Papers by Author: Isabel B. Leonor

Abstract: Chitosan membranes were subjected to a pre-treatment in a double diffusion system, with a calcium solution in one chamber and a phosphate solution in the other chamber. Both chambers were separated by the chitosan membrane and subject to three mineralization periods (5, 10 and 15 minutes). After this pre-treatment the bioactivity of the different calcium phosphate coatings formed was tested for different periods of immersion time, 7, 14 and 21 days at room temperature and 37°C, in acellular simulated body fluid (1.0x). The results obtained demonstrated that the calcium phosphate coatings formed during the pre-treatment process are bioactive. It was found that the calcification is effective just in the side of the membrane exposed to the calcium solution chamber. This enabled to develop membranes with asymmetric osteoinductive properties that can be useful in different orthopedic applications.

Abstract: This work aims to study the effect of incorporating proteins with different isoelectric points (pI) on the structure, composition and morphology of biomimetic calcium-phosphate (Ca-P) coatings. For that, bovine serum albumin (BSA) and lysozyme, having respectively acidic and basic pIs, were used as model proteins. It was observed that the incorporation of positively charged proteins, such as lysozyme, was able to significantly change the structure of the coatings, possibly due to the preferential interactions between the protein and negatively charged phosphate ions. These results indicated that proteins with different characteristics can be incorporated into biomimetic Ca-P coatings in order to obtain a hybrid coating and at the same tailoring their properties.

Abstract: Bioactive polymeric microspheres can be produced by pre-coating them with a calcium silicate solution and the subsequent soaking in a simulated body fluid (SBF). Such combination should allow for the development of bioactive microspheres for several applications in the medical field including tissue engineering. In this work, three types of polymeric microspheres with different sizes were used: (i) ethylene-vinyl alcohol co-polymer (20-30 'm), (ii) polyamide 12 (10-30 'm) and (iii) polyamide 12 (300 'm). These microspheres were soaked in a calcium silicate solution at 36.5°C for different periods of time under several conditions. Afterwards, they were dried in air at 100°C for 24 hrs. Then, the samples were soaked in SBF for 1, 3 and 7 days. Fourier transformed infrared spectroscopy, thin-film X-ray diffraction, and scanning electron microscopy showed that after the calcium silicate treatment and the subsequent soaking in SBF, the microspheres successfully formed a bonelike apatite layer on their surfaces in SBF within 7 days due to the formation of silanol (Si-OH) groups that are quite effective for apatite formation.

Abstract: Sulfonic groups (-SO3H) were covalently attached on different polymeric surfaces enabling them to induce apatite nucleation, for developing bioactive apatite-polymer composites with a bonelike 3-dimensional structure. High molecular weight polyethylene (HMWPE) and ethylene-co-vinyl alcohol co-polymer (EVOH) were used. The polymers were soaked in two types of sulphate-containing solutions with different concentrations, sulphuric acid (H2SO4) and chlorosulfonic acid (ClSO3H). To incorporate calcium ions into to the sulfonated polymers, the samples were soaked in a saturated Ca(OH)2 solution for 24 hours. After soaking of the samples in a simulated body fluid (SBF), formation of an apatite layer on both surfaces was observed. The results obtained prove the validity of the proposed concept and show that the -SO3H groups are effective on inducing apatite nucleation on the surface of these polymers.

Abstract: In this study, it is shown that it is possible to prepare carboxymethyl-chitosan/Ca-P hybrids using an innovative “auto-catalytic” co-precipitation method, namely by using an acid and an oxidant bath. The X-ray diffraction (XRD) patterns evidenced the formation of crystalline calcium-phosphate precipitates when using an acid bath, while amorphous ones were obtained for those produced in the oxidant bath. The Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM/EDS) studies revealed that the extent of the polymer precipitation and formation of calcium-phosphates is directly dependent on the pH and composition of the baths. Furthermore, by conducting bioactivity tests in a simulated body fluid (SBF) followed by the SEM/EDS analysis it was possible to detect the formation of an apatite layer with a cauliflower-like morphology on the surface of hybrids prepared by the acid bath, after 7 days of immersion. These results are quite promising because they can allow for the production of bioactive and biodegradable 3D porous scaffolds to be used in bone tissue engineering applications.

Abstract: The aim of this research was to develop a new methodology to obtain bioactive coatings on bioinert and biodegradable polymers that are not intrinsically bioactive. In this study, three types of materials were used as substrates: (i) high molecular weight polyethylene (HMWPE) and two different types of starch based blends (ii) starch/ethylene vinyl alcohol blends, SEVA-C, and (iii)starch/cellulose acetate blends, SCA. These materials were obtained by injection moulding and by extrusion with blowing agents in order to obtain compact/porous 3D architectures. Three types of baths were developed in order to produce the newly proposed auto-catalytic Ca-P coatings: (i)alkaline, (ii) acid, and (iii) oxidant bath. The obtained results indicated that it was possible to coat the materials surfaces with calcium phosphate (Ca-P) layer with only 60 min of immersion in the different types of auto-catalytic solutions. These innovative auto-catalytic electroless route allows for the production of an adherent bioactive film on the polymeric surfaces. Furthermore, it was possible observe by SEM/EDS the clear bioactive nature of the Ca-P coatings after different immersion periods, in a simulated body fluid (SBF).

Abstract: A bioactive polyethylene polymer substrate can be produced by incorporation of sulfonic functional groups (-SO3H ) on its surface. Variation of the surface potential of the polyethylene modified with -SO3H groups with soaking in SBF were investigated using a laser electrophoresis zeta-potential analyzer. To complement the study using the laser electrophoresis, the surface was examined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with an attached energy dispersive electron probe X-ray analyser (FE-SEM/EDS). It was found that the surface potential of the polyethylene was highly negative charged after soaking in SBF for 0.5 h, increased for higher soaking times (up to 48 h), and then decreased. The negative charge of the polymer at soaking time of 0.5 h is attributed to the presence of –SO3H groups on the surface. The initial increase in the surface potential was attributed to the incorporation of positively charged calcium ions to form a calcium sulphate, and then the subsequent decrease was assigned to the incorporation of negatively charged phosphate ions to form an amorphous calcium phosphate, which eventually transformed into apatite.