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Background: Currently, fat graft viability and retention cannot be reliably predicted. The reasons for this variability are not fully understood, although fat processing has been implicated. Objectives: The authors compare the in vitro quantity and in vivo fat retention from lipoaspirate processed by the Revolve system (LifeCell, Bridgewater, New Jersey) compared with centrifugation and decantation. Methods: Ten patients were enrolled in this prospective study. Lipoaspirate from each patient was processed by each of 3 methods: decantation, centrifugation, and the Revolve system. Biochemical characteristics and free oil, adipose, and aqueous phases of the processed fats were determined. Fat grafts were implanted in nude mice; volume retention and quality of the fat grafts were evaluated after 28 days. Viability of retained fat was demonstrated by intact adipocytes and neovascularization on histology. Results: Of the 10 patients, 9 were women and 1 was a man. Mean patient age was 40.7 ± 8.9 years (range, 30-55 years). Fat tissue obtained from all methods had good physiological properties with neutral pH and isotonic salt concentrations. The Revolve system yielded significantly less blood cell debris, a higher percentage of adipose tissue, and a lower percentage of free oil compared with the other 2 methods. Fat tissue retention from Revolve samples was significantly higher (73.2%) than that from decanted samples (37.5%) and similar to that from centrifuged samples (67.7%). Conclusions: The Revolve system produced physiologically compatible, preinjection fat with reduced contaminants and free oil in conjunction with high fat content. In an animal model, volume retention of Revolve-processed fat grafts was significantly greater than decanted samples. The Revolve system presents a fat-processing option that was less time-consuming, easier to use, and more efficient in this study than standard centrifugation or decantation.

During post-natal development, tendons undergo a well orchestrated process whereby extensive structural and compositional changes occur in synchrony to produce a normal tissue. Conversely, during the repair response to injury, structural and compositional changes occur, but in this case, a mechanically inferior tendon is produced. As a result, the process of development has been postulated as a potential paradigm through which improved adult tissue healing may occur. In this study we measured the mechanical, compositional, and structural properties in the post-natal mouse Achilles tendon at 4, 7, 10, 14, 21, and 28 days old. Throughout post-natal development, the mechanical properties, collagen content, fibril diameter mean, and fibril diameter standard deviation increased. Biglycan expression decreased and decorin expression and fiber organization were unchanged. This study provides a new mouse model that can be used to quantitatively examine mechanical development, as well as compositional and structural changes and biological mechanisms, during post-natal tendon development. This model is advantageous due to the large number of genetically modified mice and commercially available assays that are not available in other animal models. A mouse model therefore allows future mechanistic studies to build on this work.

CD44 plays an important role in inflammation and healing. Previous studies have investigated its role in inflammatory diseases and skin wounds; however, the role of CD44 in tendon healing is unknown. Therefore, the aim of this study was to investigate the effect of CD44 in the healing of the patellar tendon in a knockout mouse model. It was hypothesized that in comparison to wild type counterparts, CD44 knockout mice would have decreased material parameters, increased organization, decreased expression of proinflammatory cytokines and increased expression of matrix components during healing. These hypotheses were tested through an in vivo surgical model and mechanical, organizational, and gene expression analyses. Material strength and tissue organization were significantly improved in the CD44 knockout mouse. This could be attributed to increased expression of cytokines and matrix components that are elevated in regenerative healing. This study shows that the absence of CD44 in a mouse patellar tendon injury creates an environment that is conducive to regenerative healing through altered gene expression, resulting in superior material properties and reduced cross-sectional area. Therefore, this study indicates that limiting the role of CD44 may improve healing parameters in adult tendon injury.

During neonatal development, tendons undergo a well orchestrated process whereby extensive structural and compositional changes occur in synchrony to produce a normal tissue. Conversely, during the repair response to injury, structural and compositional changes occur, but a mechanically inferior tendon is produced. As a result, developmental processes have been postulated as a potential paradigm for elucidation of mechanistic insight required to develop treatment modalities to improve adult tissue healing. The objective of this study was to compare and contrast normal development with injury during early and late developmental healing. Using backwards multiple linear regressions, quantitative and objective information was obtained into the structure–function relationships in tendon. Specifically, proteoglycans were shown to be significant predictors of modulus during early developmental healing but not during late developmental healing or normal development. Multiple independent parameters predicted percent relaxation during normal development, however, only biglycan and fibril diameter parameters predicted percent relaxation during early developmental healing. Lastly, multiple differential predictors were observed between early development and early developmental healing; however, no differential predictors were observed between late development and late developmental healing. This study presents a model through which objective analysis of how compositional and structural parameters that affect the development of mechanical parameters can be quantitatively measured. In addition, information from this study can be used to develop new treatment and therapies through which improved adult tendon healing can be obtained.

During neonatal development, tendons undergo a well orchestrated process whereby extensive structural and compositional changes occur in synchrony to produce a normal tissue. Conversely, during the repair response to injury, structural and compositional changes occur, but a mechanically inferior tendon is produced. As a result, developmental processes have been postulated as a potential paradigm through which improved adult tissue healing may occur. By examining injury at distinctly different stages of development, vital information can be obtained into the structure-function relationships in tendon. The mouse is an intriguing developmental model due to the availability of assays and genetically altered animals. However, it has not previously been used for mechanical analysis of healing tendon due to the small size and fragile nature of neonatal tendons. The objective of this study was to evaluate the differential healing response in tendon at two distinct stages of development through mechanical, compositional, and structural properties. To accomplish this, a new in vivo surgical model and mechanical analysis method for the neonatal mouse Achilles tendons were developed. We demonstrated that injury during early development has an accelerated healing response when compared to injury during late development. This accelerated healing model can be used in future mechanistic studies to elucidate the method for improved adult tendon healing.

Tendons are composed of fibroblasts and collagen fibrils. The fibrils are organized uniaxially and grouped together into fibers. Collagen VI is a non-fibrillar collagen expressed in developing and adult tendons. Human collagen VI mutations result in muscular dystrophy, joint hyperlaxity and contractures. The purpose of this study is to determine the functional roles of collagen VI in tendon matrix assembly. During tendon development, collagen VI was expressed throughout the extracellular matrix, but enriched around fibroblasts and their processes. To analyze the functional roles of collagen VI a mouse model with a targeted inactivation of Col6a1 gene was utilized. Ultrastructural analysis of C ol6a1−/− versus wild type tendons demonstrated disorganized extracellular micro-domains and associated collagen fibers in the C ol6a1−/− tendon. In C ol6a1−/− tendons, fibril structure and diameter distribution were abnormal compared to wild type controls. The diameter distributions were shifted significantly toward the smaller diameters in Col6a1−/− tendons compared to controls. An analysis of fibril density (number/μm 2 ) demonstrated a ~ 2.5 fold increase in the Col6a1−/− versus wild type tendons. In addition, the fibril arrangement and structure were aberrant in the peri-cellular regions of Col6a1−/− tendons with frequent very large fibrils and twisted fibrils observed restricted to this region. The biomechanical properties were analyzed in mature tendons. A significant decrease in cross-sectional area was observed. The percent relaxation, maximum load, maximum stress, stiffness and modulus were analyzed and Col6a1−/− tendons demonstrated a significant reduction in maximum load and stiffness compared to wild type tendons. An increase in matrix metalloproteinase activity was suggested in the absence of collagen VI. This suggests alterations in tenocyte expression due to disruption of cell–matrix interactions. The changes in expression may result in alterations in the peri-cellular environment. In addition, the absence of collagen VI may alter the sequestering of regulatory molecules such as leucine rich proteoglycans. These changes would result in dysfunctional regulation of tendon fibrillogenesis indirectly mediated by collagen VI.