Articular cartilage, also called shock absorber, is a complex living soft tissue that covers gliding surfaces of joint and enables the joint to withstand weight bearing from human. Since there is no direct blood supply in the articular cartilage, it is generally hard to be repaired itself when it is injured. Although there have been several approaches to the repair of injured articular cartilage, current medical treatment is not able to give patients satisfactory treatment. Ultrasound has been used as one of physical therapy tools. Recently, there have been frequent reports that ultrasound has beneficial effect on the repair of bone fracture and soft tissue healing including articular cartilage. Although there have been appreciation of beneficial effect of ultrasound therapeutically, its mechanism is not fully understood and under investigation. From literature review, several researches tried to find optimal conditions of ultrasound such as intensity, frequency and duration on the repair of articular cartilage and it was reported that more effective ultrasound dose was found. However, different reports have different optimized ultrasound dose. It might be due to the variations of the type of ultrasound wave, intensity, frequency and duration as well as the different condition of experimental samples. Therefore, low intensity pulsed ultrasound (LIPUS) was investigated on the repair of articular cartilage and chondrocyte migration from this study. Also, optimal conditions of LIPUS dose on chondrocyte migration were investigated for the repair of articular cartilage.

Osteoarthritis (OA) is a disease that has significant individual, social, and economic impact worldwide. Although many etiologies lead to the eventual development of OA, one potentially treatable cause is the acute articular cartilage (AC) injury. These injuries are common and have a poor inherent healing capacity, leading to the formation of OA. In an effort to repair AC injuries several treatment strategies have been developed but none have proven completely successful. Studies examining AC tissue-engineering strategies have suggested that those with the most potential for success involve the introduction of autogenous or allogenous cells to the site of injury. These strategies are designed to encourage creation of a matrix with the appropriate characteristics of normal AC. However, development of a completely successful repair method has proven difficult because the biomechanical properties of normal AC are not easy to replicate, a cell source with the appropriate functional characteristics has not been optimized, and the problem of effective incorporation of a repair construct into the host tissue remains unresolved. In an effort to more fully understand the cartilage repair process, this work first focused on the development and utilization of an in vitro human explant model of AC to study the ability of seeded human chondrocytes to integrate into an AC defect. Further work elucidated the gene expression patterns of cultured adult human chondrocytes and human mesenchymal stem cell (MSC)-derived chondrocytes. Results from this work determined that cultured human chondrocytes were able to adhere to articular cartilage defects in a viable in vitro explant model and produce a matrix containing collagen type II. However, further work with the in vitro expanded chondrocytes revealed that these cells have increased expression of collagen type I which promotes the formation of a less durable fibrocartilagenous tissue. This unfavorable expression persisted despite placing the chondrocytes in an environment favoring a chondrocytic phenotype. Further work with MSC-derived chondrocytes demonstrated a similar and unfavorable production of collagen type I. This work represented an important first step towards a treatment for acute AC lesions but it is clear that further work to optimize the culture microenvironment is still required. / Experimental Surgery

Thesis (M.S.)--Mississippi State University. Department of Agricultural and Biological Engineering. / Title from title screen. Includes bibliographical references.

Habilitation-Thesis--Cologne. / Includes bibliographical references (p. 45-48) and index.

No description available.

Tissue engineering approaches have attempted to address some of the problems associated with articular cartilage defect repair, but grafts with sufficient functional properties have yet to reach clinical practice. Mechanical loads are properly controlled in the body to maintain the functional properties of articular cartilage. This inspires the inclusion of mechanical stimulation in any in vitro production of tissue engineered constructs for defect repair. This mechanical stimulation must improve the functional properties (both biochemical and structural) of engineered articular cartilage tissue. Only a few studies have applied more than two loading types to mimic the complex in vivo load/flow conditions. The general hypothesis of the present thesis proposes that the generation of functional articular cartilage substitute tissue in vitro benefits from load and fluid flow conditions similar to those occurring in vivo. It is specifically hypothesized that application of compression, shear and perfusion on chondrocyte-seeded constructs will improve their properties. It is also hypothesized that protein production of the cell-seeded constructs can be improved in a depth-dependent manner with some loading combinations. Thus, a hydromechanical stimulator system was developed that was capable of simultaneously applying compression, shear and perfusion. Functionality of system was tested by series of short-term pilot studies to optimize some of the system parameters. In these studies, agarose-chondrocytes constructs were stimulated for 2 weeks. Then, longer-term (21- 31 days) studies were performed to examine the effects of both mechanical (compression and dynamic shear) and hydromechanical (compression, dynamic shear and fluid flow) stimulation on glycosaminoglycan and collagen production. The effects of these loading conditions were also investigated for three layers of construct to find out if protein could be localized differently depth-wise. In one of the longer-term studies, the chosen mechanical and hydromechanical stimulation conditions increased total collagen production, with higher amount of collagen for hydromechanical compared with mechanical loading condition. However, their effectiveness in increasing total glycosaminoglycan production was inconclusive with the current loading regimes. The hydromechanically stimulated construct could localize higher collagen production to the top layer compared with middle and bottom layers. Some effectiveness of hydromechanical stimulation was demonstrated in this thesis. Future studies will be directed towards further optimization of parameters such as stimulation frequency and duration as well as fluid perfusion rate to produce constructs with more glycosaminoglycan and collagen.

In order to validate the appropriate functional characteristics of cartilage, we need to systematically study and understand what constitutes normality and degradation in cartilage. This thesis provides an important step in this direction. To understand the mechanical repercussions of disruption to the matrix properties, cartilage is often artificially degraded using common enzymes. Although the process of artificial degradation does not provide an accurate representation of osteoarthritis, it can provide insight into the biomechanical properties of single matrix components by examining the behaviour of the tissue following its removal. Through histological analysis utilising the optical absorbance measurements of Safranin O stain, this work has demonstrated that for a given time and enzyme concentration, the action of Trypsin on proteoglycans is highly variable and is dependent on: * The initial distribution and concentration of proteoglycans at different depths * The intrinsic sample depth * The location in the joint space, and * The medium type. These findings provide initial data towards a mathematical model which researchers can use to optimise Trypsin treatment of articular cartilage, and therefore model degeneration in vitro with a better degree of certainty. The variability noted in the distribution and concentration of proteoglycans, and most likely the collagen network, creates a large variation in the compressive and tensile stiffness of all samples, and total failure strain energy. The average values for each of these tests indicate that a loss of proteoglycan through Trypsin treatment results in decreased compressive stiffness, increased tensile stiffness, and little change to the failure strains or total failure strain energy. Conversely, disruption to the collagen network shows increased compressive and tensile stiffness, as well as failure strain and total failure strain energy. Due to the large variation in the results for each treatment group, the average values for the treated samples fall within the range of results for normal cartilage. These values cannot therefore be used as dependable parameters to benchmark cartilage, since the parameters for artificially degraded cartilage are within the normal levels. The Yeoh and Polynomial hyperelastic laws were found to best represent the material characteristics of cartilage across the range of tested samples, regardless of differences in health and strength. The results presented here provide important insight into the biomechanical outcomes of artificial degradation and provide direction for future research in this area.

Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 1998? / Errata tipped inside back end paper. Bibliography: leaves 150-190.

Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Levenston, Marc; Committee Member: Garcia, Andres; Committee Member: Koros, William; Committee Member: Sambanis, Athanassios; Committee Member: Temenoff, Johnna; Committee Member: Vidakovic, Brani.

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Boyan, Barbara; Committee Chair: Wick, Timothy; Committee Member: Brockbank, Kelvin; Committee Member: Nenes, Athanasios; Committee Member: Sambanis, Athanassios. Part of the SMARTech Electronic Thesis and Dissertation Collection.