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。     

Indentation stiffness does not discriminate between normal and degraded articular cartilage

BACKGROUND: Relative indentation characteristics are commonly used for distinguishing between normal healthy and degraded cartilage. The application of this parameter in surgical decision making and an appreciation of articular cartilage biomechanics has prompted us to hypothesise that it is difficult to define a reference stiffness to characterise normal articular cartilage. METHODS: This hypothesis is tested for validity by carrying out biomechanical indentation of articular cartilage samples that are characterised as visually normal and degraded relative to proteoglycan depletion and collagen disruption. Compressive loading was applied at known strain rates to visually normal, artificially degraded and naturally osteoarthritic articular cartilage and observing the trends of their stress-strain and stiffness characteristics. FINDINGS: While our results demonstrated a 25% depreciation in the stiffness of individual samples after proteoglycan depletion, they also showed that when compared to the stiffness of normal samples only 17% lie outside the range of the stress-strain behaviour of normal samples. INTERPRETATION: We conclude that the extent of the variability in the properties of normal samples, and the degree of overlap (81%) of the biomechanical properties of normal and degraded matrices demonstrate that indentation data cannot form an accurate basis for distinguishing normal from abnormal articular cartilage samples with consequences for the application of this mechanical process in the clinical environment.     

A review on the mechanical quality of articular cartilage - implications for the diagnosis of osteoarthritis

The functional behaviour of articular cartilage in diarthrodial joints is determined by its morphological and biomechanical properties. Whereas morphological changes are mainly detectable in the progressed stages of osteoarthritis, biomechanical properties seem to be more sensitive to early degenerative variations since they are determined by the biochemical composition and structural arrangement of the extracellular matrix. The objective of this paper is to review studies focussing on variations in the mechanical compressive properties during the early pre-osteoarthritic stage. The aim is to quantify the requirements to detect the early cartilage degeneration in pre-osteoarthritis based on the mechanical parameters and to create an updated basis for a better understanding of inherent relationships between characteristic parameters in articular cartilage.

Correlations between mechanical and biochemical parameters as well as magnetic resonance, ultrasonic, histological and structural parameters were observed. In early osteoarthritis, static moduli decrease below 80% of healthy controls and dynamic moduli below 30% of controls. To identify osteoarthritic changes of articular cartilage based on static or dynamic mechanical parameters in an early stage of the disease progression the accuracy of a mechanical testing method has to be adequate to detect changes of 10% in cartilage stiffness.     

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。     

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.     

An Ultrasound Biomicroscopic and Water Jet Ultrasound Indentation Method for Detecting the Degenerative Changes of Articular Cartilage in a Rabbit Model of Progressive Osteoarthritis

It is important to assess the early degeneration of articular cartilage associated with osteoarthritis (OA) for early intervention and treatment planning. Previously, we have developed a high frequency ultrasound and water jet indentation method for the morphologic, acoustic and mechanical assessment of articular cartilage, using the enzymatic digestion as a model of osteoarthritic degeneration. No naturally degenerated articular cartilage has been tested with the developed method. In this study, we aimed to determine the usefulness of the developed method for detecting the natural degeneration of articular cartilage in a standard surgical model of OA in rabbits. Forty adult New Zealand white female rabbits were used in this study, which included 30 experimental rabbits undergoing the right anterior cruciate ligament transection surgery and 10 control rabbits. At the 3^rd, 6^th, and 9^th week post-surgery, 10 experimental rabbits were sacrificed, respectively, for assessment of the knee cartilage quality. The cartilage at the medial and lateral femoral condyles and tibial plateaus (four points) was measured by the high frequency ultrasound biomicroscopy, the water jet ultrasound indentation and a contact mechanical indentation test before a histopathologic analysis for grading of degeneration severity. Measured parameters were compared among different groups classified either by post-surgery time or by histopathologic grade. The results showed a general trend of increase for ultrasound roughness index and a general trend of decrease for integrated reflection coefficient, stiffness coefficient from water-jet indentation and Young's modulus (E) from the mechanical indentation with the increase of post-surgery time. Comparisons among groups with different histopathologic grades showed similar trend with the increase of degeneration severity. The water jet ultrasound indentation method was demonstrated to be an effective method to measure the mechanical properties of the articular cartilage and with further development of arthroscopic ultrasound probe; it has the ability to assess the early degeneration of articular cartilage with measurement of morphologic, acoustic and mechanical properties of the cartilage in vivo.     

Translating the application of transforming growth factor‐β1, chondroitinase‐ABC,and lysyl oxidase‐like 2 for mechanically robust tissue‐engineered human neocartilage

Strategies to overcome the limited availability of human articular chondrocytes and their tendency to dedifferentiate during expansion are required to advance their clinical use and to engineer functional cartilage on par with native articular cartilage. This work sought to determine whether a biochemical factor (transforming growth factor‐β1 [T]), a biophysical agent (chondroitinase‐ABC [C]), and a collagen crosslinking enzyme (lysyl oxidase‐like 2 [L]) are efficacious in forming three‐dimensional human neocartilage from expanded human articular chondrocytes. Among the treatment regimens, the combination of the three stimuli (TCL treatment) led to the most robust glycosaminoglycan content, total collagen content, and type II collagen production. In particular, TCL treatment synergistically increased tensile stiffness and strength of human neocartilage by 3.5‐fold and 3‐fold, respectively, over controls. Applied to two additional donors, the beneficial effects of TCL treatment appear to be donor independent; tensile stiffness and strength were increased by up to 8.5‐fold and 3‐fold, respectively, over controls. The maturation of human neocartilage in response to TCL treatment was examined following 5 and 8 weeks of culture, demonstrating maintenance or further enhancement of functional properties. The present study identifies a novel strategy for engineering human articular cartilage using serially passaged chondrocytes.     

The influence of lipid-extraction method on the stiffness of articular cartilage

BACKGROUND: One of the known characteristics of osteoarthritis is the loss of articular cartilage lipids. Therefore, it is important to study how lipids influence the functions of the tissue. This can only be done successfully by indirect analysis involving the extraction of lipids and subsequent assessment of the delipidized matrix. Therefore, for accuracy, the procedure for lipid extraction must not induce any other modification in the samples to be assessed. Hence, we compare three rinsing agents and methods in this study. METHODS: Normal and delipidized articular cartilage samples were tested under compressive loading at 4 loading velocities to obtain and compare their stiffness values. FINDINGS: Chloroform rinsing resulted in a 45% decrease in the stiffness of cartilage at low strain-rates (10(-2)/s and 10(-1)/s) on average with a corresponding increase of 55% at higher strain-rate of 10/s relative to the normal. Ethanol rinsed cartilage exhibited a corresponding decrease of 40% at the low strain-rates while exhibiting an increase of about 20% at the highest loading rates. Propylene glycol rinsing resulted in a decrease of approximately 20% in stiffness, while an increase of up to 5% at high rates of loading. INTERPRETATION: The loss of lipids modifies the stiffness of articular cartilage at all loading rates. The relatively larger deviation of the stiffness of chloroform-rinsed samples relative to the normal is probably a consequence of the drying process involved in rinsing protocol. It is probable that the results of milder rinsing agents, used without vacuum drying, are more reflective of physiological delipidization effects on the tissue. Consequently, we recommend propylene glycol and its associated protocol for extracting lipids from articular cartilage.     

The pathophysiology of cartilage diseases

Treatment of traumatic or degenerative defects of articular cartilage is a well-known problem for surgeons. Temporary or permanent disablement and high cost are due to diseases of the cartilage and bone. The articular cartilage is considered a tissue without the capacity to repair so that the "mechanical wear" of joint tissues is often designated as a normal tribute to increasing age.
Different diseases like osteoarthrosis, metabolic or neuropathic arthropathia, traumatic damage of cartilage have to be distinguished. All of them have an individual cause and on individual progress. However, it is necessary to understand the physiology and pathophysiology of cartilage diseases to create new forms of treatment. This article covers principles of cartilage breakdown.
The mechanical wear is often used to describe the aetiology of osteoarthrosis. Morphological changes of the synovial fluid can be observed in the end-stage of the disease. A hypertrophic phase in the beginning of osteoarthrosis does not lead to an accumulation of extracellular matrix because catabolic processes occur. The surface of articular cartilage becomes more vulnerable and a disruption of the superficial zone becomes possible. The destruction of cartilage is followed by changes of the subchondral bone and a disruption of the articular surface.
The depth of the cartilage defect is an important factor as well as the location in the joint to undernsand the pathophysiology of articular cartilage damage. An isolated fibrillation of the superficial zone may be without any consequences whereas deeper defects without a penetration of the subchondral bone are a well-known problem. A spontaneous regeneration does not occur since immigration of mesenchymal stem cells from the blood vessels is not possible.
Osteochondrosis dissecans is not a disease of the articular cartilage in the first place but a necrosis of the subchondral bone. Secondary articular cartilage can be involved and form free bodies of cartilage or cartilage and bone. The subchondral sclerosis hinders a spontaneous regeneration from the subchondral bone-marrow.
The knowledge of the poor spontaneous regeneration of articular cartilage has lead to the development of new therapeutic approaches and techniques. A critical discussion about the results of new procedures might be easier with a good knowledge of the pathophysiology of cartilage diseases.     

Extrusion of pyrophosphate into extracellular media by osteoarthritic cartilage incubates.

The distribution of calcium pyrophosphate mineral phase, almost exclusively confined to articular cartilage in chondrocalcinosis, and the high level of pyrophosphate (PPi) ion relative to serum in synovial fluid in patients with either chondrocalcinosis or advanced osteoarthritis led to an investigation of whether cartilage cells elaborate PPi ions. Incubates of articular cartilage from young rabbits but not from mature rabbits, as well as growth plates cartilage, released PPi into incubation media during a 4h period. Control rabbit ear cartilage and synovial membrane elaborated negligible amounts of PPi. The PPi was shown to be undialyzable but could be dissociated from the alkaline phosphatase by ultracentrifugation. In 16 patients with osteoarthritis, a substantial output of PPi by samples of articular cartilage from the knee was demonstrated. It is postulated that either rapid cell division and matrix synthesis found in the base of ulcerating osteoarthritic cartilage or remodeling calcified sites are the source of the PPi in such osteoarthritic cartilage. It is further hypothesized that this PPi output accounts at least in part for the elevated PPi levels found in synovial fluid of patients with osteoarthritis.     

Contrasting alterations of apposed and unapposed articular cartilage during joint contracture formation

OBJECTIVE: To quantify histologic articular cartilage alterations after immobilization, distinguishing between apposed and unapposed sites in an animal model of joint contracture. DESIGN: Experimental controlled trial. SETTING: Laboratory, in vivo study. ANIMALS: Adult male Sprague-Dawley rats (N=128). INTERVENTIONS: One hundred seventeen animals had 1 knee internally immobilized or sham-operated for 2, 4, 8, 16, or 32 weeks. One knee in 11 nonoperated animals served as controls.Main outcome measures On standardized sections, we identified femur and tibia cartilage sites that were apposed or that were unapposed. We quantified 4 characteristics: number of chondrocytes in the superficial and deep cartilage; matrix staining intensity to toluidine blue; surface irregularity of articular cartilage; and thickness of cartilage. RESULTS: Immobilized knees harbored fewer chondrocytes in the superficial cartilage at apposed sites and in the deep cartilage at unapposed sites. Matrix staining decreased only at unapposed sites. Cartilage surface became significantly more irregular at both sites but cartilage thickness remained unchanged. Noncartilaginous tissues appeared only at unapposed sites in the superficial and deep cartilage. CONCLUSIONS: Immobilization led to contrasting patterns of cartilage degeneration at apposed sites compared with unapposed sites. These results suggest distinct pathogenetic pathways for cartilage alterations, possibly through absence of mechanical forces (negative mechanotransduction) at unapposed sites and cyclic pressure at apposed sites. Considering the limited potential for cartilage self-repair, these results support the need for early diagnosis and aggressive mobilization of joints that are developing contractures.     

Overexpression of human insulin-like growth factor-I promotes new tissue formation in an ex vivo model of articular chondrocyte transplantation

Articular cartilage, the tissue that forms the gliding surface of joints, has a poor regenerative capacity. Insulin-like growth factor-I (IGF-I) is a polypeptide that is anabolic and mitogenic for cartilage. Transfection of articular chondrocytes with an expression plasmid vector containing the cDNA for human IGF-I under the control of the cytomegalovirus promoter/enhancer led to expression of the transgene and synthesis of biologically relevant amounts of IGF-I protein. Transplantation of transfected articular chondrocytes on to the surface of articular cartilage explants led to the formation of a new tissue layer on the cartilage explant surface. The new tissue was characterized by the presence of type II collagen and proteoglycan and by the absence of type I collagen, consistent with hyaline-like cartilage. The tissue formed by the chondrocytes expressing IGF-I was thicker and contained more cells than controls transfected with an expression plasmid vector containing the Escherichia coli (E. coli) beta-galactosidase (lacZ) gene. Transplantation of articular chondrocytes that overexpress human IGF-I also increased DNA synthesis and the synthesis of glycosaminoglycans by the underlying explant cartilage chondrocytes. These results identify a mechanism by which IGF-I may simultaneously promote chondrogenesis and shift cartilage homeostasis in an anabolic direction. The data further suggest that therapeutic growth factor gene transfer may be applicable to articular cartilage.     

构建关节软骨的滚压加载装置

背景:通常使用的加载装置或反应器有灌流式生物反应器、液压系统、直接动态压缩装置、剪切系统、拉伸装置或其中部分的组合.以上每一种载荷单独作用都没有实现软骨功能化培养,但即使是这几种的组合也不足以表征软骨的力学状态,构建的软骨功能与天然软骨仍有较大差距.目的:首次提出和研制了一种用于关节软骨构建的滚压加载装置,并在滚压加载条件下分析软骨的受力状态.方法:该装置包括滚动控制系统和压缩调节机构.滚动控制系统通过步进电机、丝杠控制辊子滚动速度,由齿轮和齿条啮合形成辊子纯滚动,辊子能够以均匀速度滚过培养物.压缩调节机构通过楔形滑块的相对滑动可以保证工作面平行升降,从而可以对培养物产生均匀、可调的压缩量.结果与结论:该装置对培养物提供了滚压的力学条件,使培养物处于动态压缩变形和剪切变形的复合加载过程.在滚压的力学条件下,有限元分析表明培养物受到复杂力学状态.培养物浅表层受到交替出现的压力、拉应力;中层在滚动方向平面内应力与表面有一定夹角,角度由45°～+45°呈周期变化;深层处应力都为压应力,与3个坐标轴方向接近.该装置的加载运动方式与关节的运动方式一致,滚压加载可能有利于功能化关节软骨结构、功能的构建.     

Effects of growth factors on articular cartilage

Articular cartilage has limited intrinsic repair potential. The relative failure of many synthetic solutions has led to the growing interest in the development of cell-based repair systems for solving a number of clinical problems to articular cartilage. Many factors will dictate the success of these approaches, namely surgical technique and the repair method used, the patient's genetic make up and compliance with postoperative regimen.
Many growth factors have been shown to have effects on chondrocytes and articular cartilage. Normal articular cartilage expresses insulin-like growth factor-I (IGF-I), basic fibroblast growth factor (bFGF) and transforming growth factor-b (TGFb) and these seem to be the most important local regulators of chondrocyte function. A complete understanding of the pathogenesis of osteoarthritis requires an understading of these growth factors. The role of cytokines and growth factors and the complex interactions that exist between them needs to be understood and at the moment our knowledge is incomplete. The advances of gene therapy however are promising and with further research patients may be offered not only a solution to their problem but also ways of preventing the disease in the first place.     

Characterization of costal cartilage and its suitability as a cell source for articular cartilage tissue engineering

Costal cartilage is a promising donor source of chondrocytes to alleviate cell scarcity in articular cartilage tissue engineering. Limited knowledge exists, however, on costal cartilage characteristics. This study describes the characterization of costal cartilage and articular cartilage properties and compares neocartilage engineered with costal chondrocytes to native articular cartilage, all within a sheep model. Specifically, we (a) quantitatively characterized the properties of costal cartilage in comparison to patellofemoral articular cartilage, and (b) evaluated the quality of neocartilage derived from costal chondrocytes for potential use in articular cartilage regeneration. Ovine costal and articular cartilages from various topographical locations were characterized mechanically, biochemically, and histologically. Costal cartilage was stiffer in compression but softer and weaker in tension than articular cartilage. These differences were attributed to high amounts of glycosaminoglycans and mineralization and a low amount of collagen in costal cartilage. Compared to articular cartilage, costal cartilage was more densely populated with chondrocytes, rendering it an excellent chondrocyte source. In terms of tissue engineering, using the self‐assembling process, costal chondrocytes formed articular cartilage‐like neocartilage. Quantitatively compared via a functionality index, neocartilage achieved 55% of the medial condyle cartilage mechanical and biochemical properties. This characterization study highlighted the differences between costal and articular cartilages in native forms and demonstrated that costal cartilage is a valuable source of chondrocytes suitable for articular cartilage regeneration strategies.     

Cell-based chondral restoration

As our patients become more physically active at all ages, the incidence of injuries to articular cartilage is increasing and is causing patients significant pain and disability at a younger age. The intrinsic healing response of articular cartilage is poor, because of its limited vascular supply and capacity for chondrocyte division. Nonsurgical management for the focal cartilage lesion is successful in the majority of patients. Those patients that fail conservative management may be candidates for a cartilage reparative or reconstructive procedure. The type of treatment available depends on a multitude of lesion-specific and patient-specific variables. First-line therapies for isolated cartilage lesions have demonstrated good clinical results in the correct patient but typically repair cartilage with fibrocartilage, which has inferior stiffness, inferior resilience, and poorer wear characteristics. Advances in cell-based cartilage restoration have provided the surgeon a means to address focal cartilage lesions utilizing mesenchymal stem cells, chondrocytes, and biomimetic scaffolds to restore hyaline cartilage.     

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.     

应力环境组织培养法保存的人骨软骨移植物中胶原和基质金属蛋白酶组织抑制剂3

背景：应力可以对体内外软骨组织或软骨细胞产生多种影响。目的：观察应力环境对普通组织培养基体外保存的骨软骨移植物保存质量的影响。方法：将正常人的骨软骨移植物分成3组：对照组即新鲜移植物,普通组移植物采用普通组织培养法保存,应力组用摇床作为动态加载装置对普通组织培养法保存的骨软骨移植物进行持续周期性应力加载。结果与结论：储存移植物2周时,Western blot法和透射电镜观察显示,与静态环境下保存相比,动态加载环境使关节软骨细胞外基质中基质金属蛋白酶组织抑制剂3的表达明显提高（P〈0.01）,能更好地保护基质中胶原成分的超微结构。结果证实,应力环境有利于保存人同种异体移植物软骨细胞和胶原的超微结构,动态非接触加载可提供一种更好的库存人同种异体骨软骨移植物的方法。     

Characterization of engineered tissue construct mechanical function by magnetic resonance imaging

Non‐invasive magnetic resonance imaging (MRI) is a technology that enables the characterization of multiple physical phenomena in living and engineered tissues. The mechanical function of engineered tissues is a primary endpoint for the successful regeneration of many biological tissues, such as articular cartilage, spine and heart. Here we demonstrate the application of MRI to characterize the mechanical function of engineered tissue. Phase contrast‐based methods were demonstrated to characterize detailed deformation fields throughout the interior of native and engineered tissue, using an articular cartilage defect model as a study system. MRI techniques revealed that strain fields varied non‐uniformly, depending on spatial position. Strains were highest in the tissue constructs compared to surrounding native cartilage. Tissue surface geometry corresponded to strain fields observed within the tissue interior near the surface. Strain fields were further evaluated with respect to the spatial variation in the concentration of glycosaminoglycans ([GAG]), critical proteoglycans in the extracellular matrix of cartilage, as determined by gadolinium‐enhanced imaging. [GAG] also varied non‐uniformly, depending on spatial position and was lowest in the tissue constructs compared to the surrounding cartilage. The use of multiple MRI techniques to assess tissue mechanical function provides complementary data and suggests that deformation is related to tissue geometry, underlying extracellular matrix constituents and the lack of tissue integration in the model system studied. Specialized and advanced MRI phase contrast‐based methods are valuable for the detailed characterization and evaluation of mechanical function of tissue‐engineered constructs. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantitative arthroscopic ultrasound evaluation of living human cartilage

OBJECTIVE: To investigate whether living human articular cartilage can be evaluated quantitatively by means of a new diagnostic technique that introduces an ultrasonic probe into the knee joint under arthroscopy and then analyzes the A-mode echogram by means of wavelet transformation. DESIGN: Intact and injured sites of living human articular cartilage were evaluated under arthroscopy. The maximum magnitude and the echo duration (defined as the length of time that included 95% of echo signal) were selected as the quantitative indices on the wavelet map. BACKGROUND: Quantitative evaluation of articular cartilage in situ has the potential to contribute to our understanding of cartilage breakdown and to the effectiveness of cartilage regeneration. However, a reliable method of quantitative cartilage evaluation has yet to be developed for clinical use. METHODS: Living human articular cartilage was analyzed using an ultrasonic probe under arthroscopy and the cartilage characteristics on the echo duration-maximum magnitude graph were examined. RESULTS: Unlike the L-shape distribution of human cadaver cartilage data, the distribution of the living human articular cartilage data showed a smooth curve with a steep initial gradient that flattens gradually at the highest value of echo duration on the echo duration-maximum magnitude graph. CONCLUSIONS: The present study suggests a new quantitative evaluation system for articular cartilage with clinical potential.