Previous studies have shown fetal tissues heal in a regenerative fashion without scar formation. The objective of this study is to compare the healing properties of adult and fetal tendons. Time-mated pregnant ewes at 80-85 days of gestation were utilized. A partial, midsubstance tenotomy was performed in the lateral extensor fetal tendons, and analogous tenotomies were created in the maternal limbs. One week after injury, the fetal and adult animals were sacrificed, and tendons were histologically and mechanically evaluated. Immunohistochemical staining for transforming growth factor beta isoform 1 (TGF-beta1) was performed. Histologically, a gap with granulation tissue and inflammatory cells was visible in the site of wounding in the adult tendons. In the fetal tendons, no abnormalities were noted in the wound, with reconstitution of collagen architecture. TGF-beta1 expression was low in fetal but upregulated in the adult wounds. No significant differences were found in the biomechanical properties between groups. We identified regenerative healing properties in injured fetal tendon, while adult tendon tissue healed reparatively with scar formation. Fetal tendons demonstrated a limited recovery of mechanical properties after injury that was no better than that of the adult tendons at seven days. A better understanding of the mechanisms of fetal healing may lead to novel therapeutic strategies in the clinical setting.

Removal of cells may decrease the antigenicity and risk of disease transmission associated with tendon al-lografts and xenografts. An ideal cell removal method would not compromise graft structure and mechanical properties. This study compared the effects of three extraction chemicals [t-octyl-phenoxypolyethoxyethanol (Triton X-100), tri(n-butyl)phosphate (TnBP), and sodium dodecyl sulfate (SDS)] on tendon cellularity, structure, nativity, and mechanical properties. Rat tail tendons were soaked in extraction solutions for various time periods (12-48 h) and concentrations (0.5-2%), then they were rinsed with distilled water and ethyl alcohol. Histological analysis and tensile tests were performed on control and chemically treated tendons. Changes in collagen nativity were estimated by mechanical testing following incubation in a trypsin solution. Treatment of tendons with 1% Triton X-100 for 24 h disrupted the collagen fiber structure and did not remove cells. Treatment with 1% SDS for 24 h or 1% TnBP for 48 h resulted in an acellular tendon matrix with retention of near normal structure and mechanical properties. Consistent with previous studies demonstrating cell removal from other tissue types using SDS and TnBP, our preliminary results suggest these treatments are potentially useful for removing cells from tendon allografts or xenografts without compromising the graft structure or mechanical properties.

Removal of cells may decrease the antigenicity and risk of disease transmission associated with tendon al-lografts and xenografts. An ideal cell removal method would not compromise graft structure and mechanical properties. This study compared the effects of three extraction chemicals [t-octyl-phenoxypolyethoxyethanol (Triton X-100), tri(n-butyl)phosphate (TnBP), and sodium dodecyl sulfate (SDS)] on tendon cellularity, structure, nativity, and mechanical properties. Rat tail tendons were soaked in extraction solutions for various time periods (12-48 h) and concentrations (0.5-2%), then they were rinsed with distilled water and ethyl alcohol. Histological analysis and tensile tests were performed on control and chemically treated tendons. Changes in collagen nativity were estimated by mechanical testing following incubation in a trypsin solution. Treatment of tendons with 1% Triton X-100 for 24 h disrupted the collagen fiber structure and did not remove cells. Treatment with 1% SDS for 24 h or 1% TnBP for 48 h resulted in an acellular tendon matrix with retention of near normal structure and mechanical properties. Consistent with previous studies demonstrating cell removal from other tissue types using SDS and TnBP, our preliminary results suggest these treatments are potentially useful for removing cells from tendon allografts or xenografts without compromising the graft structure or mechanical properties.

Patellar tendon (PT) allografts for anterior cruciate ligament (ACL) reconstruction are potentially immunogenic and incorporate slowly compared with autografts. Our tissue-engineering approach to improve allograft efficacy is to (1) remove intrinsic cells from the graft to reduce antigenicity and then (2) seed the graft with extrinsic cells to improve ligamentization. To remove cells, tendons were soaked in 1% extraction solutions of tri(n-butyl)phosphate (TBP) or sodium dodecyl sulfate (SDS) for various time periods (24-72 h) and rinsed exhaustively. After treatment, we measured tendon cellularity, crimp structure, and mechanical properties. Treatment with either SDS or TBP removed approximately 70-90% of the intrinsic PT cells. Mechanical properties of treated PTs were similar to those of controls, despite changes in appearance. TBP- and SDS-treated PTs were then seeded with fibroblasts and cultured for up to 2 weeks in vitro. Fibroblast proliferation was retarded on SDS-treated PTs; in contrast, TBP-treated PTs supported cell proliferation similar to that of untreated controls. Extrinsic fibroblasts were successfully cultured on the TBP-treated PTs in vitro, creating viable tissue-engineered grafts potentially useful for ACL reconstruction. These modified allografts have the potential to be developed into mechanically functional delivery vehicles for cells, gene therapy vectors, or other biological agents.

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