Development and in vitro characterization of sol-gel derived CaO-P2O5-SiO2-ZnO bioglass

Mesoporous bioactive scaffolds prepared with cerium-, gallium- and zinc-containing glasses

Mesoporous bioactive glass scaffolds (MBG_Scs), based on 80% SiO(2)-15% CaO-5% P(2)O(5) (in mol.%) mesoporous sol-gel glasses substituted with Ce(2)O(3), Ga(2)O(3) (both 0.2% or 1.0%) and ZnO (0.4% or 2.0%), were synthesized by combination of evaporation-induced self-assembly and rapid prototyping techniques. Cerium, gallium and zinc trace elements were selected because of their inherent beneficial biological properties. Fabricated scaffolds were characterized and compared with unsubstituted scaffold (B_Sc). All of them contained well interconnected ultralarge pores (pores >400 μm) ideal for vascular ingrowth and proliferation of cells. Macropores of size 100-400 μm were present inside the scaffolds. In addition, low-angle X-ray diffraction showed that B_Sc and scaffolds with substituent contents up to 0.4% exhibited ordered mesoporosity useful for hosting molecules with biological activity. The textural properties of B_Sc were a surface area of 398 m(2) g(-1), a pore diameter of 4.3 nm and a pore volume of 0.43 cm(3) g(-1). A slight decrease in surface area and pore volume was observed upon substitution with no distinct effect on pore diameter. In addition, all the MBG_Scs except 2.0% ZnO_Sc showed quite quick in vitro bioactive response. Hence, the present study is a positive addition to ongoing research into preparing bone tissue engineering scaffolds from bioceramics containing elements of therapeutic significance.

Development and bioactivity evaluation of bioglasses with low Na2O content based on the system Na 2O-CaO-MgO-P 2O 5-SiO 2

Osteoconductive bioglasses, free of K(2)O and Al(2)O(3) and with content of Na(2)O lower than 10 mol%, were designed based on the ratio (SiO(2) + MgO)/(P(2)O(5) + CaO + Na(2)O) in the system Na(2)O-CaO-MgO-P(2)O(5)-SiO(2). The developed glasses have shown a strong potential for the formation of hydroxycarbonated apatite (HCA) in vitro. The particles of HCA aggregates tend to be of finer size with increasing the ratio of (SiO(2) + MgO)/(CaO + P(2)O(5) + Na(2)O) in the glass chemical composition indicating significant bioactivity. Critical size bone defects created in the femurs of albino adult female rats, and grafted with the glass particles for 12 weeks post implantation, were completely healed by filling with mineralized bone matrix without infection showing a strong potential for new bone formation in vivo. Osteoblasts and osteocytes were observed close to the surface of the granular implants with active areas of bone deposition, resorption and remodelling. The bioglass with lowest (SiO(2) + MgO)/(CaO + P(2)O(5) + Na(2)O) ratio has shown the highest bioactivity while the bioglass with the highest (SiO(2) + MgO)/(CaO + P(2)O(5) + Na(2)O) has shown the lowest bioactivity. The newly formed bone in vivo has shown a similar structure to that of the original bone as indicated by the histology and microstructural results. In addition, Ca/P molar ratio of the newly formed bone was found to be (~1.67), which is similar to that of the original bone.

Regression model for predicting selected thermal properties of next-generation bioactive glasses

The compositional palette traditionally used to develop bioactive glasses has grown in recent times to include therapeutic inorganic species such as zinc and strontium. Historical regression models used for predicting the properties of bioactive glasses as a function of composition have not evolved to consider this expanded compositional space. In this work, nonlinear regression analysis was applied to historical data to construct predictive models for the glass transition temperature and the coefficient of thermal expansion of next-generation bioactive glasses. The new regression models also provide some degree of improvement over existing models in predicting the properties of traditional bioactive glasses.

Silver coated bioactive glass particles for wound healing applications

Bioactive glass particles (0.42SiO(2)-0.15CaO-0.23Na(2)O-0.20ZnO) of varying size (<90 μm and 425-850 μm) were synthesized and coated with silver (Ag) to produce Ag coated particles (PAg). These were compared against the uncoated analogous particles (Pcon.). Surface area analysis determined that Ag coating of the glass particles resulted in increased the surface area from 2.90 to 9.12 m(2)/g (90 μm) and 1.09-7.71 m(2)/g (425-850 μm). Scanning electron microscopy determined that the Ag coating remained at the surface and there was little diffusion through the bulk. Antibacterial (Escherichia coli--13 mm and Staphylococcus epidermidis--12 mm) and antifungal testing (Candida albicans--7.7 mm) determined that small Ag-coated glass particles exhibited the largest inhibition zones compared to uncoated particles. pH analysis determined an overall higher pH consider in the smaller particles, where after 24 h the large uncoated and Ag coated particles were 8.27 and 8.74 respectively, while the smaller uncoated and Ag coated particles attained pH values of 9.63 and 9.35 respectively.

Metallic ions as therapeutic agents in tissue engineering scaffolds: an overview of their biological applications and strategies for new developments

This article provides an overview on the application of metallic ions in the fields of regenerative medicine and tissue engineering, focusing on their therapeutic applications and the need to design strategies for controlling the release of loaded ions from biomaterial scaffolds. A detailed summary of relevant metallic ions with potential use in tissue engineering approaches is presented. Remaining challenges in the field and directions for future research efforts with focus on the key variables needed to be taken into account when considering the controlled release of metallic ions in tissue engineering therapeutics are also highlighted.

Phytic acid derived bioactive CaO-P2O5-SiO2 gel-glasses

The possibility of using phytic acid as a precursor to synthesize CaO-P(2)O(5)-SiO(2) glasses by sol-gel method has been explored and the pseudo ternary phase diagram has been established. It was shown that gel-glasses over a broader range of compositions could be prepared compared to other phosphorus precursors or melt-quenching method. Furthermore, phytic acid was found to assist calcium being incorporated into glass networks. In vitro tests in simulated body fluid (SBF) were performed on the above gel-glasses and it was found that they were bioactive over a much broader compositional range especially at high phosphate content, thus enabling one to design bioactive materials with various degradation rates by adjusting the phosphate content.

Highly adherent bioactive glass thin films synthetized by magnetron sputtering at low temperature

Thin (380-510 nm) films of a low silica content bioglass with MgO, B(2)O(3), and CaF(2) as additives were deposited at low-temperature (150°C) by radio-frequency magnetron sputtering onto titanium substrates. The influence of sputtering conditions on morphology, structure, composition, bonding strength and in vitro bioactivity of sputtered bioglass films was investigated. Excellent pull-out adherence (~73 MPa) was obtained when using a 0.3 Pa argon sputtering pressure (BG-a). The adherence declined (~46 MPa) upon increasing the working pressure to 0.4 Pa (BG-b) or when using a reactive gas mixture (~50 MPa). The SBF tests clearly demonstrated strong biomineralization features for all bioglass sputtered films. The biomineralization rate increased from BG-a to BG-b, and yet more for BG-c. A well-crystallized calcium hydrogen phosphate-like phase was observed after 3 and 15 days of immersion in SBF in all bioglass layers, which transformed monotonously into hydroxyapatite under prolonged SBF immersion. Alkali and alkali-earth salts (NaCl, KCl and CaCO(3)) were also found at the surface of samples soaked in SBF for 30 days. The study indicated that features such as composition, structure, adherence and bioactivity of bioglass films can be tailored simply by altering the magnetron sputtering working conditions, proving that this less explored technique is a promising alternative for preparing implant-type coatings.

New approach to bone tissue engineering: simultaneous application of hydroxyapatite and bioactive glass coated on a poly(L-lactic acid) scaffold

A combination of bioceramics and polymeric nanofibers holds promising potential for bone tissue engineering applications. In the present study, hydroxyapatite (HA), bioactive glass (BG), and tricalcium phosphate (TCP) particles were coated on the surface of electrospun poly(L-lactic acid) (PLLA) nanofibers, and the capacity of the PLLA, BG-PLLA, HA-PLLA, HA-BG-PLLA, and TCP-PLLA scaffolds for bone regeneration was investigated in rat critical-size defects using digital mammography, multislice spiral-computed tomography (MSCT) imaging, and histological analysis. Electrospun scaffolds exhibited a nanofibrous structure with a homogeneous distribution of bioceramics along the surface of PLLA nanofibers. A total of 8 weeks after implantation, no sign of complication or inflammation was observed at the site of the calvarial bone defect. On the basis of imaging analysis, a higher level of bone reconstruction was observed in the animals receiving HA-, BG-, and TCP-coated scaffolds compared to an untreated control group. In addition, simultaneous coating of HA and BG induced the highest regeneration among all groups. Histological staining confirmed these findings and also showed an efficient osseointegration in HA-BG-coated nanofibers. On the whole, it was demonstrated that nanofibrous structures could serve as an appropriate support to guide the healing process, and coating their surface with bioceramics enhanced bone reconstruction. These bioceramic-coated scaffolds can be used as new bone-graft substitutes capable of efficiently inducing osteoconduction and osseointegration in orthopedic fractures and defects.

Direct cytotoxicity evaluation of 63S bioactive glass and bone-derived hydroxyapatite particles using yeast model and human chondrocyte cells by microcalorimetry

In this study, the cytotoxicity evaluation of prepared 63S bioactive glass and bone-derived hydroxyapatite particles with yeast and human chondrocyte cells was carried out using isothermal micro-nano calorimetry (IMNC), which is a new method for studying cell/biomaterial interactions. Bioactive glass particles were made via sol-gel method and hydroxyapatite was obtained from bovine bone. Elemental analysis was carried out by XRF and EDXRF. Amorphous structure of the glass and completely crystalline structure of HA were detected by XRD analysis. Finally, the cytotoxicity of bioactive glass and bone-derived HA particles with yeast and cultured human chondrocyte cells was evaluated using IMNC. The results confirmed the viability, growth and proliferation of human chondrocyte cells in contact with 63S bioactive glass, and bone-derived HA particles. Also the results indicated that yeast model which is much easier to handle, can be considered as a good proxy and can provide a rapid primary estimate of the ranges to be used in assays involving human cells. All of these results confirmed that IMNC is a convenient method which caters to measuring the cell-biomaterial interactions alongside the current methods.

Ion Release Behavior and Apatite-Forming Ability of Sol-Gel Derived 70S30C Bioactive Glass with Magnesium/Zinc Substitution

Bioactive glasses not only can bond to hard tissues of the body, are also able to release ions that have stimulatory effects on cells and so are regarded as promising candidate materials for gene activating purposes in tissue engineering applications. In this research the effect of co-substitution of Magnesium and Zinc for Calcium on bioactivity of binary sol-gel derived glass 70S30C (70 mol. % SiO2, 30 mol. % CaO) was investigated. Calcium phosphates forming ability tests and investigation of glass degradation products in simulated body fluid (SBF) were performed as follows.After sol-gel synthesis of glass powders of comparable and under 38 μm particle size distributions, their state of being amorphous was investigated using X-ray diffraction. Then for in vitro investigation of bioactivity, ion release, pH change and Calcium phosphate formation during immersion of glass powders in SBF at 37 ͦC up to 2 weeks were studied. Infrared spectroscopy was performed on the reacted glass powders.Results indicate that substitution of Zinc for Calcium suppresses crystalline apatite formation more effectively than substitution of Magnesium for Calcium and help us design modified compositions of magnesium and zinc containing bioactive glasses that can find applications in bone and also cartillage tissue engineering.

Gamma Irradiation Studies I. Dental Grafts

The development of nanoceramics-polymer composites and bioactive materials such as calcium phosphates and bioglasses and ceramics especially hydroxyapatite (HAp) and β-tricalcium phosphate (TCP) for bone regeneration has been carried out for bone regeneration. Due to their resorption in the body and direct contact with tissues, it is necessary to sterilize the dental graft before administration to the patient. Three different dental graft materials including TCP, bioglass, and equine bone tissue (G1, G2, and G3, respectively) were studied in this study. The effects of γ irradiation were evaluated with different analytical methods (organoleptic analysis, FTIR, DSC, TGA, and SEM) and microbiological analysis (sterility, pyrogenity, and sterility assurance level (SAL) determination). The physicochemical results indicated that G1 is the most γ stable (optimum) dental graft material for γ radiation sterilization with minimum changes in chemical and physical properties in comparison with other two dental graft materials. G3, was the most sensitive dental graft material according to organoleptic investigations, TGA and SEM analysis. Another aspect of this study was, to investigate the effect of ethylene oxide (EtO) sterilization on optimum dental graft material, G1 and the comparison of two sterilization methods with analytical and microbiological examinations. The resorption times and resorption characteristics of γ sterilized dental graft material (G1G) and EtO sterilized one (G1E) were evaluated on New Zealand rabbits for 12 weeks. Histological studies showed that TCP containing dental graft material, G1, did not induce inflammation in bone and soft tissue. Resorption and bone formation of G1G was faster than G1E. Total resorption time of G1 was 12 weeks for both sterilization groups. The analytical, microbiological and in vivo results suggest that the dental graft G1 can be sterilized with γ radiation safely with validated doses lower than medical γ sterilization dose, 25 kGy.

Substitutions of cerium, gallium and zinc in ordered mesoporous bioactive glasses

Ordered mesoporous glasses based on the 80% SiO(2)-15% CaO-5% P(2)O(5) system including up to 3.5% Ce(2)O(3), 3.5% Ga(2)O(3) or 7.0% ZnO (in mol.%) were synthesized by the evaporation-induced self-assembly process using Pluronic® 123 as a surfactant. An ordered hexagonal mesophase was observed in both the unsubstituted glass (denoted in this paper as B: blank) and glasses containing <0.4% of substituent by X-ray diffraction, transmission electron microscopy and electron diffraction. The increase in the amount of substituent led to a decrease in the mesopore order. B glass exhibited good textural properties: S(BET)=515m(2)g(-1), D(P)=4.7nm and V(P)=0.58cm(3)g(-1). With the inclusion of cerium, gallium and zinc oxides the textural properties decreased, but remained in amounts useful for clinical applications. Zinc-containing samples showed the highest decrement in the textural properties. Substituted glasses exhibited a quick in vitro bioactive response except when the ZnO content was over 0.4%. Taking into account the ordered mesoporosity, the quick in vitro bioactive response and the added values of the substituents, this new family of glasses are promising candidates for applications in bone tissue engineering.

A review of the biological response to ionic dissolution products from bioactive glasses and glass-ceramics

Several inorganic materials such as special compositions of silicate glasses, glass-ceramics and calcium phosphates have been shown to be bioactive and resorbable and to exhibit appropriate mechanical properties which make them suitable for bone tissue engineering applications. However, the exact mechanism of interaction between the ionic dissolution products of such inorganic materials and human cells are not fully understood, which has prompted considerable research work in the biomaterials community during the last decade. This review comprehensively covers literature reports which have investigated specifically the effect of dissolution products of silicate bioactive glasses and glass-ceramics in relation to osteogenesis and angiogenesis. Particularly, recent advances made in fabricating dense biomaterials and scaffolds doped with trace elements (e.g. Zn, Sr, Mg, and Cu) and investigations on the effect of these elements on the scaffold biological performance are summarized and discussed in detail. Clearly, the biological response to artificial materials depends on many parameters such as chemical composition, topography, porosity and grain size. This review, however, focuses only on the ion release kinetics of the materials and the specific effect of the released ionic dissolution products on human cell behaviour, providing also a scope for future investigations and identifying specific research needs to advance the field. The biological performance of pure and doped silicate glasses, phosphate based glasses with novel specific compositions as well as several other silicate based compounds are discussed in detail. Cells investigated in the reviewed articles include human osteoblastic and osteoclastic cells as well as endothelial cells and stem cells.

Porous bioactive glass scaffolds for local drug delivery in osteomyelitis: development and in vitro characterization

A new bioactive glass-based scaffold was developed for local delivery of drugs in case of osteomyelitis. Bioactive glass having a new composition was prepared and converted into porous scaffold. The bioactivity of the resulting scaffold was examined by in vitro acellular method. The scaffolds were loaded with two different drugs, an antibacterial or antifungal drug. The effects of the size of the scaffold, drug concentration, and dissolution medium on drug release were studied. The scaffolds were further coated with a degradable natural polymer, chitosan, to further control the drug release. Both the glass and scaffold were bioactive. The scaffolds released both the drugs for 6 weeks, in vitro. The results indicated that the bigger the size and the higher the drug concentration, the better was the release profile. The scaffolds appeared to be suitable for local delivery of the drugs in cases of osteomyelitis.

Biomineralization capability of adherent bio-glass films prepared by magnetron sputtering

Radiofrequency magnetron sputtering deposition at low temperature (150 degrees C) was used to deposit bioactive glass coatings onto titanium substrates. Three different working atmospheres were used: Ar 100%, Ar + 7%O(2), and Ar + 20%O(2). The preliminary adhesion tests (pull-out) produced excellent adhesion values (approximately 75 MPa) for the as-deposited bio-glass films. Bioactivity tests in simulated body fluid were carried out for 30 days. SEM-EDS, XRD and FTIR measurements were performed. The tests clearly showed strong bioactive features for all the prepared films. The best biomineralization capability, expressed by the thickest chemically grown carbonated hydroxyapatite layer, was obtained for the bio-glass coating sputtered in a reactive atmosphere with 7% O(2).

Physico-chemical and in vitro biological evaluation of strontium/calcium silicophosphate glass

Strontium is known to reduce bone resorption and stimulate bone formation. Incorporation of strontium into calcium phosphate bioceramics has been widely reported. In this work, calcium and calcium/strontium silicophosphate glasses were synthesized from the sol-gel process and their rheological, thermal, and in vitro biological properties were studied and compared to each other. The results showed that the gel viscosity and thus the rate of gel formation increased by using strontium in glass composition and by increasing aging temperature. In strontium-containing glass, the crystallization temperature increased and the type of the crystallized phase was different to that of strontium-free glass. Both glasses favored precipitation of calcium phosphate layer when they were soaked in simulated body fluid; however strontium seemed to retard the rate of precipitation slightly. The in vitro biodegradation rate of the strontium/calcium silicophosphate glass was higher than that of strontium-free one. The cell culture experiments carried out using rat calvaria osteoblasts showed that the incorporation of strontium into the glass composition stimulated proliferation of the cells and enhanced their alkaline phosphatase activity, depending on cell culture period.

Zinc-containing bioactive glasses: surface reactivity and behaviour towards endothelial cells

This paper reports a physico-chemical study devoted to reactivity towards hydroxo-carbonate apatite (HCA) formation of bioactive glass 45S5 (H glass; commercially known as Bioglass) and of two preparations of zinc-doped 45S5-derived systems (HZ5, HZ20), immersed in Tris(hydroxymethyl)aminomethane (Tris) and Dulbecco's modified Eagle's medium (DMEM) buffer solutions. The activity/toxicity of the glasses was also tested using endothelial cells (EC). Zn caused a drastic reduction in the overall leaching activity of glasses and, at high Zn concentration (HZ20), the formation of HCA on the glass surface was thoroughly inhibited. The presence of Zn also decreased the increment of pH after glass immersion in both Tris and DMEM solution. EC are known to be very sensitive to pH changes and, for this reason, the rapid increase in pH brought about by H glass dissolution is likely to affect cell adhesion and spreading, whereas the high zinc release from HZ20 causes a drastic reduction in cell proliferation after a long contact time (approximately 1 week). This study shows that only HZ5 glass containing 5 wt.% Zn presents at the same time: reduced solubility, bioactivity (monitored by HCA formation) and conditions allowing EC growth over a 6-day period.