G. Fuentes

Development and Characterization of a Novel Bioresorbable and Bioactive Biomaterial Based on Polyvinyl Acetate, Calcium Carbonate and Coralline Hydroxyapatite

Coralina® HAP-200 (coralline hydroxyapatite obtained by hydrothermal treatment of marine corals) and POVIAC® (polymeric matrix based on PVAc), commercial trade marks were mixed with a natural product from the Cuban sea costs, i.e. calcium carbonate from Porites Porites coral, to obtain a novel bioactive composite with potential use as bone restoration material. The samples were characterized by physical-chemical (FTIR, XRD, SEM, EDS) and mechanical studies. It was shown that there is no chemical interaction between the inorganic filler and the polymer matrix, each conserving the original properties of the raw materials. The studied formulation had a compressive strength similar to that reported for trabecular bone. Scanning electron microscopy examination revealed that the addition of CaCO3 induces a change on the morphologic structure of the composite obtained after 30 days of SBF immersion. These composites generate novel biomaterials capable of promoting the deposition of a new phase, a Ca-P layer due to the bioactivity of a Ca2+ precursors.

Application of New Statistical Approach to Study Drug Release from OCP Coating on Titanium Sheets

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.

In vitro release kinetics and physical, chemical and mechanical characterization of a POVIAC®/CaCO3/HAP-200 composite

Coralline calcium-hydroxyapatite and calcium carbonate from Porites Porites coral were added to a polymeric matrix based on polyvinyl acetate (POVIAC®), to obtain a novel bone substitute composite as well as a system for the controlled drug (cephalexin) release. Composite samples with different compositions were characterized by physical–chemical and mechanical methods. Furthermore, the in vitro release profile of cephalexin and the kinetic behavior of its release from these composites were analyzed by appropriate mathematical models. It was shown that there is no chemical interaction between the inorganic filler and the polymer matrix, each conserving the original properties of the raw materials. The compressive mechanical strength and Young modulus of the composite with 17.5% of POVIAC®, has better mechanical properties than those of cancellous bone. The variation of POVIAC® content can affect the cephalexin release kinetic in the composite. The cephalexin release mechanism from the composites can be considered as the result of the joint contribution of a prevailing Fickian diffusion and of polymer chain relaxation. It was also demonstrated that cephalexin is occluded inside the composites and not on their surface.

Sistemas de Liberación Controlada de Fármacos a Partir de Materiales para la Restauración del Tejido Óseo

Nowadays, two of the most important problems are the high incidence of bone infections and the inflammatory response of the human organism when an implant is used. For this reason, the inclusion of drugs in materials for bone restoration is an interesting and promising approach to solve this problem. On this paper, drug delivery systems from bone restoration materials making little modifications to classic materials such as calcium phosphate cements, PMMA acrylic cements and coating metals were prepared, characterized and evaluated. All the prepared matrixes showed no-interaction between main components of formulation allowing the composition to lead the behavior of drug profile. The modifications made to classic bone materials on hydrophilicity and porosity, two important characteristics, helped to improve the drug delivery capacity. The ending results of delivery moved between 40-95 % in different time ranges according to composition which allows different possible application of these materials.

Preparation and characterization of hydrophilic composites AA/EPMA loaded with hydroxyapatite.

Copolymeric composites of acrylamide (AA) and 2,3-epoxypropyl methacrylate (EPMA) with hydroxyapatite (HA) load were studied. Swelling studies reports an anomalous or non-Fickian behavior following a good fitting to a pseudo second order mathematical treatment (α = 0.05, p < 0.0001). The composites showed a strong dependence on pH, related with the variations in the swelling behavior. The addition of load induces a diminution of swelling capacity and an increase of diametric tensile strength (DTS) ranging between 20 and 90 kPa. The calorimetric experiments showed two steps at 78°C and 255°C assigned to water loss and samples Tg. The drug control released was adjusted to a two-term equation obtaining a diffusion coefficient around 10(-5) cm(2) /s. The samples showed a significant bioactivity in vitro and it was certified by SEM, EDS and surface area calculus.