Celso A. Bertran

Hydroxyapatite surface solubility and effect on cell adhesion.

In living organisms the biological hydroxyapatite is in constant contact with body fluids, such as blood serum and saliva. Thus, dissolution, solubility and precipitation take place as part of the interaction of this material with biological fluids in tissues. In this work we have obtained the solubility constant for the system formed from aqueous solutions in equilibrium with hydroxyapatite and thus indirectly obtained the composition of the modified hydroxyapatite surface. In order to check the effects of this equilibrium and of the modification that the surface of hydroxyapatite suffers in aqueous solutions, we cultured pre-osteoblasts onto hydroxyapatite discs before and after equilibrium. The results revealed key steps of the mechanism for the bioactivity of hydroxyapatite, which are the solubilization of hydroxyapatite and the equilibrium that is formed on the surface. These processes modify the hydroxyapatite surface, whose composition is changed to a new calcium phosphate compound with the chemical formula of CaHPO4. A clear description of the transformations that occur on the surface of hydroxyapatite and of the interplay between these transformations and cell activity are two fundamental aspects of processes in which hydroxyapatite takes part, such as bone substitution, bone remodeling, osteoporosis and caries.

Biocerâmicas: tendências e perspectivas de uma área interdisciplinar

The need for new materials to substitute injured or damaged parts of the human body has led scientists of different areas to the investigation of bioceramics since the 70s, when other materials in use started to show implantation problems. Bioceramics show some advantages like being the material that best mimics the bone tissue but also, present low mechanical strength due to its ceramic nature. This paper presents a general view about the topic.

Bioactivation of alumina by surface modification: a possibility for improving the applicability of alumina in bone and oral repair

OBJECTIVES In regenerative medicine, surface engineering of bioinert synthetic materials is often required in order to introduce bioactive species that can promote cell adhesion, proliferation, viability and enhanced ECM-secretion functions. The aim of this work is to study cell interaction with alumina-modified surfaces. MATERIAL AND METHODS In this work, chemical properties of alumina surface were changed by a reaction at the surface of alumina with low molecular weight dicarboxylic acid, which produced carboxyl groups. RESULTS These carboxyl groups were able to complex with Ca2+ on the surface, forming sites of precipitation for calcium phosphates that make alumina biocompatible, as indicated by cell culture of pre-osteoblasts (MC3T3-E1 cell line). CONCLUSIONS The procedure presented in this work shows that the insertion of specific functional groups on the surface of alumina increases cell interaction with the surface of alumina. This knowledge can be important in oral science and orthopedics, for the construction of prosthesis.

Hydroxyapatite-based electrode: a new sensor for phosphate

Hydroxyapatite, prepared by precipitation from a calcium hydroxide suspension with phosphoric acid at 60 °C and a pH of 9, was used to develop a potentiometric sensor for phosphate. The electrodes were made in two ways: firstly, by mixing hydroxyapatite powder with an epoxy polymer and graphite; and secondly, by sealing porous hydroxyapatite sticks to the extremity of a glass tube. The first sensor showed a very small linear range of response (6.0 × 10–5 to 2.0 × 10–4 mol l–1) to log [phosphate] at pH = 5.0, with a slope of 55 mV decade–1 of phosphate concentration and a detection limit of 4.0 × 10–5 mol l–1. The second showed a higher linear response range from 5.0 × 10–5 up to 5.0 × 10–2 mol l–1, with a slope of 33 mV decade–1 and a detection limit of 2.5 × 10–5 mol l–1, under the same conditions. The response time was about 25 s in the first case and 40 s in the second. The effects of interfering ions were investigated and the Kpot values for Cl–, NO3–, SO42–, ClO4–, acetate and citrate were determined, showing only a small interference with the electrode response. The powder electrode is not stable but the stick has good stability.

Chemiluminescent Emission Data For Kinetic Modeling Of Ethanol Combustion

ABSTRACT Kinetic modeling is a powerful tool for combustion investigations and has been widely used. The validation of the model is a very important element of the work, to achieve realistic results, and it normally uses concentration profiles of some participant species. In this work, a kinetic model was validated using the chemiluminescent emissions of excited radicals produced in ethanol vapor combustion in a closed chamber, where a fixed mass of premixed reagents was ignited. A reaction mechanism made up of 128 reactions and 40 species was simulated with the SENKIN code of the CHEMKIN-III software package and it was able to reproduce with good accuracy the chemiluminescent profiles of OH*, HCO*, CH2O*, CH*, and C2* species recorded experimentally from ethanol combustion. Analysis of the developed ethanol combustion mechanism showed that the CH3 radical is the main precursor to the chain reaction for the production of the most excited species.

Mechanical, biochemical and morphometric alterations in the femur of mdx mice.

The bone tissue abnormalities observed in patients with Duchenne muscular dystrophy are frequently attributed to muscle weakness. In this condition, bones receive fewer mechanical stimuli, compromising the process of bone modeling. In the present study we hypothesize that other factors inherent to the disease might be associated with bone tissue impairment, irrespective of the presence of muscle impairment. Mdx mice lack dystrophin and present cycles of muscle degeneration/regeneration that become more intense in the third week of life. As observed in humans with muscular dystrophy, bone tissue abnormalities were found in mdx mice during more intense muscle degeneration due to age. Under these circumstances, muscle deficit is probably one of the factors promoting these changes. To test our hypothesis, we investigated the changes that occur in the femur of mdx mice at 21 days of age when muscle damage is still not significant. The mechanical (structural and material) and biochemical properties and morphometric characteristics of the femur of mdx and control animals were evaluated. The results demonstrated a lower strength, stiffness and energy absorption capacity in mdx femurs. Higher values for structural (load and stiffness) and material (stress, elastic modulus and toughness) properties were observed in the control group. Mdx femurs were shorter and were characterized by a smaller cortical area and thickness and a smaller area of epiphyseal trabecular bone. The hydroxyproline content was similar in the two groups, but there was a significant difference in the Ca/P ratios. Thermogravimetry showed a higher mineral matrix content in cortical bone of control animals. In conclusion, femurs of mdx mice presented impaired mechanical and biochemical properties as well as changes in collagen organization in the extracellular matrix. Thus, mdx mice developed femoral osteopenia even in the absence of significant muscle fiber degeneration. This weakness of the mdx femur is probably due to genetic factors that are directly or indirectly related to dystrophin deficiency.

Repair of cranial bone defects with calcium phosphate ceramic implant or autogenous bone graft.

Autogenous bone grafts have frequently been used in the treatment of bone defects; however, this procedure can cause clinical complications after surgery. Besides, the amount of available bone is sometimes insufficient. Therefore, synthetic biomaterials have been researched as an alternative to autogenous bone graft implants. The objective of this study was to evaluate the repair of bone defects treated with compact autogenous bone graft or porous calcium phosphate ceramics. Three defects 3 mm in diameter were produced in the skull of 21 rats. One the defects was produced in the frontal bone, which remained empty, while the others were produced in the right and left parietal bones, which were filled respectively with ceramics and autogenous bone graft. The animals were sacrificed 1, 2, 4, and 24 weeks after surgery and analyzed by light microscopy and radiography. In the twenty-fourth week, the defects filled with autogenous bone graft and ceramics had similar volumes of newly formed bone tissue. The ceramics offered favorable conditions to bone tissue growth. Thus, we concluded that the calcium phosphate ceramic implant proved to be effective in repairing defects produced in the skull of rats.

Citric acid effect on aqueous sol-gel cordierite synthesis

Cordierite was synthesized by a simple aqueous sol-gel route. Citric acid action as a chelant for the Al 3+ ion, and for controlling phase segregation during the drying and initial thermal treatment of the gel, results in an amorphous precursor that crystallizes to μ-cordierite and spinel. The changes in the ratios of the crystalline phases, formed during dry gel calcination at 1000°C for 12 h were dependent on the ratio (L/M) of citric acid/Al 3+ (mol/mol). For L/M3 and L/M5 samples, the ratio between the amount of μ-cordierite phase and the amount of spinel phase was the same, while, for the sample L/Ml, the amount of μ-cordierite was larger than that found in the other samples.

Mullite formation from mixtures of alumina and silica sols: mechanism and pH effect

This work reports the effect of pH on the process of mullite formation from mixtures of alumina and silica sols. The pH of the mixtures determines the charges of particle surfaces and affects their interactions and distributions. Mullite formation from amorphous precursors with an Al:Si molar ratio of 1:3, prepared from the sols mixture, was not affected by pH. In this case, the higher concentration of silica determined its distribution around alumina, which led to tetragonal mullite formation, according to the Sundaresan and Aksay mechanism. However, for mullite formation from precursors with Al:Si = 3:1, the pH played an important role on the interactions between alumina and silica particles, as well as on the predominant aluminum species. At pH 1, octahedrically coordinated Al3+ ions predominated in the alumina sol while tetrahedrically coordinated Al3+ ions predominated in the sol at pH ~6. The interactions between silica and alumina particles and their distributions in these precursors determined the minimum temperature required for orthorhombic mullite formation.

A simple method for enhancing cell adhesion to hydroxyapatite surface

OBJECTIVES Increase cell adhesion on hydroxyapatite (HA) surface, in a simple, fast and inexpensive way. MATERIAL AND METHODS Hydroxyapatite powder was immersed into deionized water for 15 days, dried and pressed into discs. On those discs, pre-osteoblasts cells were cultured for 30 min and 24 h, and adhesion was analyzed by MTT reduction. RESULTS The results show that HA treatment in equilibrium with water drastically increases cell adhesion when compared with cultures on HA with no treatment. The results also show that one essential factor required for a complete modification of HA is the amount of time of immersion in water. CONCLUSIONS The work presented here suggests a new, simple and effective method to improve the success of different implants. The method is simple, inexpensive and can be used in the daily routine of different contexts where implants are used, from bone substitution to dental procedures.