Hydroxyapatite/poly(ɛ-caprolactone) double coating on magnesium for enhanced corrosion resistance and coating flexibility

Hydroxyapatite was deposited on pure magnesium (Mg) with a flexible poly(ɛ-caprolactone) interlayer to reduce the corrosion rate of Mg and enhance coating flexibility. The poly(ɛ-caprolactone) interlayer was uniformly coated on Mg by a spraying method, followed by hydroxyapatite deposition on the poly(ɛ-caprolactone) using an aerosol deposition method. In scanning electron microscopy observations, inorganic/organic composite-like structure was observed between the hydroxyapatite and poly(ɛ-caprolactone) layers, resulting from the collisions of hydroxyapatite particles into the poly(ɛ-caprolactone) matrix at the initial stage of the aerosol deposition. The corrosion resistance of the coated Mg was examined using potentiodynamic polarization tests. The hydroxyapatite/poly(ɛ-caprolactone) double coating remarkably improved the corrosion resistance of Mg in Hank’s solution. In the in vitro cell tests, the coated Mg showed better cell adhesion compared with the bare Mg due to the reduced corrosion rate and enhanced biocompatibility. The stability and flexibility of hydroxyapatite/poly(ɛ-caprolactone) double coating was investigated by scanning electron microscopy inspections after the coated Mg was deformed. The hydroxyapatite coating on the poly(ɛ-caprolactone) interlayer revealed enhanced coating stability and flexibility without cracking or delamination during bending and stretching compared with the hydroxyapatite single coating. These results demonstrated that the hydroxyapatite/poly(ɛ-caprolactone) double coating significantly improved the surface corrosion resistance of Mg and enhanced coating flexibility for use of Mg as a biodegradable implant.

Use of a poly(ether imide) coating to improve corrosion resistance and biocompatibility of magnesium (Mg) implant for orthopedic applications

This study investigated the utility of poly(ether imide) (PEI) coating for improving the corrosion resistance and biocompatibility of magnesium (Mg) implants for orthopedic application. In particular, the microstructure of the PEI coating layers was controlled by the adjustment of the temperature used to dry the spin-coated wet PEI films. When a wet PEI film was dried at 4°C, a relatively thick and porous coating layer was achieved as a result of an extensive exchange of the solvent with water in a moist environment. In contrast, when a wet PEI film was dried at 70°C, a relatively thin and dense layer was created due to the faster evaporation of the solvent with a negligible exchange of the solvent with water. The porous PEI coating layer showed higher stability than did the dense one when immersed in a simulated body fluid (SBF), which was presumably attributed to the formation of chemical bonding between the PEI and the Mg substrate. Both the porous and the dense PEI coated Mg specimens showed significantly improved in vitro biocompatibility, which were assessed in terms of cell attachment, proliferation and differentiation. However, interestingly, the dense PEI coating layer showed greater cell proliferation and differentiation than did the porous layer. .

Reverse freeze casting: a new method for fabricating highly porous titanium scaffolds with aligned large pores

Highly porous titanium with aligned large pores up to 500 μm in size, which is suitable for scaffold applications, was successfully fabricated using the reverse freeze casting method. In this process we have newly developed, the Ti powders migrated spontaneously along the pre-aligned camphene boundaries at a temperature of 45.5°C and formed a titanium-camphene mixture with an aligned structure; this was followed by freeze drying and sintering. As the casting time increased from 24 to 48 h, the initial columnar structures turned into lamellar structures, with the porosity decreasing from 69 to 51%. This reduction in porosity caused the compressive yield strength to increase from 121 to 302 MPa, with an elastic modulus of the samples being in the range of 2-5 GPa. In addition, it was demonstrated that reverse freeze casting can also be successfully applied to various other raw powders, suggesting that the method developed in this work opens up new avenues for the production of a range of porous metallic and ceramic scaffolds with highly aligned pores.

In vitro evaluation of migratory capacity of human liver stem cells influenced by soluble factors

Although several studies have addressed the engraftment of stem cells into the liver, the exact mechanisms in vivo remain unclear. In this study, we investigated the effects of soluble factors on cell migration using purified, expanded human liver stem cells (HLSCs) obtained from a pediatric liver resection. Using a in vitro transwell migration assay, we evaluated the migratory capacity of HLSCs under the influence of the cytokines tumor necross factor- [TNF]-α, interleukin [IL]-6, and interferon (IFN)-γ or the growth factors vascular endothelial growth factor [VEGF], basic fibroblast growth factor [bFGF], and hepatocyte growth factor [HGF], which are known to be highly secreted during liver injury. We also evaluated the migratory capacity indirectly influenced by cryopreserved human hepatocytes. The migration across the transwell membrane was promoted by VEGF, bFGF, TNF-α, IFN-γ, or hepatocytes. The cryopreserved human hepatocytes especially induced significant migration. These results suggested the presence of unidentified soluble factors from hepatocytes. This experiment described a reliable system for quantitative migration studies to broaden our understanding of the directional nature of cell migration.

The impact of immobilization of BMP-2 on PDO membrane for bone regeneration

Poly(dioxanone) (PDO) is colorless, crystalline, a biodegradable synthetic polymers that is used for biomedical applications, such as surgical sutures, cardiovascular applications, orthopedics, and plastic surgery. Recently, bone morphogenetic protein-2 (BMP-2) is widely used for bone tissue engineering. For the first time we report here on the in vitro performance of an electrospun PDO membrane immobilized with BMP-2. Immobilized BMP-2 on PDO membrane enhanced ALPase activity, the osteogenic differentiation gene expressions as well as cell attachment, except cell proliferation when compared to that of PDO membrane alone. These results suggest that PDO membrane with BMP-2 is helpful to promote bone healing and regeneration.

Silica-chitosan hybrid coating on Ti for controlled release of growth factors

A hybrid material composed of a silica xerogel and chitosan was coated on Ti for the delivery of growth-factors. Fibroblast growth factor (FGF) and green fluorescence protein were incorporated into the coatings for hard tissue engineering. Silica was chosen as a coating material because of its high surface area as well as its good bioactivity. Chitosan provides mechanical stability and contributes to the control of the release rate of the growth factors. When the chitosan composition was 30% or more, the hybrid coating was stable physically and mechanically. The release of the growth-factors, observed in phosphate buffer solution at 37°C, was strongly dependent on the coating material. The hybrid coating containing FGF showed significantly improved osteoblast cell responses compared to the pure xerogel coating with FGF or the hybrid coating without FGF. These results indicate that the hybrid coating is potentially very useful in enhancing the bioactivity of metallic implants by delivering growth-factors in a controlled manner.

Fibrous membrane of nano-hybrid poly-L-lactic acid/silica xerogel for guided bone regeneration

Nanofibrous membranes, consisting of a poly(L-lactic acid) (PLLA)-silica xerogel hybrid material, were successfully fabricated from a hybrid sol using the electrospinning technique for guided bone regeneration (GBR) application. These hybrid nanofibers exhibited a homogeneous and continuous morphology, with a nano-sized dispersed silica xerogel phase in the PLLA fiber matrix. The mechanical properties, such as the tensile strength and the elastic modulus, were improved as the silica xerogel content increased up to 40%. All of the hybrid membranes exhibited highly hydrophilic surfaces and good proliferation levels. After culturing for 13 days, the cells that were cultured on the hybrid membranes exhibited a significantly higher ALP activity compared to the pure PLLA membrane. Moreover, the in vivo animal experiments that used the rat calvarial defect model revealed a remarkably improved bone regeneration ability for the hybrid membrane compared to pure PLLA. These results demonstrated the feasibility of these hybrid membranes for efficient GBR.

Hydroxyapatite coating on magnesium with MgF₂ interlayer for enhanced corrosion resistance and biocompatibility

Hydroxyapatite (HA) was coated onto pure magnesium (Mg) with an MgF(2) interlayer in order to reduce the surface corrosion rate and enhance the biocompatibility. Both MgF(2) and HA were successfully coated in sequence with good adhesion properties using the fluoride conversion coating and aerosol deposition techniques, respectively. In a simulated body fluid (SBF), the double layer coating remarkably enhanced the corrosion resistance of the coated Mg specimen. The in vitro cellular responses of the MC3T3-E1 pre-osteoblasts were examined using a cell proliferation assay and an alkaline phosphatase (ALP) assay, and these results demonstrated that the double coating layer also enhanced cell proliferation and differentiation levels. In the in vivo study, the HA/MgF(2) coated Mg corroded less than the bare Mg and had a higher bone-to-implant contact (BIC) ratio in the cortical bone area of the rabbit femora 4 weeks after implantation. These in vitro and in vivo results suggested that the HA coated Mg with the MgF(2) interlayer could be used as a potential candidate for biodegradable implant materials.

Deposition of TiN films on Co-Cr for improving mechanical properties and biocompatibility using reactive DC sputtering

This study reports the deposition of TiN films on Co-Cr substrates to improve the substrates' mechanical properties and biological properties. In particular, the argon to nitrogen (Ar:N(2)) gas flow ratio was adjusted to control the microstructure of the TiN films. A Ti interlayer was also used to enhance the adhesion strength between the Co-Cr substrate and TiN films. A series of TiN films, which are denoted as TiN-(Ar/N(2))1:1, Ti/TiN-(Ar/N(2))1:1, and Ti/TiN-(Ar:N(2))1:3, were deposited by reactive DC sputtering. All the deposited TiN films showed a dense, columnar structure with a preferential orientation of the (200) plane. These TiN films increased the mechanical properties of Co-Cr, such as the critical load during scratch testing, hardness, elastic modulus and plastic resistance. In addition, the biological properties of the Co-Cr substrates, i.e. initial attachment, proliferation, and cellular differentiation of the MC3T3-E1 cells, were improved considerably by deposition of the TiN films. These results suggest that TiN films would effectively enhance both the mechanical properties and biocompatibility of biomedical Co-Cr alloys.

Effect of fluorine addition on the biological performance of hydroxyapatite coatings on Ti by aerosol deposition

Dense and well-adherent fluoridated hydroxyapatite [Ca10(PO4)6(OH)2− xF x, FHA] coatings with various amounts of fluorine contents ( x = 0, 0.5, 1.0, 1.5, and 2.0) were deposited on commercially available pure titanium by aerosol deposition using FHA powders in order to investigate the effect of fluorine content on the properties of the coatings. FHA powders with different compositions were synthesized by solid-state reactions of hydroxyapatite (HA) and fluorapatite (FA) powders at various ratios. X-ray diffraction and Fourier transform infrared spectroscopy results showed that fluoride ions were successfully incorporated into the HA lattice for both the FHA powders and the FHA coatings. Scanning electron microscopy analysis revealed dense microstructures and good substrate adhesion of the coatings with high adhesion strengths of more than 33.1 MPa. The dissolution behavior in a tris-buffered saline solution indicated that the dissolution rate of the FHA coatings decreased as a result of increasing the fluorine content in the coatings. In addition, in vitro cellular tests, including cell attachment, proliferation, and alkaline phosphatase activity of MC3T3-E1 preosteoblast cells grown on the coatings, demonstrated that an FHA coating with a moderate degree of F− substitution, x = 1.0, had a stronger stimulating effect on cell proliferation and differentiation. These results suggested that there exists an optimum fluorine content level in the FHA coatings for the best long-term stability and cellular responses.

Enhancing biocompatibility and corrosion resistance of Mg implants via surface treatments

Oxide coating layers were formed on a pure magnesium (Mg) substrate through anodization and micro-arc oxidation (MAO) in order to enhance the biocompatibility and reduce the degradation rate. A thin, smooth MgO coating layer was formed after the anodization. On the other hand, when the Mg was treated using the MAO process, a relatively thick, rough MgO layer was formed. The corrosion properties were investigated using electrochemical and ion release tests in a simulated body fluid. Both the anodization and the MAO treatment enhanced the corrosion resistance of the Mg specimens. However, the MgO layers that formed on the surface were not stable enough to render favorable environments for cell growth. The anodized and MAO-treated specimens were post-treated in a cell-culturing medium in order to improve the stability of the coating layer. The biocompatibility was evaluated using in vitro cell tests, including cell attachment, DNA measurement, and alkaline phosphatase (ALP) activity tests. The DNA levels of the surface-treated Mg were about 6–10 times higher than the bare Mg. The ALP activity levels were also more than double after either the anodization or the MAO followed by the post-treatments. These results demonstrated that the biocompatibility and the corrosion resistance of Mg were significantly improved by the series of surface treatments.

Nanostructured poly(epsilon-caprolactone)-silica xerogel fibrous membrane for guided bone regeneration

A novel fibrous membrane was developed for guided bone regeneration (GBR) through electrospinning a uniform poly(epsilon-caprolactone) (PCL)-silica hybrid sol. The membrane was composed of fibers with a mean diameter of approximately 400 nm. The hybrid fibers were nano-sized with uniform patterns throughout the fibers, in contrast to the homogeneous structure of pure PCL fibers. The tensile strengths and elastic moduli of the membranes were significantly enhanced with increasing silica content up to 40%. The surfaces of the hybrid membranes were highly hydrophilic with a water contact angle of almost zero. The hybrid membranes possessed excellent in vitro cellular responses in terms of proliferation and differentiation of pre-osteoblast cells. The in vivo animal tests not only confirmed excellent biocompatibility but also revealed bioresorbability of the membranes. These mechanical and biomedical properties make the hybrid membranes very attractive as GBR applications.

Silica xerogel-chitosan nano-hybrids for use as drug eluting bone replacement

Silica xerogel-chitosan hybrids containing vancomycin were fabricated by the sol-gel process at room temperature and their potential as a drug eluting bone replacement was evaluated in terms of their mechanical properties and drug release behaviors. Regardless of the content of chitosan, all of the prepared hybrids had a uniform mesoporous structure, which would allow the effectual loading of vancomycin. As the content of chitosan was increased, the strength, strain to failure, and work of fracture of the hybrids were significantly enhanced, while the elastic modulus was decreased. These changes in the mechanical properties were mainly attributed to the mitigation of the brittleness of the silica xerogel through its hybridization with the flexible chitosan phase. In addition, the initial burst-effect was remarkably reduced by increasing the content of chitosan. The hybrids with more than 30% chitosan could release the vancomycin for an extended period of time in a controlled manner.

In vitro/in vivo biocompatibility and mechanical properties of bioactive glass nanofiber and poly(epsilon-caprolactone) composite materials

In this study, a poly(epsilon-caprolactone) (PCL)/bioactive glass (BG) nanocomposite was fabricated using BG nanofibers (BGNFs) and compared with an established composite fabricated using microscale BG particles. The BGNFs were generated using sol-gel precursors via the electrospinning process, chopped into short fibers and then incorporated into the PCL organic matrix by dissolving them in a tetrahydrofuran solvent. The biological and mechanical properties of the PCL/BGNF composites were evaluated and compared with those of PCL/BG powder (BGP). Because the PCL/BG composite containing 20 wt % BG showed the highest level of alkaline phosphatase (ALP) activity, all evaluations were performed at this concentration except for that of the ALP activity itself. In vitro cell tests using the MC3T3 cell line demonstrated the enhanced biocompatibility of the PCL/BGNF composite compared with the PCL/BGP composite. Furthermore, the PCL/BGNF composite showed a significantly higher level of bioactivity compared with the PCL/BGP composite. In addition, the results of the in vivo animal experiments using Sprague-Dawley albino rats revealed the good bone regeneration capability of the PCL/BGNF composite when implanted in a calvarial bone defect. In the result of the tensile test, the stiffness of the PCL/BG composite was further increased when the BGNFs were incorporated. These results indicate that the PCL/BGNF composite has greater bioactivity and mechanical stability when compared with the PCL/BG composite and great potential as a bone regenerative material.

Mechanical and in vitro biological performances of hydroxyapatite-carbon nanotube composite coatings deposited on Ti by aerosol deposition

Hydroxyapatite (HA)-carbon nanotube (CNT) composite coatings on Ti plate, produced by aerosol deposition using HA-CNT powders, were developed for biomedical applications. For the deposition process HA-CNT powder mixtures with CNT contents of 1 and 3 wt.% were used. Dense coatings with a thickness of 5 microm were fabricated, irrespective of the content of CNTs. No pores or microcracks were observed in the coatings. The coatings had good adhesion to the substrate, exhibiting a high adhesion strength, ranging from 27.3 to 29.0 MPa. Microstructural observation using field-emission gun scanning electron microscopy and transmission electron microscopy showed that CNTs with a typical tubular structure were found in the HA-CNT composite coatings. Nanoindentation tests revealed that the mechanical properties, such as the hardness and elastic modulus, were significantly improved by the addition of the CNTs to the HA coating. In addition, the proliferation and alkaline phosphatase (ALP) activity of MC3T3-E1 pre-osteoblast cells grown on the HA-CNT composite coatings were higher than those on the bare Ti and pure HA coating. The ALP activity of the composite coatings considerably improved as the CNT content increased. These results suggest that CNTs would be an effective reinforcing agent to enhance both the mechanical and biological performances of HA coatings.

Formation of hydroxyapatite within porous TiO(2) layer by micro-arc oxidation coupled with electrophoretic deposition

Micro-arc oxidation (MAO) is commonly used to modify the surface of Ti-based medical implants with a bioactive and porous titanium oxide (TiO(2)) layer. This study reports a novel method of incorporating hydroxyapatite (HA) within the TiO(2) layer by coupling MAO with an electrophoretic deposition (EPD) process. A HA-incorporated, porous TiO(2) layer was produced successfully on the Ti substrate using the EPD-coupled MAO treatment, as confirmed by electron microscopy observations. Addition of ethanol to the electrolyte solution containing the fine HA particles was essential to reduce the level of gaseous emission on the anode, which obstructs the attachment of HA particles. In vitro cellular assays showed that the incorporation of HA significantly improved the osteoblastic activity on the coating layer.

Identification and characterization of a novel heparin-binding peptide for promoting osteoblast adhesion and proliferation by screening an Escherichia coli cell surface display peptide library

Heparin/heparan sulfate (HS) plays a key role in cellular adhesion. In this study, we utilized a 12-mer random Escherichia coli cell surface display library to identify the sequence, which binds to heparin. Isolated insert analysis revealed a novel heparin-binding peptide sequence, VRRSKHGARKDR, designated as HBP12. Our analysis of the sequence alignment of heparin-binding motifs known as the Cardin-Weintraub consensus (BBXB, where B is a basic residue) indicates that the HBP12 peptide sequence contains two consecutive heparin-binding motifs (i.e. RRSK and RKDR). SPR-based BIAcore technology demonstrated that the HBP12 peptide binds to heparin with high affinity (KD = 191 nM). The HBP12 peptide is found to bind the cell surface HS expressed by osteoblastic MC3T3 cells and promote HS-dependent cell adhesion. Moreover, the surface-immobilized HBP12 peptide on titanium substrates shows significant increases in the osteoblastic MC3T3-E1 cell adhesion and proliferation.