Study of visible light activated polymerization in BisGMA-TEGDMA monomers with Type 1 and Type 2 photoinitiators using Raman spectroscopy.

OBJECTIVE: The goal of the study was to characterize the efficiency of polymerization of Type 1 and Type 2 initiators for visible light cure of a BisGMA-TEGDMA monomer mixture. METHODS: Raman spectroscopy was used to follow conversion during polymerization of a BisGMA-TEGDMA mixture using a Type I photoinitiator diphenyl(2,4,6 dimethylbenzoyl)phosphine oxide (TPO) and a Type II photoinitiator camphorquinone (CQ) and an amine, both initiators at 0.5wt.%. Different light exposure times and storage times after light curing were used as variables. RESULTS: There was a significant difference between the relative exposure times of TPO and CQ/amine (5s for TPO vs. 20s for CQ/Amine) for attaining maximum % conversion (78% in TPO vs. 65% in CQ/Amine). There was also a significant difference in the effect of storage time (no effect in TPO vs. increased % conversion with CQ/Amine). These effects are attributed to differences in the rate controlling steps of free radical generation in Type 1/Type 2 initiators, and the potential for radiative and non-radiative energy losses in CQ/Amine in its excited state. CONCLUSIONS: The results confirm that photo-polymerization of BisGMA is much more efficient with TPO than with CQ/amine. Both exposure and storage times were important variables in CQ/amine, but not in TPO. SIGNIFICANCE: TPO photolysis generates significantly more free radicals with potentially very little radiative and non-radiative energy loss in comparison with CQ/amine. The resulting improved monomer conversion is of major importance in resisting chemical and mechanical degradation and preventing toxicological adverse effects.

Silver nanoparticle impregnated poly (ɛ-caprolactone) scaffolds: optimization of antimicrobial and noncytotoxic concentrations.

Use of silver nanoparticles (SNPs) for control of implant-associated infection is a promising strategy, if optimum antimicrobial yet nontoxic dose to mammalian cells is identified. This study was done to determine essential quantity of SNPs, which stimulate antimicrobial activity without cytotoxicity, when immobilized on poly (ɛ-caprolactone) (PCL) scaffold proposed for vascular tissue engineering. During SNP synthesis and scaffold preparation, nanoparticle aggregation was protected using poly (ethylene glycol). Transmission electron microscopy was used to characterize SNP size and to detect its mobilization from scaffold to culture medium. Antimicrobial property of the SNP and its dose response was tested using both Gram-positive and Gram-negative bacteria by zone of inhibition assay. Endothelial cells (ECs), the main cell type required for vascular tissue engineering, were grown on scaffolds to identify the nontoxic dose. After seeding EC on scaffolds, cell attachment, spreading, and viability/survival were detected using specific markers by flow cytometric/fluorescence microscopic analysis. Real-time polymerase chain reaction detected effect of SNPs on mRNA expression of selected EC-specific functional proteins. Results suggest that even devoid of antibiotics in the medium, 0.1% (w/w) SNP on PCL scaffold is antimicrobial while nontoxic to EC at cellular and molecular level once cultured on the SNP-PCL scaffold.

Development of a fibrin composite-coated poly(epsilon-caprolactone) scaffold for potential vascular tissue engineering applications.

Poor cell adhesion, cytotoxicity of degradation products and lack of biological signals for cell growth, survival, and tissue generation are the limitations in the use of a biodegradable polymer scaffold for vascular tissue engineering. We have fabricated a hybrid scaffold by integrating physicochemical characteristics of poly(epsilon-caprolactone) (PCL) and biomimetic property of a composite of fibrin, fibronectin, gelatin, growth factors, and proteoglycans to improve EC growth on the scaffold. Solvent cast porous films of poly(epsilon-caprolactone) was prepared using PEG as a porogen. Porosity varied between 5 and 200 microm, and FTIR spectroscopy confirmed structural aspects of PCL. Films kept in PBS for 60 days showed tensile strength and elongation matching native blood vessel. Slow degradation of the scaffold was demonstrated by gravimetric analysis and molecular weight determination. Human umbilical vein endothelial cell (HUVEC) adhesion and proliferation on bare films were minimal. FTIR spectroscopy and environmental scanning electron microscopy (ESEM) of PCL-fibrin hybrid scaffold confirmed the presence of fibrin composite on PCL film. HUVEC was subsequently cultured on hybrid scaffold, and continuous EC lining was observed in 15 and 30 days of culture using ESEM. Results suggest that the new hybrid scaffold can be a suitable candidate for cardiovascular tissue engineering.