Xiangdong Zhu

Effect of surface structure on protein adsorption to biphasic calcium-phosphate ceramics in vitro and in vivo

Protein adsorption affects the function of cells and determines the bioactivity of biomaterial implants. Surface structure and properties of materials determine the behavior of protein adsorption. In the present study, two biphasic calcium-phosphate ceramics (BCPs) with different surface structures were fabricated by pressing and H2O2 foaming methods. Their surface characteristics were analyzed and the in vitro and in vivo protein adsorption on them was investigated. Porous BCP showed higher ability to adsorb proteins, and transforming growth factor-beta1 (TGF-beta1) adsorption notably increased with increasing in vivo implantation time. The strong affinity of BCP to TGF-beta1 might provide important information for exploring the mechanism of the osteoinduction of calcium phosphates.

Effect of phase composition and microstructure of calcium phosphate ceramic particles on protein adsorption

The biological performance of biomaterials is strongly influenced by their protein adsorption characteristics, which are related to the structures and properties of both the biomaterial and the protein. In the present study two groups of hydroxyapatite (HA) and biphasic calcium phosphate (BCP) ceramic powders were fabricated by different drying processes. The roles of the phase composition and microstructure of the powders in the adsorption of various model proteins were evaluated. The experimental results showed that BCP always had a higher ability to adsorb fibrinogen, insulin or type I collagen (Col-I) than HA. The microporosity and micropore size of the CaP particles also had a strong impact on their protein adsorption characteristics. HA and BCP particles with higher microporosities and/or more micropores >20 nm in diameter could adsorb more fibrinogen or insulin. However, amounts of adsorbed Col-I were largely unaffected by the microstructure of HA and BCP particles.

RETRACTED: Effect of nanostructure on osteoinduction of porous biphasic calcium phosphate ceramics

In order to evaluate the effect of the nanostructure of calcium phosphate ceramics on osteoinductive potential, porous biphasic calcium phosphate (BCP) ceramics with a nano- or submicron structure were prepared via microwave sintering and compared to conventional BCP ceramics. The selective protein adsorption of bovine serum albumin and lysozyme (LSZ) and the osteogenic differentiation of human mesenchymal stem cells in vitro was investigated. Porous BCP nanoceramics showed higher ability to adsorb proteins, especially low molecular weight protein of LSZ, than conventional BCP ceramics, and the BCP nanoceramics promoted bone sialoprotein expression more than conventional BCP did. Further in vivo study to investigate ectopic bone formation and bone repair efficiency proved the highly osteoinductive potential of nanostructured BCP ceramics. The results suggest that nanostructured BCP ceramics have the potential to become a new generation of bioceramics for bone tissue engineering grafts.

Enhanced effect of β-tricalcium phosphate phase on neovascularization of porous calcium phosphate ceramics: In vitro and in vivo evidence

Neovascularization plays a key role in bone repair and regeneration. In the present study, four types of porous calcium phosphate (CaP) ceramics, namely hydroxyapatite (HA), biphasic calcium phosphates (BCP-1 and BCP-2) and β-tricalcium phosphate (β-TCP), with HA to β-TCP ratios of 100/0, 70/30, 30/70 and 2/98, respectively, were investigated in terms of their angiogenic induction. The in vitro cell culture revealed that the ceramics could promote proliferation and angiogenesis of human umbilical vein endothelial cells (HUVECs). This result could be achieved by stimulating CCD-18Co human fibroblasts to secrete angiogenic factors (vascular endothelial growth factor, basic fibroblast growth factor and transforming growth factor-β) as a paracrine effect, as well as by up-regulating HUVECs to express these angiogenic factors and their receptors (KDR, FGFR1 and ACVRL1) and the downstream eNOS as an autocrine effect. These effects were more significant in β-TCP and BCP-2, which had a higher content of β-TCP phase. In the in vivo implantation into the thigh muscles of mice, the process of neovascularization of the ceramics was initiated at 2 weeks and the mature vascular networks were formed at 4 weeks as visualized by hematoxylin and eosin staining and scanning electron microscopy. Microvessel density count confirmed that β-TCP and BCP-2 induced more microvessels to form than HA or BCP-1. This phenomenon was further confirmed by the significantly up-regulated expressions of angiogenesis-related genes in the ingrowth of cells into the inner pores of the two ceramics. All the results confirmed the angiogenic induction of porous CaP ceramics, and a higher content of β-TCP phase had an enhanced effect on the neovascularization of the ceramics.

Effect of phase composition on protein adsorption and osteoinduction of porous calcium phosphate ceramics in mice

The purpose of this study was to investigate the effect of phase compositions of porous calcium phosphate (CaP) ceramics on their protein adsorption behaviors in vitro and osteoinductive potentials in vivo in mice. Under competitive conditions, a high adsorption of bone morphogenetic protein 2 (BMP-2) was observed at a high initial concentration of BMP-2 in the multi-protein solution on all the four types of ceramics, indicating their strong affinity for BMP-2. No significant difference in BMP-2 adsorption between the ceramics was noted, indicating that phase composition could have little influence on BMP-2 adsorption. After implantation into the thigh muscles of mice for 45 and 90 days, the histological and histomorphometric analyses showed that porous biphasic calcium phosphate (BCP) ceramic consisting of 30% hydroxyapatite HA and 70% tricalcium phosphate (β-TCP), i.e. BCP-2 had stronger osteoinductive ability than the other three groups of ceramics. The immunohistochemical staining showed the highest expression of BMP-2 and osteocalcin (OCN) in BCP-2 group. Osteoinduction of porous CaP ceramics might be influenced by the amount of BMP-2 present in the local microenvironment in the implant, which was regulated by the phase composition of the ceramics. BCP-2 promoted the highest expression of BMP-2 and then showed the strongest osteoinduction in mice.

Osteoinduction of porous titanium: A comparative study between acid-alkali and chemical-thermal treatments

In this study, a slurry foaming method was developed to fabricate porous titanium, and two different surface treatments were applied to investigate their effects on the osteoinduction of the implants. Three types of implants, that was porous titanium with no treatment, with chemical-thermal treatment (CTPT), and with acid-alkali treatment (AAPT), were implanted in the dorsal muscles of adult dogs for 3 and 5 months. After implantation for 3 months, new bone was only found in the inner pores of AAPT by histological analysis and field emission scanning electron microscopy observation. After implantation for 5 months, new bone was also found in CTPT, but it was absent in AAPT. This study not only confirmed that porous titanium with appropriate surface treatments could possess osteoinduction but also showed that its osteoinductive potential was tightly related to the surface treatment. As a simpler method, acid-alkali treatment could endow porous titanium with faster osteoinduction, and AAPT might have potential in clinical application.

Dynamic competitive adsorption of bone-related proteins on calcium phosphate ceramic particles with different phase composition and microstructure.

The biocompatibility and bioactivity of biomaterials used for hard tissue repair are closely related to their adsorption capacities for bone-related proteins. In the present study, three types of calcium phosphate (CaP) ceramic particles with different phase composition or microstructure were fabricated, and their protein adsorption abilities were investigated by a self-made device under the simulated dynamic physiological circumstance. The results of X-ray diffraction, field emission scanning electron microscopy, mercury penetration test, and nitrogen sorption test showed that the irregular hydroxyapatite (HA) ceramic particles obtained by conventional drying and sintering (named as HA-C) had fewer micropores and lower specific surface area (SSA) than did the spherical HA or biphasic calcium phosphate (BCP) ceramic particles made by spray drying and sintering (named as HA-S and BCP-S, respectively). The dynamic protein adsorption study proved that both the phase composition and microstructure of CaP ceramic particles affected their adsorption capacities for those bone-related proteins. The spherical HA-S and BCP-S particles with abundant micropores and high SSA showed higher adsorption of serum proteins, including fibronectin and vitronectin, than the irregular HA-C did. On the other hand, in spite of the relatively high concentration of bovine serum albumin (BSA) in the binary bone morphogenetic protein 2 (BMP-2)/BSA solution, BMP-2 adsorption on the three CaP ceramic particles increased with the increase in its initial concentration. Similarly, HA-S and BCP-S particles had a larger amount of the adsorbed BMP-2 per gram solid than HA-C did. Therefore, it could be believed that the difference of various CaP ceramics in the phase composition and microporous structure would affect their binding capacity for those bone-related proteins and thus lead to their difference in osteoinduction.

An improved polymeric sponge replication method for biomedical porous titanium scaffolds

Biomedical porous titanium (Ti) scaffolds were fabricated by an improved polymeric sponge replication method. The unique formulations and distinct processing techniques, i.e. a mixture of water and ethanol as solvent, multiple coatings with different viscosities of the Ti slurries and centrifugation for removing the extra slurries were used in the present study. The optimized porous Ti scaffolds had uniform porous structure and completely interconnected macropores (~365.1μm). In addition, two different sizes of micropores (~45.4 and ~6.2μm) were also formed in the skeleton of the scaffold. The addition of ethanol to the Ti slurry increased the compressive strength of the scaffold by improving the compactness of the skeleton. A compressive strength of 83.6±4.0MPa was achieved for a porous Ti scaffold with a porosity of 66.4±1.8%. Our cellular study also revealed that the scaffolds could support the growth and proliferation of mesenchymal stem cells (MSCs).

Fabrication of porous titanium scaffolds by stack sintering of microporous titanium spheres produced with centrifugal granulation technology.

Microporosity plays a key role in bioactivity and osteoinductivity of a biomaterial scaffold. A simple new approach to fabricating load-bearing porous titanium (Ti) scaffolds with uniform porous structure, highly controllable pore size and excellent biocompatibility was developed in the present study. This method was based on stack sintering of microporous Ti spheres produced with centrifugal granulation of commercial Ti powders. Macropores (180.0-341.8 μm) and micropores (6.1-11.8 μm) of the scaffolds were dependent on the sizes of the Ti spheres and the Ti powders, respectively. The compressive strength of the scaffolds (83.4-108.9 MPa) was high enough for the repair of load-bearing bone defects. Besides, the abundant micropores occurred on the rough and convex surface of the Ti spheres in the scaffolds were more favorable for adsorption of serum proteins, and thus promoted the growth of mesenchymal stem cells (MSCs).

The enhanced effect of surface microstructured porous titanium on adhesion and osteoblastic differentiation of mesenchymal stem cells.

Porous titanium with appropriate surface treatments can be osteoinductive. To investigate the effect of surface treatments of porous titanium on the attachment and differentiation of mesenchymal stem cells (MSCs), two kinds of surface microstructured porous titaniums, H2O2/TaCl5 treated one (HTPT), and H2O2/TaCl5 and subsequent simulated body fluid (SBF) treated one (STPT) were fabricated, and non-treated one (NTPT) was used as control. The morphology, specific surface area (SSA), pore distribution and mechanical strength of these materials were characterized respectively, and the results showed that H2O2/TaCl5 treatment led to a significant increase in both SSA and micropores of HTPT, and the further SBF immersion resulted in the formation of a layer of bone-like apatite on the surface of STPT. Although the surface treatments had a little negative impact on the compressive strength and elasticity modulus of porous titanium, the mechanical strength of HTPT or STPT was enough for the bone defect repair of the load-bearing sites. The protein adsorption and cell adhesion experiments confirmed that the microstructured surface notably enhanced porous titanium’s protein binding capacity and promoted MSCs adhesion on the surface. More importantly, cell differentiation experiments proved that the microstructured surface evidently elevated the osteoblastic gene expressions of MSCs compared to NTPT. The enhanced biological effect by the surface treatments was more robust on STPT. Therefore, our results suggest that the microstructured surface has great potential for promoting MSCs differentiation towards osteoblasts, giving excellent support for the osteoinduction of porous titanium with appropriate surface treatments.