Shape Memory Polymer Based On Poly(d,l-lactide) For Oviduct Contraception

A novel poly(DL-lactic acid)-based poly(urethane-urea) (PDLLA-PUU) has been previously designed and prepared using PDLLA-based macrodiol as soft segments, hexamethylene diisocynate (HDI) and butanediamine (BDA) as hard segments. It has been proved of good shape memory properties and biodegradability. These properties make PDLLA-PUU suitable for oviduct contraceptive devices which may be non-invasively implanted into oviducts through vagina and uterus. Moreover, this PDLLA-PUU SMPs based oviduct contraceptive device may induce hyperplastic fibrous tissue with its degrading, and finally the oviduct is blocked by the fibrous tissue instead of the foreign device. Therefore, evaluating the short-term and long-term cytotoxicity by using oviduct epithelial cells as the model cell, and further in vivo examining the contraceptive effects are indispensable to both direct the modification of PDLLA-PUU SMP and push its clinical tests. PDLLA-PUU SMP1K1.1, a PDLLA-PUU with a soft segment of Mn=2100 and molar ratio of the macrodiol to HDI equal to 1:1.1, has a Tg of 38.08℃, which is close to the body temperature and thus suitable for the contraceptive device fabrication. In this study, the shape memory properties and degradability of PDLLA-PUU SMP1K1.1 were firstly determined, and then the short-term cytotoxicity was examined by co-culture of oviduct epithelial cells with PDLLA-PUU SMP1K1.1 films and long-term cytotoxicity by testing the cell viability in PDLLA-PUU SMP1K1.1 degradation products, and finally the contraceptive effect was preliminarily evaluated. The main work and conclusions are listed as follows:(1) The weight loss ratio and pH value changes of PDLLA-PUU SMP1K1.1 during 12-week degradation were tested to characterize the in vitro degradation behavior by using PDLLA as controls. The results revealed that the weight loss ratio of PDLLA and pH value change of the medium decreased significantly, exhibiting obvious acid catalyzed auto-accelerating degradation. However, the weight loss ratio and pH value changes of SMPs decreased slowly and the weight loss ratio was less than 30% after degrading for 12-week, which may due to the existence of alkaline BDA during the degradation of SMPs which could partially neutralize the acidic degradation products of PDLLA segments.(2) Scratch assay and then repetitive differential attachment methods were established to isolate and purify rabbit oviduct epithelial cells. Observations by inverted fluorescence microscope and identifications by immunofluorescence assays indicated that the obtained cells demonstrated typical morphology and biological characteristics of oviduct epithelial cells.(3) The short-term cytotoxicity and cytocompatibility of PDLLA-PUU SMP1K1.1 were evaluated by detecting the cell morphology and viability of oviduct epithelial cells co-cultured on PDLLA-PUU SMP1K1.1 films. PDLLA films were employed as controls. The results indicated that the cells on PDLLA-PUU SMP1K1.1 exhibited much better cell morphology and higher viability, suggesting decreased cytotoxicity and improved cytocompatibility compared to PDLLA films.(4) The cell viability of oviduct epithelial cells cultured in PDLLA-PUU SMP1K1.1 degrading products was measured. The results revealed that the viability of the cells cultured in the degrading products of various concentration was slightly lower than that in the negative control. The USP level is level 1, suggesting PDLLA-PUU SMP1K1.1 has no obvious long-term cytotoxicity and is safe for oviduct contraception.(5) A series of oviduct contraceptive devices with a diameter of 2mm and a length of 10mm was fabricated from PDLLA-PUU SMP1K1.1 and their contraceptive effect was evaluated by implanting the devices into the isthmus of female New Zealand rabbits. The histopathologic changes of oviduct mucosa were observed. The results indicated that obvious fibrous hyperplasia tissues were induced after implantation of 3 month which blocked most of the oviduct and there was no observable synthetic polymer, and after implantation of 6 month, the oviduct was almost completely blocked. This shows that the PDLLA-PUU SMP1K1.1 based contraceptive devices are effective in oviduct contraception. A longer term in vivo test is on-going.