Preparation Of Porous Bioceramics With Controlled Microstructure For The Treatment Of Avascular Necrosis Of The Femoral Head

Avascular necrosis of the femoral head is currently one of the main therapeutic challenges in orthopedics.This disease can have multiple different causes,resulting in the disruption of the microvascularization in the femoral head.It begins with venous stasis,which develops to the clogging of the arteries,finally leading to the avascular necrosis of bone tissue.Symptom varies from pain in the afflicted member to total crippling.This affliction can severely impact the quality of life and is commonly treated with total hip replacement.THR is a heavy surgery,and the artificial joints have short life spans,which make it only suitable for late stage patients.On the other hand,bone graft substitutes,especially bioceramics,are widely used in orthopedic surgery since the beginning of the 20^th century.Researchers have proved that certain microstructures and materials have osteoconductive properties,promoting revascularization of bony void.The goal of this research is to develop a porous bioceramic which would guide blood vessels from the trochanter region to the femoral head,thus restoring blood supply and promoting osteogenesis.Simultaneously,a set of dedicated surgery tools and an operating procedure were designed to simplify the surgery and minimize trauma.This research invented a manufacturing process which allows precise control on the size of both pores（300-700μm）and interconnections（70-200μm）of porousβ-tricalcium phosphate bioceramics.Using a 3D-stacking organic template technique,an organic porogen scaffold with controlled structure was manufactured.The material was obtained by pouring the ceramic slurry into the scaffold,debinding and sintering.Improvement of the mechanical properties was achieved by controlling the size distribution of the porogen in the scaffold,resulting in both reinforced bioceramic cylinders with dense surrounding or dense center.The technique used allowed precise control on the microstructure of the scaffolds.Mechanical properties of the material were greatly enhanced from 2.14MPa for fully porous ceramics to 11.88MPa for dense center reinforced bioceramics.Biological properties（cell adhesion,proliferation,vascularization,bone growth）of the material with different internal sizes were then tested both in-vitro and in-vivo.From the in-vitro tests,the highest cell proliferation rate was obtained for bioceramics with pore diameter of 500-600μm and interconnection diameter of 120μm.In-vivo tests showed optimal vascularization and bone growth for pore diameter of 400-600μm and interconnection diameter of 120μm.Thus,a reinforced bioceramic with dense core and porous surface（pore diameter of 400-600μm,interconnection diameter of 120μm）was chosen for further clinical testing.In order to reduce surgery time,increase the ease of use of the treatment,and achieve minimally-invasiveness,a dedicated operative protocol was designed.Three years clinical follow-up showed no relapse,preserved sphericity of the femoral head and restauration of mobility,proving the efficiency of this treatment.To conclude,the research led to the invention and development of an innovative minimally invasive joint-preserving treatment for the avascular necrosis of the femoral head,including bioceramic implants and a surgery protocol.Experiments showed the capacity of this controlled porous structure to conduct the growth of new tissues and the improvement of mechanical properties through the combination of porous and dense ceramics.The resulting reinforced bioceramic rod did not only conduct blood supply from the trochanter to the necrotic zone,but it also solved the mechanical defiency of traditional core decompression surgeries.The dedicated surgery tools also allowed to greatly reduce both operation time and trauma for the patient.The results of three-years follow-up are promising and proved the huge potential of this innovative treatment.