Chongyun Bao

The effect of surface immobilized bisphosphonates on the fixation of hydroxyapatite-coated titanium implants in ovariectomized rats

Immobilized bisphosphonates (BPs) have been introduced to improve implant fixation, however, no information could be found about the efficiency of this approach in osteoporotic bone. This study was designed to evaluate the bone response to surface immobilized BPs on implants inserted in tibiae of ovariectomized (OVX) rats. Three months after bilateral ovariectomy, 40 rats were randomly assigned into four groups for implantation of hydroxyapatite-coated titanium implants with or without immobilized BPs: (1) control group (without BP treatments); (2) pamidronate (PAM) group (1mg/ml of PAM immersing); (3) ibandronate group (1mg/ml of ibandronate immersing); and (4) zoledronic acid (ZOL) group (1mg/ml of ZOL immersing). After implantation periods of 3 months, the peri-implant-bone density, trabecular microstructure, bone-implant interface and mechanical fixation of implants were evaluated by dual energy X-ray absorptiometry, micro-computed tomography, histology and push-out test. We found that three BPs triggered pronounced bone-implant integration and early bone formation around implants in OVX rats, with a rank order of ZOL>ibandronate>PAM. These results provide new evidence that immobilized BPs have positive effects on implant fixation in osteoporotic bone, in addition to their well-documented potency to inhibit implant loosening in normal bone.

The homing of bone marrow MSCs to non-osseous sites for ectopic bone formation induced by osteoinductive calcium phosphate

Osteoinductive biomaterials are promising for bone repair. There is no direct proof that bone marrow mesenchymal stem cells (BMSCs) home to non-osseous sites and participate in ectopic bone formation induced by osteoinductive bioceramics. The objective of this study was to use a sex-mismatched beagle dog model to investigate BMSC homing via blood circulation to participate in ectopic bone formation via osteoinductive biomaterial. BMSCs of male dogs were injected into female femoral marrow cavity. The survival and stable chimerism of donor BMSCs in recipients were confirmed with polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH). Biphasic calcium phosphate (BCP) granules were implanted in dorsal muscles of female dogs. Y chromosomes were detected in samples harvested from female dogs which had received male BMSCs. At 4 weeks, cells with Y-chromosomes were distributed in the new bone matrix throughout the BCP granule implant. At 6 weeks, cells with Y chromosomes were present in newly mineralized woven bone. TRAP positive osteoclast-like cells were observed in 4-week implants, and the number of such cells decreased from 4 to 6 weeks. These results show that osteoprogenitors were recruited from bone marrow and homed to ectopic site to serve as a cell source for calcium phosphate-induced bone formation. In conclusion, BMSCs were demonstrated to migrate from bone marrow through blood circulation to non-osseous bioceramic implant site to contribute to ectopic bone formation in a canine model. BCP induced new bone in muscles without growth factor delivery, showing excellent osteoinductivity that could be useful for bone tissue engineering.

The effect of hydrofluoric acid treatment on titanium implant osseointegration in ovariectomized rats

This study aimed to investigate the effects of hydrofluoric acid (HF) treatment of grit-blasted Ti implants on osseointegration in ovariectomized (OVX) rats. After blasting with aluminium oxide particles, half implants were treated with 0.2 vol.% HF, and the other half were kept non-modified as control. The topographical and chemical changes of implant surface were determined by Scanning Electron Microscope, Atomic Force Microscope, and X-ray Photoemission Spectroscopy. 12 Weeks after bilateral ovariectomy, each rat accepted two implants in distal femora, with the control implant on the left and the fluoride-modified on the right. As a result, fluoride modification induced markedly changed surface topography and chemical composition. 12 Weeks after implant insertion, the fluoride-modified implants showed improved osseointegration compared to control, with the bone area ratio and bone-to-implant contact increased by 0.9- and 1.4-fold in histomorphometry, the bone volume ratio and percent osseointegration by 0.8- and 1.3-fold in micro-CT evaluation, and the maximal push-out force and ultimate shear strength by 1.2- and 2.0-fold in biomechanical test. These promising results indicated that HF treatment of Ti surface improved implant osseointegration in OVX rats, and suggested the feasibility of using fluoride modification to improve Ti implant osseointegration in osteoporotic bone.

Delivery of Growth Factors Using a Smart Porous Nanocomposite Scaffold to Repair a Mandibular Bone Defect

Implantation of a porous scaffold with a large volume into the body in a convenient and safe manner is still a challenging task in the repair of bone defects. In this study, we present a porous smart nanocomposite scaffold with a combination of shape memory function and controlled delivery of growth factors. The shape memory function enables the scaffold with a large volume to be deformed into its temporal architecture with a small volume using hot-compression and can subsequently recover its original shape upon exposure to body temperature after it is implanted in the body. The scaffold consists of chemically cross-linked poly(ε-caprolactone) (c-PCL) and hydroxyapatite nanoparticles. The highly interconnected pores of the scaffold were obtained using the sugar leaching method. The shape memory porous scaffold loaded with bone morphogenetic protein-2 (BMP-2) was also fabricated by coating the calcium alginate layer and BMP-2 on the surface of the pore wall. Under both in vitro and in vivo environmental conditions, the porous scaffold displays good shape memory recovery from the compressed shape with deformed pores of 33 μm in diameter to recover its porous shape with original pores of 160 μm in diameter. In vitro cytotoxicity based on the MTT test revealed that the scaffold exhibited good cytocompatibility. The in vivo micro-CT and histomorphometry results demonstrated that the porous scaffold could promote new bone generation in the rabbit mandibular bone defect. Thus, our results indicated that this shape memory porous scaffold demonstrated great potential for application in bone regenerative medicine.

Effects of electrospun submicron fibers in calcium phosphate cement scaffold on mechanical properties and osteogenic differentiation of umbilical cord stem cells.

Fibrous scaffolds are promising for tissue engineering because of the high surface area and fibrous features mimicking the extracellular matrix in vivo. Calcium phosphate cements (CPCs) can be injected and self-set in the bone defect. A literature search revealed that there have been no reports on stem cell seeding on CPC containing electrospun submicron fibers. The objective of this study was to investigate for the first time the effects of electrospun fibers in CPC on mechanical properties and human umbilical cord mesenchymal stem cell (hUCMSC) proliferation, osteogenic differentiation and mineralization. Poly(D,L-lactide-co-glycolide) fibers were made via an electrospinning technique to yield an average fiber diameter of 650 nm. The fibers were incorporated into CPC consisting of tetracalcium phosphate, dicalcium phosphate anhydrous and chitosan lactate. Fiber volume fractions were 0%, 2.5%, 5% and 10%. CPC with 10% fibers had a flexural strength that was twice that of CPC without fibers, and a work-of-fracture (toughness) that was an order of magnitude larger than that of CPC without fibers. hUCMSCs proliferated rapidly and synthesized bone minerals when attached to the electrospun fiber-CPC scaffolds. Alkaline phosphatase, osteocalcin and collagen I expressions of hUCMSCs were doubled, while mineralization was increased by 40%, when fiber volume fraction in CPC was increased from 0% to 10%. The enhanced cell function was attributed to the high surface area and biomimetic features of the fiber-CPC scaffold. In conclusion, incorporating submicron fibers into CPC greatly improved the strength and toughness of the CPC. Creating submicron fibrous features in CPC was a useful method for enhancing the osteogenic differentiation and mineralization of stem cells. The novel electrospun fiber-CPC-hUCMSC construct is promising for stem cell delivery and bone tissue engineering.

Umbilical cord stem cells released from alginate–fibrin microbeads inside macroporous and biofunctionalized calcium phosphate cement for bone regeneration

The need for bone repair has increased as the population ages. The objectives of this study were to (1) develop a novel biofunctionalized and macroporous calcium phosphate cement (CPC) containing alginate-fibrin microbeads encapsulating human umbilical cord mesenchymal stem cells (hUCMSC) and, for the first time, (2) investigate hUCMSC proliferation and osteogenic differentiation inside the CPC. A macroporous CPC was developed using calcium phosphate powder, chitosan, and a gas-foaming porogen. Five types of CPC were fabricated: a CPC control, CPC+0.05% fibronectin (Fn), CPC+0.1% Fn, CPC+0.1% arginine-glycine-aspartate (RGD), and CPC+0.1% Fn+0.1% RGD. Alginate-fibrin microbeads containing 10(6) hUCMSC per ml were encapsulated in the CPC paste. After the CPC had set, the degradable microbeads released hUCMSC within it. The hUCMSC proliferated inside the CPC, with the cell density after 21 days being 4-fold that on day1. CPC+0.1% RGD had the highest cell density, which was 4-fold that of the CPC control. The released cells differentiated along the osteogenic lineage and synthesized bone mineral. The hUCMSC inside the CPC+0.1% RGD construct expressed the genes alkaline phosphatase, osteocalcin and collagen I, at twice the level of the CPC control. Mineral synthesis by hUCMSC inside the CPC+0.1% RGD construct was 2-fold that in the CPC control. RGD and Fn incorporation in the CPC did not compromise its strength, which matched the reported strength of cancellous bone. In conclusion, degradable microbeads released hUCMSC which proliferated, differentiated and synthesized minerals inside the macroporous CPC. The CPC with RGD greatly enhanced cell function. The novel biofunctionalized and macroporous CPC-microbead-hUCMSC construct is promising for bone tissue engineering applications.

Sustained Release of Adiponectin Improves Osteogenesis Around Hydroxyapatite Implants by Suppressing Osteoclast Activity in Ovariectomized Rabbits

Lack of estrogen could lead to decreased bone mass and increased risk for osteoporosis, which has a negative influence on biomaterial implantation. Adiponectin (APN), an adipose-derived hormone, has been shown to increase bone density by inhibiting osteoclast formation and promoting the formation of osteoblasts. This study was designed to investigate the direct effects of APN released from the Matrigel controlled-release system on the activity of rabbit mature osteoclasts and osteoclast precursor RAW264.7 cells in vitro, and to determine its effects by improving osteogenesis around the hydroxyapatite (HA) implant in ovariectomized (OVX) rabbits. APN+Matrigel+HA, APN+HA, Matrigel+HA and HA were implanted into mandibular defects of OVX rabbits. At 4 weeks after implantation, the mandibles were examined by histology, microcomputed tomography and biomechanical testing. The results demonstrated that Matrigel extended the length of APN released to achieve long-term persistence. The sustained release of APN suppressed the osteoclastic activity both in vitro and in vivo, and improved the peri-implant osteogenesis in OVX rabbits, while the short-term APN treatment did not. Sustained release of APN may be an effective strategy to improve the restoration of bone defects by the use of HA materials under osteoporotic conditions in which osteoclasts are highly activated.

Effect of particle size on osteoinductive potential of microstructured biphasic calcium phosphate ceramic

Material factors such as chemistry, surface microstructure and geometry have shown their influence on osteoinduction of calcium phosphate ceramics. Hereby we report that osteoinduction of a micro-structured biphasic calcium phosphate ceramic (BCP) has a relation with the particle sizes. BCP particles with the size of 212-300 µm, 106-212 µm, 45-106 µm, and smaller than 45 µm were prepared and implanted in paraspinal muscle of dogs for 12 weeks. Histological evaluation of the explants showed abundant bone in all samples with particle size of 212-300 µm, 106-212 µm, and 45-106 µm, while no bone was seen in any sample having particle size smaller than 45 µm. Bone was formed as early as 3 weeks after implantation in implants having BCP particles bigger than 45 µm and the volume of the formed bone was similar among the implants with particles larger than 45 µm after 12 weeks implantation. The results herein show that a size limitation of microstructured calcium phosphate ceramic particles for osteoinduction. It is most likely that the particle size affect inductive bone formation via macroporous structures for body fluid infiltration, cell/tissue ingrowth and angiogenesis.

The physicochemical/biological properties of porous tantalum and the potential surface modification techniques to improve its clinical application in dental implantology.

More rapid restoration and more rigid functionality have been pursued for decades in the field of dental implantology. Under such motivation, porous tantalum has been recently introduced to design a novel type of dental implant. Porous tantalum bears interconnected porous structure with pore size ranging from 300 to 600μm and a porosity of 75-85%. Its elastic modulus (1.3-10GPa) more closely approximates that of natural cortical (12-18GPa) and cancellous bone (0.1-0.5GPa) in comparison with the most commonly used dental materials, such as titanium and titanium alloy (106-115GPa). Porous tantalum is highly corrosion-resistant and biocompatible. It can significantly enhance the proliferation and differentiation of primary osteoblasts derived from elderly people than titanium. Porous tantalum can allow bone ingrowth and establish not only osseointegration but also osseoincorporation, which will significantly enhance the secondary stability of implants in bone tissue. In this review, we summarize the physicochemical, mechanical and biological properties of porous tantalum. We further discuss the performance of current tantalum dental implants and present the methodologies of surface modifications in order to improve their biological performance.

The effect of surface composition of titanium films on bacterial adhesion

We show that bacterial adhesion on titanium (Ti) films could be radically minimized by tailoring the surface chemical stoichiometry of the films. Using a dc magnetron sputtering system, Ti films with various surface compositions, such as oxide and nitride combinations, were prepared by controlling processing parameters such as cathode power, sputtering pressure and base vacuum. The surface topography of the films was observed to be smooth and similar in all the films prepared under different conditions. The order of adhesion of the oral bacterial Porphyromonas gingivalis varied with the surface chemical stoichiometry of the Ti films. Few surface stoichiometries of typical oxide nitride combination resulted in nearly nil bacterial adhesion.