Structure Of Cartilage Tissue Research Articles

Building a Poly(amino acid)/Chitosan-Based Self-Healing Hydrogel via Host-Guest Interaction for Cartilage Regeneration.

Cartilage injury is a very common joint disease, and cartilage repair is a great challenge in clinical treatment due to the specific structure of cartilage tissue and its microenvironment in vivo. The injectable self-healing hydrogel is a very promising candidate as a cartilage repair material because of its special network structure, high water retention and self-healing properties. In this work, a self-healing hydrogel cross-linked by host-guest interaction between cyclodextrin and cholic acid was developed. The host material was composed of β-cyclodextrin and 2-hydroxyethyl methacrylate-modified poly(l-glutamic acid) (P(LGA-co-GM-co-GC)), while the guest material was chitosan modified by cholic acid, glycidyl methacrylate, and (2,3-epoxypropyl)trimethylammonium chloride (EPTAC) (QCSG-CA). The host-guest interaction self-healing hydrogels, named as HG hydrogels (HG gel), exhibited excellent injectability and self-healable property, and the self-healing efficiency was greater than 90%. Furthermore, in order to enhance the mechanical properties and slow down the degradation of the HG gel in vivo, the second network was constructed by photo-cross-linking in situ. Biocompatibility tests showed that the enhanced multi-interaction hydrogel (MI gel) was extremely suitable for cartilage tissue engineering both in vitro and in vivo. In addition, the adipose derived stem cells (ASCs) in MI gel were able to differentiate cartilage effectively in vitro in the presence of inducing agents. Subsequently, the MI gel without ASCs was transplanted into rat cartilage defects in vivo for the regeneration of cartilage. After 3 months postimplantation, new cartilage tissue was successfully regenerated in a rat cartilage defect. All results indicated that the injectable self-healing host-guest hydrogels have important potential applications in cartilage injury repair.

The optimal way to fill the deficiency of essential substances for the well-being of the joints

The article presents basic information about the role and structure of cartilage tissue and its components, the impact of an imbalance in the structure of nutrition on the well-being of the joints, evidence of the symptomatic and structural-modifying effect of chondroitin and glucosamine in the composition of original drugs and dietary supplements in the treatment of osteoarthritis. Particular attention is paid to the structure and synthesis of collagen, its biological role in the body in the formation of the cell structure of various tissues, especially cartilage. Found 28 types of collagen, differing in amino acid sequence and degree of modification, which are encoded by more than 40 genes. It was noted that the activity of enzymes involved in the synthesis of collagen depends on sufficient intake of products containing ascorbic acid (vitamin C), and the degradation and decrease in the amount of collagen is associated with the development and progression of osteoarthritis and other diseases of the musculoskeletal system. The use of type 2 collagen, including in combination with chondroitin and glucosamine, is considered as a promising method for preventing joint problems. It is emphasized that the main substances necessary for the syn thesis of cartilage components come from food. An imbalance in the structure of nutrition (reducing the consumption of proteins, microelements and vitamins, excessive consumption of fats and carbohydrates) negatively affects the state of the connective tissue and causes problems for all structures that form the joint. One way to correct eating behavior and replenish essential deficiencies is through the use of vitamin-mineral complexes and dietary supplements, which are gaining interest in the medical community as evidence accumulates for their effectiveness in supporting joint well-being.

Adjacent cartilage tissue structure after successful transplantation: a quantitative MRI study using T2 mapping and texture analysis

ObjectivesThe aim of this study was to assess the texture of repair tissue and tissue adjacent to the repair site after matrix-associated chondrocyte transplantation (MACT) of the knee using gray-level co-occurrence matrix (GLCM) texture analysis of T2 quantitative maps.MethodsTwenty patients derived from the MRI sub-study of multicenter, single-arm phase III study underwent examination on a 3 T MR scanner, including a T2 mapping sequence 12 and 24 months after MACT. Changes between the time points in mean T2 values and 20 GLCM features were assessed for repair tissue, adjacent tissue, and reference cartilage. Differences in T2 values and selected GLCM features between the three cartilage sites at two time points were analyzed using linear mixed-effect models.ResultsA significant decrease in T2 values after MACT, between time points, was observed only in repair cartilage (p < 0.001). Models showed significant differences in GLCM features between repair tissue and reference cartilage, namely, autocorrelation (p < 0.001), correlation (p = 0.015), homogeneity (p = 0.002), contrast (p < 0.001), and difference entropy (p = 0.047). The effect of time was significant in a majority of models with regard to GLCM features (except autocorrelation) (p ≤ 0.001). Values in repair and adjacent tissue became similar to reference tissue over time.ConclusionsGLCM is a useful add-on to T2 mapping in the evaluation of knee cartilage after MACT by increasing the sensitivity to changes in cartilage structure. The results suggest that cartilage tissue adjacent to the repair site heals along with the cartilage implant.Key Points• GLCM is a useful add-on to T2mapping in the evaluation of knee cartilage after MACT by increasing the sensitivity to changes in cartilage structure.• Repair and adjacent tissue became similar to reference tissue over time.• The results suggest that cartilage tissue adjacent to the repair site heals along with the cartilage implant.

Study on the Protective Effect and Mechanism of the Rhizoma Drynariae-Epimedium Formula on Osteoarthritis in Rats.

Purpose The aim of the study was to study the protective effect of the Rhizoma Drynariae-Epimedium formula on osteoarthritis in rats and to explore its mechanism. Methods Fifty SD rats were randomly divided into 5 groups, namely, the control group, model group, Rhizoma Drynariae group, Epimedium group, and Rhizoma Drynariae-Epimedium group, with 10 rats in each group. Knee arthritis models were established by injecting papain solution (10% papain + 0.03 mol/L L-cysteine mixture) into the knee joint cavity of SD rats on the 0th, 3rd, and 6th days of the experiment, respectively. The model group, Rhizoma Drynariae group, Epimedium group, and Rhizoma Drynariae-Epimedium group were given modeling treatment, while the control group was not given modeling treatment. The Rhizoma Drynariae group, Epimedium group, and the Rhizoma Drynariae-Epimedium group were, respectively, given corresponding solvent gavage treatment. Both the model group and the control group were given an equal volume of normal saline. Once a day, a total of 4 w were administered. The general conditions of the rats were observed and recorded, and the knee joint width and the knee joint swelling degree of the affected side were measured and compared. HE staining and Safranin O-fast green staining were used to compare the structural changes of cartilage. The concentrations of inflammatory factors IL-1β, IL-6, and TNF-α in the joint cavity lavage fluid were determined by using ELISA. The expression of key proteins of the MAPK signaling pathway (p38, p-p38, ERK, p-ERK, JNK, and p-JNK) in joint synovial tissue was determined by western blotting. Results After modeling, except for the normal activities of the SD rats in the control group, the rest of the groups showed lack of energy and a slight limp in the knee joints. The SD rats in the model group, Rhizoma Drynariae group, Epimedium group, and Rhizoma Drynariae-Epimedium group had local swelling of the knee joint, and the knee joint width was greater than those in the control group (p < 0.05). Compared with the model group, the knee joint swelling of SD rats in the Rhizoma Drynariae group, the Epimedium group, and the Rhizoma Drynariae-Epimedium group was significantly reduced. The knee joint swelling degree of SD rats in the Rhizoma Drynariae-Epimedium group was significantly lower than that in the Rhizoma Drynariae and Epimedium groups. HE staining and Safranin O-fast green staining showed that the cartilage structure of SD rats was severely damaged and eroded, and the subchondral bone mass was reduced. Compared with the model group, the damage of cartilage tissue in the Rhizoma Drynariae group, Epimedium group, and Rhizoma Drynariae-Epimedium group was less severe. In the Rhizoma Drynariae-Epimedium group, cartilage tissue structure damage and erosion were lighter than those of the Rhizoma Drynariae group and the Epimedium group. The concentrations of inflammatory factors IL-1β, IL-6, and TNF-α in the articular cavity lavage fluid of SD rats in the model group, Rhizoma Drynariae group, Epimedium group, and Rhizoma Drynariae-Epimedium group were higher than those in the control group. Compared with the model group, the concentrations of IL-1β, IL-6, and TNF-α in the joint cavity lavage fluid of the Rhizoma Drynariae group, Epimedium group, and Rhizoma Drynariae-Epimedium group were significantly decreased. In the Rhizoma Drynariae-Epimedium group, IL-1β, IL-6, and TNF-α concentrations were lower than those of the Rhizoma Drynariae and Epimedium groups. Compared with the control group, the expression levels of p-p38, p-ERK, and p-JNK proteins in the model group, Rhizoma Drynariae group, Epimedium group, and Rhizoma Drynariae-Epimedium group were significantly increased. The expression levels of p-ERK, p-p38 and p-JNK in the Drynariae group, Epimedium group, and Drynariae-Epimedium group were significantly lower than those in the model group. The expression levels of p-ERK, p-p38, and p-JNK in the Rhizoma Drynariae-Epimedium group were significantly lower than those in the Rhizoma Drynariae and Epimedium groups. Conclusion The Rhizoma Drynariae-Epimedium formula can play a protective role in the process of osteoarthritis by inhibiting the phosphorylation levels of p38, ERK, and JNK-related proteins in the cartilage tissue MAPK signaling pathway, reducing the inflammatory response.

Age-related histological changes in rat tibia.

At present, studies on osteochondral morphogenesis only focus on a certain period of time or only provide a pattern diagram, but lack of dynamic tracking observation from the initiation of development to maturity. This study was aimed to dynamically observe the changes of skeleton morphology and structure from embryo to adult, to provide research data for enriching the knowledge of bone and cartilage tissue structure. In the intrauterine experiment, 5 normal pregnant Wistar rats were sacrificed under anaesthesia at gestational day (GD) 14, 17, 20, respectively. One of their offspring was randomly selected, and a total of 5 offspring were obtained at each time point. In the postnatal experiment, on the 7th and 10th day after birth and at postnatal weeks (PW) 2, 3, 6, 12, 28, 5 offspring rats from 5 different pregnant Wistar rats were randomly selected and sacrificed under anaesthesia at each time point. After obtaining the above offspring, the soft tissue was removed, and the tibia of hind limbs was retained for paraffin-embedded section. After stained with Safranin-O-fast-green and haematoxylin, the morphological development of the tibia was observed under an optical microscope. At GD14, there was no obvious joint space, the whole hind limb was cartilage and bone tissue was not visible. At GD17, visible joint space was seen and the chondrocytes in the centre region appeared to hypertrophy. At GD20, the primary ossification centre was obvious, and a typical epiphysis growth plate structure could be seen. On the 7th day after birth, the chondrocytes in the centre of epiphysis cartilage were hypertrophic and differentiated, the cartilage canal grows from the cartilage surface toward the centre of the epiphysis cartilage, at postnatal day 14, the secondary ossification centre was formed. At this time, the tibia had typical morphological characteristics of the metaphysis, however, there was no obvious layered structure of articular cartilage; the stratified structure of articular cartilage could be seen at PW6, but its mature marker (tidemark) was still not visible; however, at PW12, typical 4 layers of articular cartilage appeared, and the tidemark was visible. The growth plates were clearly visible at PW2, 6 and 12. At PW28, growth plates could still be observed, but its morphology is abnormal. Our results, for the first time, dynamically observed the morphological changes of osteochondral at critical period of development from embryo to adult, especially the process of cartilage canal participating in the formation of secondary ossification centre.

Undenatured Type II Collagen (UC-II) in Joint Health and Disease: A Review on the Current Knowledge of Companion Animals.

Simple SummaryOsteoarthritis (OA), the most common joint disease affecting humans and animals, is a painful, degenerative, and inflammatory disease that affects synovial joints and ultimately leads to loss of mobility. Non-pharmacological preventive approaches, several pharmaceutical therapeutic agents, and some medicines may reduce the progression of OA in animals. Many clinical and experimental studies have revealed that the undenatured form of type II collagen (UC-II) offers common health benefits to patients with OA.OA is quite common in companion animals, especially in large breed dogs and horses. Collagen, the most abundant protein of mammals, has specific connective tissue types for skin, bones, reticulate, basal lamina, bones, cell surfaces, while type II collagen (UC-II) forms the main structure of cartilage tissue. Even at the smaller dosages, UC-II has also been reported to be more effective than the glucosamine and chondroitin sulfate supplements, which are the supplements most frequently used in the market. In this review, we summarize the effects of UC-II on joint health and function in health and disease conditions in companion animals.

ЭФФЕКТИВНОСТЬ ФОТОМАГНИТОТЕРАПИИ ПРИ ЭКСПЕРИМЕНТАЛЬНОМ АРТРИТЕ

Background. The choice of physiotherapeutic method in the treatment of joint diseases remains an urgent problem in physiotherapy. The aim: а comparative study of the efficiency of a low-frequency pulsed magnetic field (LPMF) and its combination with infrared light (photomagnetic therapy) in experimental arthritis. Material and methods. Studies were performed on 50 male rats. A zymosan model of arthritis was used. The animals were divided into 4 groups, the 1st group – intact animals, the 2nd – animals with arthritis without treatment, in the 3rd group they underwent course exposure to LPMF, in the 4th group LPMF in combination with infrared light. Clinical, laboratory, morphological and histochemical studies were performed. Results. It was revealed that photomagnetic therapy to a greater extent than a LPMF reduces the activity of the inflammatory process, and also leads to a partial normalization of the structure of cartilage tissue. Conclusions. The data obtained can be used to develop differentiated methods of physiotherapy in rheumatology.

Biopharmaceutical analysis of the interaction of L-thyroxin, diclofenac sodium and chondroitin sulphate as components of pharmacotherapy of osteoarthritis manifestations resulted from hypothyroidism.

The article deals with the issue of the biopharmaceutical interaction of L-thyroxin, diclofenac sodium and chondroitin sulfate as components of pharmacotherapy of osteoarthritis manifestations with concomitant hypothyroidism. It is known that functional insufficiency of the thyroid gland has a negative effect on all types of metabolism and in particular on the condition of the bone and cartilage tissue, leading to the development of osteoarthritis. Existing pharmacotherapeutic approaches to the medical treatment of this pathology require the use of basic hormone replacement therapy for the correction of thyroid insufficiency, and NSAIDs as drugs for the symptomatic treatment of osteoarthritis. However, to date, questions of the biopharmaceutical interaction of L-thyroxin and diclofenac sodium are not covered, and the prevention of osteoarthritis against the background of hypothyroidism with the help of chondroitin sulfate and its interaction with the components of pharmacotherapy has not been sufficiently studied. Based on the conducted research, it was established that, proceeding from the theoretical analysis of the physicochemical and chemical properties of these drugs, predominantly reversible acid-base interactions are assumed. The probability of strong and irreversible physicochemical reactions is very low and the physical mixtures of these drugs are not subject to negative interactions which can lead to profound destructive changes on the part of the dosage forms. Since L-thyroxin, diclofenac sodium and chondroitin sulfate are absorbed mainly by simple diffusion, have different transport mechanisms through biological membranes, have different degrees of binding to plasma proteins and various enzyme systems involved in their metabolism and excretion, pharmacokinetic interactions between them are excluded. At the level of pharmacological interaction, the combined and unidirectional effects of the combination of active substances L-thyroxin, diclofenac sodium and chondroitin sulfate are expected, in particular, in degenerative-dystrophic disorders due to functional insufficiency of the thyroid gland, for restoration of the structure of cartilage tissue and for a complex etiotropic and symptomatic treatment of osteoarthritis and related states.

Research of the effect of combined application of L-thyroxine (levotiroxine),doclofenac sodium and chondroitin sulphate on the histological structure of the cartilage tissue for hypothyroidism and osteoarthritis.

Background. The study of thyroid pathology revealed the connection of this pathology with degenerative-dystrophic diseases of the musculoskeletal system. It is known that thyroid hormones affect the metabolism of cartilage and bone tissues and conditions are created for the development of osteoarthritis in the hypofunction of the thyroid gland. For correction of pathological changes in the clinical setting, L-thyroxine is prescribed for basic replacement therapy for thyroid hypofunction, however, developed osteoarthritis requires the use of NSAIDs and chondroprotectors, the purpose of which is governed by clinical protocols for the treatment of osteoarthritis. Objective. To investigate the effect of the combined use of L-thyroxine, diclofenac sodium and chondroitin sulfate on the histological structure of cartilage tissue in hypothyroidism and osteoarthritis in experimental animals. Methods. The work used 30 white adult outbred rats of both sexes weighing 220-230 g. Experimental modeling of hypothyroidism consisted in using a 0.02% solution of carbimazole (5 mg per 250 ml of saline) in the rats' drinking diet for 6 weeks. Experimental osteoarthritis was reproduced by a single intra-articular injection of 0.1 ml of monoiodoacetic acid solution into knee joint of rats, which was prepared at the rate of 3 mg of reagent per 50 μl of sterile saline. The administration of drugs was carried out daily from the 42nd day of the experiment at the peak of an increase in pathological changes for 5 days. When the formation of experimental models was completed, animals were removed from the experiment by decapitation under thiopental anesthesia to study histo-morphological changes in the cartilage tissue of the knee joints. Results. Analysis of the histological structure of the cartilage of the knee joints of rats of experimental group number 3 showed that the cartilage and bone tissue of the knee joint of rats was almost the same in intact animals of group number 1 with the main parameters with the only difference that there was active regeneration of both cartilage and bone tissue with areas of neovascular genesis in group number 3. Conclusion. The studied effect of the combined use of L-thyroxine, diclofenac sodium and chondroitin sulfate on the histological structure of cartilage tissue in hypothyroidism and osteoarthritis in experimental animals established active regeneration of both cartilage and bone tissue with areas of neovascular genesis.

Comparison of rabbit bone marrow mesenchymal stem cells and chondrocytes co-cultured in vitro for the establishment of four kinds of cartilage without scaffold

Objective A large number of cells in four groups were cultured without scaffold in centrifuge tube, observing size and biological characteristics of aggregation co-culture system of cartilage tissue, and evaluate co-culture technology without support by centrifugal tube, which provides methodological guidance and experimental basis for the clinical repair of articular cartilage defect. Methods New Zealand white rabbits underwent puncture of bone marrow. Rabbit articular cartilage chondrocytes were separated, obtain relatively pure by type Ⅱ trypsin and collagenase, and then cultured. Isolation and culture of bone marrow mesenchymal stem cells by density gradient centrifugation to obtain the 3 passage of purified Bone marrow mesenchymal stem cells (BMSCs). Using alcian blue staining, safranin O-light green staining and type Ⅱ collagen immunohistochemical staining of Articular Chontrocytes (ACs) were identified. CD34, CD44, CD45 and CD105 molecular surface markers by immunofluorescence identification of BMSCs. BMSCs and ACs were mixed into co-culture (CO) groups according to the ratio of 1∶3 and 2∶2, the total number of cells was 4×107, 1 500 r/min centrifugation for 5 minutes, and the cell aggregation was co cultured in 15 ml centrifuge tube. The equivalent chondrocytes were taken as AC group, and the same amount of BMSCs was induced into the BMSCs induction group (transforming growth factor-beta 1, TGF-β1), and cultured in the centrifuge tube as comparative research. Four groups of high number of cells were cultured for 1 weeks, 2 weeks, 3 weeks and 4 weeks after paraffin tissue sections were dewaxed by alcian blue staining, saffron O -light green staining and immunohistochemical staining for type Ⅱ collagen. HE staining was used to observe the morphology and structure of cartilage tissue in each group under the condition of in vitro culture. Using alcian blue colorimetric method for quantitative detection of liquid supernatant of glycosaminoglycan content, enzyme-linked immunosorbent adsorption method was used to detect the liquid supernatant of type Ⅱ collagen content. Results ACs alcian blue, safranin O-light green and type Ⅱ collagen immunohistochemical staining were positive, the adherent subculture could obtain satisfactory purity of BMSCs and ACs. BMSCs immunofluorescence staining of CD44 (+ ), CD105 (+ ), CD45 (-), CD34 (-). AC group, 2∶2 and 1∶3 co-culture group, alcian blue staining, safranin O-light green staining and type Ⅱ collagen immunohistochemical staining were positive. The staining of BMSC induced group was weakly positive. HE showed that AC group and 1∶3 group were gradually fused into initial cartilage tissue. Gradually the integration of group cells induced by 2∶2 And BM, but no cartilage formed after four weeks. After 4 weeks, group AC [(179.43±59.19) μg/ml] and 2∶2 [(158.06±23.77) μg/ml], 1∶3 group [(160.06±30.58) μg/ml] GAG content had no significant difference (F=0.210, P=0.812). After 4 weeks, group AC [(185.13±35.96) ng/ml] and 2∶2 [(169.72±32.56) ng/ml], 1∶3 [(148.91±33.16) ng/ml] type Ⅱ collagen content had no significant difference (F=0.680, P=0.515); AC group [(179.43±59.19) μg/ml] and BM induced group [(70.74±40.17) μg/ml] GAG content was statistically significant (t=3.980, P=0.001); AC group [(185.13±35.96) ng/ml] and BM induced group [(116.83±40.17) ng/ml] type Ⅱ collagen content was statistically significant (t=3.434, P=0.003). Conclusion BMSCs and ACs were cultured in centrifuge tube by aggregation can induce differentiation of BMSCs to ACs, and get the biological characteristics of the AC. The AC group and 1∶3 co-culture group formed the rudiment of cartilage tissue after four weeks with HE staining, but BM induced group and 2∶2 group did not. Key words: Articular chondrocytes; Mesenchymal stem cells; Co-culture; No-scaffold; Tissue engineering cartilage

Characterization of Hydroxyapatite/ Silk Fibroin/ Chitosan Scaffold for Cartilage Tissue Engineering

Tissue engineering (TE) is a modern medical approach to reconstruct damage tissue in a shorter period. Scaffold is the main structure for cells adhesion and provides 3D space for cell proliferation and growth. Biomaterials were selected to fabricate a scaffold according to properties and target tissues. In this study, Hydroxyapatite (HA), Silk Fibroin (SF), and Chitosan (CS) were selected to fabricate the scaffold in different combination ratios by freeze drying (FD) technique. According to the physical properties of the fabricated scaffold, cartilage tissue was selected as a study target area for the future medical application. Scaffold characterization was performed to observe the scaffolds properties in each materials ratio. In this study, CS scaffold provided highest abilities which related to cartilage tissue structure. Moreover, the combination of SF in CS provided highest ability for cartilage cell proliferation in vitro. Therefore, CS could be used as a cartilage scaffold for cartilage TE and SF could be added to increased the cells viability of the scaffold.

Facet joint degeneration in adolescent idiopathic scoliosis.

Adolescent idiopathic scoliosis (AIS) is a poorly understood deformity of the thoracolumbar spine which affects the intervertebral discs (IVDs) and the articular facet joints. The knowledge concerning facet joints in this context is very limited, although facet joint degeneration is a known contributor of back pain. In this study, a comprehensive investigation was performed to characterize the facet joint chondrocytes and extracellular matrix within the scoliotic spine. Surgically removed articular facet joint tissues were collected from patients undergoing spinal corrective surgery for AIS deformities, while non‐scoliotic articular facet joint tissues were obtained from cadaveric organ donors. Alterations in cartilage tissue structure were evaluated histologically with safranin‐O fast green and a modified OARSI grading scale. Pro‐inflammatory cytokines, matrix‐degrading proteases, and fragmented matrix molecules associated with cartilage degradation were analyzed by immunohistochemistry and western blotting. Safranin‐O fast green staining revealed that young scoliotic facet joints show clear signs of degeneration with substantial proteoglycan loss, similar to osteoarthritis (OA). The proteoglycan levels were significantly lower than in healthy asymptomatic non‐scoliotic control individuals. In comparison to controls, scoliotic articular facets showed increased cell density, increased expression of the proliferation marker Ki‐67, and higher expression of MMP‐3, MMP‐13, and IL‐1β. Expression and fragmentation of the small leucine‐rich proteins (SLRPs) chondroadherin, decorin, biglycan, lumican, and fibromodulin were analyzed with western blot. Chondroadherin and decorin were fragmented in cartilage from patients with a curve greater than 70°, whereas biglycan and fibromodulin did not show curve‐related fragmentation. AIS facet joint cartilage shows hallmarks of OA including proteoglycan loss, overexpression of pro‐inflammatory mediators, increased synthesis of matrix‐degrading proteases and fragmentation of SLRPs. As with patients with age‐related OA, the premature joint degeneration seen in scoliotic patients is likely to contribute to the pain perceived in some individuals.

The Effect of Biomolecular Gradients on Mesenchymal Stem Cell Chondrogenesis under Shear Stress

Tissue engineering is viewed as a promising option for long-term repair of cartilage lesions, but current engineered cartilage constructs fail to match the mechanical properties of native tissue. The extracellular matrix of adult human articular cartilage contains highly organized collagen fibrils that enhance the mechanical properties of the tissue. Unlike articular cartilage, mesenchymal stem cell (MSC) based tissue engineered cartilage constructs lack this oriented microstructure and therefore display much lower mechanical strength. The goal of this study was to investigate the effect of biomolecular gradients and shear stress on MSCs undergoing chondrogenesis within a microfluidic device. Via poly(dimethyl siloxane) soft-lithography, microfluidic devices containing a gradient generator were created. Human MSCs were seeded within these chambers and exposed to flow-based transforming growth factor β1 (TGF-β1) gradients. When the MSCs were both confluent and exposed to shear stress, the cells aligned along the flow direction. Exposure to TGF-β1 gradients led to chondrogenesis of MSCs, indicated by positive type II collagen staining. These results, together with a previous study that showed that aligned MSCs produce aligned collagen, suggest that oriented cartilage tissue structures with superior mechanical properties can be obtained by aligning MSCs along the flow direction and exposing MSCs to chondrogenic gradients.

Chondrocyte deformation under extreme tissue strain in two regions of the rabbit knee joint

Articular cartilage and its native cells—chondrocytes—are exposed to a wide range of mechanical loading. Chondrocytes are responsible for maintaining the cartilage matrix, yet relatively little is known regarding their behavior under a complete range of mechanical loads or how cell mechanics are affected by region within the joint. The purpose of this study was to investigate chondrocyte deformations in situ under tissue loads ranging from physiological to extreme (0–80% nominal strain) in two regions of the rabbit knee joint (femoral condyles and patellae). Local matrix strains and cell compressive strains increased with increasing loads. At low loads the extracellular matrix (ECM) strains in the superficial zone were greater than the applied tissue strains, while at extreme loads, the local ECM strains were smaller than the applied strains. Cell compressive strains were always smaller than the applied tissue strains and, in our intact, in situ preparation, were substantially smaller than those previously found in hemi-cylindrical explants. This resulted in markedly different steady-state cell volume changes in the current study compared to those working with cartilage explants. Additionally, cells from different regions in the knee exhibited striking differences in deformation behavior under load. The current results suggest: (i) that the local extracellular and pericellular matrix environment is intimately linked to chondrocyte mechanobiology, protecting chondrocytes from potentially damaging strains at high tissue loads; and (ii) that cell mechanics are a function of applied load and local cartilage tissue structure.

Properties of Cartilage on Micro- and Nanolevel

Results of investigation of the elastic modulus for cartilage tissue using a technique of micro- and nanoindentation performed with help of an atomic force microscope are presented. SEM and AFM methods were applied to visualize a topography of surface layers of the entire cartilage and as well as its slices and thus to reveal features of the collagen fibers orientation. The technique used for a quantitative evaluation of the elastic modulus under compression against a ball microindenter (curvature radius - 350 micron) and a nanoindenter (30 nm) is described. It was shown that the cartilage behavior is highly stabile under the load if the entire composite structure of cartilage tissue is engaged into the deformation process. Tribological characteristics were investigated using the ball indenter oscillated by a tuning fork. Dependence of the friction coefficient from applied loads was obtained that revealed strong influence of an interstitial fluid on friction properties. Friction coefficient of a rat cartilage tissue as 0.08 was obtained using a developed plant prototype for tribological measurements based on the AFM construction.

Initiation of Mesenchymal Condensation in Alginate Hollow Spheres—A Useful Model for Understanding Cartilage Repair?

A promising strategy for the regeneration of degenerated cartilage tissue structure in osteoarthritic joints is the use of mesenchymal precursor cells. These cells can be triggered to undergo differentiation into functional active chondrocytes resulting in newly synthesized cartilage. Because chondrogenic differentiation is initiated by the step of mesenchymal condensation in vitro, it is of great interest to fully characterize the first lineage specific step in vitro. Therefore, a modified culture system was developed which mimics the process in vitro and may finally help to identify the key factors that are essential for the induction of chondrogenic differentiation in vivo. Compared to other established 3D culture systems like alginate beads and micromass cultures, the use of alginate hollow spheres bears the advantage to analyze different phases of cell aggregation starting from a single cell suspension of previously isolated and expanded human primary cells of mesenchymal origin.