Poly(vinyl alcohol) hydrogel as an artificial articular cartilage: evaluation of biocompatibility.

We have developed a new poly(vinyl alcohol) hydrogel (PVA-H) of increased physical strength through a new manufacturing process. Its mechanical properties have been found to be preferable as a substitute for articular cartilage. To evaluate its biocompatibility as an artificial articular cartilage, a series of in vivo tests within the intraarticular, as well as the intramuscular, environment were conducted. Tissue reactions of cartilage, bone, synovium, and muscle to PVA-H were studied histologically. In the experimental group, in which PVA-H was implanted, inflammatory reactions of all of these tissues were very slight. In the control group, in which ultra-high molecular weight polyethylene (UHMWPE) was implanted, although tissue reactions of bone and muscle were as slight as in the experimental group, those of cartilage and synovium were somewhat more conspicuous. By way of these findings, the better biocompatibility of PVA-H was documented.     

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。     

组织工程修复关节软骨缺损的力学状态研究

背景：力学状态对软骨的正常生理有重要影响,若应力集中过大将造成人工软骨退变和原宿主软骨退化,影响治疗效果。目前的各种力学手段很难实现活体软骨力学状态测量,而有限元动态分析能有效地模拟修补后软骨的受力情况。目的：通过有限元仿真研究组织工程修复膝关节软骨缺损后人工软骨和宿主软骨的力学状态。方法：以人体膝关节软骨受滚压部分为研究对象,建立滚动运动下关节软骨的有限元模型。根据行走过程中股骨与胫骨间的滚压边界条件,对软骨在取不同弹性模量、不同压缩量、不同载荷速度及不同缺损大小的情况进行了滚压受力分析。结果与结论：在滚压载荷下,植入人工软骨弹性模量和软骨压缩量的不同都使人工软骨和宿主软骨受到的Mises应力值变化,二者对修复缺损处软骨Mises应力分布的影响比较明显,是临床治疗软骨缺损和术后康复阶段值得注意的因素。模拟中使用的载荷速度和缺损大小对软骨应力值的影响不明显。当人工软骨弹性模量取某个值时,人工软骨和宿主软骨的Mises应力差别可以达到很小值,二者趋于吻合。应力差别还和个体宿主软骨的力学性能有关,据此,应针对不同病例选择最佳弹性模量的人工软骨植入。     

The tribology of cartilage: Mechanisms,experimental techniques,and relevance to translational tissue engineering

Diarthrodial joints, found at the ends of long bones, function to dissipate load and allow for effortless articulation. Essential to these functions are cartilages, soft hydrated tissues such as hyaline articular cartilage and the knee meniscus, as well as lubricating synovial fluid. Maintaining adequate lubrication protects cartilages from wear, but a decrease in this function leads to tissue degeneration and pathologies such as osteoarthritis. To study cartilage physiology, articular cartilage researchers have employed tribology, the study of lubrication and wear between two opposing surfaces, to characterize both native and engineered tissues. The biochemical components of synovial fluid allow it to function as an effective lubricant that exhibits shear-thinning behavior. Although tribological properties are recognized to be essential to native tissue function and a critical characteristic for translational tissue engineering, tribology is vastly understudied when compared to other mechanical properties such as compressive moduli. Further, tribometer configurations and testing modalities vary greatly across laboratories. This review aims to define commonly examined tribological characteristics and discuss the structure-function relationships of biochemical constituents known to contribute to tribological properties in native tissue, address the variations in experimental set-ups by suggesting a move toward standard testing practices, and describe how tissue-engineered cartilages may be augmented to improve their tribological properties.     

A constitutive study of the age-dependent mechanical behaviour of deep articular cartilage: Model construction and simulated failure

The tensile properties of deep articular cartilage of the human femoral head have been simulated using a model based on the expected mechanical behaviour of an electrostatically cross-linked network of collagen fibrils. Articular cartilage requires a model incorporating two types of interactions, referred to as type I and type II, which differ in the amount of energy required to bring about their mechanical failure. This modified two-population (MTP) model is shown to accurately simulate the experimental tensile behaviour of 14 specimens of deep articular cartilage. Also, the MTP model simulates a failure behaviour which appears to be comparable to the actual experimental fracture of the articular cartilage specimens. A reduction in the fracture stress of the deep articular cartilage specimens with age can be interpreted through age-related changes which occur in the values of the parameters of the MTP model. This shows that the younger tissues derive their superior tensile properties through an optimum structural arrangement which is associated with a high proportion of binding equivalent to the type I interaction in the tissue model. A decline in the tensile properties with age occurs as the tissue structure falls from its optimal configuration as the proportion of type II interactions increases. Such changes may predispose the articular cartilage to the mechanical damage and deterioration which leads to the osteoarthritic degeneration of a joint.

Relevance

An understanding of the process of osteoarthritic degeneration requires a knowledge of the relationship between the biochemical composition and mechanical behaviour of articular cartilage. An approach is developed to examine this relationship in order to gain insight into the ultrastructural basis of the mechanical weakening of articular cartilage with age.     

Effective lubrication of articular cartilage by an amphiphilic hyaluronic acid derivative

Background

Intra-articular injection of hyaluronic acid based therapies is gaining popularity as a treatment option for non-operative management of patients with symptomatic osteoarthritis. Although there is an abundance of evidence for both biological and mechanical mechanisms of joint protection by hyaluronic acid, one clear intention of viscosupplementation is to reduce friction and wear by providing an extrinsic lubricant. We tested the in vitro friction response of a novel hyaluronic acid derivative that presents amphiphilic features to promote adhesion to the cartilage surface and thereby improve cartilage lubrication.

Methods

Migrating Contact Area and Static Contact Area friction tests were conducted on bovine articular cartilage to assess the efficacy of two lubricants, a chemically modified amphiphilic hyaluronic acid and synovial fluid from a healthy joint, as well as a phosphate buffered saline negative control.

Findings

No differences in lubrication (P = 0.34) were evident between the three test articles during the Migrating Contact Area test, which represents articulation of healthy articular cartilage.The modified hyaluronic acid presented an equilibrium friction coefficient 2.8 times less than that of the synovial fluid (P ≤ 0.0005) and five times less than that of the PBS control (P ≤ 0.0001) during the Static Contact Area test, representing a mixed lubrication condition.

Interpretation

The present study demonstrated that a chemically modified amphiphilic hyaluronic acid can provide equivalent lubrication to synovial fluid during articulation of loaded healthy articular cartilage and can provide superior lubrication as indicated by a lower coefficient of friction than synovial fluid under loading conditions potentially associated with cartilage wear.     

兔关节软骨损伤生物标志物的蛋白质组学检测

背景:采用蛋白质组学的方法可以检测出关节、血液、尿液等体液中一些能反映关节软骨损伤程度的特异性标志物的水平。目的:进一步验证采用生物芯片技术发现兔关节软骨损伤生物标志物。方法:采用改良的Hulth方法建立兔关节软骨损伤模型,建模后自由活动,不固定伤肢。30min/d分2次驱赶,连续12周。以不做任何处理兔膝关节为正常对照。并在造模后0,4,8,12周时采取部分标本(血清、关节液),验证观察关节软骨的损伤程度;各个时间点的动物关节液、血清样本放入采用PBSⅡ-C型蛋白质芯片阅读机,采用CM10芯片检测。结果与结论:改良的Hulth造模方法建立膝关节软骨损伤模型,比较全面地反映了关节软骨损伤从早、中、晚、失代偿各期的变化。与正常对照组相比,血清学样品:模型组3475蛋白表达下调,7558,15475,33665蛋白表达上调;关节液样品:模型组7558,33278蛋白表达下调,3950,16055蛋白表达上调;质核比3475,7558,16884为血清学和关节液样本共有差异蛋白质谱波峰显著蛋白。结果提示样本中出现的部分差异蛋白质可能为关节软骨损伤的生物标志物。     

Mechanical characteristics of articular cartilage bonds

BACKGROUND: Sutures for adaptation of articular cartilage are used in arthritis therapy techniques. However, little is known about the mechanical functionality of these sutures. The objective of the present work was to compare the mechanical properties of articular cartilage bonds either generated by suture, or, alternatively, by chemical cross-linking of the opposing surfaces or in vitro integrative repair of cartilage blocks. METHODS: Bonding was achieved by suture in varying numbers, positions and orientations, by surface cross-linking using carbodiimide in combination with pepsin or guanidine (immediate bonding), or by cultivation for 14 days, either with or without testosterone. The mechanical properties of the cartilage bonds were measured under tensile loading. FINDINGS: Suture led to the highest maximal load at failure and by far to the highest strain and lowest stiffness of the bonded samples. Immediate bonding by chemical cross-linking in combination with pepsin led to a low force at failure, but the highest stiffness, as compared to all other groups. Cultivation in the presence of testosterone led to a higher force at failure and a higher strain than chemical cross-linking. INTERPRETATION: Suture technique for bonding of cartilage surfaces leads to a very elastic adaptation which allows synovial fluid flow in between the interface of cartilage wounds. Long-term bonding of cartilage wounds would be counteracted by a fluid flow through the interface during motion of the joint. Immediate bonding of cartilage wounds by chemical cross-linking reagents might be a useful alternative tool. Even more promising, with regard to the mechanical properties, appears to be integrative repair of cartilage blocks stimulated by testosterone.     

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。     

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。     

Characterization of a macroporous polyvinyl alcohol scaffold for the repair of focal articular cartilage defects

Focal cartilage defects reduce the ability of articular cartilage to resist mechanical loading and provide lubrication during joint motion. The limitations in current surgical treatments have motivated the use of biocompatible scaffolds as a future treatment option. Here we describe a second generation macroporous, polyvinyl alcohol (PVA) scaffold with independently tunable morphological and mechanical properties. The compressive moduli of the PVA scaffold increased with increasing polymer concentration and applied compressive strain, with values in the range for human articular cartilage (H_A > 1000 kPa, E_Y > 500 kPa). Scaffolds also possessed strain‐dependent permeability and Poisson's ratio. The interconnected macroporous network was found to facilitate chondrocyte seeding and proliferation through the scaffold over one week in culture. Overall, these promising characteristics demonstrate the potential of this macroporous scaffold for future studies in focal cartilage defect repair. Copyright © 2012 John Wiley & Sons, Ltd.     

Is classical consolidation theory applicable to articular cartilage deformation?

In this paper, classical consolidation theory has been used to investigate the time-dependent response of articular cartilage to static loading. An experimental technique was developed to measure simultaneously the matrix internal pressure and creep strain under conditions of one-dimensional consolidation. This is the first measurement of the internal stress state of loaded cartilage. It is demonstrated that under static compression the applied load is shared by the components of the matrix (i.e. water, the proteoglycans, and the collagen fibrillar meshwork), during which time a maximum hydrostatic excess pore pressure is developed as initial water exudation occurs. This pressure decays as water is further exuded from the matrix and effective consolidation begins with a progressive transfer of the applied stress from water to the collagen fibrils and proteoglycan gel. Consolidation is completed when the hydrostatic excess pore pressure is reduced to zero and the solid components sustain in full the applied load.     

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。     

Arthroscopic evaluation of cartilage degeneration using indentation testing--influence of indenter geometry

BACKGROUND: It has been suggested that the early onset of cartilage degeneration might be detected with a handheld indentation probe during knee arthroscopy, prior to any visible change on the articular surface. Collagen degradation has been considered as the first sign of cartilage degeneration. Therefore, it is important to consider the collagen network as a distinct constituent in the study of arthroscopic evaluation of cartilage degeneration. METHODS: The tip of an arthroscopic probe (indenter) was modeled as rigid and in contact with a cartilage/bone disk of sufficiently large radius to simulate an indentation in a joint. A fibril-reinforced model of cartilage, including streaming potentials and distinct constitutive laws for the proteoglycan matrix and collagen network, was used to determine the contact mechanics of indenter and cartilage. The finite element package ABAQUS was employed to obtain numerical solutions. FINDINGS: A spherical indenter produces a relatively uniform deformation in cartilage, but can easily slide on the articular surface. In contrast, a cylindrical indenter produces great deformation gradients for quick compression rates, but does not slide as easily on the articular surface as the spherical indenter. Small porous and large solid indenters should be used to evaluate the properties of the proteoglycan matrix and collagen network, respectively, in order to minimize or maximize the fluid pressure in the corresponding case. When the collagen network is substantially degraded, the gradients of fluid pressure and deformation are greatly reduced regardless of indenter geometry. INTERPRETATION: The indenter geometry including its porosity is important to the material safety of articular cartilage in indentation and precise evaluation of cartilage degeneration.     

新型生物复合材料聚乙烯醇／纳米羟基磷灰石＋聚己二酰己二胺修复关节软骨及软骨下骨缺损的生物力学研究

目的：探讨新型生物复合材料聚乙烯醇／纳米羟基磷灰石＋聚己二酰己二胺（Polyvinyl alcohol hydrogel／nano-hydroxyapatite＋polyamide66，PVA／n-HA＋PA66）修复兔关节软骨及软骨下骨缺损的生物力学性能。方法：实验于2006-01/2007-05在四川大学华西医院骨科组织工程实验室完成。①通过原位合成技术及冷冻．融合循环方法制备PVA／n-HA＋PA66，并检测材料体外力学性能。②在兔股骨关节面上打孔，包括关节表面软骨和软骨下骨，制成关节软骨缺损的模型。将PVA／n-HA＋PA66复合材料植入兔膝关节，对侧肢体打孔作空白对照组或单纯PVA植入，分别于植入12，24周后行局部组织学切片观察，扫描电镜观察，生物材料体内力学性能测试。结果：36只兔全部进入结果分析。①上层材料在100mm／min拉力状态下，抗拉强度为3．42MPa，下层材料的抗拉强度为6．33MPa。上层材料在3mm／min的压力强度下，抗压强度为3．12MPa。下层材料的抗压强度为5．3MPa。②生物复合材料植入动物体内12，24周，下层材料中有骨组织长入，上层材料与下层材料紧密连接；生物复合材料在5mm／min的冲击强度下，其抗冲击强度在植入12周时已达正常松质骨抗冲击强度。结论：新型生物复合材料PVA／n-HA＋PA66修复兔关节软骨及软骨下骨缺损具有良好的生物力学性能。     

Reversibility of immobilization-induced articular cartilage degeneration after remobilization in rat knee joints

Joint immobilization is commonly used for the treatment of joint injuries, but it causes articular cartilage degeneration. The purpose of this study was to clarify the reversibility of immobilization-induced articular cartilage degeneration using rat knee joints. Immobilization of rat knee joints induces atrophic changes in the non-contact area, loss of chondrocytes in the contact area, and hypertrophy of chondrocytes in the transitional area of the articular cartilage. The unilateral knee joints of adult male rats were rigidly immobilized at 150° of flexion with a plate and screws for 1, 2, and 4 weeks. After the experimental periods, the fixation devices were removed and the rats moved freely for 16 weeks. Sham-operated rats were used as a control. Sagittal sections at medial midcondylar regions of the knee were assessed with histological and histomorphometric methods. Mechanical properties were assessed by measuring the sound speed with scanning acoustic microscope. Reduction of cartilage proteoglycan in the non-contact area was almost reversible, but hypertrophy of chondrocytes in the transitional area and loss of chondrocytes in the contact area were irreversible even at 1-week immobilization-remobilization group. Sound speed of the articular cartilage in the contact area was not restored. These results indicate that atrophic changes through decreased mechanical stress in the non-contact area were reversible, but loss of chondrocytes and hypertrophy of chondrocytes in the contact and transitional areas through increased mechanical stress by rigid immobilization were irreversible after remobilization. Clinicians should be aware that even a short-term rigid immobilization could cause irreversible articular cartilage damage.     

Influence of an interpositional spacer on the behaviour of the tibiofemoral joint: a finite element study

BACKGROUND: Interpositional arthroplasty is considered by many surgeons for the treatment of isolated medial compartment osteoarthritis of the knee. In this procedure, an interpositional spacer is inserted into the medial compartment of the joint with no bone resection and no mechanical fixation. Major problems such as implant dislocation, severe pain or need for revision have been reported post-operatively. METHODS: In this study, the kinematics of a knee implanted with an interpositional spacer made of either polyurethane or cobalt-chrome during walking, stair ascent and squatting cycles have been predicted and compared to the normal knee using finite element analysis. In addition, articular cartilage stress histories have been examined to obtain distributions of cumulative stress, a measure of the likelihood of articular cartilage degeneration. FINDINGS: The insertion of a polyurethane interpositional spacer in the medial side of the knee did not affect knee kinematics as compared to the normal knee, but caused an increase of articular cartilage cumulative contact stress exposures in the medial compartment of the joint. The knee implanted with the Co-Cr spacer exhibited similar trends in knee kinematics, however significantly different ranges of motion were observed during some periods of the activity cycles, specifically during the first half of the walking cycle where lower ranges of motion were predicted. In addition, higher articular cartilage cumulative contact stress exposures were observed in both compartments of the knee. In both cases, cumulative contact stress exposures of the tibial articular cartilage were more affected than those of the femoral articular cartilage. INTERPRETATION: These results suggest implant material as an important parameter in the design phase of interpositional spacers.     

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.     

Hydrostatic and boundary lubrication of joints--nature of boundary lubricant

A very low coefficient of friction in joints makes it difficult to define clearly the mechanism of cartilage lubrication. The present paper describes the two currently predominant and mutually complementary views aiming to elucidate this mechanism. The first mechanism, referred to as hydrostatic lubrication, involves interstitial fluid pressurization from the cartilage and its importance for the formation of a layer separating the weight-bearing surfaces. The second mechanism, called boundary lubrication, assumes the existence of a substance that binds to the cartilage surface, permanently separating the friction elements. It has not been clearly determined which substances occurring in the synovial fluid function as boundary lubricants. The authors briefly describe the physicochemical properties of lubricin, surface-active phospholipids and hyaluronic acid, including their role in boundary lubrication.     

间充质干细胞向软骨细胞表型分化的研究进展

软骨细胞是关节软骨中唯一的细胞,负责维持细胞外基质的稳态与平衡,软骨细胞数量的丢失和功能的失衡在骨关节炎的发病中起关键作用。但是由于关节软骨几乎没有再生能力,目前临床上用来治疗关节软骨缺损的方法和药物难以获得满意的疗效。软骨组织工程致力于通过人工手段在体内外生成透明软骨,为关节软骨缺损的修复提供了一条新的方法。间充质干细胞作为软骨组织工程的种子细胞可在特定诱导条件下分化为软骨细胞。因此,阐明该过程中软骨形成的相关转录因子和具体机制对于未来软骨再生医学的成功至关重要。