Kei Oya

Investigation of a sterilization system using active oxygen species generated by ultraviolet irradiation.

We have been investigating an advanced sterilization system that employs active oxygen species (AOS). We designed the sterilization equipment, including an evacuation system, which generates AOS from pure oxygen gas using ultraviolet irradiation, in order to study the conditions necessary for sterilization in the systems chamber. Using Geobachillus stearothermophilus spores (10(6) CFU) in a sterile bag as a biological indicator (BI) in the chamber of the AOS sterilization apparatus, we examined the viability of the BI as a function of exposure time, assessing the role of the decompression level in the sterilization performance. We found that the survival curves showed exponential reduction, and that the decompression level did not exert a significant influence on the survival curve. Subsequently, we investigated the sterilization effect as influenced by the spatial and environmental temperature variation throughout the chamber, and found that the sterilization effect varied with position, due to the varying environmental temperature in the respective areas. We confirmed that temperature is one of the most important factors influencing sterilization in the chamber, and estimated the temperature effect on the distribution of atomic oxygen concentration, using the quartz crystal microbalance (QCM) method with fluorocarbon thin film prepared by radio frequency sputtering.

37 Mechanical And Structural Properties Of Stem Cell-based Tissue Engineered Constructs (tec) Cultured With Collagen Sheets

Introduction Stem cell-based tissue engineered construct (TEC) biosynthesized from synovium-derived mesenchymal stem cells (MSCs) has a great potential for repairing and regenerating ligaments and tendons1. However, the mechanical and structural properties of the TEC were insufficient for clinical applications. A candidate solution to the problem is to promote the generation of the extracellularmatrix inthe TECusing a special culture withcollagen sheets (CS). Previous studies indicated thattheCS has an abilitytorepair fibrous tissuesin vivo4. In addition, the biosynthesis of extracellular matrix is promoted by cell culturing in the existence of collagen.2 In the present study, TECwas culturedwiththe CS, then the tensile properties of TEC/CS composite were assessed. Materials and Methods The CS wasproduced from porcine corium-derived collagen-rich tissues, through homogenization, centrifugal separation, filtering, and dehydration. It should be noted that the sheets are porous and chemical agent-free materials with collagen density between 20 and 30%. MSCswere obtained from the synovial membranes of human knee joint by means of collagenase treatment. After 5 time passages, the cells were plated at the density of 4.0 × 105 cells/cm2 on the CS (TEC/CS), and ontissue culturepolystyrenedishes (TEC). The cells were culturedto produce construct of extracellular matrix for 1, 4, and 8 weeks in the DMEM1. In addition, the CS was also immersed in the same medium without cells for 4 weeks (CS). TEC/CS, TEC, and CS weresubjected to tensiletest at arate of 0.05 mm/s in a PBS solution at 37 °C using acustom-made micro tensile tester.3 Morphological observations of the tissues were carried out using a scanning electron microscopic (SEM)and an optical microscope with hematoxylin-eosin (HE) staining. Results and discussion The tangent modulus and tensile strengthofTEC/CSgroupwere continuously increased. In addition, those of TEC/CS after 8-week cultivation were significantly higher than those of CS. The load at failure of TEC/CS group was significantly lower than those of CS and TEC groups at 1 week. However, it was increased subsequently and reached to 0.18 ± 0.05 N at 8 weeks, with significant differences vs. CS (0.07 ± 0.02 N) and TEC (0.12 ± 0.05 N) groups. Abstract 37 Figure 1 Morphological observation of TEC/CS composites (S: Surface, C: Cross section). Morphological observation indicated that CS was partially degraded with MSCs invasion into shallow CS layers for 2–4 weeks. However, newly formed fibrous tissues were observed in the CS layers at 8 weeks (Figure 1). It is suggested that these morphological changes corresponded well with the changes in mechanical and structural properties of the TEC/CS composites. References 1 Ando W, et al. Biomaterials. 2007;28:5462–5470 2 Gentleman E, et al. Biomaterials. 2003;24: 3805–3813 3 Nagai H, et al. Japanese Jounal of Clinical Biomechanics. 2006;27:89–93 [in Japanese] 4 Suzuki D, et al. abstract. Jounal of Japanese Clinical Biomechanics. 39