The Study Of An Injectable Nano-Hydroxyapatite And Polyamide Composite Cement For The Prophylactic Augmentation Of Osteoporotic Cancellous Bone And Management Of Osteoprotic Fracture Of Cancellous Bone

As the prolonged longevity of population, osteoprosis (OP) has been more and more common among the aged people. Due to low bone mass, microarchitectural degeneration, high fragility of bone and biomechanical fall, it may eventually leads to osteoporotic fracture. One solution to the severe osteoporotic comminuted fracture with loss of bone may involve the use of autogenous grafts, allografts, polymethylmethacrylate bore cement (PMMA) or calcium phosphate cement (CPC) etc. However, some problems related to the availability of graft material, immunogenictity, biomechanical integrity, and long-term compatibility have limited the success of these methods.Recent developments in nano-biomaterials make medical biomaterials new properties. A new type of inorganic-organic biomimetic bone cement mainly included of nano-hydroyapatite (n-HA) and Polyamide 66 (PA66) composite. Analytical and testing results indicate that n-HA distributes homogeneously in polyamide matrix. Nanograde, needle-shape apatite crystals of n-HA is similar to bone apatite. Polyamide 66 has long-term use in clinical field with a good compatibility. The cement consists of two parts: the nano-composite fine powder and the ethanol solution with a little amount of metal salt. As the cement can be made a paste with the formation or break of hydrogen bonding, this cement can be used as injectable biomaterials. The purpose of the present study is biomechanical and histological evaluation of the n-HA/PA composite cement. This study had two separate parts: (1) in vitro, the thoracic vertebral bodies injected with n-HA/PA composite cement were tested during axial compressive testing; the cancellous bone in distal femoral metaphysis was tested during torsional testing. (2) The cement was injected into the fracture site of distal femoral metaphysis of rabbits and the callous bone in proximal tibial metaphysis of rabbits. Histological examination and biomechanical testing were evaluated from the 1st week to the 12th week, postoperatively.The results were showed as follows:1. Biomechanical testing in vitro. Vertebral bodies or cancellous bones of the femur injected with 60%, 70% and 80% n -HA/PA composite cement (HP1, HP2, HP3) were stronger than the osteoporotic vertebrae (OP) in compressive testing and torsional testing in the osteoporotic cancellous bone of femur The initial compressive strength of vertebral bodies injected with HP1 and HP2 had reached 76.05 and 81.33 percent of that of normal vertebral bodies (N). The torsional strength of cancellous bones of femur injected with HP1, HP2 and HP3 had reached 85.24,62.52 and 28.43 percent of that of normal bone.2. The study of the osteoporotic fracture of the distal femoral metaphysis of rabbits. Histological and scanning electron microscopy (SEM) examination showed the monocytes and fibrous callus were observed around the cement. Then, the cement began to be separated into various granules and degrade. A bulk of trabecular bone filled into most of the fracture site through newly formed by endochondral ossification. In the whole course, the bone formation in injection groups was about 2 weeks later than that in control groups. However, in the late course of bone healing, new bone formation of the injection groups became more rapidly than early. Mechanical testing showed that, from the 4th week to 6th week, the torsional strength and stiffness of injection groups were lower than that of control groups (P＜0.05); when came to the 12 week,the torsional properties of injection groups were closed to that of control groups (P＞0.05); the finding paralleled the histological observations.3. The study of the osteoporotic cancellous bone of the proximal tibial metaphysis of rabbits. Histological and SEM examination showed a bulk of the cement could be filled into the trabecular gaps; the monocyte-mediated and solution-mediated resorption led to the degradation of the cement; then , the newly formed bone by osteoblasts was incorporated in the surface of the old trabecular bone, it led...