Young Hag Koh

The electron beam deposition of titanium on polyetheretherketone (PEEK) and the resulting enhanced biological properties

The surface of polyetheretherketone (PEEK) was coated with a pure titanium (Ti) layer using an electron beam (e-beam) deposition method in order to enhance its biocompatibility and adhesion to bone tissue. The e-beam deposition method was a low-temperature coating process that formed a dense, uniform and well crystallized Ti layer without deteriorating the characteristics of the PEEK implant. The Ti coating layer strongly adhered to the substrate and remarkably enhanced its wettability. The Ti-coated samples were evaluated in terms of their in vitro cellular behaviors and in vivo osteointegration, and the results were compared to a pure PEEK substrate. The level of proliferation of the cells (MC3T3-E1) was measured using a methoxyphenyl tetrazolium salt (MTS) assay and more than doubled after the Ti coating. The differentiation level of cells was measured using the alkaline phosphatase (ALP) assay and also doubled. Furthermore, the in vivo animal tests showed that the Ti-coated PEEK implants had a much higher bone-in-contact (BIC) ratio than the pure PEEK implants. These in vitro and in vivo results suggested that the e-beam deposited Ti coating significantly improved the potential of PEEK for hard tissue applications.

In vitro/in vivo biocompatibility and mechanical properties of bioactive glass nanofiber and poly(ε-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.

Effect of CaF2 on densification and properties of hydroxyapatite-zirconia composites for biomedical applications

Hydroxyapatite (HA) composites with zirconia (ZrO2) up to 40 vol% were fabricated with the addition of CaF2. The sinterability of the composites was found to be enhanced markedly by the addition of small amounts of CaF2 (< 5 vol%). Decomposition of HA to beta-TCP was suppressed due to the substitution of F- for OH-, consequently forming fluor-hydroxyapatite (FHA) solid solution. This suppression of decomposition allowed the production of a fully dense body, which retained both high flexural strength and fracture toughness. The osteoblast-like cell (MG63) response to these F- ion-containing composites displayed comparable cell viability to pure-HA by in vitro proliferation test.

Formation of hydroxyapatite within porous TiO2 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.

Nanostructured poly(ε-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.

Strontium substituted calcium phosphate biphasic ceramics obtained by a powder precipitation method

Strontium (Sr) substituted calcium phosphate ceramics were fabricated using a powder precipitation method. The Sr ions were added up to 8 mol % to replace the Ca ions during the powder preparation. Composition analysis showed that the added Sr was not fully incorporated within the as-precipitated apatite structure, presumably being washed out during the powder preparation. After calcination, the Sr containing powders were crystallized into apatite and tricalcium phosphate (TCP), that is, biphasic calcium phosphates were formed. The amount of TCP increased with increasing the Sr addition. The lattice parameters of the calcined powders increased gradually with Sr substitution in both the a- and c-axis. However, the obtained values deviated slightly from the calculated ones at higher Sr additions (>4%) due to the partial substitution of Sr ions. The microstructure of the sintered bodies changed with the Sr addition due to the formation of TCP. The Vickers hardness increased slightly from 5.2 to 5.5 MPa with increasing Sr addition, which was driven by the HA+TCP biphasic formation. The osteoblast-like cells cultured on the Sr-substituted biphasic sample spread and grew actively. The proliferation rate of the cells was higher in the samples containing more Sr. The alkaline phosphate activity of the cells was expressed to a higher degree with increasing Sr addition. These observations confirmed the enhanced cell viability and differentiation of the Sr-substituted biphasic calcium phosphate ceramics.

Nanofibrous gelatin–silica hybrid scaffolds mimicking the native extracellular matrix (ECM) using thermally induced phase separation

We herein propose a novel way of producing nanofibrous gelatin–silica hybrid scaffolds through thermally induced phase-separation (TIPS) particularly using mixtures of gelatin solution and silica sol, which can mimic the physical structure, chemical composition, and eventually functions of the native bone extracellular matrix (ECM). The gelatin solutions were homogeneously hybridized with various contents of a silica sol using simple magnetic stirring, which enabled the construction of a nanofibrous structure with a uniform distribution of the silica in the gelatin nanofibers. The nanofibrous gelatin–silica hybrid scaffolds showed much better mechanical properties and in vitro biodegradation stability and apatite-forming ability than the nanofibrous pure gelatin scaffold, which were achieved by the presence of a stiff, bioactive silica phase in the nanofibers and the interaction between the silica hydroxyls and the amino group in the gelatin polymer. In addition, the nanofibrous gelatin–silica hybrid scaffold with a silica content of 30 wt% showed reasonably high in vitro biocompatibility. These findings suggest that the highly porous, nanofibrous hybrid structure mimicking the bone ECM can provide an excellent matrix for bone tissue regeneration.

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.

Dynamic freeze casting for the production of porous titanium (Ti) scaffolds.

This paper proposes dynamic freeze casting as a new manufacturing technique for producing porous Ti scaffolds with a uniform porous structure and good ductility. In this method, Ti/camphene slurries with various initial Ti contents (15, 20, and 25 vol.%) were frozen at 44 °C for 12 h in rotation, which allowed for the extensive growth of camphene crystals and the uniform construction of walls made of Ti particles. All the fabricated samples showed spherical-like pores surrounded by dense Ti walls that were uniformly formed after sintering at 1300 °C for 2 h in a vacuum. The porosity decreased from 71 to 52 vol.% with an increase in Ti content from 15 to 25 vol.%, whereas the pore size decreased from 362 to 95 μm. On the other hand, the compressive strength and stiffness increased considerably from 57±4 to 183±6 MPa and from 1.3±0.5 to 5.0±0.8 GPa, respectively, due to the decrease in the porosity of the samples.

Fabrication of porous titanium scaffold with controlled porous structure and net-shape using magnesium as spacer.

This paper reports a new approach to fabricating biocompatible porous titanium with controlled pore structure and net-shape. The method is based on using sacrificial Mg particles as space holders to produce compacts that are mechanically stable and machinable. Using magnesium granules and Ti powder, Ti/Mg compacts with transverse rupture strength (~85 MPa) sufficient for machining were fabricated by warm compaction, and a complex-shape Ti scaffold was eventually produced by removal of Mg granules from the net-shape compact. The pores with the average size of 132-262 μm were well distributed and interconnected. Due to anisotropy and alignment of the pores the compressive strength varied with the direction of compression. In the case of pores aligned with the direction of compression, the compressive strength values (59-280 MPa) high enough for applications in load bearing implants were achieved. To verify the possibility of controlled net-shape, conventional machining process was performed on Ti/Mg compact. Compact with screw shape and porous Ti scaffold with hemispherical cup shape were fabricated by the results. Finally, it was demonstrated by cell tests using MC3T3-E1 cell line that the porous Ti scaffolds fabricated by this technique are biocompatible.