Biomedical subjects

J D Santos

Publications and source records attributed to J D Santos.

At least 19 recordsLinked to original sources

PubMed2006

Physicochemical degradation studies of calcium phosphate glass ceramic in the CaO-P2O5-MgO-TiO2 system.

The aim of this work was to evaluate the in vitro degradation behaviour of a 45CaO-37P(2)O(5)-5MgO-13TiO(2) (mol.%) glass ceramic, under two different simulated physiological conditions: normal physiological pH 7.4, and pH 3.0, which was designed to simulate the acidic conditions produced by osteoclast cells. The in vitro testing was carried out at 37 degrees C for up to 42 days for the pH 7.4 solution and for up to 1 day for the pH 3.0 solution. The incorporation of TiO(2) into the glass structure leads to the precipitation of specific crystalline phases in the glass matrix, namely alpha- and beta-Ca(2)P(2)O(7), TiP(2)O(7) and CaTi(4)(PO(4))(6). The degradation testing at pH 3.0 showed a higher weight loss compared with degradation testing at pH 7.4; the weight loss under the acidic condition after 1 day (24 h) was about 10 times higher than the weight loss after 42 days of immersion at pH 7.4. The ionic release profile of Ca(2+), PO(4)(3-), Mg(2+) and Ti(4+) showed a continuous increase in concentration over all immersion times for both testing solutions. After 1 day of immersion at pH 3.0, the concentration levels of Mg(2+), Ca(2+), PO(4)(3-) were about six times higher than the levels achieved after 42 days of immersion at pH 7.4. The glass ceramic showed similar degradation to hydroxyapatite, and therefore has potential to be used in certain clinical applications where relatively slow resorption of the implant and replacement by bone is required, e.g. cranioplasty.

Biocompatible Materials↗

PubMed2006

Human osteoblast response to silicon-substituted hydroxyapatite.

Human osteoblasts were cultured on hydroxyapatite (HA), 0.8 wt % silicon substituted hydroxyapatite (Si-HA) and 1.5 wt % Si-HA discs. The influence of these substrates on cell behaviour in vitro was assessed by measuring total protein in the cell lysate and the production of several phenotypic markers: collagen type I (COL I), alkaline phosphatase (ALP), osteocalcin (OC), and the formation of bone mineral. After 7 days, beta-glycerophosphate and physiological levels of hydrocortisone were added to the culture medium to stimulate cell differentiation and mineral production. There was a significantly higher production of ALP on 1.5 wt % Si-HA at day 7 following which, the addition of hydrocortisone promoted the differentiation of cells on the other two substrates. Hydrocortisone addition also decreased the production of OC. During the period, when hydrocortisone was present, no significant difference in behavior was seen between cells on Si-HA and HA; however, following removal of hydrocortisone, cells responded to 0.8 wt % Si-HA with a significant increase in protein production. Using fluorescence microscopy, nodular structures labeled with tetracycline were observed on the surface of all substrates after 21 days. These structures were deposited on areas of high cell density but were not related to the presence or level of silicon in the substrate. These results indicate that human osteoblasts are affected by the presence of silicon in the HA substrate and that the timing of these effects may be dependent upon the level of silicon substitution.

Cells, Cultured↗

PubMed2006

Differentiation of mononuclear precursors into osteoclasts on the surface of Si-substituted hydroxyapatite.

In healthy bone, resorption and synthesis are in perfect coordination. In previous studies we demonstrated that the incorporation of silicon into the hydroxyapatite (HA) lattice enhances the proliferation and differentiation of human osteoblasts. Therefore, the aim of this study was to demonstrate the effect of silicon-substituted HA (0.8 and 1.5 wt % Si-HA) on the differentiation of mononuclear cells into osteoclasts, using two different starting cultures, peripheral blood mononuclear cells (PBMC) and monocytes expressing the CD14 antigen (CD14+). Through this study, it was possible to demonstrate that Si-HA allows the differentiation of mononuclear cells into mature osteoclasts, independent of the starting culture, PBMC or CD14+. Most of the cells on the surface of the materials expressed osteoclastic markers: actin rings, several nuclei, positivity for tartrate-resistant acid phosphatase (TRAP), and vitronectin receptor. In the presence of osteoclasts, a higher release of calcium and phosphate into the medium from the 1.5 wt % Si-HA substrate was detected when compared to the HA substrate; therefore, these results indicate higher osteoclastic resorptive activity on the 1.5 wt % Si-HA surface. Si-HA can be resorbed by cellular mechanisms and have a stimulatory effect on osteoclasts, although the underlying mechanism is still poorly understood.

Cell Differentiation↗

PubMed2006

Histological and scanning electron microscopy analyses of bone/implant interface using the novel Bonelike synthetic bone graft.

Synthetic bone grafts provide an alternative to autografts and allografts. Bonelike is a patented synthetic bone graft that mimics the mineral composition of bone. The aim of the present work was to assess the biological behavior of Bonelike graft in humans, before using the material in orthopedic applications of bone regeneration, for example, in opening wedge high tibial osteotomies for medial knee osteoarthritis. Bonelike granules were implanted in cortical bone of 11 patients undergoing osteotomies, and new bone formation, osteoconductive properties, and resorption characteristics of the granules were analyzed. The granules ranged from 500 to 1000 microm and were implanted in the lateral aspect of the tibia. The patients' mean age was 59 years (range 48 to 70 years); there were eight women and three men, all suffering from medial compartment osteoarthritis of the knee. At surgery, a 1 x 1 x 1-cm cortical defect was created 3 cm distal to the entry point of the screws, in line with the long axis of tibia. The implanted Bonelike graft sample was extracted for analysis during removal of the metallic prosthesis after implantation times of 6, 9, and 12 months. Radiological follow-up, scanning electron microscopy, histological analysis, and histomorphometric measurements were conducted on the retrieved samples to assess bone regeneration in the defect area. Osteoconductive capacity was demonstrated by extensive mature bone formation around the implanted granules and high levels of percentage bone-to-graft contact (from 67-84%). Bonelike acted as an excellent bioactive scaffold, allowing the migration, proliferation, and differentiation of bone cells on its surface, and therefore regeneration of the defects was achieved in a rapid, controlled manner. Our results suggest that Bonelike graft is an excellent candidate for orthopedic applications where rapid new bone formation is a fundamental requirement.

Aged↗

PubMed2006

In vivo performance of biodegradable calcium phosphate glass ceramics using the rabbit model: histological and SEM observation.

Two MK5 (45CaO-45P(2)O(5)-5MgO-5K(2)O, in mol%) and MT13 (45CaO-37P(2)O(5)-5MgO-13TiO(2), in mol%) glasses are prepared in the meta- and pyrophosphate regions and crystallized to obtain MK5B and MT13B, respectively. MK5B was obtained by controlled crystallization, and MT13B by powder sintering. As a result of these heat treatment processes, the crystalline phases precipitated in the glassy matrix are KCa(PO(3))(3), beta-Ca(PO(3))(2), beta-Ca(2)P(2)O(7) and Ca(4)P(6)O(19) phases for MK5B and CaTi(4)(PO(4))(6), TiP(2)O(7), alpha- and beta-Ca(2)P(2)O(7) phases for MT13B. To assess the in vivo biological behavior of these glass ceramics, a mixed granulometry in the range 250-355 mum and 355-425 mum with a ratio of 1/1 was implanted for 2, 4, and 12 weeks in the tibiae of Japanese white rabbits. The results showed that the in vivo behavior was strongly affected by their solubility. All implanted materials, MK5B and MT13B, and beta-tricalcium phosphate (beta-TCP) as control material, showed signs of degradation in vivo. However, the levels of degradation were quite different throughout the implantation periods. The highest degradation was observed for MK5B glass ceramic and the lowest for MT13B with beta-TCP in-between. All implanted materials allow for new bone formation in the bone defect area. At the longest implantation period (12 weeks), the MT13B and beta-TCP materials were almost completely surrounded by new bone tissue, whereas MK5B showed some unfilled spaces. This behavior is discussed in terms of the high degradation observed in previous studies.

Absorbable Implants↗

PubMed2005

Intracellular Ca2+ concentration in the N1E-115 neuronal cell line and its use for peripheric nerve regeneration.

Entubulation repair of peripheral nerve injuries has a lengthy history. Several experimental and clinical studies have explored the effectiveness of many biodegradable and non-degradable tubes with or without addition of molecules and cells. The main objective of the present study was to develop an economical and also an easy way for culturing a neural cell line which is capable of growing, differentiating and producing locally nerve growth factors, that are otherwise extremely expensive, inside 90 PLA/10 PLG nerve guides. For this purpose the authors have chosen the N1E-115 cell line, a clone of cells derived from mouse neuroblastoma C-1300 with the perspective of using this differentiated cellular system to cover the inside of 90 PLA/10 PLG nerve guides placed to bridge a nerve gap of 10 mm in the rat sciatic nerve experimental model. The N1E-115 cells proliferate in normal culture medium but undergo neuronal differentiation in response to DMSO. Upon induction of differentiation, proliferation of N1E-115 cells ceases, extensive neurite outgrowth is observed and the membranes become highly excitable. While it is known that Ca2+ serves as an important intracellular signal for cellular various processes, such as growth and differentiation, be toxic to cells and be involved in the triggering of events leading to excitotoxic cell death in neurons. The [Ca2+]i in non-differentiated N1E-115 cells and after distinct periods of differentiation, have been determined by the epifluorescence technique using the Fura-2-AM probe. The results of this quantitative assessment, revealed that N1E-115 cells which undergo neuronal differentiation for 48 hours in the presence of 1.5% DMSO are best qualified to be used to cover the interior of the nerve guides since the [Ca2+]i was not found to be elevated indicating thus that the onset the cell death processes was not occurred.

Animals↗

PubMed2005

In vitro studies of calcium phosphate glass ceramics with different solubility with the use of human bone marrow cells.

Two glass ceramics in the CaO--P2O5--MgO system with the incorporation of K2O or TiO2 oxides were prepared with the goal of using them as potential bone graft substitutes. The incorporation of TiO2 and K2O led to the preparation of specific crystalline phases in the structure of the glass ceramics, which show different degrees of biodegradation. In fact, the 45CaO--45P2O5--5MgO--5K2O has been previously demonstrated to be much more soluble in aqueous solutions than the 45CaO--37P2O5--5MgO--13TiO2 glass ceramic. The in vitro biological activity of the two calcium phosphate glass ceramics was studied with the use of human bone marrow osteoblast cell cultures maintained for 28 days, and seeded materials were assessed for cell proliferation and function. The Ti-containing glass ceramic showed a stable surface throughout the culture time, on macroscopic and SEM observation. Osteoblast cells proliferated gradually, especially during the third week, with a high alkaline phosphatase activity and formation of a mineralized matrix. On SEM observation, attached cells appeared with a spread-polygonal morphology typical of the osteoblast cells, with extensive cell-to-cell contact. Cell behavior on the seeded material was similar to that found on cultures performed on tissue-culture-grade polystyrene; except for the presence of lower cell numbers during the first 2 weeks. By contrast, the K-containing glass ceramic showed a highly instable surface with dissolution/precipitation processes occurring throughout the culture time. Few cells adhered to the material surface, and subsequent proliferation was also hindered, especially from the first week onwards. Cell numbers were significantly lower than those observed in the Ti-containing glass ceramic during most of the incubation time. Results suggest that the different in vitro biological behavior of these two glass ceramics is mainly due to the significant differences in the surface degradation rate, which is directly correlated to the chemical composition of the mother glass.

Alkaline Phosphatase↗

PubMed2005

Development of a system to adsorb drugs onto calcium phosphate materials.

Several studies were carried out in order to reduce the systemic use of antibiotics due to the high concentration required to provide the minimum inhibitory concentration (MIC) at infected sites. The aim of this study was to develop a system of drug adsorption onto commercial hydroxyapatite (HA, Ca10(PO4)6(OH)2) and glass reinforced hydroxyapatite (GR-HA) granules. The drug will then be released for the local treatment of periodontitis. The antibiotics used in this study were metronidazole, a specific antibiotic indicated for the systemic treatment of periodontitis, and ampicillin, a wide spectrum antibiotic. UV spectroscopy was used to measure the amount of drug adsorbed onto HA and GR-HA granules. Results showed that metronidazole was unable to adsorb on the material's surface, as opposed to ampicillin which adsorbed both onto HA and GR-HA. Preliminary release kinetics studies were carried out using a flow through dissolution system. Results are discussed in terms of the influence of the different surface characteristics of the materials on the adsorption processes.

Adsorption↗

PubMed2005

Bonelike/PLGA hybrid materials for bone regeneration: preparation route and physicochemical characterisation.

Bonelike/PLGA hybrid materials have been developed using gamma-MPS as silane-coupling agent between the inorganic and organic phases for controlled drug delivery applications. Silanization showed to be more effective when cyclohexane was used as a non-polar solvent (nP method) due to a chemical interaction between Bonelike, and the silane film, while by using a 95/5 (V/V) methanol/water as a polar solvent (P method), a much thinner film was achieved. Functional groups of PLGA, such as the carbonyl group (C=O), were identified using Raman and FTIR-ATR analysis and therefore these groups may be used to link therapeutic molecules. These novel hybrid materials prepared by combining silanization and post-hybridisation processes are expected to find use in medical applications of bone regeneration and as drug delivery carrier for therapeutic molecules.

Bone Regeneration↗

PubMed2005

Determination of the intracellular Ca2+ concentration in the N1E-115 neuronal cell line in perspective of its use for peripheric nerve regeneration.

Entubulation repair of peripheral nerve injuries has a lengthy history. Several experimental and clinical studies have explored the effectiveness of many biodegradable and non-degradable tubes with or without addition of molecules and cells. The main objective of the present study was to develop an economical and also an easy way for culturing a neural cell line which was capable of growing, differentiating and producing locally nerve growth factors that are otherwise extremely expensive, inside 90 PLA/10 PLG nerve guides. For this purpose the authors have chosen the N1E-115 cell line, a clone of cells derived from mouse neuroblastoma C-1300 with the perspective of using this differentiated cellular system to cover the inside of 90 PLA/10 PLG nerve guides placed to bridge a gap in the rat sciatic nerve experimental model. The N1E-115 cells proliferate in normal culture medium but undergo neuronal differentiation in response to DMSO. Upon induction of differentiation, proliferation of N1E-115 cells ceases, extensive neurite outgrowth is observed and the membranes become highly excitable. While it is known that Ca2+ serves as an important intracellular signal for various cellular processes, such as growth and differentiation. It is also known that can be toxic to cells and is involved in the triggering of events leading to excitotoxic cell death in neurons. The [Ca2+]i in non-differentiated N1E-115 cells and after distinct periods of differentiation, have been determined by the epifluorescence technique using the Fura-2-AM probe. The results of this quantitative assessment revealed that N1E-115 cells which undergo neuronal differentiation for 48 hours in the presence of 1.5% DMSO are best qualified to be used to cover the interior of the nerve guides since the [Ca2+]i was not found to be elevated indicating thus that the onset the cell death processes was not occurred.

Animals↗

PubMed2003

[Bone tissue engineering scaffolds].

Bone tissue engineering may provide an alternative to the repairs to skeletal defects resulting from disease, trauma or surgery. Scaffold has played an important role in bone tissue engineering, which functions as the architecture for bone in growth. In this paper, the authors gave a brief introduction about the requirement of bone tissue engineering scaffold, the key of the design of scaffolds and the current research on this subject.

Biodegradation, Environmental↗

PubMed2002

Densification route and mechanical properties of Si3N4-bioglass biocomposites.

The processing route and the final microstructural and mechanical characteristics of a novel biomaterial composite are described. This new material is composed of 70 wt% Si3N4 ceramic phase and 30 wt% bioglass, the later performing as a liquid sintering aid system and simultaneously providing bioactivity characteristics to the composite. The conditions for fabrication of an almost fully dense material (approximately 98% of relative density) were pursued. Optimised parameters were 1350 degrees C-40 min-30 MPa by hot-pressing technique. The very fast densification rate of the process avoided the crystallisation of the bioglass intergranular phase and therefore its intrinsic properties were maintained. Also, the large amount of glassy phase assured the densification by liquid phase assisted grain rearrangement without Si3N4 phase transformation. The final mechanical properties of the Si3N4 bioglass were as follows: fracture toughness, K(IC) = 4.4 MPa m(1/2); Vickers hardness, Hv = 10.3 GPa; Young's modulus, E = 197 GPa; bending strength, sigma(g) = 383 MPa; Weibull modulus, m = 8.3. These values provide an attractive set of properties among other bioactive materials, namely by upgrading the main drawback of bioceramcs and bioglasses for high-load medical applications, which is the lack of satisfactory fracture toughness.

Biocompatible Materials↗

PubMed2002

Wettability and surface charge of Si3N4-bioglass composites in contact with simulated physiological liquids.

Wettability and surface charge studies were performed on a novel Si3N4-30wt% bioglass biocomposite. Contact angle and surface tension variation with time were determined at 25 degrees C, respectively, by the sessile and pendant drop techniques, for distinct testing liquids: water, diiodomethane, simulated body fluid (SBF) and bovine serum albumin (BSA) dissolved in SBF solution. This biocomposite revealed a hydrophilic character (theta = 26.6 +/- 2.0 degrees) and a surface tension value (66.6 mJ m(-2)) comparatively higher than those of the most common bioceramics. An important characteristic is the high work of adhesion towards SBF + BSA (96.4 +/- 0.2mJ m(-2)) that was measured. The Si3N4-bioglass material is negatively surface charged above the pH(IEP) = 2.5 in aqueous SBF + BSA solution, as a result of the presence at the surface of unsaturated Si-O bonds and Si-OH groups. The very high negative zeta potential at pH approximately 7 (-58.6 +/- 5.5mV) influenced albumin adsorption and mechanisms are discussed in terms of entropy and enthalpy gains from conformational unfolding and cations coadsorption.

Glass↗

PubMed2002

Si(3)N(4)-bioglass composites stimulate the proliferation of MG63 osteoblast-like cells and support the osteogenic differentiation of human bone marrow cells.

The in vitro osteocompatibility of a novel Si(3)N(4)-bioglass composite (70-30% weight proportion) with improved mechanical properties (fracture toughness = 4.4 M Pa m(1/2); bending strength = 383 +/- 47 MPa) is reported. Immersion of the composite samples in culture medium (30 min to 7 days) resulted in rapid protein adsorption to the surface and, also, dissolution of the intergranular phase of bioglass (time-dependent process) with the formation of different size cavities. "As-received" and pre-treated material samples presented a similar behaviour concerning the proliferation of MG63 osteoblast-like cells, evaluated during a 5-day culture period. Seeded materials showed a higher cell growth rate as compared to cultures performed on the standard plastic culture plates. To assess the osteogenic potential of the composite, "as-received" material samples were seeded with human bone marrow cells and cultured for 35 days in experimental conditions that favour the development of the osteoblastic phenotype. The cell adhesion process was similar to that observed in control cultures. Cells successfully adapted to the irregularities of the surface and were able to grow towards inside the cavities; in addition, osteogenic differentiation occurred with the formation of abundant cell-mediated mineralised deposits. Results suggest that this Si(3)N(4)-bioglass composite seems to be a promising candidate for high-stress medical applications.

Adsorption↗

PubMed2002

Structural analysis of Si-substituted hydroxyapatite: zeta potential and X-ray photoelectron spectroscopy.

The aim of this study was to determine the effect of the incorporation of silicon on the surface charge of hydroxyapatite (HA) and to assess surface structural changes of HA and Si-HA induced by dissolution in both static and dynamic systems. X-ray photoelectron spectroscopy (XPS) analysis showed that SiO(4)(4-) groups were substituted for PO(4)(3-) groups in the silicon-hydroxyapatite (Si-HA) lattice according to a previously proposed substitution mechanism without the formation of other crystalline phases, such as tricalcium phosphate or calcium oxide. The substituted silicon induced a decrease in the net surface charge and the isoelectric point of HA as determined by zeta potential (ZP) measurements. At physiological pH=7.4 the surface charge of Si-HA was significantly lowered compared to unmodified HA, i.e. -50+/-5 to -71+/-5 eV, caused by the presence of silicate groups in the HA lattice, which may account for a faster in vitro apatite formation using SBF testing. XPS results indicated that silicon seems to be preferentially leached out from Si-HA surface compared to other ionic species after dissolution studies in tris-buffer using a dynamic system.

Journal Article↗

PubMed2001

Push-out testing and histological evaluation of glass reinforced hydroxyapatite composites implanted in the tibia of rabbits.

In vitro and in vivo bioactivity studies were performed to assess the biocompatibility of CaO-P2O5 glass-reinforced hydroxyapatite (GR-HA) composites. The ability to form an apatite layer by soaking in simulated body fluid (SBF) was examined and surfaces were characterized using FTIR reflection and thin-film X-ray diffraction analyses. Qualitative histology, histomorphometric measurements, and push-out testing were performed in a rabbit model for characterizing bone/implant bonding. Under the in vitro conditions using SBF, an apatite layer could not be formed on GR-HA composites within 8 weeks. Results of push-out testing showed bonding between the composites and bone, ranging from 130-145 N after 2 weeks of implantation. After the longest implantation period, 16 weeks, the GR-HA composite prepared with the higher content of CaO-P2O5 glass showed the highest bonding force, 606 +/- 45 N, compared to 459 +/- 30 N for sintered HA. Development of immature bone and modifications in the turnover of a more mature bone on the surface of GR-HA composites were similar to those on sintered HA.

Animals↗

PubMed2001

Adsorption and release studies of sodium ampicillin from hydroxyapatite and glass-reinforced hydroxyapatite composites.

As a potential therapy for periodontitis, sodium ampicillin, a broad spectrum antibiotic, was adsorbed onto hydroxyapatite (HA) and glass-reinforced hydroxyaptite (GR-HA) composites, and was subsequently released in vitro. The sodium ampicillin, was adsorbed more on HA compared to the GR-HA composites. X-ray diffraction (XRD) and Rietveld analysis were used to identify and quantify the levels of HA and beta-tricalcium phosphate (beta-TCP) in the microstructure of the GR-HA composites. Lattice parameters changes were observed for the beta-TCP phase dependant on the amount of glass added. The release kinetics were shown to be divided into three stages, the first of which where a large amount of sodium ampicillin is released, followed by a slower release rate and then a final stage where the release amount approaches zero, until no more sodium ampicillin was present. X-ray photoeletron spectroscopy (XPS) studies were carried out in order to ensure that the entire antibiotic adsorbed onto the materials had been released. These kinetics studies have indicated the possibility of using these materials as possible carriers for drug delivery.

Adsorption↗

PubMed2001

Effect of chemical composition on hydrophobicity and zeta potential of plasma sprayed HA/CaO-P2O5 glass coatings.

Multilayered plasma sprayed coatings on the surface of Ti-6Al-4V alloys have been prepared, which were composed of an underlayer of HA and a surface layer of a CaO-P2O5 glass-HA composite, with 2 or 4wt% of glass. Contact angle and surface tension variation with time, for both water and a protein solution, were determined by the sessile and pendent drop methods respectively using the ADSA-P software. Wettability studies showed that hydrophobicity of the coatings increase with the glass addition. The work of adhesion of albumin was also altered in a controlled manner by the addition of the CaO-P2O5 glass, being lower on the composite coatings than on HA. Zeta potential (ZP) results showed that composite coatings presented a higher net negative charge than HA coatings and that ZP values were also influenced by the content of the glass. This study demonstrated that the surface properties of those coatings may be modified by the addition of CaO-P2O5 glass.

Calcium Compounds↗