Fabrication Of Micro-/Nano-Structured Calcium Phosphate Bioceramics And Their Performance In Osteoporotic Bone Regeneration

Osteoporosis is a common disease characterized by a systemic impairment of bone mass and microarchitecture that results in fragility fractures.Bioactive materials combining load-bearing capacity and interconnected porous structures are frequently used to accelerate fracture healing,especially under the condition of poor osteogenesis.Calcium phosphate bioceramics such as hydroxyapatite(HA)and tricalcium phosphate(TCP)have been widely used in clinic because of their good osteoinductivity and osteoconductivity.However,the mechanical properties and biological activity of the calcium phosphate bioceramics are still insufficient for the osteoporotic bone repair.To increase osteoinductive,osteoconductive,and mechanical properties of bioceramics,one strategy is endowing them with micro/nano-sized structure to promote bone formation while providing adequate initial mechanical properties to match those of tissue at the site of implantation under osteoporotic condition.And along with the continuous growth of bone tissue,a porous material-bone composite material is gradually formed,thereby improving the mechanical properties and implant stabilityof the bioceramics.Therefore,we designed a series of micro-/nano-structured bioceramics and explored those effect in osteoporotic bone repair.First of all,we fabricated a bioceramic scaffold composed of nanoparticles-reinforced micro-whiskers backbone(nw CaP)with a two-step method.Moreover,we established an ovariectomized rat metaphyseal femur defect model to assess the in vivo performance of the nw CaP bioceramics with micro computed tomography(micro CT)and histological analysis.The alterations at the cellular and genetic levels induced by the micro-/nanostructure were further investigated in vitro using MSCs and primary osteoblasts derived from osteoporotic animals.The primary conclusions of this section are:This sandwich-structured bioceramic exhibited a higher compressive strength,a suitable degradation rate and better cell attachment than traditional or intermediate bioceramics.In a rat model of osteoporotic bone defects,the nw CaP group showed a reduced fracture occurrence and an effective new bone substitution rate,as characterized by micro CT analysis.The increased bone formation rate and greater amount of new bone formed within the defected area of the nw CaP group was revealed by the serum PINP level and histological staining.A gene microarray study indicated that the promotion of osteogenesis might be attributed to selectively upregulated fibroblast growth factor 23(FGF23)expression in cells co-cultured with the nw CaP bioceramic.Moreover,the JAK2 signal pathway was confirmed to be involved in the nw CaP-induced elevation of FGF23 expression.The above experiments suggested that the micro-/nano-structured bioceramic could enhance osteoporotic bone regeneration.However,serious bone loss around the implants was occurred in later stage of implantation,which may account for slower bone healing.Therefore,an advanced strategy for osteoporotic bone regenerating bioceramics should not only focus on the direct osteogenesis of the implant within the defect but also a favourable surrounding environment near the defect.We then fabricated strontium-incorporated whiskered calcium phosphate bioceramic(Sr WCP)and pure HA whiskers by hydrothermal treatment and respectively named Sr WCP and WCP.Both bioceramics had similar three-dimensional(3D)porous structures and mechanical strengths,but the Sr WCP bioceramic was capable of releasing Sr under physiological conditions.In an osteoporotic rat metaphyseal femoral bone defect model,both bioceramic scaffolds were implanted,and another group that received WCP plus strontium ranelate drug administration(Sr-Ran+WCP)was studied for comparison.At week 1 post-implantation,osteogenesis coupled blood vessels were found to be more common in the Sr WCP and Sr-Ran+WCP groups,with substantial vascular-like structures.After12 weeks of implantation,comparable to the Sr-Ran+WCP group,the Sr WCP group showed induction of more new bone formation within the defect as well as at the implant-bone gap region than that of the WCP group.Both the Sr WCP and Sr-Ran+WCP groups yielded a beneficial effect on the surrounding trabecular bone microstructure to resist osteoporosis-induced progressive bone loss.While an abnormally high blood Sr ion concentration was found in the Sr-Ran+WCP group,Sr WCP showed little adverse effect.In this section,our results demonstrated that the Sr WCP bioceramic is a safe bone substitute for treatment of osteoporotic bone defects,which promotes bone regeneration and implant osseointegration.In addition,we found that the release of Sr enhanced osteointegration,prevented surrounding bone resorption,but exerted little effect on increased bone ingrowth inside the implants.To further improve the bioactivity of the material,modification of multilevel nano surface is a promising strategy.Next,we fabricated new micro-/nano-structured hydroxyapatite(nw HA)bioceramics loaded with different amounts of hydroxyapatite nanoparticles(n HA).The in vitro results demonstrate that all nw HA bioceramic groups promote osteoporotic osteoblasts proliferation and attachment,and osteogenic factors are enhanced in nw HA2,loaded with moderate amount of hydroxyapatite nanoparticles.More volume of newly formed bone tissues with more blood vessels is augmented in the nw HA2 bioceramics when implanted in femoral bone defect of an ovariectomized rat model.Furthermore,micro CT analysis reveal that more bone grows adjacent to the implant and that nw HA2 can effectively maintain trabecular bone structure to resist osteoporosis-induced bone loss.These findings indicate micro-/nano-structured bioceramics loaded with appropriate amount of hydroxyapatite nanoparitcles can facilitate vascularization and bone formation under osteoporotic condition.Finally,we synthesized different morphologies of hydroxyapatite nanoparitcles(needle-like,short rod-like,amorphous,corn-like and raspberry-like)and loaded them on the surface of whiskered bioceramics according to the previous parameters.In a rat model of osteoporotic bone defects,it was found that the micro-/nano-structured bioceramics loaded with needle-like n HA could significantly promote bone formation and improve bone mineral density in the defects.Moreover,the micro-/nano-structured hydroxyapatite bioceramics loaded with corn-like n HA yielded a beneficial effect on maintenance of the trabecular bone microstructure near the implants.Our findings recommend that the micro-/nano-structured hydroxyapatite bioceramics with specific structure can be used as a bone substitute for osteoporosis and is expected to achieve rapid healing of bone defects under pathological conditions.Collectively,micro-/nano-structured calcium phosphate bioceramics offer expansive scope of biomimetic scaffolds for bone tissue engineering,especially for those to serve the patients with challenging conditions such as osteoporosis.