Induction of bioactivity of a non-bioactive glass-ceramic by a chemical treatment

Mechanical and physical properties of calcium silicate/alumina composite for biomedical engineering applications

The focus of this study is to investigate the effect of Al2O3 on α-calcium silicate (α-CaSiO3) ceramic. α-CaSiO3 was synthesized from CaO and SiO2 using mechanochemical method followed by calcinations at 1000°C. α-CaSiO3 and alumina were grinded using ball mill to create mixtures, containing 0-50w% of Al2O3 loadings. The powders were uniaxially pressed and followed by cold isostatic pressing (CIP) in order to achieve greater uniformity of compaction and to increase the shape capability. Afterward, the compaction was sintered in a resistive element furnace at both 1150°C and 1250°C with a 5h holding time. It was found that alumina reacted with α-CaSiO3 and formed alumina-rich calcium aluminates after sintering. An addition of 15wt% of Al2O3 powder at 1250°C were found to improve the hardness and fracture toughness of the calcium silicate. It was also observed that the average grain sizes of α-CaSiO3 /Al2O3 composite were maintained 500-700nm after sintering process.

Synthesis and inflammatory response of a novel silk fibroin scaffold containing BMP7 adenovirus for bone regeneration

Gene therapy has garnished tremendous awareness for the repair of osseous defects. It exhibits high efficiency gene transfer and osteogenic differentiation potential making it well suitable for the sustained delivery of growth factors to local tissues. In the present study a simplified solution-based in situ biomimetic synthesis method is demonstrated for bone morphogenetic protein 7 (BMP7) adenovirus combined with silk fibroin scaffolds. This scaffold not only provides the three dimensional space for bone ingrowth, but also releases the BMP7 adenovirus which targets its secretion by host cells in vivo. Scaffolds were tested both in vitro for their osteogenic potential as well as in vivo in a critical-size calvarial defect in mice. Scaffolds loaded with bone morphogenetic protein 7 adenovirus (adBMP7) were able to sustain release of adBMP7 for up to 21 days and support cell proliferation and differentiation to bone forming osteoblasts. Calvarial defects treated with scaffolds containing adBMP7 significantly induced new bone formation in vivo. To demonstrate immuno-compatibility with host tissues, IL-2, IL-6 and TNF-α were measured up to 4 weeks post-implantation. Although these scaffolds demonstrated an initial pro-inflammatory response, levels of IL-2, IL-6 and TNF-α returned to baseline control values at either 2 or 4 weeks post-implantation demonstrating long term compatibility for growth factor delivery via gene therapy. The results from the present study indicate the promise of gene delivery scaffold systems for robust, low cost, and high quality bone tissue engineering applications.

Preparation of luminescent and mesoporous Eu3+/Tb3+ doped calcium silicate microspheres as drug carriers via a template route

Luminescent and mesoporous Eu(3+)/Tb(3+) doped calcium silicate microspheres (LMCS) were synthesized by using mesoporous silica spheres as the templates. The LMCS and drug-loaded samples were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), N(2) adsorption/desorption, and photoluminescence (PL) spectra. The results reveal that the LMCS have uniform spherical morphology with a diameter around 400 nm and the mesopore size of 6 nm. The prepared samples exhibit little cytotoxicity at concentrations below 5 mg mL(-1) via MTT assay. In addition, drug storage/release properties of the LMCS were demonstrated for ibuprofen (IBU). The obtained LMCS can be used to encapsulate drugs and release them. Under excitation by UV light, the IBU-loaded samples still show the characteristic (5)D(0)-(7)F(1-3) emission lines of Eu(3+) and the characteristic (5)D(4)-(7)F(3-6) emission lines of Tb(3+). The PL intensity of Eu(3+) in the drug carrier system increases with the cumulative released amount of IBU, making the drug release able to be tracked or monitored by the change of luminescence of Eu(3+). The LMCS reported here with mesoporous structure, good biocompatibility and luminescent property can be a promising drug delivery carrier.

Sol-gel bioactive glass-ceramics Part II: Glass-ceramics in the CaO-SiO2-P2O5-MgO system

Ceramics, with basic composition based on the CaO-SiO2-P2O5-MgO system with different Ca+ Mg/P+Si molar ratio (R), were prepared via polystep sol-gel technique. The structure of the obtained ceramic materials has been studied by XRD, FTIR spectroscopy, and SEM. X-ray diffraction showed the presence of akermanite and HA for the sample with R = 1.68 and Mg substituted β-TCP and silicocarnotite for the sample with R = 2.16, after thermal treatment at 1200°C/2 h. The obtained results are in good agreement with FTIR. In vitro test for bioactivity in static condition proved that the carbonate containing hydroxyapatite (CO3HA) can be formed on the surface of the synthesized samples. CO3HA consisted of both A- and B-type CO 32− ions. SEM micrographs depicted different forms of HA particles, precipitated on the surface after soaking in 1.5 simulated body fluid (SBF).

Evaluation of physical-chemical properties and biocompatibility of a microrough and smooth bioactive glass particles

The purpose of this study was to evaluate physical-chemical and biocompatibility characteristics of a simple synthesis and low cost experimental bioactive glass. Physical and chemical properties were analyzed using scanning electron microscopy (SEM), X-ray energy dispersive (EDX), X-ray fluorescence (XRF) and X-ray diffraction (XRD). The biomaterials were subcutaneously implanted into rats, according to the following groups: G1, PerioGlastrade mark; G2, Biograntrade mark, G3, Experimental Bioactive Glass U (BGU) and G4, Control (Sham). After 7, 15, 21, 45, and 60 days, 5 animals/group/period were sacrificed and the subcutaneous tissue was dissected for histological and histometric analysis, considering inflammatory reaction and granulation area, presence of polymorphonuclear (PMN), monuclear (MN) and fibroblast (F) cells. SEM analysis of biomaterials showed irregular particles with different surface characteristics. EDX showed calcium, oxygen, sodium, phosphorus and silicon; XRF revealed silica oxide (SiO(2)), sodium oxide (Na(2)O), calcium oxide (CaO) and phosphorus oxide (P(2)O(5)). XRD indicated non crystalline phase. Measurement of tissue reaction showed similar results among the experimental groups at 45 and 60 days. No difference was found for PMN, MN and F cell counts. All biomaterials exhibited partial resorption. In conclusion, the experimental bioactive glass analyzed showed physical and chemical characteristics similar to the commercially available biomaterials, and was considered biocompatible, being partially reabsorbed in the subcutaneous tissue.

A template route to the preparation of mesoporous amorphous calcium silicate with high in vitro bone-forming bioactivity

The mesoporous amorphous calcium silicate (MACS) was first synthesized using mesoporous silica SBA-15 as both the template and silicon source, and Ca(NO(3))(2) as the calcium source. The MACS shows a well-defined mesoporous structure with high specific surface area. In vitro bioactivity studies of the MACS were carried out by soaking it in simulated body fluid (SBF) solutions for 4 h up to 5 days. Owing to the high specific surface area and pore volume, the MACS had a significantly enhanced bone-forming bioactivity compared with the conventional amorphous CaSiO(3). The MACS did develop a carbonate-containing hydroxyapatite (HCA) layer on the surface after being immersed in SBF for 4 h with near-spherical agglomerated hydroxyapatite (HA) nanoparticles. At longer soaking times, the number of agglomerated HA particles increased and the surface structure of the samples became more compact. Such MACS could be useful in developing new biomaterials and may have potential use in implanting and drug delivery for tissue regeneration.

The in vivo performance of a sol-gel glass and a glass-ceramic in the treatment of limited bone defects

The in vivo evaluation, in New Zealand rabbits, of a SiO(2)-P(2)O(5)-CaO sol-gel glass and a SiO(2)-P(2)O(5)-CaO-MgO glass-ceramic, both bioactive in Kokubo's simulated body fluid (SBF), is presented. Bone defects, performed in the lateral aspect of distal right femoral epiphysis, 5mm in diameter and 4mm in depth, were filled with (i) sol-gel glass disks, (ii) glass-ceramic disks, or (iii) no material (control group). Each group included 8 mature and 8 immature rabbits. A 4-month radiographic study showed good implant stability without axial deviation of extremities in immature animals and periosteal growth and remodelling around and over the bone defect. After sacrifice, the macroscopic study showed healing of bone defects, with bone coating over the implants. The morphometric study showed a more generous bone formation in animals receiving sol-gel glass or glass-ceramic disks than in control group. Histomorphometric study showed an intimate union of the new-formed bone to the implants. This study allows considering both materials as eligible for bone substitution or repair. Their indications could include cavities filling and the coating of implant surfaces. The minimum degradation of glass-ceramic disks suggests its application in locations of load or transmission forces. As specific indication in growth plate surgery, both materials could be used as material of interposition after bony bridges resection.

Direct measurement of interactions between adsorbed vitronectin layers: The influence of ionic strength and pH

Vitronectin (Vn) is an adhesive protein in the plasma serum and plays an important role in cell attachment, spreading, and proliferation. The interactions between protein bovine vitronectin layers adsorbed onto a silica probe and a mica surface have been investigated with the use of atomic force microscopy (AFM). Adsorption of vitronectin was confirmed by XPS surface analysis. The force-separation curves and pull-off forces were measured as a function of ionic strength and solution pH. The pull-off force (adhesion force) decreased as the salt concentration increased, which suggests that some binding domains of this protein may associate with the ionic species and reduce its binding ability. Discrete jumps, or discontinuities, in the separation force curve were observed to extend to a maximum of 300 nm, evidence that the protein molecules bridge between the surfaces. As a function of pH, the adhesion force on separation of the protein-coated surfaces showed a maximum at pH 5 (i.e.p. of vitronectin), decreasing in magnitude at lower and higher pH values. At pH 5, the approaching curves illustrated a jump-in force; whereas for pH values away from 5, the approaching force curves were repulsive. Correlation of the interaction forces with Vn conformational changes in different pH environments, directly visualized with the use of AFM imaging, was developed. In its i.e.p. region, the Vn molecular conformation appeared to be dense and compact. Significantly, at wounds/injured sites the pH is low (approximately 5) which this study discovered to facilitate adsorption and formation of vitronectin aggregates, known to trigger their subsequent biological functions.

Role of acid attack in the in vitro bioactivity of a glass-ceramic of the 3CaO.P2O5-CaO.SiO2-CaO.MgO.2SiO2 system

A non-bioactive glass-ceramic (GC13) that contains hydroxyapatite (Ca5(PO4)3OH), diopside (CaMg(SiO3)2) and althausite (Mg2 PO4OH) as crystalline phases has been obtained by thermal treatment of a parent bioactive glass (G13) of nominal composition (wt%) 40.0 CaO-34.5 SiO2-16.5 P2O5-8.5 MgO-0.5CaF2. To induce bioactivity, GC13 was chemically treated with 1 M HCl for different periods of time. After chemical etching the in vitro studies showed formation of an apatite-like surface layer. In this article the influence of etching time both on the surface composition of the glass-ceramic and on the growth rate of the apatite layer is studied. It is concluded that the presence of hydroxyapatite in the glass-ceramic, associated to microstructural fluctuations, can favour apatite deposition in vitro.

In vitro bioactivity of glass and glass-ceramics of the 3CaO x P2O5-CaO x SiO2-CaO x MgO x 2SiO2 system

A glass of nominal composition (wt%) 40.0 CaO-34.5 SiO2-16.5 P2O5-8.5 MgO-0.5 CaF2 has been obtained (G13). The glass showed in vitro bioactivity evidenced by the formation on its surface of a calcium phosphate-rich layer when soaked in a solution with ionic composition analogous to human plasma. By thermal treatments of G13, a glass-ceramic (GC13) containing apatite, diopside, althausite and akermanite as crystalline phases was developed. GC13 as-made did not show in vitro bioactivity. However, after chemical treatment of GC13 with 1 M HCl (GC13-HCl), the in vitro studies showed the formation of an apatite-like layer covering certain areas of the material surface. The influence of both chemical and morphological factors on the in vitro bioactivity has been studied.