Study And Fabrication Of Biodegradable Shape Memory Cement Restrictor

Objective:A septic loosening is a common long-term complication of cemented femoral components in hip armroplasty.Improved cementing technique could increases cemented femoral component survival.The use of a cement restrictor in cemented femoral fixation during hip arthroplasty is an important part of modern cementing technique.Cement restrictor can increase intramedullar cement pressure significantly and create an optimum cementing of the femoral stem.Compared of the limitation and disadvantage of the UHMWPE cement restrictor in potential revision surgery or used below the femoral isthmus,the biodegradable and sharp memory cement restrictor has immense advantages.Poly lactic acid is a well-known synthetic polymer with excellent biocompatibility and degradability,which has been approved by American FDA and used in various biomedical fields.In this thesis,the preparation, cytocompatibility and biomechanical properties of copolymer of PLLA and PDLLA were studied.We designed a novel restrictor with the copolymer,which can degrade in medullary cavity and can reliable resist distal migration and pressure created by cement pressurized.Methods:We fabricatied the copolymer P(D,L-LA-CO-L,L-LA) by PLLA and PDLLA via in site intercalative polymerlization and made a novel biodegradable sharp memory cement restrictor.Biocompatibility of the copolymer with rabbit bone marrow stem cell was investigated by means of cell morphology and cell proliferation.The morphology of the cells was observed by inverted phase contrast microscope and cell proliferation determined by CCK-8 assay. Hemolysis was evaluated in vitro through measuring erythrocyte lyses and ferrohemoglobin freeing degree with indirect contact method.We used human femora preserved by formalin in all experiments.The femora were sectioned distally at the epicondylar and preserved 15 mm of the calear femorale.Insert soft reamer by gradually increased size until the reamer contacted with the cortex of the femoral isthmus.The size of the reamer was regarded as the diameter of the isthmus.We selected two pairs of femur whose diameter was 12mm as the specimen.The femoral canal is prepared with a series of broaches that create an envelope for the implant.Remove the broach and measure the size of the canal,and then insert a suitable cement restrictor.The mechanical proprieties of the restrictors were test above and below the femoral isthmus.The relationship of pressure resists ability and distal migration was recorded.Results:The number of rabbit bone marrow stem cells increased significantly and the morphology was normal.The growth and morphology of the cells in different concentration of P(D,L-LA-CO-L,I.-LA) extraction medium had no difference to control group.Cytotoxicity test showed that P(D,L-LA-CO-L,L-LA) did not have obvious toxicity to rabbit bone marrow stem cells.Hemolysis test suggested that the P(D,L-LA-CO-L,L-LA) did not have obvious hemolysis reaction.The hemolysis index was 0.28%,which was less than the national standard(5%).There was variation in the performance of the three cement restrictors and changed with the position.When used above the isthmus of the femur,all kinds of restrictors were successful to resist pressures greater than 345KPa,which has been described by Noble in an earlier publication.But,most of UHMWPE cement restrictors failed at low pressures when deployed below the isthmus,except a larger diameter restrictor which had serious wear on the wings. P(D,L-LA-CO-L,L-LA) cement restrictor could resist the greatest pressures when the restrictor used below the femoral isthmus.The novel cement restrictor could resist cement pressures of more than 740KPa in vitro.Conclusions:The P(D,L-LA-CO-L,L-LA) copolymer has an excellent biocompatibility.The novel restrictor can reliably resist intramedullar cement pressure and distal migration at the proximal femur as well as the two types of UHMWPE restrictors.The UHMWPE restrictors with a smaller diameter failed at low pressures when deployed below the isthmus and the restrictor with a larger diameter could resist pressures of 345KPa but may create wear particles.The biodegradable shape memory cement restrictor can reliably resist intramedullar cement pressure.When used below the isthmus,this kind of restrictor had some advantages because of its sharp memory and degradable property.How to decrease its Tg temperature and find an easy to use method for the novel restrictor still need to be further study.More study should be performed to prove its degradable character in vivo.