Li-Hsiang Perng

Hydroxyapatite coating on Ti6Al4V alloy using a sol-gel derived precursor

A simple rapid-heating method was successfully developed for calcium phosphate coatings on Ti6Al4V substrates deposited by using a sol–gel derived precursor. After five repetitions of coating procedures and heat treatment at 600 ◦ C, the formation of hydroxyapatite (HA) has been confirmed by X-ray diffractometry (XRD) analyses and the substrate material was found to be slightly oxidized. The residual organics, as revealed by X-ray photoelectron spectroscopy (XPS) spectra of a coating calcined at 400 ◦ C, might retard the formation of calcium phosphate phase, thus only small amount of calcium phosphate phase is present. After calcining at 600 ◦ C, calcium phosphate phase is the only one identifiable by XPS spectra. The adhesive strength of the five-coating layer on the substrate is around 60 MPa. The surface morphology of the thick HA film, calcined at 400 ◦ C and then consolidated at 600 ◦ C, displays porous structure arisen from rapid-heating of the bulk precursor.

Phase purity of sol–gel-derived hydroxyapatite ceramic

Calcium oxide was reported in the sol-gel-derived hydroxyapatite (HA) as an unavoidable major impurity. In this study phase purity of HA synthesized by sol-gel route was explored using precursors of calcium nitrate tetrahydrate and triethyl phosphate. Two different drying methods, the fast drying of as-prepared precursors and the slow drying of aged precursors were adopted as major processing variables. The dried gels were subsequently calcined up to 600 degrees C. In the calcined powder from fast-dried gel, X-ray diffraction (XRD) patterns revealed an intense CaO peak. For the slow-dried gel, thermogravimetric analysis revealed a 2-step weight-loss behavior during heating. XRD analysis of the calcined powder, corresponding to the second weight-loss step, showed major peaks of hydroxyapatite and a very weak CaO peak. P-31 NMR analysis indicated formation of calcium phosphate complex during aging. Complete incorporation of Ca(NO3)2 into the complex due to proper aging therefore diminishes CaO formation. It was also found that the minor CaO derived in the slow drying method can be easily and completely washed out just by distilled water.

Preparation of Porous HA/Beta-TCP Biphasic Bioceramic Using a Molten Salt Process

Bioceramics based on calcium phosphate is convinced to be well biocompatible after abundant researches. In this study, a biphasic bioceramic block (10 mm by 5 mm) (BBB) composed of hydroxyapatite and beta-tricalcium phosphate (40/60 in wt%) was prepared using a molten salt approach. At 800oC, the molten sodium chloride well helped the sintering of the precursor powders. A second calcination at 1000oC was then used to evaporate the salt so that a pure biphasic bioceramic block was obtained. This approach can provide porous BBB with 60% porosity, and powder x-ray diffraction patterns ensured the phasic compositions. However, the electrom probe microanalysis showed that around 2 at% of sodium was retained in the BBB. Scanning electron microscope revealed well-dispersed connective micro-pores of 3 micron and random macro-pores of >100 micron in the BBB. Because the salt was evaporated during the preparation of the BBB, the spatial voids were created, and, as a result. The compressive strength of the BBB can only reach a value of 3 MPa. Subcutaneous implantation of the BBB in mice showed that both acute and chronic imflammation were mild. In summary, the molten salt approach is feasible to fabricate biphasic calcium phosphate ceramics having controlled porosity.

Organic-Inorganic Hybrids of Collagen or Biodegradable Polymers with Hydroxyapatite

In this research we utilize three polymers, including collagen, di block PEG-PLGA copolymer and triblock PEG-PLGA-PEG copolymer for biomimetic hydroxy apatite (HAp) preparation. Average crystallite sizes of precipitated HAp from polymer solutions were estimated from XRD patterns to be ca. 23 nm for those in collagen-HAp hybrids and 30 nm for those without polymer addition. Scanning electron micrographs showed that the organic macromolecules induced HAp with regular plate-like shape and nano-sized structure. Thermogra vimetric analyses showed 2-3 wt% polymer content in the hybrids. Solid state NMR revealed polymer inco poration in HAp crystal. The hybrids containing these biodegradable polymers can be processed to va rious morphologies for tissue engineering applications. Introduction Biomimetic syntheses of organic-inorganic hybrid draw a lot of res earch interests. Among those novel attempts, self-assembly of hydroxyapatite (HAp) in calcium and phos phate-containing solutions gains a lot of attention because organic-inorganic HAp hybrids (org-HAp) ca n be tailor-made. These hybrids are categorized as biomimetic HAp or bio-inspired HAp, since preparation methods are adopted from natural development of mammalian bones and teeth. Organic te mplates, ranging from macromolecules of various shapes, linear, branched or dendrite[1-3], to sim ple molecules like citric acid [4], affect precipitation of HAp crystals. In previous reports, HAp crystals with a c-axis-preferred orientation were obtained using collagen and chondroitin sulfate fibrils [5]. These macromolecular fibrils provide their axial space for nucleation of HAp when local c lcium and phosphate ion concentrations exceed solubility products of HAp. It may be noted that H Ap has been used as gene delivery vehicle [6]. Positively charged Ca 2+ sited on HAp surface was proposed as binding sites of phosphate linkages on DNA chains. However, other than electrostatic inte raction, research on how the van der Waal (VDW) interaction affects HAp precipitation is still in its infancy. But some literature, focused on surface energy, have coined ways to explore thi s VDW interaction [7]. The aim of this study is to investigate org-HAp formation in the presence of collagen or biodegrabale PEG-PLGA-PEG copolymer, that is a non-ionic, hydrophilic PEG-hydrophobic P LGA alternating triblock polyester, and to discuss the mechanism of org-HAp formation ba sed on structural analyses of org-HAp. Experimental Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 473-476 doi:10.4028/www.scientific.net/KEM.254-256.473

Formation Mechanisms of Sol-Gel-Derived Hydroxyapatite Using Different Thermal Processings

Sol-gel-derived hydroxyapatite (HA) precursors were calcined by two thermal processings, a rapid-thermal-calcine (RTC) heating at 100–600°C/min and a conventional-furnace-calcine (CFC) heating at 1.67°C/min, respectively. X-ray diffraction patterns revealed that the onset temperature of HA crystallization is lower in RTC, 350°C, as compared to 600°C in CFC. Pyrolytic-GC/MS programs showed that the evolved gases out of a sample subjected to RTC are mainly H2O, N2O and ethylamine, while those of a sample subjected to CFC are CO2 and small organic molecules. The results leads to models that RTC can quickly remove organic portion of the gel networks, leading to a porous surface morphology and a collapse of gel networks at local areas, so that HA crystallite nucleation is facilitated due to intimate contacts among inorganic species at lower temperatures. On the other hand, slow evolution of organics during CFC leads to carbonaceous residues that isolate the inorganic species and inhibit nucleation of HA crystallites until at a higher temperature.

MESHED SCAFFOLDS MADE OF α, α′ -BIS(2-HYDROXYETHYL METHACRYLATE) POLY(ETHYLENE GLYCOL) THROUGH 3D STEREOLITHOGRAPHY

Recent development of tissue engineering scaffolds that mimic anatomical structures exhibits a tendency to use rapid prototyping technology, because it can be applied to precisely manufacture the designed objects from the computer-generated model. Among all of rapid prototyping approaches, combining with lithography is characterized with a high throughput of fabrication, especially for the fabrication of polymeric scaffolds. In this study, the aims were to: (1) synthesize the 2-hydroxyethyl methacrylate (HEMA)-capped poly(ethylene glycol) (PEG), which served as the cross-linker of the continuous phase of a poly(lactide-co-glycolide) (PLGA) scaffold and (2) fabricate the composite scaffolds through stereolithography. The synthetic process of the cross-linker was traced, and the end-point of the process was found to lie in 3 to 4 h depending on the molecular weight of the PEG used. The chemical structure of the cross-linker was found to be linear and symmetric to PEG and with a 1:2 molar ratio of PEG and HEMA. It was anticipated to form an interpenetrating network upon irradiating under UV light with PLGA serving as the main body of the scaffold. PEG1000–HEMA had better biocompatibility than those with shorter PEG chains. Scaffolds with two structural variants, square and hexagonal pores, designed by computer were demonstrated. It may further combine medical images to reconstruct tissues and organs for regenerative medicine.