was investigated using two hybrid scaffolds with pore sizes of 200 ± 20 and 300 ± 27 μm. After post-seeding for 7 days, the cell proliferation with pore size, 200 ± 20 μm, was greater than that with pore size, 300 ± 27 μm, due to the high surface area of the scaffold.     

PCL基复合骨组织工程支架研究现状及发展

三维骨组织工程支架已成为成骨研究领域的热点。聚己内酯(PCL)具有良好的生物相容性,在骨组织工程研究中被广泛应用于三维支架的制备。但纯PCL支架亲水性差、生物活性低,限制了其在生物医学领域的应用。随着骨组织工程材料研究的发展,大量研究者将PCL与各种无机物、金属元素或胶原等活性材料进行复合,以改善支架性能或引入新的性能。针对PCL基骨组织工程复合支架的材料选择,从PCL复合无机材料、PCL复合水凝胶材料、PCL复合金属元素、PCL复合小分子药物以及PCL复合生物活性分子等5个方面,对各类复合支架的性能及体内外成骨效果等方面进行综述,希望对PCL在骨组织工程中的研究及临床应用提供一定的帮助。     

制备软骨组织工程支架的方法

背景：软骨组织工程支架作为软骨细胞外基质的替代物,其外形和孔结构对实现其作用和功能具有非常重要的意义。 目的：回顾目前若干种常用软骨组织工程中三维多孔支架的制备方法。 方法：由第一作者检索2000至2013年PubMed数据库,ELSEVIER SCIENCEDIRECT、万方数据库、中国知网数据库。英文检索词为“Cartilage tissue engineering;scaffolds;fabrication”,中文检索词为“软骨组织工程;制备方法;支架材料;多孔支架”。 结果与结论：制备软骨组织工程支架的方法有相分离/冷冻干燥法、水凝胶技术、快速成型技术、静电纺丝法、溶剂浇铸/粒子沥滤法及气体发泡法等。目前研究发现,支架中孔径的大小对组织的重建有着直接的影响,孔径为100-250 μm的孔有益于骨及软骨组织的再生。通过溶液浇铸/粒子沥滤法、气体发泡法所制备的支架孔径大小在这一范围内,因此比较适合用于骨、软骨组织工程支架的构建。研究人员通常将多种方法结合起来,以期能制备出生物和力学性能方面更加仿生的组织工程多孔支架。中国组织工程研究杂志出版内容重点：生物材料;骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性;组织工程全文链接：     

Biomimetic materials for tissue engineering

The development of biomaterials for tissue engineering applications has recently focused on the design of biomimetic materials that are capable of eliciting specific cellular responses and directing new tissue formation mediated by biomolecular recognition, which can be manipulated by altering design parameters of the material. Biomolecular recognition of materials by cells has been achieved by surface and bulk modification of biomaterials via chemical or physical methods with bioactive molecules such as a native long chain of extracellular matrix (ECM) proteins as well as short peptide sequences derived from intact ECM proteins that can incur specific interactions with cell receptors. The biomimetic materials potentially mimic many roles of ECM in tissues. For example, biomimetic scaffolds can provide biological cues for cell-matrix interactions to promote tissue growth, and the incorporation of peptide sequences into materials can also make the material degradable by specific protease enzymes. This review discusses the surface and bulk modification of biomaterials with cell recognition molecules to design biomimetic materials for tissue engineering. The criteria to design biomimetic materials such as the concentration and spatial distribution of modified bioactive molecules are addressed. Recent advances for the development of biomimetic materials in bone, nerve, and cardiovascular tissue engineering are also summarized.     

Biologically inspired synthesis of bone-like composite: self-assembled collagen fibers/hydroxyapatite nanocrystals

Replacement of bone tissue by graft materials and products of tissue engineering having composition, structure, and biological features that mimic natural tissue is a goal to be pursued. A biomimetic synthesis was performed to prepare new bone-like composites constituted of hydroxyapatite nanocrystals and self-assembled type I collagen fibers. We used a biological inspired approach that proved that the biological systems stored and processed information at the molecular level. Two different methodologies were used: dispersion of synthetic hydroxyapatite in telopeptides free collagen molecules solution and direct nucleation of hydroxyapatite into reconstituted collagen fibers during their assembling. The different preparation techniques were experimented then the composites thoroughly characterized and compared. Composite obtained by direct nucleation showed an intimated interaction of the inorganic and proteic components, which modified the apatitic phase and made its composition, morphology and structure similar to the mineral component of natural bone.     

Electro-spinning of pure collagen nano-fibres - just an expensive way to make gelatin?

Scaffolds manufactured from biological materials promise better clinical functionality, providing that characteristic features are preserved. Collagen, a prominent biopolymer, is used extensively for tissue engineering applications, because its signature biological and physico-chemical properties are retained in in vitro preparations. We show here for the first time that the very properties that have established collagen as the leading natural biomaterial are lost when it is electro-spun into nano-fibres out of fluoroalcohols such as 1,1,1,3,3,3-hexafluoro-2-propanol or 2,2,2-trifluoroethanol. We further identify the use of fluoroalcohols as the major culprit in the process. The resultant nano-scaffolds lack the unique ultra-structural axial periodicity that confirms quarter-staggered supramolecular assemblies and the capacity to generate second harmonic signals, representing the typical crystalline triple-helical structure. They were also characterised by low denaturation temperatures, similar to those obtained from gelatin preparations (p>0.05). Likewise, circular dichroism spectra revealed extensive denaturation of the electro-spun collagen. Using pepsin digestion in combination with quantitative SDS-PAGE, we corroborate great losses of up to 99% of triple-helical collagen. In conclusion, electro-spinning of collagen out of fluoroalcohols effectively denatures this biopolymer, and thus appears to defeat its purpose, namely to create biomimetic scaffolds emulating the collagen structure and function of the extracellular matrix.     

Influence of a novel calcium-phosphate coating on the mechanical properties of highly porous collagen scaffolds for bone repair

Lyophilised collagen scaffolds have shown enormous potential in tissue engineering in a number of areas due to their excellent biological performance. However, they are limited for use in bone tissue engineering due to poor mechanical properties. This paper discusses the development of a calcium-phosphate coating for collagen scaffolds in order to improve their mechanical properties for bone tissue engineering.Pure collagen scaffolds produced in a lyophilisation process were coated by immersing them in sodium ammonium hydrogen phosphate (NaNH₄HPO₄) followed by calcium chloride (CaCl₂). The optimal immersing sequence, duration, as well as the optimal solution concentration which facilitated improved mechanical properties of the scaffolds was investigated. The influence of the coating on composition, structural and material properties was analysed.This investigation successfully developed a novel collagen/calcium-phosphate composite scaffold. An increase in the mechanical properties of the scaffolds from 0.3 kPa to up to 90 kPa was found relative to a pure collagen scaffold, while the porosity was maintained as high as 92%, indicating the potential of the scaffold for bone tissue engineering or as a bone graft substitute.     

In vitro evaluation of a poly(lactide-co-glycolide)-collagen composite scaffold for bone regeneration

Numerous materials have been proposed for bone tissue regeneration. However, none has been shown to be entirely satisfactory. In this study we fabricated a hybrid composite scaffold composed of poly(D,L-lactide-co-glycolide) (PLGA) and a naturally derived collagen matrix derived from porcine bladder submucosa matrix (BSM), and evaluated the biological activities and physical properties of the scaffold for use in bone tissue regeneration. The BSM-PLGA composite scaffolds are able to promote cellular interactions and possess uniformly interconnected pores with adequate structural integrity. The composite scaffolds were tested with both human embryonic stem (hES) cells and bovine osteoblasts (bOB). Cells seeded on the composite scaffolds readily attached, infiltrated and proliferated, as confirmed by cell viability and mitochondrial metabolic activity. Use of the composite scaffolding system with cells may enhance the formation of bone tissue for therapeutic regeneration.     

Preparation and in vitro characterization of electrospun PVA scaffolds coated with bioactive glass for bone regeneration

An important objective in bone tissue engineering is to fabricate biomimetic three-dimensional scaffolds that stimulate mineralization for rapid regeneration of bone. In this work, scaffolds of electrospun poly(vinyl alcohol) (PVA) fibers (diameter = 286 ± 14 nm) were coated with a sol-gel derived bioactive glass (BG) and evaluated in vitro for potential applications in bone repair. Structural and chemical analyses showed that the BG coating was homogeneously deposited on the PVA fibers. In vitro cell culture studies showed that the BG-coated PVA scaffold had a greater capacity to support proliferation of osteogenic MC3T3-E1 cells, alkaline phosphatase activity, and mineralization than the uncoated PVA scaffold. The BG coating improved the tensile strength of the PVA scaffold from 18 ± 2 MPa to 21 ± 2 MPa, but reduced the elongation to failure from 94 ± 4% to 64 ± 5%. However, immersion of the BG-coated PVA scaffolds in a simulated body fluid for 5 days resulted in an increase in the tensile strength (24 ± 2 MPa) and elongation to failure (159 ± 4%). Together, the results show that these BG-coated PVA scaffolds could be considered as candidate materials for bone tissue engineering applications.     

Applications of knitted mesh fabrication techniques to scaffolds for tissue engineering and regenerative medicine

Knitting is an ancient and yet, a fresh technique. It has a history of no less than 1,000 years. The development of tissue engineering and regenerative medicine provides a new role for knitting. Several meshes knitted from synthetic or biological materials have been designed and applied, either alone, to strengthen materials for the patching of soft tissues, or in combination with other kinds of biomaterials, such as collagen and fibroin, to repair or replace damaged tissues/organs. In the latter case, studies have demonstrated that knitted mesh scaffolds (KMSs) possess excellent mechanical properties and can promote more effective tissue repair, ligament/tendon/cartilage regeneration, pipe-like-organ reconstruction, etc. In the process of tissue regeneration induced by scaffolds, an important synergic relationship emerges between the three-dimensional microstructure and the mechanical properties of scaffolds. This paper presents a comprehensive overview of the status and future prospects of knitted meshes and its KMSs for tissue engineering and regenerative medicine.     

Synthesis of bone-like nanocomposites using multiphosphorylated peptides

There is a great need for novel materials for mineralized tissue repair and regeneration. Two examples of such tissue, bone and dentin, are highly organized hierarchical nanocomposites in which mineral and organic phases interface at the molecular level. In contrast, current graft materials are either ceramic powders or physical blends of mineral and organic phases with mechanical properties far inferior to those of their target tissues. The objective of this study was to synthesize composite nanofibrils with highly integrated organic/inorganic phases inspired by the mineralized collagen fibrils of bone and dentin. Utilizing our understanding of bone and dentin biomineralization, we have first designed bioinspired peptides containing 3 Ser-Ser-Asp repeat motifs based on the highly phosphorylated protein, dentin phosphophoryn (DPP), found in dentin and alveolar bone. We demonstrate that up to 80% of serines in the peptide can be phosphorylated by casein kinases. We further tested the ability of these peptides to induce biomimetic calcium phosphate mineralization of collagen fibrils. Our mineralization studies have revealed that in the presence of these phosphorylated peptides, mineralized collagen fibrils structurally similar to the mineralized collagen fibrils of bone and dentin were formed. Our results demonstrate that using phosphorylated DPP-inspired peptides, we can successfully synthesize biomimetic composite nanofibrils with integrated organic and inorganic phases. These results provide the first step in the development of biomimetic nanostructured materials for mineralized tissue repair and regeneration using phosphopeptides.     

An aligned nanofibrous collagen scaffold by electrospinning and its effects on in vitro fibroblast culture

Fabrication of nanofibrous scaffolds with well-defined architecture mimicking native extracellular matrix analog has significant potentials for many specific tissue engineering and organs regeneration applications. The fabrication of aligned collagen nanofibrous scaffolds by electrospinning was described in this study. The structure and in vitro properties of these scaffolds were compared with a random collagen scaffold. All the collagen scaffolds were first crosslinked in glutaraldehyde vapor to enhance the biostability and keep the initial nano-scale dimension intact. From in vitro culture of rabbit conjunctiva fibroblast, the aligned scaffold exhibited lower cell adhesion but higher cell proliferation because of the aligned orientation of fibers when compared with the random scaffold. And the alignment of the fibers may control cell orientation and strengthen the interaction between the cell body and the fibers in the longitudinal direction of the fibers.     

Preparation and characterization of a three-dimensional printed scaffold based on a functionalized polyester for bone tissue engineering applications

At present there is a strong need for suitable scaffolds that meet the requirements for bone tissue engineering applications. The objective of this study was to investigate the suitability of porous scaffolds based on a hydroxyl functionalized polymer, poly(hydroxymethylglycolide-co-ε-caprolactone) (pHMGCL), for tissue engineering. In a recent study this polymer was shown to be a promising material for bone regeneration. The scaffolds consisting of pHMGCL or poly(ε-caprolactone) (PCL) were produced by means of a rapid prototyping technique (three-dimensional plotting) and were shown to have a high porosity and an interconnected pore structure. The thermal and mechanical properties of both scaffolds were investigated and human mesenchymal stem cells were seeded onto the scaffolds to evaluate the cell attachment properties, as well as cell viability and differentiation. It was shown that the cells filled the pores of the pHMGCL scaffold within 7 days and displayed increased metabolic activity when compared with cells cultured in PCL scaffolds. Importantly, pHMGCL scaffolds supported osteogenic differentiation. Therefore, scaffolds based on pHMGCL are promising templates for bone tissue engineering applications.