Regeneration of osteochondral defects in vivo by a cell‐free cylindrical poly(lactide‐co‐glycolide) scaffold with a radially oriented microstructure

A scaffold with an oriented porous architecture to facilitate cell infiltration and bioactive interflow between neo‐host tissues is of great importance for in situ inductive osteochondral regeneration. In this study, a poly(lactide‐co‐glycolide) (PLGA) scaffold with oriented pores in its radial direction was fabricated via unidirectional cooling of the PLGA solution in the radial direction, following with lyophilization. Micro‐computed tomography evaluation and scanning electron microscopy observation confirmed the radially oriented microtubular pores in the scaffold. The scaffold had porosity larger than 90% and a compressive modulus of 4 MPa in a dry state. Culture of bone marrow stem cells in vitro revealed faster migration and regular distribution of cells in the poly(lactide‐co‐glycolide) scaffold with oriented pores compared with the random PLGA scaffold. The cell‐free oriented macroporous PLGA scaffold was implanted into rabbit articular osteochondral defect in vivo for 12 weeks to evaluate its inductive tissue regeneration function. Histological analysis confirmed obvious tide mark formation and abundant chondrocytes distributed regularly with obvious lacunae in the cartilage layer. Safranin O‐fast green staining showed an obvious boundary between the two layers with distinct staining results, indicating the simultaneous regeneration of the cartilage and subchondral bone layers, which is not the case for the random poly(lactide‐co‐glycolide) scaffold after the same implantation in vivo. The oriented macroporous PLGA scaffold is a promising material for the in situ inductive osteochondral regeneration without the necessity of preseeding cells.     

Carbon nanotube reinforced polyvinyl alcohol/biphasic calcium phosphate scaffold for bone tissue engineering

In this paper, a well-developed porous carbon nanotube (CNT) reinforced polyvinyl alcohol/biphasic calcium phosphate (PVA/BCP) scaffold was fabricated by a freeze-thawing and freeze-drying method. The microstructure, mechanical properties and the composition of the scaffolds were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The results illustrate that after the incorporation of CNTs, the compressive strength of the hydrogels (moisture state) reached 81 ± 6 kPa, presenting a significantly higher value than that of pure PVA/BCP hydrogels (48 ± 2 kPa). Meanwhile, CNT reinforced PVA/BCP scaffolds exhibited a porous structure and high interconnectivity (80 ± 0.6%). The degradation analysis indicated that the degradation ratio of scaffolds can be varied by changing the concentrations of BCP powders and CNTs. Cell culture results show that PVA/BCP/CNT porous scaffolds have no negative effects on the survival and proliferation of cells. These results strongly show that the composite scaffolds may possess a potential application in the field of bone tissue engineering and regeneration.

In this paper, a well-developed porous carbon nanotube (CNT) reinforced polyvinyl alcohol/biphasic calcium phosphate (PVA/BCP) scaffold was fabricated by a freeze-thawing and freeze-drying method.     

A novel method for the direct fabrication of growth factor-loaded microspheres within porous nondegradable hydrogels: Controlled release for cartilage tissue engineering

Because of similar mechanical properties to native cartilage, synthetic hydrogels based on poly(vinyl alcohol) (PVA) have been proposed for replacement of damaged articular cartilage, but they suffer from a complete lack of integration with surrounding tissue. In this study, insulin-like growth factor-1 (IGF-1), an important growth factor in cartilage regeneration, was encapsulated in degradable poly(lactic-co-glycolic acid) (PLGA) microparticles embedded in the PVA hydrogels in a single step based on a double emulsion. The release of IGF-1 from these hydrogels was sustained over 6 weeks in vitro. Poly(glycolic acid) (PGA) fiber scaffolds were wrapped around the hydrogels, seeded with chondrocytes, and implanted subcutaneously in athymic mice. The release of IGF-1 enhanced cartilage formation in the layers surrounding the hydrogels, in terms of the content of extracellular matrix components and mechanical properties, and increased integration between the cartilage layers and the hydrogels, according to gross observation of the cross-sections and histology. The compressive modulus of the cartilage-hydrogel constructs without IGF-1 was 0.07 ± 0.02 MPa, compared to 0.17-0.2 MPa for hydrogels that contained IGF-1. The biochemical and mechanical markers of cartilage formation were not different between the low and high concentrations of IGF-1, despite an order of magnitude difference in concentration. This study shows that the sustained release of IGF-1 can enhance tissue formation and points to a possible strategy for effecting integration with surrounding tissue.     

Mechanical and physicochemical behavior of a 3D hydrogel scaffold during cell growth and proliferation

Some of the essential properties for cellular scaffolding are the capability to maintain the three-dimensional (3D) structure, good adhesion, and adequate elastic modulus during cell growth, migration, and proliferation. Biocompatible synthetic hydrogels are commonly used as cellular scaffolds because they can mimic the natural extracellular matrices (ECMs). However, it is possible that the physicochemical and mechanical behavior of the scaffold changes during cell proliferation and loses the scaffold properties but this is rarely monitored. In this work, the physicochemical and mechanical properties of a macroporous soft material based on poly(N-isopropyl acrylamide) (PNIPAM) have been studied during a period of 75 days at culture condition while bovine fetal fibroblasts (BFF) were grown within the matrix. The interconnected macroporous hydrogel was obtained by cryogelation at −18 °C. The swelling capacity of the scaffold was not altered during cell proliferation but changes in the mechanical properties were observed, beginning with the high elastic modulus (280 kPa) that progressively decreased until mechanical stability (40 kPa) was achieved after 20 culture days. It was observed that the matrix–cell interactions together with collagen production favor normal cellular processes such as cell morphology, adhesion, migration, and proliferation. Therefore, the observed behavior of macroporous PNIPAM as a 3D scaffold during cell growth indicates that the soft matrix is cytocompatible for a long time and preserves the suitable properties that can be applied in tissue engineering and regenerative medicine.

3D cell scaffold based on macroporous PNIPAM is cytocompatible and preserves the cell viability for more than 75 culture days.     

Quantitative Assessment of Articular Cartilage with Morphologic,Acoustic and Mechanical Properties Obtained Using High-Frequency Ultrasound

Osteoarthritis (OA) is one of the most common joint diseases among adults, and its early detection is still not possible. In this study, high-frequency ultrasound and ultrasound-assisted mechanical testing systems were used to quantitatively measure the morphologic, acoustic and mechanical properties of normal and enzymatically degraded bovine articular cartilages in vitro. A total of 40 osteochondral cartilage plugs were prepared from 20 bovine patellae (n = 20 × 2) and divided into two groups for collagenase and trypsin digestions, respectively. A high-frequency ultrasound system (center frequency: 40 MHz) was used to analyze the surface integrity (ultrasound roughness index, URI), thickness and acoustic properties of the articular cartilages before and after enzymatic degradations. Acoustic parameters included the integrated reflection coefficient (IRC) from the cartilage surface, reflection from the cartilage-bone interface (AIB_bone), integrated attenuation (IA) and integrated backscatter (IBS) of the internal cartilage tissue. A newly developed ultrasound water jet indentation system was used to assess the mechanical properties of the cartilage samples. The results showed that the URI increased significantly (p < 0.05) after collagenase digestion while no significant change (p > 0.05) was found after trypsin digestion. With regard to acoustic parameters, the IRC decreased significantly (p < 0.05) after collagenase digestion while no significant change (p > 0.05) was found after trypsin digestion. The AIB_bone demonstrated an insignificant change after collagenase digestion (p > 0.05) but a significant decrease after trypsin digestion (p < 0.05). Both enzymatic degradation groups showed insignificant differences (p > 0.05) in the IA but a significant increase (p < 0.05) in the IBS after both enzymatic degradations. The apparent stiffness measured by ultrasound water jet indentation suggested that articular cartilage from both groups became significantly softer (p < 0.05) after the enzymatic degradations. A significant relationship was found to exist between the IRC and URI (p < 0.05). This study showed that high-frequency ultrasound can be a comprehensive tool to quantitatively and systematically analyze the morphologic, acoustic and mechanical properties of articular cartilage in association with its degeneration. (E-mail: ypzheng@ieee.org)     

Contrary response of porcine articular cartilage below and over 1000 s−1

BackgroundKnee joints experience excessive loads quite frequently during sports activities, and these shocks could accelerate progressive degeneration in articular cartilage.MethodsQuasi-static and dynamic response of porcine knee articular cartilages were investigated in this research. Split Hopkinson Pressure Bars (SHPB) were utilized to examine the articular cartilage properties at strain rates between 0.01–2000 s⁻¹.FindingsThe results showed that strain rate is an important factor for articular cartilages, distinctively divided into above and below 1000 s⁻¹. The articular cartilages exhibit a strain hardening phenomenon when shock loaded at strain rates under 1000 s⁻¹. When loaded at strain rates over 1000 s⁻¹, their ultimate strength and elastic modulus decreased with increasing strain rates.InterpretationThe biphasic structure of the cartilage explained the change of modulus. At the lower strain rates, fibers realigned and solidified the structure, while at higher strain rates, there is not enough time for the tissue fluid to move inside the cartilage, leading to a reduction in the deformability of the specimen and raising of Young's modulus. The results can be utilized to provide some useful data for biomaterial and computational works in the future.     

Mechanical stimulations on human bone marrow mesenchymal stem cells enhance cells differentiation in a three‐dimensional layered scaffold

Scaffolds laden with stem cells are a promising approach for articular cartilage repair. Investigations have shown that implantation of artificial matrices, growth factors or chondrocytes can stimulate cartilage formation, but no existing strategies apply mechanical stimulation on stratified scaffolds to mimic the cartilage environment. The purpose of this study was to adapt a spraying method for stratified cartilage engineering and to stimulate the biosubstitute. Human mesenchymal stem cells from bone marrow were seeded in an alginate (Alg)/hyaluronic acid (HA) or Alg/hydroxyapatite (Hap) gel to direct cartilage and hypertrophic cartilage/subchondral bone differentiation, respectively, in different layers within a single scaffold. Homogeneous or composite stratified scaffolds were cultured for 28 days and cell viability and differentiation were assessed. The heterogeneous scaffold was stimulated daily. The mechanical behaviour of the stratified scaffolds were investigated by plane–strain compression tests. Results showed that the spraying process did not affect cell viability. Moreover, cell differentiation driven by the microenvironment was increased with loading: in the layer with Alg/HA, a specific extracellular matrix of cartilage, composed of glycosaminoglycans and type II collagen was observed, and in the Alg/Hap layer more collagen X was detected. Hap seemed to drive cells to a hypertrophic chondrocytic phenotype and increased mechanical resistance of the scaffold. In conclusion, mechanical stimulations will allow for the production of a stratified biosubstitute, laden with human mesenchymal stem cells from bone marrow, which is capable in vivo to mimic all depths of chondral defects, thanks to an efficient combination of stem cells, biomaterial compositions and mechanical loading.     

Strain-Dependent Modulation of Ultrasound Speed in Articular Cartilage Under Dynamic Compression

Mechanical properties of articular cartilage may be determined by means of mechano-acoustic indentation, a clinically feasible technique for cartilage diagnostics. Unfortunately, ultrasound speed varies in articular cartilage during mechanical compression. This can cause significant errors to the measured mechanical parameters. In this study, the strain-dependent variation in ultrasound speed was investigated during dynamic compression. In addition, we estimated errors that were induced by the variation in ultrasound speed on the mechano-acoustically measured elastic properties of the tissue. Further, we validated a computational method to correct these errors. Bovine patellar cartilage samples (n = 7) were tested under unconfined compression. Strain-dependence of ultrasound speed was determined under different compressive strains using an identical strain-rate. In addition, the modulation of ultrasound speed was simulated using the transient compositional and structural changes derived from fibril-reinforced poroviscoelastic (FRPVE) model. Experimentally, instantaneous compressive strain modulated the ultrasound speed (p < 0.05) significantly. The decrease of ultrasound speed was found to change nonlinearly as a function of strain. Immediately after the ramp loading ultrasound speed was found to be changed –0.94%, –1.49%, –1.84%, –1.87%, –1.89% and –2.15% at the strains of 2.4%, 4.9%, 7.3%, 9.7%, 12.1% and 14.4%, respectively. The numerical simulation revealed that the compression-related decrease in ultrasound speed induces significant errors in the mechano-acoustically determined strain (39.7%) and dynamic modulus (72.1%) at small strains, e.g., at 2.4%. However, at higher strains, e.g., at 14.4%, the errors were smaller, i.e., 12.6% for strain and 14.5% for modulus. After the proposed computational correction, errors related to ultrasound speed were decreased. By using the correction, with e.g., 2.4% strain, errors in strain and modulus were decreased from 39.7% to 7.2% and from 72.1% to 35.3%, respectively. The FRPVE model, addressing the changes in fibril orientation and void ratio during compression, showed discrepancy of less than 1% between the predicted and measured ultrasound speed during the ramp compression. (E-mail: juha.toyras@kuh.fi)     

羟基丁酸与羟基辛酸共聚物一体化骨软骨组织工程支架的制备及性能

背景:单层支架难以满足关节软骨损伤修复的要求,现提出骨软骨共同修复的一体化支架,以弥补了单一支架的部分缺陷。目的:以羟基丁酸与羟基辛酸共聚物为基础材料,羟基磷灰石等为复合材料研制一体化骨软骨组织工程支架,测试该支架的物理特性和细胞黏附性。方法:采用溶剂浇铸/颗粒沥滤法,以支架孔径、孔隙率、力学强度和细胞黏附生长率为检测指标,以羟基丁酸与羟基辛酸共聚物为连续相,通过改变致孔剂NaCl粒径和羟基磷灰石材料配比制备不同形态结构、力学强度和生物学功能的三层一体化骨软骨组织工程支架。结果与结论:致孔剂与支架材料的最佳质量配比分别为软骨层4.5/1,过渡层2.5/1,硬骨层3.5/1。扫描电镜观察显示支架的三层结构明显不同且紧密结合,其软骨层、过渡层、硬骨层的孔径分别为150~250μm,≤60μm,150~450μm;孔隙率检测结果依次为84%,60%,75%;力学强度测定依次为2.93,6.43,4.30MPa;支架对骨髓间充质干细胞无毒性,细胞黏附与生长状态良好。结果表明该一体化骨软骨组织工程支架具有仿生学特性,符合骨软骨组织工程支架的基本条件。     

运动性关节软骨缺损支架材料的选择及其生物相容性

背景：骨软骨支架是用于承载细胞,供细胞黏附、生长、增殖、分化的载体。目的：总结运动性关节软骨缺损支架材料的应用进展及其生物替代材料的生物相容性。方法：以＂关节软骨,生物材料,工程软骨,支架材料,生物相容性＂为中文关键词,以＂tissue enginneering,articular cartilage,scaffold material＂为英文关键词,采用计算机检索维普数据库、PubMed数据库1993-01/2010-11相关文章。纳入与有关修复关节软骨损伤、生物材料、支架材料、生物相容性等相关的文章。以20篇文献为重点对运动性关节软骨缺损修复用的生物材料的生物相容性进行了讨论。结果与结论：天然软骨支架材料因其具有细胞识别信号,故生物相容性好,细胞黏附率高,但力学性能较差。有些人工合成材料生物相容性不理想、亲水性差、对细胞吸附不足,人工合成高分子聚合物生物相容性良好。复合支架利用不同生物材料的优点克制材料的局限性制备理想的复合支架,其混合比例、混合技术还有待进一步研究。目前尚无一种材料完全满足组织工程的要,通过材料制备技术的改进或将几种不同材料的复合,材料的性能会不断的提高。     

运动性关节软骨损伤修复材料的选择及其生物力学特征

背景：关节软骨是无血管、淋巴管和神经的组织,通常情况下软骨细胞不能进行有丝分裂,这导致自身修复能力有限。生理负荷下,关节软骨经常处在应力环境中。根据软骨自身的结构和特点,作为人工软骨的替代材料应具有良好的生物力学性能。目的：总结运动性关节软骨损伤修复材料的应用进展及其生物替代材料的生物力学特征。方法：以＂关节软骨,生物材料,生物力学＂为中文关键词,以＂tissue enginneering,articular cartilage,scaffold material,biomechanics＂为英文关键词,采用计算机检索中国期刊全文数据库、PubMed数据库1993-01/2010-10相关文章。纳入与运动有关的关节软骨损伤修复、目前常用于修复关节软骨损伤的生物材料以及生物替代材料的生物力学特征研究文章;排除重复研究或Meta分析类文章。以20篇文献为主重点对运动性关节软骨缺损修复材料的生物力学特征进行讨论。结果与结论：关节软骨是一种各向异性、非均质、具有黏弹性并充满液体的可渗透物质,具有独特的力学性能。损伤的关节软骨在生物力学方面均与原来的软骨不同,且极易退变。骨软骨柱移植力学性能近期效果最佳;脱细胞软骨基质、小肠黏膜下基质具有一定的力学强度;普通聚乙烯醇水凝胶的最大缺陷是力学性能的不足;聚乙烯醇材料其良好的柔韧性和高弹性能,具有与人关节软骨相似的力学性能;n-HA浆料与聚酰胺66在溶剂中复合,无论在力学性能还是化学组成上都与自然骨相似。提示在众多关节软骨替代材料中,无论是人工合成材料、天然材料、复合材料其生物力学性能各有不同,且目前还无法再造与天然生成的软骨具有相同力学性能的软骨组织。     

Reliability of Human Lumbar Facet Joint Degeneration Severity Assessed by Magnetic Resonance Imaging

ObjectiveThe purpose of this study was to determine the reliability of the assessment of lumbar facet joint degeneration severity by analyzing degeneration subscales using magnetic resonance imaging (MRI) in human participants.MethodsThe reliability of articular cartilage degeneration, subchondral bone sclerosis, and osteophyte formation subscales of lumbar facet joint degeneration severity was assessed in MRI images from n = 10 human participants. Each scale was applied to n = 20 lumbar facet joints (L4/5 level). Three examiners were trained. A first assessment of MRI images was provided by the examiners followed by a second assessment 30 days later. Intraobserver and interobserver reliability were determined using percent agreement, the weighted kappa coefficient κ_w for paired comparisons, and the overall weighted kappa κ_o. The minimum threshold for reliability was set at moderate levels of agreement, κ_w > 0.40, based upon previous recommendations.ResultsThe articular cartilage subscale had acceptable intraobserver (κ_o = 0.51) and interobserver (κ_o = 0.41) reliability. Scales for subchondral bone sclerosis (intraobserver κ_o = 0.28; interobserver κ_o = 0.10) and osteophyte formation (intraobserver κ_o = 0.26; interobserver κ_o = 0.20) did not achieve acceptable reliability.ConclusionOf the 3 subcategories of lumbar facet joint degeneration, only articular cartilage degeneration demonstrated acceptable reliability. Subscales of lumbar facet joint degeneration should be considered independently for reliability before combining subscales for a global degeneration score. Owing to the inherent difficulty of assessing lumbar facet joint degeneration, the use of multiple examiners independently assessing degeneration with reliable scales and then coming to a consensus score upon any disagreements is recommended for future clinical studies.     

Mechanical alterations in the avascular region of the meniscus following partial meniscectomy: A cadaveric porcine longitudinal meniscal tear model

BackgroundAlthough partial meniscectomy is a common treatment for the tears in the avascular region of the meniscus, mechanical alterations following meniscectomy are known to initiate mechanically-induced osteoarthritis. We aimed to measure the articular cartilage contact pressure distributions in the knees with surgically repaired and partially resected menisci in the avascular region.MethodsA pneumatic loading device was developed to apply a 1000 N compressive load on the cadaveric porcine knee samples at the flexion angles of 20, 35, 50, and 65°. We simulated longitudinal meniscal tears in the avascular inner 1/3 portion and the well-vascularized middle 1/3 portion of the meniscus. Articular cartilage contact pressures for the knees with intact, torn, repaired, and resected menisci were compared.FindingsFor the tears in well-vascularized regions, meniscal repairs restored articular cartilage contact pressures to the levels in intact joints. However, partial meniscectomy significantly increases the maximum contact pressures and the average contact pressures in highly compressed areas. However, partial meniscectomy in the avascular region did not alter the maximum articular cartilage contact pressures and the average contact pressures in highly compressed areas. Stabilities in knee samples were not significantly altered following partial meniscectomy in both inner and middle regions.InterpretationAlthough repair surgeries are beneficial for the tears in well-vascularized areas because the articular cartilage contact mechanics are reconstructed, partial meniscectomy may be a viable alternative treatment for the tears in avascular regions without introducing significant mechanical alterations.     

生物材料复合支架与运动性关节软骨缺损的修复

目的：探讨复合支架的组织工程学特性及其修复关节软骨缺损的性能评价。方法：以＂关节软骨、生物材料、工程软骨、复合材料、复合支架＂为中文关键词,以＂tissue enginneering,articularcartilage,scaffold material＂为英文关键词,采用计算机检索中国期刊全文数据库、PubMed数据库（1993-01/2010-11）相关文章。纳入复合支架材料-细胞复合物修复关节软骨损伤相关的文章,排除重复研究或Meta分析类文章。结果：共入选18篇文章进入结果分析。复合支架是当前软骨组织工程中应用较多的支架,它是将具有互补特征的生物相容性可降解支架,按一定比例和方式组合,设计出结构与性能优化的复合支架。较单一支架材料具有显著优越性,具有更好的生物相容性和一定强度的韧性,较好的孔隙和机械强度。复合支架的制备不仅包括同一类生物材料的复合,还包括不同类别生物材料之间的交叉复合。可分为纯天然支架材料、纯人工支架材料以及天然与人工支架材料的复合等3类。结论：复合支架使生物材料具有互补特性,一定程度上满足了理想生物支架材料应具有的综合特点,但目前很多研究仍处于实验阶段,还有一些问题有待于解决,如不同材料的复合比例、复合工艺等。     

The effects of dynamic compressive loading on human mesenchymal stem cell osteogenesis in the stiff layer of a bilayer hydrogel

Bilayer hydrogels with a soft cartilage‐like layer and a stiff bone‐like layer embedded with human mesenchymal stem cells (hMSCs) are promising for osteochondral tissue engineering. The goals of this work were to evaluate the effects of dynamic compressive loading (2.5% applied strain, 1 Hz) on osteogenesis in the stiff layer and spatially map local mechanical responses (strain, stress, hydrostatic pressure, and fluid velocity). A bilayer hydrogel was fabricated from soft (24 kPa) and stiff (124 kPa) poly (ethylene glycol) hydrogels. With hMSCs embedded in the stiff layer, osteogenesis was delayed under loading evident by lower OSX and OPN expressions, alkaline phosphatase activity, and collagen content. At Day 28, mineral deposits were present throughout the stiff layer without loading but localized centrally and near the interface under loading. Local strains mapped by particle tracking showed substantial equivalent strain (~1.5%) transferring to the stiff layer. When hMSCs were cultured in stiff single‐layer hydrogels subjected to similar strains, mineralization was inhibited. Finite element analysis revealed that hydrostatic pressures ≥~600 Pa correlated to regions lacking mineralization in both hydrogels. Fluid velocities were low (~1–10 nm/s) in the hydrogels with no apparent correlation to mineralization. Mineralization was recovered by inhibiting ERK1/2, indicating cell‐mediated inhibition. These findings suggest that high strains (~1.5%) combined with higher hydrostatic pressures negatively impact osteogenesis, but in a manner that depends on the magnitude of each mechanical response. This work highlights the importance of local mechanical responses in mediating osteogenesis of hMSCs in bilayer hydrogels being studied for osteochondral tissue engineering.     

The use of fractionated Kraft lignin to improve the mechanical and biological properties of PVA-based scaffolds

The mechanical properties of poly(vinyl alcohol) (PVA)-based scaffolds were successfully improved. The improvements in mechanical properties correlated with the amount of Kraft lignin in PVA matrices. The critical property for any scaffold is its capacity to allow cells to ingrow and survive within its internal structure. The ingrowth of cells was tested using bioreactors creating simulated in vivo conditions. In the context of all the mentioned parameters, the most advantageous properties were exhibited by the scaffold containing 99 wt% PVA and 1 wt% Kraft lignin. The composites with 1 wt% Kraft lignin exhibited sufficient mechanical stability, a lack of cytotoxicity, and mainly the ability to allow the ingrowth of cells into the scaffold in a rotation bioreactor.

The mechanical properties of poly(vinyl alcohol) (PVA)-based scaffolds were successfully improved.     

Ultrasound speed in articular cartilage under mechanical compression

Ultrasound elastography is a method that can be used to determine the elastic properties of soft tissues and it has been recently applied to study of articular cartilage. While ultrasound elastography techniques assume a constant ultrasound speed in tissue under mechanical compression, ultrasound speed in articular cartilage has been found to vary depending on the loading conditions. This may limit the quantitative use of the technique for determination of the elastic properties of articular cartilage along the axis of ultrasound propagation. The aim of the present study was to investigate the origin of the load-related variation in ultrasound speed. Samples of human and bovine articular cartilage (n = 82) were mechanically and acoustically tested during unconfined compression. A statistically significant (p < 0.05) variation of ultrasound speed was found in cartilage during a stress-relaxation test. A finite element model was constructed by exploiting microscopically determined collagen and proteoglycan contents, collagen orientation and biochemical analyses of water content. From the finite element simulations, collagen orientation and the void ratio (fluid-to-solid ratio) as a function of time were assessed and, together with the experimentally determined ultrasound speed, a linear model predicting variation of the ultrasound speed in human articular cartilage under mechanical compression was established. The model predicted compression-related ultrasound speed with an error of <0.3% at each time point. The effect of strain rate on variation of ultrasound speed was tested in bovine cartilage samples. The decrease in ultrasound speed was found to be proportional to the strain rate. The results suggest that ultrasound speed in articular cartilage is controlled mainly by collagen orientation and the void ratio and depends on the imposed strain rate. A numerical simulation revealed that the compression-related decrease in ultrasound speed induces notable errors in mechano-acoustically determined strain. A method to eliminate the compression-related errors in measured strain and elastic properties may be needed in mechano-acoustic measurements of articular cartilage.     

Development of 3D PVA scaffolds for cardiac tissue engineering and cell screening applications

The aim of this study was the design of a 3D scaffold composed of poly(vinyl) alcohol (PVA) for cardiac tissue engineering (CTE) applications. The PVA scaffold was fabricated using a combination of gas foaming and freeze-drying processes that did not need any cross-linking agents. We obtained a biocompatible porous matrix with excellent mechanical properties. We measured the stress–strain curves of the PVA scaffolds and we showed that the elastic behavior is similar to that of the extracellular matrix of muscles. The SEM observations revealed that the scaffolds possess micro pores having diameters ranging from 10 μm to 370 μm that fit to the dimensions of the cells. A further purpose of this study was to test scaffolds ability to support human induced pluripotent stem cells growth and differentiation into cardiomyocytes. As the proliferation tests show, the number of live stem cells on the scaffold after 12 days was increased with respect to the initial number of cells, revealing the cytocompatibility of the substrate. In addition, the differentiated cells on the PVA scaffolds expressed anti-troponin T, a marker specific of the cardiac sarcomere. We demonstrated the ability of the cardiomyocytes to pulse within the scaffolds. In conclusion, the developed scaffold show the potential to be used as a biomaterial for CTE applications.

The aim of this study was the design of a 3D scaffold composed of poly(vinyl) alcohol (PVA) for cardiac tissue engineering (CTE) applications.     

不同生物材料复合支架对关节软骨缺损的修复评价

背景：不同生物材料制备的复合软骨支架其修复软骨缺损也各具特点。目的：探讨不同生物材料制备复合支架的组织工程学特性及其修复关节软骨缺损的性能评价。方法：以＂软骨组织工程,生物材料,工程软骨,复合支架＂为中文关键词,以＂tissue enginneering,articular cartilage,scaffold material＂为英文关键词,采用计算机检索中国期刊全文数据库、PubMed数据库（1993-01/2010-11）相关文章。纳入复合支架材料-细胞复合物修复关节软骨损伤等相关的文章,排除重复研究或Meta分析类文章。结果与结论：复合支架是当前软骨组织工程中应用较多的支架,它是将具有互补特征的生物相容性可降解支架,按一定比例和方式组合,设计出结构与性能优化的复合支架。较单一支架材料具有更好的生物相容性和一定强度的韧性,较好的孔隙和机械强度。复合支架的制备不仅包括同一类生物材料的复合,还包括不同类别生物材料之间的交叉复合。可分为纯天然支架材料、纯人工支架材料以及天然与人工支架材料的复合等3类。复合支架使生物材料具有互补特性,一定程度上满足了理想生物材料支架应具的综合特点,但目前很多研究仍处于实验阶段,还有一些问题有待于解决,如不同材料的复合比例、复合工艺等。     

Biomimetic scaffolds and dynamic compression enhance the properties of chondrocyte‐ and MSC‐based tissue‐engineered cartilage

Adult chondrocytes are surrounded by a protein‐ and glycosaminoglycan‐rich extracellular matrix and are subjected to dynamic mechanical compression during daily activities. The extracellular matrix and mechanical stimuli play an important role in chondrocyte biosynthesis and homeostasis. In this study, we aimed to develop scaffold and compressive loading conditions that mimic the native cartilage micro‐environment and enable enhanced chondrogenesis for tissue engineering applications. Towards this aim, we fabricated porous scaffolds based on silk fibroin (SF) and SF with gelatin/chondroitin sulfate/hyaluronate (SF‐GCH), seeded the scaffolds with either human bone marrow mesenchymal stromal cells (BM‐MSCs) or chondrocytes, and evaluated their performance with and without dynamic compression. Human chondrocytes derived from osteoarthritic joints and BM‐MSCs were seeded in scaffolds, precultured for 1 week, and subjected to compression with 10% dynamic strain at 1 Hz, 1 hr/day for 2 weeks. When dynamic compression was applied, chondrocytes significantly increased expression of aggrecan (ACAN) and collagen X (COL10A1) up to fivefold higher than free‐swelling controls. In addition, dynamic compression dramatically improved the chondrogenesis and chondrocyte biosynthesis cultured in both SF and SF‐GCH scaffolds evidenced by glycosaminoglycan (GAG) content, GAG/DNA ratio, and immunostaining of collagen type II and aggrecan. However, both chondrocytes and BM‐MSCs cultured in SF‐GCH scaffolds under dynamic compression showed higher GAG content and compressive modulus than those in SF scaffolds. In conclusion, the micro‐environment provided by SF‐GCH scaffolds and dynamic compression enhances chondrocyte biosynthesis and matrix accumulation, indicating their potential for cartilage tissue engineering applications.