Biomedical subjects

J D Santos

Publications and source records attributed to J D Santos.

At least 19 recordsLinked to original sources

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↗

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↗

PubMed2000

Direct and indirect effects of P2O5 glass reinforced-hydroxyapatite composites on the growth and function of osteoblast-like cells.

Human osteoblast-like cells were plated on hydroxyapatite and P2O5-glass reinforced hydroxyapatite composite discs. They were also cultured in the presence of media obtained by incubating the discs in the absence of cells. The effects of these direct and indirect interactions were examined by measuring cell proliferation and the expression of certain key extracellular matrix antigens. One composite was found to initially delay cell growth, while the extract of a different composite appeared to down-regulate DNA synthesis. Flow cytometry analysis showed that growth directly on the discs had little effect on collagen type I, but reduced fibronectin and osteocalcin levels. The extracts of the materials generally had less effect, although one extract obtained from the glass-reinforced hydroxyapatite significantly down-regulated fibronectin. These in vitro studies thus suggest that there were only few differences overall in the growth of the cells directly on the glass-reinforced compared with the hydroxyapatite discs and also only relatively small effects of the extracts on the cells. However, the flow cytometry results suggest that both the materials and the extracts may have a potentially important influence on connective tissue production, and that these effects are both material- and antigen-specific.

Antigens↗

PubMed2000

Structural insights of glass-reinforced hydroxyapatite composites by Rietveld refinement.

Phase transformations and interstitial and/or substitution of trace elements during the liquid-phase sintering process of P2O5-CaO-MgO glass-reinforced hydroxyapatite (GR-HA) composites were examined by X-ray diffraction and Rietveld analyses. Using the Rietveld method for structure refinement, changes in the lattice parameters of the two main phases of the composites, hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), as well as changes in several bond lengths and in the occupancy of the hydroxyl oxygen site in the HA phase structure were assessed. The glasses gave rise to formation of between approximately 45 and 50% of beta-TCP, with evidence for the Mg2+ enhancing the formation of beta-TCP. Between 1,300 and 1,350 degrees C, the beta-TCP inverts to alpha-TCP, without further decomposition of the residual HA. The glasses showed evidence for stabilisation of the hydroxyl group located in the hydroxyl channels. This is supported by measurements of the hydroxyl channel radius (Rc), the Ca2-OH bond length and the hydroxyl oxygen occupancy (Oocc). Results showed that the Mg2+ containing glasses induced the beta-TCP phase formation in the structure of GR-HA composites and retarded the beta-TCP into alpha-TCP transformation at higher temperatures. The chemical composition of the P2O5 glasses also induces modifications in the lattice parameters of the crystallographic phases present in the microstructure of the composites. This suggests some substitution of Mg2 + -for-Ca2+ in the beta-TCP structure during the liquid-phase sintering process.

Biocompatible Materials↗

PubMed2000

Microstructural dependence of Young's and shear moduli of P2O5 glass reinforced hydroxyapatite for biomedical applications.

P2O5 glass reinforced hydroxyapatite composite materials were prepared through a liquid-phase sintering process. Secondary phases, beta- and alpha-tricalcium phosphates (beta-TCP and alpha-TCP), were formed in the microstructure of the composites, due to the reaction between the liquid glassy phase and the hydroxyapatite matrix. The dynamic Young's modulus (E) and shear modulus (G) of these composites were determined using an impulse excitation method. By applying the Duckworth-Knudsen equation, the elastic property results were correlated with the relative proportion of beta-TCP and alpha-TCP phases and with the porosity percentage present in the microstructure. Glass reinforced hydroxyapatite composites showed lower Young's and shear moduli than unmodified hydroxyapatite, mainly due to the presence of beta-TCP phase. The Duckworth-Knudsen model demonstrated an exponential dependence of E and G modulus with porosity and mathematical equations were derived for composite materials with porosity correction factors (b) of 4.04 and 4.11, respectively, indicating that porosity largely decreased both E and G moduli.

Biocompatible Materials↗

PubMed2000

Flow cytometry analysis of the effects of pre-immersion on the biocompatibility of glass-reinforced hydroxyapatite plasma-sprayed coatings.

Multilayered coatings composed of mixtures of HA and P2O5-based bioactive glasses are of potential clinical benefit in orthopaedic and dental surgery. Pre-immersion of these materials has been reported to further enhance their efficacy in vivo, although the precise biological effects of this treatment are not yet known. In this study we have therefore prepared double-layer plasma-sprayed coatings and evaluated the effects of pre-immersion on the growth and function of human osteosarcoma cells in vitro, using the MTT assay and flow cytometry analysis, respectively. The results showed that the increase in numbers of viable cells was the same or elevated following incubation on the pre-immersed HA and glass-reinforced HA coatings compared with the non-immersed materials. In addition, the expression of bone sialoprotein and fibronectin, two key connective tissue antigens, was up-regulated in cultures grown on the pre-immersed surfaces compared with the non-treated materials. Moreover, cell numbers and antigen expression both improved as the proportion of glass increased, particularly in the pre-immersed samples. Our findings thus suggest that the immersion treatment of these materials appeared to improve the response of these bone-like cells.

Biocompatible Materials↗

PubMed1999

Flow cytometry analysis of effects of glass on response of osteosarcoma cells to plasma-sprayed hydroxyapatite/CaO-P(2)O(5) coatings.

Multilayered coatings composed of mixtures of hydroxyapatite (HA) and P(2)O(5)-based bioactive glasses offer potential clinical benefits in orthopedic and dental surgery. In this study double-layer plasma-sprayed coatings were prepared and the biological response evaluated in tissue culture using two human osteosarcoma cell lines, MG63 and HOS TE85 (HOS). The cells were cultured on the materials and the effects on cell growth were determined using a spectrophometric assay of a mitochondrial enzyme that is active in viable cells. While none of the materials influenced the growth of the MG63 cells, the HOS cells appeared to undergo less proliferation on all the HA materials. Flow cytometry analysis was carried out using rabbit antibodies against osteonectin, osteopontin, bone sialoprotein, fibronectin, and collagen type I to measure the effects of the materials on key cellular functions. The results showed that the materials downregulated the expression of these extracellular matrix antigens by MG63 cells whereas they had less effect on the HOS cells compared to the same cells incubated on a plastic surface. Notably, with both cell lines the composite with the higher percentage of glass restored the production of connective tissue proteins to levels that were more similar to those present in the control cells.

Animals↗

PubMed1999

Hydrophobicity, surface tension, and zeta potential measurements of glass-reinforced hydroxyapatite composites.

Wettability and zeta potential studies were performed to characterize the hydrophobicity, surface tension, and surface charge of P2O5-glass-reinforced hydroxyapatite composites. Quantitative phase analysis was performed by the Rietveld method using GSAS software applied to X-ray diffractograms. Surface charge was assessed by zeta potential measurements. Protein adsorption studies were performed using vitronectin. Contact angles and surface tensions variation with time were determined by the sessile and pendent drop techniques, respectively, using ADSA-P software. The highest (-18.1 mV) and lowest (-28.7 mV) values of zeta potential were found for hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), respectively, with composite materials presenting values in between. All studied bioceramic materials showed similar solid surface tension. For HA and beta-TCP, solid surface tensions of 46.7 and 45.3 mJ/m2, respectively, were obtained, while composites presented intermediate surface tension values. The dispersive component of surface tension was the predominant one for all materials studied. Adhesion work values between the vitronectin solution and HA and beta-TCP were found to be 79.8 and 88.0 mJ/m2, respectively, while the 4.0 wt % glass composites showed slightly lower values than the 2.5 wt % ones. The presence of beta-TCP influenced surface charge, hydrophobicity, and protein adsorption of the glass-reinforced HA composites, and therefore indirectly affected cell-biomaterial interactions.

Adsorption↗

PubMed1999

CaO-P2O5 glass hydroxyapatite double-layer plasma-sprayed coating: in vitro bioactivity evaluation.

Double-layer composite coatings composed of a P2O5-based glass/Ca10(PO4)6(OH)2 (HA) mixture top layer and a simple HA underlayer, on Ti-6Al-4V substrates, were prepared using a plasma-spraying technique. The in vitro bioactivity of these coatings was assessed by immersion testing in simulated body fluid. Both scanning electron microscopy (SEM) analysis and the ionic solution changes followed by atomic absorption spectroscopy and the molybdenum blue method demonstrated that these composite coatings induce a faster surface Ca-P layer formation than the simple HA coatings used as a control. X-ray photoelectron spectroscopy (XPS) analysis demonstrated that the Ca-P layer formed was apatite. The combination of SEM and XPS analyses showed that the apatite layer was a calcium-deficient hydroxyapatite with a Ca/P ranging from 1.3 to 1.4 with CO3(2-) groups contained in the structure.

Alloys↗

PubMed1999

Glass-reinforced hydroxyapatite composites: secondary phase proportions and densification effects on biaxial bending strength.

CaO-P(2)O(5) glasses with additions of MgO and CaF(2) were used as a sintering aid of hydroxyapatite, and glass-reinforced hydroxyapatite composites obtained. Glasses promoted significant changes in the microstructure of the composites, namely with the formation of tricalcium phosphate secondary phases, beta and alpha-TCP. Quantitative phase analysis was performed by the Rietveld method using General Structure Analysis Software. Grain size measurements were carried out on SEM photomicrographs, using a planimetric procedure according to ASTM E 112-88. Flexural bending strength was determined from concentric ring-on-ring testing. Flexural bending strength (FBS) of glass-reinforced hydroxyapatite composites was found to be about twice or three times higher than that of unreinforced hydroxyapatite and tended to depend more on porosity and beta and alpha-TCP secondary phases, rather than on grain size. Traces of alpha-tricalcium phosphate significantly enhanced the strength of the composites. Using the rule of mixtures to estimate the zero porosity bending strength, the Duckworth-Knudsen model applied to the composites gave a porosity correction factor, b, with a value of 4.02. Weibull statistics were also used to analyze biaxial strength data and the level of reinforcement obtained by comparing failure probability for the composites and for the unreinforced hydroxyapatite. Lower activation energies for grain growth were observed for the composites compared to unreinforced hydroxyapatite, which should be attributed to the presence of a liquid glassy phase that promotes atomic diffusion during the sintering process.

Biocompatible Materials↗

PubMed1999

Glass-reinforced hydroxyapatite composites: fracture toughness and hardness dependence on microstructural characteristics.

Fracture toughness and hardness properties of CaO-P2O5 glass-reinforced hydroxyapatite composites have been assessed using indentation techniques and results calculated according to Laugier and Evans' equations. Both properties showed to be dependent upon several microstructural characteristics, namely residual porosity and the percentage of secondary beta and alpha tricalcium phosphate phases in the structure of the composites. Composites presented a Palmqvist-type indentation crack system, which is the specific crack system addressed by Laugier's approach. Fracture toughness determinations according to Evan's equation, which is a universal one and adapted to both median and Palmqvist crack systems, did not correlate well with Laugier determinations.

Biocompatible Materials↗

PubMed1998

Flow cytometry for assessing biocompatibility.

Flow cytometry (FCM) was examined as a possible procedure for measuring in vitro the biocompatibility of implant materials for orthopedic and dental surgery. The human osteoblast-like cell line MG63 was grown on hydroxyapatite (HA) and P2O5 glass-reinforced HA composite discs and compared with the same cells grown on polystyrene culture dishes. While morphological observation at the light and electron microscopic levels showed no major deleterious effects, FCM indicated that cell size was somewhat reduced, particularly by growth on the HA composite. Morever, this material also appeared to delay the progression of the cells from the G0/G1 into the S phase of the cell cycle. In addition to this low level of inhibition of cell growth relative to control cultures, FCM analysis also demonstrated that the glass-reinforced HA caused some down-regulation of the expression of osteocalcin and fibronectin, two antigens which play a vital part in the integrity and function of bone and soft connective tissue, respectively. These results thus show, first, that although HA and the HA composite used in these experiments were generally biocompatible, they nevertheless had certain suboptimal effects on the cells; and second, that FCM could be a highly useful procedure for effectively screening and evaluating important biological responses to implant materials.

Biocompatible Materials↗

PubMed1998

Glass-reinforced hydroxyapatite: a comprehensive study of the effect of glass composition on the crystallography of the composite.

Glass-reinforced HA composites were produced using phosphate-based glasses, and a structure refinement was carried out to determine the effect of the glass on the structure of the residual HA. Quantitative phase analysis showed that the glass causes some of the HA to decompose to beta-TCP and, at higher temperatures, to alpha-TCP. It also was indicated that when three phases were present, the formation of the alpha-TCP arose from decomposition of the beta-TCP and not from further decomposition of HA to alpha-TCP. The unit cell dimensions showed a decrease in the a axis and an increase in the c axis, giving an overall unit cell decrease in volume. There also was a significant effect based on the amount of glass added. The changes found in the composite containing the 4 wt% glass were attributed to the loss of carbonate and loss of hydroxyl. This was expected to cause shrinkage in the unit cell; however this was not seen, and therefore the major changes in the unit cell were attributed to the ions from the glass taking an interstitial role in the HA structure, thus not allowing the unit cell to shrink as much as expected.

Ceramics↗