Einfluss von biodegradierbaren PLLA(Poly-L-Lactid-Nanofasern auf die Knochenheilung am standardisierten Critical-Size-Defektmodell der Ratte

Summary Pseudarthrosis and other bone defects are common problems in orthopaedic treatment. In addition to that, when harvesting bone from the iliac crest and other places, these procedures are charged with high donor morbidity. Postoperative pain, low amount of material, infections and instabilities at the donor side are to be ruled out. Allogenic grafts are limited and still have, despite very high precautions, the possibility of disease transmission. Tissue engineering is a part of modern medicine, which tries to solve these problems. Three-dimensional, porous nanofibres made of poly-l-lactid acid (PLLA) are of huge scientific interest. Until now, data from in vivo studies testing biocompatibility of PLLA-nanofibres are still missing. The aim of this study was to test the biocompatibility and possible osteoinductiv properties of PLLA nanofibres on a standardized rat-calotte model. Therefore, 90 rats (Sprague Dawley) were divided into three groups: negative control, Tutobone® and PLLA. Two calotte defects, each measuring 5mm in diameter, were placed and were either left unfilled, filled with Tutobone or PLLA. After four, eight and twelve weeks, 10 animals of each group were sacrificed and examined radiologically, per blood analysis and (immuno) histologically. In blood analysis, there were no signs of systemic inflammatory response. By measuring the alkaline phosphatase, bone repair was evaluated. By measuring CRP, a systemic inflammatory reaction was excluded. There were now statistic significant differences between the groups concering blood samples. Moreover, there was no increase of infection parameters at all. A systemic relevant rejection reaction could not be seen. In histological staining by HE and Masson Goldner, no inflammatory reaction by invasion of granulocytes, lymphocytes or loosening of tissue could be seen. However, PLLA implants were infiltrated with a large amount of cells. As a characteristic sign, large giant cells without forming granulomas were seen. Due to these foreign body cells, a local inflammatory reaction on the operation side could not be excluded. Furthermore, cellcounts were performed to evaluate the adequacy of the implants as a leading compound for cell invasion. No significant differences were seen between the groups after four weeks. After eight and twelve weeks a difference between PLLA and negative control was seen. In PLLA-group, there were more cells. The same is true for the Tutobone© group. However, these differences were not significant. PLLA therefore seems to be an adequate leading structure for the invasion of cells and maybe is superior to negative control. Histological sections were performed in order to quantify the rate of new formed bone. In every group, there was a significant increase of new formed bone between four and twelve weeks except to the negative control group. However there was now significant difference between the groups, although there was a difference of 20% between negative control and Tutobone© at 12 weeks. More bone was formed in the PLLA group compared to the negative control but less bone when compares to Tutobone©. Hence there was no advantage for PLLA over Tutobone or negative control. The radiological examinations support these findings. Therefore, the hypothesis, that PLLA does not act osteoinductively, can be confirmed. Immunohistological staining against COL1A1, Osteocalcin, BMP-2 and SMAD5 were performed and positive cells were counted. While in the negative control group low counts were measured, in the Tutobone© group, after a decrement from four to eight weeks, there was a maximum of positive cells at twelve weeks. In the PLLA group, this was contrary. After eight weeks there was a peak, which fell down to values under those of the negative control after twelve weeks. This could be associated with the downregulation of osteoblast genes by PLLA, which had been proofed by in vitro experiments before. In summary, a good biocompatibility of PLLA-nanofibres without local or systemic signs of inflammatory reaction could be seen. There were significantly higher cell counts compared to negative control group, yet without apposition of new bone. This lack of osteoinductivity was confirmed by immunohistological staining.