Analysis of surface layers on bioactive glasses

FT-Raman spectroscopy proves to be a powerful technique to study surface reactions on bioactive glasses and it eliminates the fluorescence of the organic phase of whole bone, thereby making it possible to compare the reaction layers formed on bioactive glasses with the mineral phase of bone. The spectrum of hydroxycarbonate apatite (HCA) developed on the bioactive glasses is closer to that of bone than synthetic hydroxyapatite (HA) and closely matches that of bone mineral obtained by deproteination of whole human femoral cortical bone.     

Genetic design of bioactive glass

This paper reviews the discovery that controlled release of biologically active Ca and Si ions from bioactive glasses leads to the up-regulation and activation of seven families of genes in osteoprogenitor cells that give rise to rapid bone regeneration. This finding offers the possibility of creating a new generation of gene activating glasses designed specially for tissue engineering and in situ regeneration of tissues. Recent findings also indicate that controlled release of lower concentrations of ionic dissolution products from bioactive glasses can be used to induce angiogenesis and thereby offer potential for design of gene activating glasses for soft tissue regeneration.     

Bioceramics

Ceramics used for the repair and reconstruction of diseased or damaged parts of the musculo-skeletal system, termed bioceramics, may be bioinert (e.g., alumina and zirconia), resorbable (e.g., tricalcium phosphate), bioactive (e.g., hydroxyapatite, bioactive glasses, and glass-ceramics), or porous for tissue ingrowth (e.g., hydroxyapatite-coated metals). Applications include replacements for hips, knees, teeth, tendons, and ligaments and repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jaw bone, spinal fusion, and bone repair after tumor surgery. Pyrolytic carbon coatings are thromboresistant and are used for prosthetic heart valves. The mechanisms of tissue bonding to bioactive ceramics have resulted in the molecular design of bioceramics for interfacial bonding with hard and soft tissue. Bioactive composites are being developed with high toughness and elastic modulus that match with bone. Therapeutic treatment of cancer has been achieved by localized delivery of radioactive isotopes via glass beads. Clinical success of bioceramics has led to a remarkable advance in the quality of life for millions of people.     

In situ spectral monitoring of mRNA translation in embryonic stem cells during differentiation in vitro

Raman microspectroscopy was used to determine biochemical markers during the differentiation of embryonic murine stem cells (mES) in vitro. Such markers are useful to determine the differentiation status of ES cells cultured on biomaterials. Raman spectra of mES cells as undifferentiated, spontaneously differentiated (4 days), and differentiated cells via formation of embryoid bodies (16, 20 days) were analyzed. Unsupervised hierarchical cluster analysis and principal component analysis were used to determine biochemical differences between mES cells in various states of differentiation. The undifferentiated cells were characterized by high scores of the first principal component (PC1, 49% variance). Similarity between the PC1 loading and the Raman spectrum of RNA indicated a high concentration of RNA in mES cells compared to differentiated cells. The ratio between the peak areas of RNA and proteins was used as a measure of mRNA translation. Using the same peak area ratio, it was possible to differentiate even between mES as undifferentiated and in early stages of differentiation (4 days). These findings were correlated with biological studies reporting high levels of nontranslated mRNA during early embryonic development. Therefore, the RNA translation obtained from the Raman spectra can be used as marker of differentiation state of mES cells.     

Effect of surfactant concentration and composition on the structure and properties of sol-gel-derived bioactive glass foam scaffolds for tissue engineering

Bioactive glasses are known to have the ability to regenerate bone, and to release ionic biological stimuli that promote bone cell proliferation by gene activation, but their use has been restricted mainly to the form of powder, granules or small monoliths. Resorbable 3D macroporous bioactive scaffolds have been produced for tissue engineering applications by foaming sol-gel-derived bioactive glasses. The foams exhibit a hierarchical structure, with interconnected macropores (10–500 m), which provide the potential for tissue ingrowth and mesopores (2–50 nm), which enhance bioactivity and release of ionic products. The macroporous matrices were produced by the foaming of sol-gel glasses with the use of a surfactant. Three glass systems SiO₂, SiO₂-CaO and SiO₂-CaO-P₂O₅were foamed using various concentrations of surfactant, in order to investigate the effect of surfactant concentration and composition on the structure and properties of the hierarchical construct.     

SURFACE CHARGE OF SOL-GEL DERIVED ALUMINAS AS A FUNCTION OF CALCINATION TEMPERATURE

The sol-gel route for preparing alumina is thought to yield a unique molecular structure. Thus the powder characteristics of sol-gel derived aluminas are expected to be different from alumina powders derived by traditional processing methods. In this study wet alumina gels, after the sol-gel reaction was completed, were dried and calcined at 25^°C, 300^°C, 500^°C, 800^°C, 1100^°C, and 1400^°C following the methods of Yoldas and Clark and Lannutti. The initial points of zeta potential reversal (PZR) of the calcined powders determined from electrophoretic mobilities are 9.4, 10.2, 8.6, 10.6, 4.2 and 8.3, respectively for the above calcination series. The PZR of the alumina powders increased with calcination temperature up to 800^°C, with the exception of the alumina calcined at 500^°C. The PZR's of powders calcined between 800-1400^°C decreased. The anomalous PZR of the alumina calcined at 500^°C is due to catalytically formed carboxylates from the residual sec-butano1. The general trend of PZR change for other phases of gel derived alumina was compared with previously reported electrolcinetic behavior of traditional alumina powders and no significant differences were found.     

Nuclear waste solids

Glass and polycrystalline materials for high-level radioactive waste immobilization are discussed. Borosilicate glass has been selected as the waste form for defence high-level radwaste in the US. Since release of the radionuclides to the biosphere is the major concern, this paper focuses on the potential interactions between the waste form and its surroundings. In addition to laboratory data, results from field testing are also presented in order to provide a comprehensive overview of glass leaching under near repository-like conditions.     

The effect of micro-gravity and bioactive surfaces on the mineralization of bone

The loss of bone density with age especially for women, is one of the most serious health complications affecting humans An increased incidence of fractured hips and long bones, and collapse of vertebrae are all due to loss of bone density. Demineralization of bone also poses one of the most severe limitations on long-duration manned space flight. This study investigates the hypothesis that chemical effects responsible for enhanced osteoblast differentiation and proliferation observed in-vitro and in-vivo at 1-gravity with bioactive glasses may be sufficient to prevent the turn-off of bone cells that occurs in μ-g or other reduced loading environments as a consequence of age or immobility. To conduct this work, the authors developed an embryonic mouse long-bone model to examine the interaction of bioactive surfaces and ions with the influence of a simulated μ-g environment.     

Biomaterials: a forecast for the future

The survivability half-life of prostheses made with current bio-inert materials is approximately 15 years, depending upon clinical applications. Bioactive materials improve device lifetime but have mechanical limitations. This paper proposes that biomaterials research needs to focus on regeneration of tissues instead of replacement. Alternatives are: use hierarchical bioactive scaffolds to engineer in vitro living cellular constructs for transplantation, or use resorbable bioactive particulates or porous networks to activate in vivo the mechanisms of tissue regeneration.