Structural design and evaluation of bone remodeling effect of fracture internal fixation implants with time-varying stiffness
The stiffness of an ideal fracture internal fixation implant should have a time-varying performance,so that the fracture can generate reasonable mechanical stimulation at different healing stages,and biodegradable materials meet this performance.A topology optimization design method for composite structures of fracture internal fixation implants with time-varying stiffness is proposed,considering the time-dependent degradation process of materials.Using relative density and degradation residual rate to describe the distribution and degradation state of two materials with different degradation rates and elastic modulus,a coupled mathematical model of degradation simulation mechanical analysis was established.Biomaterial composite structures were designed based on variable density method to exhibit time-varying stiffness characteristics.Taking the bone plate used for the treatment of tibial fractures as an example,a composite structure bone plate with time-varying stiffness characteristics was designed using the proposed method.The optimization results showed that material 1 with high stiffness formed a columnar support structure,while material 2 with low stiffness was distributed at the degradation boundary and inside.Using a bone remodeling simulation model,the optimized bone plates were evaluated.After 11 months of remodeling,the average elastic modulus of callus using degradable time-varying stiffness plates,titanium alloy plates,and stainless steel plates were 8 634 MPa,8 521 MPa,and 8 412 MPa,respectively,indicating that the use of degradable time-varying stiffness plates would result in better remodeling effects on the callus.
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