In vitro behavior of sintered powder injection molded Ti-6Al-4V/HA

This article reports the morphology and mechanical properties of sintered powder injection molded Ti-6Al-4V/HA parts in a simulated physiological environment. Sintered Ti-6Al-4V/HA parts were immersed in a simulated body fluid (SBF) with ion concentrations that were comparable to those of human blood plasma for a total period of 12 weeks. At intervals of 2 weeks, the immersed Ti-6Al-4V/HA parts were analyzed with the use of scanning electron microscopy (SEM), X-ray diffractometry (XRD), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Mechanical properties such as flexural strength, flexural modulus, compressive strength, and compressive modulus were also evaluated. Results showed that complete dissolution of the more soluble phases such as tricalcium phosphate (TCP), tetracalcium phosphate (TTCP), and calcium oxide (CaO) were found after 2 weeks of immersion in SBF. ICP analysis showed that high calcium concentration release of around 200 ppm was observed in the SBF solution after 2-4 weeks of immersion, indicating that dissolution has taken place. Next, a gradual decrease in calcium concentration release in the SBF solution was observed after immersion for 4-6 weeks, with increasing amounts of calcium phosphate precipitates being observed on the Ti-6Al-4V/HA surface. Mechanical properties such as strength and modulus were found to deteriorate during 2-4 weeks of immersion, followed by gradual increment as the immersion period increased. This study also showed that parts sintered at 1150 C exhibited faster dissolution and precipitation rates than parts sintered at 1050 C in a physiological environment.     

Processing of HA-coated Ti-6Al-4V by a ceramic slurry approach: an in vitro study

Hydroxyapatite-coated titanium alloy composite powders (Ti-6Al-4V/HA) was produced by a ceramic slurry approach. The aim was to evaluate the stability of the coating when subjected to a physiological medium simulated body fluid (SBF). Three consolidation conditions (700 degrees C for 5 h, 700 degrees C for 8 h and 700 degrees C for 11 h) were used in the production of the Ti-6Al-4V/HA composite powders. Results showed that biodissolution followed by apatite precipitation had taken place after soaking in SBF. In addition, it was found that consolidation at 700 degrees C for 5 h resulted in a weak mechanical locking of calcium phosphate on the Ti-6Al-4V surfaces; and the formation of small crystallites, which would increase the dissolution rate.     

Wound dressing with sustained anti-microbial capability

Amphiphilic poly(ether ester amide) (PEEA) multiblock copolymers were synthesized by polycondensation in the melt from hydrophilic poly(ethylene glycol) (PEG), 1,4-dihydroxybutane and short bisester-bisamide blocks. These amide blocks were prepared by reaction of 1,4-diaminobutane with dimethyl adipate in the melt. A range of multiblock copolymers were prepared, with PEG contents varying from 23-66 wt %. The intrinsic viscosity of the PEEA polymers varied from 0.58-0.78. Differential scanning calorimetry showed melting transitions for the PEG blocks and for the amide-ester blocks, suggesting a phase separated structure. Both the melting temperature and the crystallinity of the hard amide-ester segments decreased with increasing PEG content of the polymers. The equilibrium swelling ratio in phosphate buffered saline (PBS) increased with increasing amount of PEG in the polymers and varied from 1.7 to 3.7, whereas the polymer that contained 66 wt % PEG was soluble in PBS. During incubation of PEEA films in PBS, weight loss and a continuous decrease in the resulting inherent polymer viscosity was observed. The rate of degradation increased with increasing PEG content. The composition of the remaining matrices did not change during degradation. A preliminary investigation of the protein release characteristics of these PEEA copolymers showed that release of the model protein lysozyme was proportional to the square root of time. The release rate was found to increase with increasing degree of swelling of the polymers.     

Effect of spark plasma sintering on the microstructure and in vitro behavior of plasma sprayed HA coatings

The crystalline phases and degree of crystallinity in plasma sprayed calcium phosphate coatings on Ti substrates are crucial factors that influence the biological interactions of the materials in vivo. In this study, plasma sprayed hydroxyapatite (HA) coatings underwent post-spray treatment by the spark plasma sintering (SPS) technique at 500 degrees C, 600 degrees C, and 700 degrees C for duration of 5 and 30 min. The activity of the HA coatings before and after SPS are evaluated in vitro in a simulated body fluid. The surface microstructure, crystallinity, and phase composition of each coating is characterized by scanning electron microscopy and X-ray diffractometry before, and after in vitro incubation. Results show that the plasma sprayed coatings treated for 5 min in SPS demonstrated increased proportion of beta-TCP phase with a preferred-orientation in the (214) plane, and the content of beta-TCP phase corresponded to SPS temperature, up to 700 degrees C. SPS treatment at 700 degrees C for 30 min enhanced the HA content in the plasma spray coating as well. The HA coatings treated in SPS for 5 min revealed rapid surface morphological changes during in vitro incubation (up to 12 days), indicating that the surface activity is enhanced by the SPS treatment. The thickest apatite layer was found in the coating treated by SPS at 700 degrees C for 5 min.     

In vitro studies of plasma-sprayed hydroxyapatite/Ti-6Al-4V composite coatings in simulated body fluid (SBF)

The bioactivity of plasma-sprayed hydroxyapatite (HA)/Ti-6Al-4V composite coatings was studied by soaking the coatings in simulated body fluid (SBF) for up to 8 weeks. This investigation was aimed at elucidating the biological behaviour of plasma-sprayed HA/Ti-6Al-4V composite coatings by analyzing the changes in chemistry, and crystallinity of the composite coating in a body-analogous solution. Phase composition, microstructure and calcium ion concentration were analyzed before, and after immersion. The mechanical properties, such as tensile bond strength, microhardness and Young's modulus were appropriately measured. Results demonstrated that the tensile bond strength of the composite coating was significantly higher than that of pure HA coatings even after soaking in the SBF solution over an 8-weeks period. Dissolution of Ca-P phases in SBF was evident after 24h of soaking, and, a layer of carbonate-apatite covered the coating surface after 2 weeks of immersion. The mechanical properties were found to diminish with soaking duration. However, slight variation in mechanical properties was found after supersaturation of the calcium ions was attained with the precipitation of the calcium phosphate layers.     

Simultaneous determination of retinol and α-tocopherol by high pressure liquid chromatography in micro-volumes of serum

The lack of biochemical data to indicate the prevalence of marginal vitamin A deficiency (VAD) in the country is largely because of the difficulty of obtaining enough serum for analysis, especially from malnourished children. Efforts were therefore made to establish a high-pressure liquid chromatography system (HPLC) for the determination of retinol in micro-volumes of serum. Since our previous studies showed that tocopherol could be simultaneously determined in the same system, studies have been carried out for the determination of both vitamins using retinol acetate and -tocopherol acetate as internal standards. Trials were carried out to determine the most suitable sample treatment procedures and chromatographic system including composition of the mobile phase for handling 20 ml of serum. The HPLC system proposed enables successful separation and quantitation of retinol and α-tocopherol and their respective internal standards, retinol acetate and -tocopherol in less than 14 minutes. Reproducibility studies carried out with pooled sera showed a within day and between day variation of less than 8% and 13% respectively for retinol, whilst variations for α-tocopherol were higher, ranging from 8-16%. The proposed method is currently being applied to the determination of retinol and α-tocopherol in a group of malnourished children under six years of age.     

Simultaneous determination of B-vitamins and ascorbic acid in multi-vitamin preparations by reversed-phase HPLC

The tedious and time consuming methods employed for the analysis of individual B-vitamins can now be replaced by ion-pair reversed-phase high-performance liquid chromatographic (HPLC) methods. This laboratory has previously reported the simultaneous determination of eight water-soluble vitamin standards that is, B1, B2, B6, B12, C, niacin, niacinamide and folic acid. The proposed isocratic HPLC method, employing 3 channels of detection, adequately separated all eight vitamins in less than 20 minutes. This study reports another phase of the project whereby the method was employed for the analysis of pharmaceutical preparations. Different extraction procedures were first evaluated, namely acid, acid plus enzyme and alkaline hydrolysis methods, using vitamin standards, individual vitamin tablets and multivitamin preparations. The amounts obtained from the analysis were compared with the declared values. Recovery studies were also carried out. The method of acid hydrolysis with 0.1N sulphuric acid was found suitable for use and was thus adopted as the extraction procedure for the analysis of 10 multivitamin preparations obtained from various pharmaceutical outlets. For most of these preparations, the amount obtained were close to the declared values, except for folic acid and cyanocobalamin. Further trials on folic acid showed that the problem could be resolved by omitting the filtration step in the final extract after acid hydrolysis and diluting with 0.01N sodium hydroxide before processing for chromatography. Vitamin B12 was not detectable using the present chromatography system probably because of its low concentration in the samples studied.     

Pharmacokinetics and pharmacodynamics of 3,3′-diindolylmethane (DIM) in regulating gene expression of phase II drug metabolizing enzymes

3,3′-Diindolylmethane (DIM) has been investigated as a potential anti-cancer chemopreventive agent in many preclinical and clinical studies. In this study, we sought to characterize the pharmacokinetics of DIM and to build a pharmacokinetic (PK) and pharmacodynamic (PD) model of the DIM-induced gene expression of phase II drug metabolizing enzymes (DME), which potentially links DIM’s molecular effects to its in vivo chemopreventive efficacy. DIM (10 mg/kg) was administered intravenously (i.v.) to male Sprague–Dawley rats and blood samples were collected at selected time points for 48 h. The plasma concentration of DIM was determined using a validated HPLC method. The mRNA expression of NQO1, GSTP1 and UGT1A1 in blood lymphocytes was measured using quantitative PCR. An indirect response model was employed to relate the concentration of DIM to the expression of the genes NQO1, GSTP1 and UGT1A1, which were chosen as PD markers for DIM. After i.v. administration, the plasma concentration of DIM declined quickly, and the expression of target genes increased significantly, peaking at 1–2 h and then returning to basal levels after 24 h. The parameters in the PK–PD model were estimated. The PK–PD model aptly described the time delay and magnitude of gene expression induced by DIM. Our results indicate that DIM is effective at inducing various phase II DME, which are capable of detoxify carcinogens. This PK–PD modeling approach provides a framework for evaluating the acute effects of DIM or other similar drugs in clinical trials.