| Background:With the improvement of social development level,people’s awareness of oral health has gradually awakened in recent years.As the main treatment method and development direction of restoration for missing teeth,dental implantation has shown its promising technical advantages and reliable therapeutic effects with a trend of explosive growth,which has a profound impact on the entire dental medicine and health industry.However,the jaw atrophy and defect caused by the congenital dysplasia,trauma,tumors,inflammation and other reasons,especially the alveolar bone defects in the vertical direction,with difficulty in treatment and uncertainty of the osteogenesis effects,is one of the most urgent problems to be solved in the clinical practice of oral implantation.Onlay bone grafting is one of the main methods to reconstruct the vertical bone defects in clinic.Although autologous bone grafts could achieve relatively promising therapeutic effects,but there are many intraoperative and postoperative complications,such as pain,bleeding,swelling,nerve injury,sensory abnormality,therefore,its application in clinic is limited by the low acceptances of the patients.Accordingly,the research for suitable bone block substitutes has become a hot topic in recent years.With the lower risk of biological contamination and immune incompatibility than the allogeneic and heterogeneous grafts,alloplastic materials,which can be easily processing and mass-produced,is more suitable for clinical practice in theory with personalized customization features,making it a potential solution for massive bone substitutes.The most used research strategy is to prepare highly biomimetic composite scaffolds by dispersing inorganic materials into organic matrix according to the principle of biomimetic mineralization.Nano-hydroxyapatite is similar to inorganic components of bone tissue.If the architectural design is conducive to vascularization,it can promote bone tissue regeneration.Type Ⅰ collagen fibers are the template of bone tissue biomineralization,and are one of the most commonly used scaffolds in tissue engineering.While the mechanical strength of the pure collagen scaffolds is insufficient,it needs to be combined with bioceramics to enhance the mechanical properties,dimensional stability and bone conductivity of scaffolds to enhance osteogenesis.Hydroxyapatite and collagen type Ⅰ can simulate the compositions and 3-dimensional structure of bone tissues and meet the basic requirements of cell growth after biomimetic mineralization.A large number of animal experiments and clinical studies have proved that these materials have good osteogenesis.The powdered,spongy and block materials have been applied in orthopaedics,neurosurgery and maxillofacial surgery,such as site preservation,etc.However,there is few reports of the application of the block bone graft in Onlay grafting.Objective:In this study,two groups of nano-hydroxyapatite-I collagen composite scaffolds with different porosity were prepared based on biomimetic mineralization principle,and the properties of scaffolds were detected.To establish models of rabbit calvariae defects and Onaly bone graft,observing the imaging and histological changes of scaffold materials in bone defects at different healing stages,evaluating the osteogenesis effectiveness,and analyzing the possibility of using these scaffold materials as Onlay bone grafts,so as to provide references for further improvement of scaffold materials in oral clinical use.Methods:1.The nano-hydroxyapatite-Ⅰ collagen composite scaffolds were prepared by in situ synthesis based on the self-assembly theory of collagen fibers-hydroxyapatite.According to the pre-design of the experiment,the scaffolds with approximately 60%porosity(abbreviated as Group A)and 40%porosity(abbreviated as Group B)were prepared respectively.The properties of the composite scaffolds A and B were tested,including gross observation of the materials’configuration,scanning electron microscopy analysis of surface morphology,measurement of density and porosity of scaffolds,determination of compressive strength of scaffolds,and determination of liquid absorption of materials by simulated body fluid absorption test.2.Three half-layer bone defect models were prepared in 24 New Zealand rabbits’craniums.According to the designs,nano-hydroxyapatite-collagen composite scaffolds of group A and B was implanted into the two defects,and the other defect was filled with blood clot as blank control group.Gross observation,micro-CT examination,HE staining and Masson staining were used for histological examination.The osteogenic properties and changes of the composite scaffolds in the two groups were analyzed,and the feasibility of the composite scaffolds as Onlay bone graft materials was evaluated.Results:1.There are some differences between the two groups in the performance of stent materials.Scanning electron microscopy images showed that the scaffolds of the two groups were three-dimensional porous structure,and the pores are connected with each other.The surface of group A was dispersed with(451±23)μm macropores and(78±16)μm micropores,while that of group B was mainly(63±22)μm micropores.The density of scaffolds in group A and B were(0.402±0.005)g/cm~3 and(0.748±0.013)g/cm~3respectively;the porosity was(58.4±4.7)%and(37.9±3.3)%;the compressive strength was(2.01±0.10)MPa and(4.97±0.07)MPa respectively.The simulated body fluid absorption experiment suggested that the scaffolds did neither deform,nor becoming soft and fractured in the simulated body fluid environment,and the space maintenance ability was sufficient.2.The in vivo results revealed that in group A,1 case,1 case and 2 cases of scaffolds material fragmentation occurred in 4 weeks,8 weeks and 12 weeks respectively,while other scaffolds were intact.All of the Scaffolds in the Group B are intact.Micro-CT images showed that the scaffolds and bone tissues were integrated more closely with the time coursing.The effect of osteogenesis in group A was better than that in group B.Histological examinations showed that with the passage of time,the scaffold materials gradually degraded and a large number of osteocytes migrated into the scaffolds.According to time and materials grouping,there was significant difference in collagen fiber area percentage between group A,group B and blank group(P<0.05).The area percentage of collagen fibers in group A at 8 weeks after implantation was higher than that in group A at 4 weeks after implantation(P<0.05).The same results occurred in Group B(P<0.05).Conclusions:1.By biomimetic mineralization,nano-hydroxyapatite-I collagen composite scaffolds with controllable porosity and compressive strength can be prepared in a certain range.The scaffolds have certain physical properties and space maintenance abilities.2.In this study,the two groups of nano-hydroxyapatite-type Ⅰ collagen composite scaffolds have certain osteogenic capacity.With the increase of scaffold porosity,the osteogenic capacity of the scaffolds increases significantly,but with the decrease of compressive strength.Animal experiments show that when the porosity of the scaffold material reaches 60%and the compressive strength is about 2 MPa,the other scaffolds can maintain the osteogenic space well except for individual scaffolds which disintegrate under the physiological pressure.The scaffolds can basically meet the requirements of Onlay bone graft materials and have certain clinical application potential. |
PDF Full Text Request