The effects of irradiation dose and storage time following treatment on the viscoelastic properties of decellularised porcine super flexor tendon

Decellularised porcine super flexor tendon (pSFT) offers a promising solution to the replacement of damaged anterior cruciate ligament. It is desirable to package and terminally sterilise the acellular grafts to eliminate any possible harmful pathogens. However, irradiation techniques can damage the collagen structure and consequently reduce the mechanical properties. The aims of this study were to investigate the effects of irradiation sterilisation of varying dosages on the viscoelastic properties of the decellularised pSFT.Decellularised pSFT tendons were subjected to irradiation sterilisation using either 30 kGy gamma, 55 kGy gamma, 34 kGy E-beam, 15 kGy gamma, 15 kGy E-beam and (15 + 15) kGy E-beam (fractionated dose). Specimens then underwent stress relaxation testing at 0 and 12 months post sterilisation to determine whether any effect on the viscoelastic properties was progressive.Significant differences were found which demonstrated that all irradiation treatments had an effect on the time-independent and time-dependent viscoelastic properties of irradiated tendons compared to peracetic acid only treated controls. No significant differences were found between the irradiated groups and no significant differences were found between groups at 0 and 12 months. These results indicate the decellularised pSFT graft has a stable shelf-life.     

Understanding cellular and molecular mechanisms of pathogenesis of diabetic tendinopathy

There is accumulating evidence of an increased incidence of tendon disorders in people with diabetes mellitus. Diabetic tendinopathy is an important cause of chronic pain, restricted activity, and even tendon rupture in individuals. Tenocytes and tendon stem/progenitor cells (TSPCs) are the dominant cellular components associated with tendon homeostasis, maintenance, remodeling, and repair. Some previous studies have shown alterations in tenocytes and TSPCs in high glucose or diabetic conditions that might cause structural and functional variations in diabetic tendons and even accelerate the development and progression of diabetic tendinopathy. In this review, the biomechanical properties and histopathological changes in diabetic tendons are described. Then, the cellular and molecular alterations in both tenocytes and TSPCs are summarized, and the underlying mechanisms involved are also analyzed. A better understanding of the underlying cellular and molecular pathogenesis of diabetic tendinopathy would provide new insight for the exploration and development of effective therapeutics.     

Role of tissue engineered collagen based tridimensional implant on the healing response of the experimentally induced large Achilles tendon defect model in rabbits: a long term study with high clinical relevance

Background

Tendon injury is one of the orthopedic conditions poses with a significant clinical challenge to both the surgeons and patients. The major limitations to manage these injuries are poor healing response and development of peritendinous adhesions in the injured area. This study investigated the effectiveness of a novel collagen implant on tendon healing in rabbits.

Results

Seventy five mature White New-Zealand rabbits were divided into treated (n = 55) and control (n = 20) groups. The left Achilles tendon was completely transected and 2 cm excised. The defects of the treated animals were filled with collagen implants and repaired with sutures, but in control rabbits the defects were sutured similarly but the gap was left untreated. Changes in the injured and normal contralateral tendons were assessed weekly by measuring the diameter, temperature and bioelectrical characteristics of the injured area. Clinical examination was done and scored. Among the treated animals, small pilot groups were euthanized at 5, 10, 15, 20, 30, 40 and 60 (n = 5 at each time interval) and the remainder (n = 20) and the control animals at 120 days post injury (DPI). The lesions of all animals were examined at macroscopic and microscopic levels and the dry matter content, water delivery and water uptake characteristics of the lesions and normal contralateral tendons of both groups were analyzed at 120 DPI.No sign of rejection was seen in the treated lesions. The collagen implant was invaded by the inflammatory cells at the inflammatory phase, followed by fibroplasia phase in which remnant of the collagen implant were still present while no inflammatory reaction could be seen in the lesions. However, the collagen implant was completely absorbed in the remodeling phase and the newly regenerated tendinous tissue filled the gap. Compared to the controls, the treated lesions showed improved tissue alignment and less peritendinous adhesion, muscle atrophy and fibrosis. They also showed significantly better clinical scoring, indices for water uptake and water absorption, and bioelectrical characteristics than the controls.

Conclusion

This novel collagen implant was biodegradable, biocompatible and possibly could be considered as a substitute for auto and allografts in clinical practice in near future.     

Posttranslational Modifications in Type I Collagen from Different Tissues Extracted from Wild Type and Prolyl 3-Hydroxylase 1 Null Mice

Type I collagen extracted from tendon, skin, and bone of wild type and prolyl 3-hydroxylase 1 (P3H1) null mice shows distinct patterns of 3-hydroxylation and glycosylation of hydroxylysine residues. The A1 site (Pro-986) in the α1-chain of type I collagen is almost completely 3-hydroxylated in every tissue of the wild type mice. In contrast, no 3-hydroxylation of this proline residue was found in P3H1 null mice. Partial 3-hydroxylation of the A3 site (Pro-707) was present in tendon and bone, but absent in skin in both α-chains of the wild type animals. Type I collagen extracted from bone of P3H1 null mice shows a large reduction in 3-hydroxylation of the A3 site in both α-chains, whereas type I collagen extracted from tendon of P3H1 null mice shows little difference as compared with wild type. These results demonstrate that the A1 site in type I collagen is exclusively 3-hydroxylated by P3H1, and presumably, this enzyme is required for the 3-hydroxylation of the A3 site of both α-chains in bone but not in tendon. The increase in glycosylation of hydroxylysine in P3H1 null mice in bone was found to be due to an increased occupancy of normally glycosylated sites. Despite the severe disorganization of collagen fibrils in adult tissues, the D-period of the fibrils is unchanged. Tendon fibrils of newborn P3H1 null mice are well organized with only a slight increase in diameter. The absence of 3-hydroxyproline and/or the increased glycosylation of hydroxylysine in type I collagen disturbs the lateral growth of the fibrils.     

Proteomic differences between native and tissue‐engineered tendon and ligament

Tendons and ligaments (T/Ls) play key roles in the musculoskeletal system, but they are susceptible to traumatic or age‐related rupture, leading to severe morbidity as well as increased susceptibility to degenerative joint diseases such as osteoarthritis. Tissue engineering represents an attractive therapeutic approach to treating T/L injury but it is hampered by our poor understanding of the defining characteristics of the two tissues. The present study aimed to determine differences in the proteomic profile between native T/Ls and tissue engineered (TE) T/L constructs. The canine long digital extensor tendon and anterior cruciate ligament were analyzed along with 3D TE fibrin‐based constructs created from their cells. Native tendon and ligament differed in their content of key structural proteins, with the ligament being more abundant in fibrocartilaginous proteins. 3D T/L TE constructs contained less extracellular matrix (ECM) proteins and had a greater proportion of cellular‐associated proteins than native tissue, corresponding to their low collagen and high DNA content. Constructs were able to recapitulate native T/L tissue characteristics particularly with regard to ECM proteins. However, 3D T/L TE constructs had similar ECM and cellular protein compositions indicating that cell source may not be an important factor for T/L tissue engineering.     

A cellular lineage analysis of the chick limb bud

The chick limb bud has been used as a model system for studying pattern formation and tissue development for more than 50 years. However, the lineal relationships among the different cell types and the migrational boundaries of individual cells within the limb mesenchyme have not been explored. We have used a retroviral lineage analysis system to track the fate of single limb bud mesenchymal cells at different times in early limb development. We find that progenitor cells labeled at stage 19-22 can give rise to multiple cell types including clones containing cells of all five of the major lateral plate mesoderm-derived tissues (cartilage, perichondrium, tendon, muscle connective tissue, and dermis). There is a bias, however, such that clones are more likely to contain the cell types of spatially adjacent tissues such as cartilage/perichondrium and tendon/muscle connective tissue. It has been recently proposed that distinct proximodistal segments are established early in limb development; however our analysis suggests that there is not a strict barrier to cellular migration along the proximodistal axis in the early stage 19-22 limb buds. Finally, our data indicate the presence of a dorsal/ventral boundary established by stage 16 that is inhibitory to cellular mixing. This boundary is demarcated by the expression of the LIM-homeodomain factor lmx1b.     

Tapping-mode atomic force microscopy in fluid of hydrated extracellular matrix

Fragments of native, hydrated rat tail tendon were imaged by tapping-mode atomic force microscopy while immersed in fluid. The specimens were soft and sensitive to the operating parameters, and with minimal imaging pressure the collagen fibrils appeared covered by irregular blobs or by filamentous material. A slight increase in pressure caused the underlying fibril surface to appear, with an evident D-period, gap- and overlap-zones and three intraperiod ridges. Fibrils often ran parallel and in phase, implying some coupling mechanism. Longitudinal subfibrils, 8-9 nm thick, occasionally appeared. The simultaneous acquisition of the "tapping amplitude" along with the usual "height" channel clearly confirmed the presence of longitudinal subfibrils, indicative of the inner architecture of the fibril.     

防止肌腱粘连及促进其愈合的研究进展

随着对肌腱愈合研究的不断深入和发展,预防肌腱粘连以及促进其愈合的方法越来越多。通过改进缝合方法、修复腱鞘或采用替代品、置入药物或药物薄膜及早期康复等治疗来有效预防肌腱粘连;通过重建腱鞘、药物、生长因子、基因干预等促进肌腱愈合。本文就近年来防止肌腱粘连及促进其愈合方面的研究予以综述。     

Differential expression of Tenomodulin and Chondromodulin-1 at the insertion site of the tendon reflects a phenotypic transition of the resident cells

The insertion site of the tendon to the skeletal element is hypovascular and is one of the most common sites of dysfunction in the musculoskeletal system. However, the resident cells have been poorly defined due to a lack of a specific marker for tenocytes. We previously reported that Tenomodulin (Tnmd) and Chondromodulin-1 (Chm1) are homologous angiogenesis inhibitors and predominantly expressed in the avascular region of tendons and cartilage, respectively. In this study, we analyzed the expression of Tnmd, Chm1, alpha 1 chain of the type I collagen (Col1a1) and alpha 1 chain of the type II collagen (Col2a1) at the insertion site of the Achilles, patellar, or rotator cuff tendons of 1-week-old rabbits by in situ hybridization analysis. Tnmd was co-expressed with Col1a1 in tenocytes of these tendons, while Chm1 and Col2a1 were detected in chondrocytes of the hyaline cartilage. Interestingly, the cell population between Tnmd/Col1a1 positive tenocytes and Chm1/Col2a1 positive chondrocytes expressed Col1a1 but none of the other markers (Tnmd, Chm1, and Col2a1). Red blood cells were exclusively present at the interface between the tendon substance and cartilage in the insertion site of the Achilles tendon. Lack of Tnmd and Chm1 in this newly characterized cell population may allow the transitional zone between the poorly vascularized tendon and cartilage to establish the unique vascular pattern for blood supply.     

Role of water content in dielectric properties and delayed luminescence of bovine Achilles' tendon

In order to investigate the role of water network in collagen structure, measurement of dielectric permittivity was performed on bovine Achilles' tendon as a function of water content. The data show a sudden decrease of the permittivity at each measured frequency value when the tendon humidity decreases. A similar behaviour is shown by the total number of photons emitted in delayed luminescence (DL) experiments. The comparison of the two results is in agreement with the hypothesis that DL is connected to the excitation and subsequent decay of collective electronic states, whose properties depend on the organized structure of the system.