Key Engineering Materials Vols. 396-398

Abstract: A lot of attention has been given to bone cements due to their lack of mechanical properties. The improvement of this property is essential, once it makes possible the usage of these biomaterials in sites that require a significant mechanical strength resistance. To do so, reinforcement agents, such as fibers, in particular biocompatible fibers, have been synthesized [1]. This study reports the synthesis of stequiometric Hydroxyapatite whisker-like fibers utilizing the Molten Salt Synthesis process of nanometric Hydroxyapatite with a salt flux mixture of KCl/NaCl. According to SEM images, EDS analysis and X-ray diffraction, the fibers obtained presented well defined and elongated (main length of about 70µm) hexagonal morphology with Ca/P ratio of 1.66.

Abstract: Biocompatible fibers has been studied and synthesized in order to improve the mechanical and general properties of bone cements. In order to do so, this work presents the synthesis of Whisker-like fibers of Silicon doped Hydroxyapatite by alkaline hydrolysis of Silicon doped α-TCP. The main fibers analyzed by SEM showed an aspect ratio of about 18 (l = 3.9 µm, d = 0.22 µm), well defined superficial aspect and hexagonal structure. XRD and EDX characterization presented Calcium Deficient Hydroxyapatite peaks and Ca/P ratio of 1.47.

Abstract: Insulin delivery carriers using low crystalline porous zinc hydroxyapatite (ZnHAp) microparticles with different crystal sizes and novel formulation method of poly (lactic acid) (PLA) have been developed to achieve the sustained-release of insulin. The adsorption isotherm curves of insulin dissolved into acetic acid of pH4.5 onto ZnHAp nanocrystals show non-Langmuir type due to the dissolution of the ZnHAp microparticles; the adsorption amounts were increased with the increase of crystalline sizes. The PLA formulation, coating the outer layer of microparticles, showed the apparent reduction of initial burst for insulin. The amounts of initial release of insulin decreased with the increase of crystalline sizes of ZnHAp, which could be attributed to the different meso-porous structure depending on its crystal sizes.

Abstract: In this study, commercially pure titanium (Ti-cp) discs were used as substrates. Octacalcium phosphate (OCP) layers were deposited by immersion of Ti-cp discs up to 7 days into Solution for Bioactivity Evaluation (SBE) and characterized by SEM-EDS and XRD. The OCP coatings were doped with cephazolin or cefalexin by individual immersion in 300 ppm of each solution for 24 h at room temperature. The non-existence of mathematical models to explain drug release from these matrixes made the choosing of correct model, a complex process. Five non-linear mathematical methods were employed in order to identify the possible drug release mechanism using Akaike and Bayesian Information Criterion (AIC and BIC respectively) and its derivatives. The best model was Peppas & Sahlin that consider two stages in release: pure diffusion in first stage, and drug dissolution and migration through the porous matrix at second stage.

Abstract: The purpose of this study was to develop bioceramics with a well-defined porous structure in order to control drug loading and release over time. Porous structures were obtained through colloidal processing, using polymethyl methacrylate (PMMA) microspheres as templates (core) and hydroxyapatite (HA) nanoparticles as inorganic building blocks (shell). Dispersed HA suspensions were prepared and their electrokinetic properties were studied to determine a dispersant giving a high positive zeta potential (opposite to the negative zeta potential of PMMA). Upon mixture of well-dispersed HA and PMMA suspensions of opposite charge, core-shell structures were formed via heterocoagulation. After consolidation, polymers were removed by calcination, resulting in a porous structure of controlled size and distribution.

Abstract: Apatite nuclei were precipitated in the pores of silicagel microspheres by raising pH of simulated body fluid (SBF). By a soak in SBF, hydroxyapatite (HAp) was induced from the apatite nuclei and spread over whole surface area of the silicagel microspheres. Then encapsulated silicagel microspheres with HAp were fabricated.

Abstract: The aim of this study was to investigate if it is possible to fast load hydroxyapatite with antibiotics and still obtain a slow but therapeutic release of drugs during several hours. Physical vapour deposition was used to coat commercially pure titanium with a layer of anatase TiO2. On top of this, a layer of hydroxyapatite was deposited using biomimetic precipitation. This hydroxyapatite coating was then soaked in solutions containing antibiotics for various amounts of times. The release rate of the antibiotics was measured in PBS during 22 hours. The released amount was compared with the results from an antimicrobial susceptibility test and proved to be sufficient to kill several ml of bacterial broth during the time of the release measurements. It was shown that the soaking time does not affect the release rate and the results suggest that it is possible to develop implants with the option to add antibiotics to their surface at the site of surgery by a simple soaking method.

Abstract: Gentamicin sulphate was mixed with two different sol-gel derived calcium silicates (akermanite or wollastonite). Each of the mixtures was isostatically pressed. Samples were immersed in simulated body fluid for 21 days. The presence of the antibiotic showed no effect on the in vitro bioactivity of the ceramics. For evaluating the gentamicin sulphate release, samples were immersed in a phosphate buffered saline solution for different periods of time. Most of the gentamicin sulphate was released during the first 7 days. However, akermanite showed a lower antibiotic release rate than that observed for wollastonite.

Abstract: Chlorhexidine (CHX), a cationic antiseptic, is an antimicrobial agent with many applications. In this work, the antimicrobial action of CHX associated with hydroxyapatite (HA) was evaluated for treating oral infections. Based on the determination of MIC (6,25 mg/mL HACHX), the material showed growth inhibition of E. faecalis for up to 08 days.

Abstract: Spherical porous calcium phosphate pellets were fabricated by high shear wet granulation using native starch as a binder. After a heat treatment to eliminate the organic template, pellets were loaded with ibuprofen by solvent evaporation method. In vitro drug release kinetics was determined using an USP II apparatus (Prolabo Dissolution Tester, France). Results showed the interest of the calcination and of the increase in the binder-porogen content, to improve the drug loading (higher drug content) and prolong the release of the drug substance.