Typical silicate bioactive glasses are known to crystallize readily during the processing of porous scaffolds. While such crystallization does not fully suppress the bioactivity, the presence of significantly large amounts of crystals leads to a decrease in the rate of reaction of the glass and an uncontrolled release of ions. Furthermore, due to the non-congruent dissolution of silicate glasses, these materials have been shown to remain within the surgical site even 14 years postoperation. Therefore, a need for bioactive materials that can dissolve with higher conversion rates and more effectively are required. Within this work, boron was introduced, in the FDA approved S53P4 glass, at the expense of SiO2. The crystallization and sintering-ability of the newly developed glasses were investigated by differential thermal analysis. All the glasses were found to crystallize primarily from the surface, and the crystal phase precipitating was dependent upon the quantity of B2O3 incorporated. The rate of crystallization was found to be lower for the glasses were 25, 50 and 75 % of the SiO2 was replaced with B2O3. These glasses were further sintered into porous scaffolds using simple heat sintering. The impact of glass particles size and heat treatment temperature on the scaffolds porosity and average pore size was investigated. Scaffolds with porosity ranging from 10 to 60 % with compressive strength ranging from 1 to 35 MPa, were produced. The scaffolds remained amorphous during processing and their ability to rapidly precipitate hydroxycarbonated apatite was maintained. This is of particular interest in the field of tissue engineering as the scaffolds degradation and reaction was generally faster and offers higher controllability as opposed to current partially/fully crystallized scaffolds obtained from the FDA approved bioactive glasses.
IntroductionAs of today, autografts are still the gold standard for the repair of large bone defects. However, with the aging and growing population, the number of surgical intervention to regenerate bone defects are increasing. The limited supply and patient site morbidity is a well-known disadvantage and problem [1][2]. Allografts are an option. However, the limited tissue bank as well as the higher risk for infection and cellular and humoral immune reactions limits their usage [3]. The quest for synthetic biomaterials to replace the autografts is more than two decades old. However, as of today no materials have shown as promising a result as autografts. Q. Chen et al. have reported the optimum characteristic that the synthetic materials should have to find great potential as bone grafts [4]. The bone graft should be a 3D construct (3D scaffold) not only biocompatible, but ultimately biodegradable and osteoconductive with highly interconnected porosity. Pore size should be no less than 100 µm to allow cell and fluid penetration as well as angiogenesis. In general, interconnected pores of at least 100 µm and an open porosity of over 50% is considered the minimum requirement for ti...
We present an experimental study on the effect of the photonic stop-band (PSB) on the random laser (RL) emission characteristics of a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) doped polyvinyl alcohol (PVA) film (DCM-PVA). The film, having its refractive index greater than the substrate and density variations at the microscopic scale, acts as a disordered active planar waveguide. The propagation losses for the transverse magnetic (TM) and transverse electric (TE) modes of the waveguide are observed to be 0.50 and 0.74 dB/cm, respectively, at λ = 632.8 nm. The waveguiding DCM-PVA film is then sandwiched between two silica 3-D photonic crystals (opals). The overlap of the DCM-PVA photoluminescence with the PSB of the opals is controlled by the choice of the particle size used for opal fabrication. The random lasing threshold studies have been carried out for both TM and TE polarizations for opals with different particle sizes. A reduction in the threshold of RL emission, with respect to the DCM-PVA waveguide, by about 20 times (to 0.67 mJ/cm2) is observed when the photoluminescence of the DCM-PVA film overlaps with the PSB of the opal structure for TM polarization, showing that the embedding of an RL in an engineered PSB material is an effective way to reduce the thresholds of RLs.
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