Histological evaluation of type I collagen scaffolds preparde under different dehydrothermal cross-linking conditions in a rat model / 中国组织工程研究

BACKGROUND:In previous studies, the dehydrothermal cross-linking method was modified by the authors to improve the degradation property of colagen scaffolds. The cross-linking time was increased from 24 to 48 hours, and the cross-linking temperature increased from 105 to 115℃. OBJECTIVE:To verify the anti-degradation ability of colagen scaffolds prepared using the modified dehydrothermal cross-linking method and to obtain the optimal efficacy of the scaffolds on damaged tissue repair and regeneration. METHODS: Highly-purified type I colagen scaffolds with native triple helix structure were prepared and subjected to three different dehydrothermal cross-linking conditions: 105℃ for 24 hours, 105℃ for 48 hours and 115℃ for 24 hours. Material samples, 1 cm×1 cm, were implanted subcutaneously into the rat dorsum. The specimens were harvested at 3 days, 14 days and 42 postoperative days folowed by fixation and histological analysis using hematoxylin-eosin staining. RESULTS AND CONCLUSION:No untoward foreign body and immunological reactions were observed in any groups. In the group of 105℃ for 48 hours, the scaffold retention and degree of pore openness were better than the other two groups at 14 days after scaffold implantation (P < 0.05). These findings indirectly suggest that the anti-degradation ability of colagen scaffolds can be strengthened under certain dehydrothermal cross-linking conditions: the cross-linking time is increased from 24 to 48 hours.

Self-complementary AAV2.5-BMP2-coated femoral allografts mediated superior bone healing versus live autografts in mice with equivalent biomechanics to unfractured femur.

Structural allografts used for critical bone defects have limited osteogenic properties for biointegration. Although ex vivo tissue-engineered constructs expressing bone morphogenetic protein-2 (BMP2) have demonstrated efficacy in critical defect models, similar success has not been achieved with off-the-shelf acellular approaches, including allografts coated with freeze-dried single-stranded adeno-associated virus (ssAAV-BMP2). To see whether the self-complementary AAV serotype 2.5 vector (scAAV2.5-BMP2) could overcome this, we performed side-by-side comparisons in vitro and in the murine femoral allograft model. Although ssAAV-BMP2 was unable to induce BMP2 expression and differentiation of C3H10T1/2 cells in culture, scAAV2.5-BMP2 transduction led to dose-dependent BMP2 expression and alkaline phosphatase activity, and displayed a 25-fold increased transduction efficiency in vivo. After 6 weeks, the ssAAV-BMP2 coating failed to demonstrate any significant effects. However, all allografts coated with 10(10) scAAV2.5-BMP2 formed a new cortical shell that was indistinguishable to that formed by live autografts. Additionally, coated allografts experienced reduced resorption resulting in a threefold increase in graft bone volume versus autograft. This led to biomechanical superiority versus both allografts and autografts, and equivalent torsional rigidity to unfractured femur. Collectively, these results demonstrate that scAAV2.5-BMP2 coating overcomes the major limitations of structural allografts, which can be used to heal critical defects of any size.

Standardized criterion to analyze and directly compare various materials and models for peripheral nerve regeneration.

Progress in understanding conditions for optimal peripheral nerve regeneration has been stunted due to lack of standardization of experimental conditions and assays. In this paper we review the large database that has been generated using the Lundborg nerve chamber model and compare various theories for their ability to explain the experimental data. Data were normalized based on systematic use of the critical axon elongation, the gap length at which the probability of axon reconnection between the stumps is just 50%. Use of this criterion has led to a rank-ordering of devices or treatments and has led, in turn, to conclusions about the conditions that facilitate regeneration. Experimental configurations that have maximized facilitation of peripheral nerve regeneration are those in which the tube wall comprised degradable polymers, including collagen and certain synthetic biodegradable polymers, and was cell-permeable rather than protein-permeable. Tube fillings that showed very high regenerative activity were suspensions of Schwann cells, a solution either of acidic or basic fibroblast growth factor, insoluble ECM substrates rather than solutions or gels, polyamide filaments oriented along the tube axis and highly porous, insoluble analogs of the ECM with specific structure and controlled degradation rate. It is suggested that the data are best explained by postulating that the quality of regeneration depends on two critical processes. The first is compression of stumps and regenerating nerve by a thick myofibroblast layer that surrounds these tissues and blocks synthesis of a nerve of large diameter (pressure cuff theory). The second is synthesis of linear columns of Schwann cells that serve as tracks for axon elongation (basement membrane microtube theory). It is concluded that experimental configurations that show high regenerative activity suppress the first process while facilitating the second.