Key Engineering Materials Vols. 342-343

Abstract: Meniscus is the most commonly injured structure in the knee joint. Resection of the meniscus as well as the torn menisci is known to induce the degeneration of the articular cartilage. Replacement of the resected meniscus by allograft is limited by its availability and potential disease transmission. Artificial prostheses are being tried in an attempt to regenerate the meniscal tissue and we developed the biodegradable porous polycaprolactone(PCL) scaffold, which acts as a temporary scaffold to enable the regeneration of a new tissue in time. We report the results of rabbit implantation model. Biodegradable PCL scaffold coated with type I collagen with pores sized 100~150 +m and with compression modulus 400 kpa were fabricated by melt-molding particulate- leaching method. The molds were made using the native meniscus of the rabbit. Medial meniscus of right knee was partially removed through arthrotomy, leaving anterior 1/5 of the meniscus, after sectioning medial collateral ligament. The implant was attached to the peripheral capsule and remnant anterior meniscus with sutures. The medial meniscus of the left knee was removed and served as a control without replacement. The regenerated meniscus was harvested at 4 & 12wks after implantation. In addition to the routine histology of the tissue regenerated and remnant scaffold, junction between the normal meniscus and the regenerated tissue, and cartilage surface degeneration was observed. After 4 and 12 weeks the scaffolds, although considerable amount of the materials remained, were largely filled and covered with fibrous tissue which was assumed to be derived from synovial tissue of peripheral capsule. The tissue grossly resembling the native meniscus was maintained and spindle shaped cells with extracellular matrices were observed histologically. Neither cells with chondrocytic phenotype nor distinct cartilage matrices were observed until 12 weeks. The bonding between the regenerated tissue and the peripheral synovial capsule was firm and solid in all cases. The tissue bridges between the native meniscus and the regenerated tissue were found in 9/10 operated knees. Articular surface degeneration was not different between experimental and control groups except one case. More or less, the extrusion of the meniscus was found in almost all knees. This study revealed that meniscal replacement with PCL polymer prosthesis was feasible and led to adequate tissue formation. Long term studies on adaptive remodeling will be required.

Abstract: Considerable researchers analyzed the effects of hormone treatment on osteoporotic vertebral bones. Hormone treatment of age-related osteoporotic bone has a potential to decrease an incidence of osteoporosis. In the present paper, experimental and simulated tests for the mechanical characteristics of osteoporotic models and their hormone-treated models were investigated. Three dimensional (3D) geometries of the models (rapid prototyped and finite element models) were generated from high resolution micro-computed tomography ($-CT, Skyscan 1076, Skyscan, Belgium) scan data for the central parts of the second lumbar vertebrae. From these 3D geometries, cubic specimens with side length 6.5mm were formed and analyzed. Rapid prototyped (RP) models, instead of the real bone specimen, of vertebral trabecular bones were created in the fused deposition modeling (FDM) machine. In the present study, experimental compressions test for RP models were carried out by the INSTRON testing machine (8874 series, Instron, UK). The mechanical characteristics of finite element (FE) models for simulated compression tests were compared with physical predictions from RP models for experimental compression test. As a result, it is found that the hormone therapy is likely to be less effective than reported by previous researchers. A remarkable agreement was achieved between the results obtained from the experimental tests for RP models and simulated tests for FE models.

Abstract: Several researchers investigated the mechanical characteristics of human trabecular bone using finite element analysis (FEA) based on micro computed tomography (μ-CT). There were few investigations on morphological and mechanical characteristics of vertebral trabecular bones. This study analyzed the relationship between morphological and mechanical characteristics in the regional vertebral trabecular bones using μ-CT and μ-FEA. Two specimens were obtained from the 12th thoracic vertebral bodies of cadavers (85 years female and 48 years male). In each vertebral body, fifteen regions were selected from two-dimensional (2D) images acquired from μ-CT. Voxelbased three-dimensional (3D) finite element models, with 4
4
4 cubic block, were generated from each region for simulated compression test. The relationship between morphological characteristics, such as bone volume fraction, trabecular thickness, trabecular separation, trabecular number and structure model index, and mechanical characteristics, such as structural modulus (E†), was analyzed by bivariate correlation coefficient. As a result, the region of center column and inferior layer had the highest density. However, structural moduli in center column and middle layer were the biggest. The results indicated that there was a regional difference between morphological and mechanical characteristics of vertebral trabecular bone. In addition, for more exact evaluation of osteoporosis, it was recommended to analyze not only the mechanical characteristics but also the morphology characteristics.

Abstract: L9 (34) orthogonal array design was employed to optimize experimental conditions for the preparation of the composite using in situ synthesis method and to analyze the relationships between experimental parameters and mechanical property of the composites. Bending strength of the composite was considered as a target property of the composites. Hydroxyapatite content in the composite, synthesis temperature and pH were chosen as main parameters. As a result of this study, bending strength of the composite appeared in peak with the increase of the hydroxyapatite content of the composites and synthesis pH, while with the increase of temperature, bending strength decreased. Optimum experimental conditions for the synthesis of the composites with higher bending strength were determined. The bending strength of the composites was 90 MPa at the optimal synthesis conditions.

Abstract: Hydroxyapatite/polymer scaffolds with proper biomechanical properties and stable 3-D porous structure were fabricated by combining gas foaming with solvent-casting/particle-leaching technique, in which novel solid H2O2 were used as a porogen. During the manufacturing process, we found that the porosity, compressive strength and microstructure of the composites are varied from each other while different solvents (dichloromethane, acetone, chloroform and 1,4-dioxane) were used. Porosities of the specimens increase from 72±5 to 87±5% in accordance with the increase of boiling point from 39.75 to 101.32 °C, while compressive strength decreased (4.8±0.7- 0.5±0.3 MPa). Interactions of HA/solvent and PLA/solvent together with evaporation dynamic tests of different solvents were investigated. The results show that the evaporation rate of the solvents is the most important factor affecting the final properties of the scaffolds.

Abstract: We fabricated micro-patterned 2.5-D scaffolds using micro-end-milling with controlled pore and island sizes and interconnectivity to determine the effects of the micro-patterns on the cell culturing process. Micro-end-milling can easily realize a high aspect ratio and accuracy, and can be applied to various materials, including those that are biocompatible and biodegradable. Sixteen types of micro-patterned scaffolds were designed and fabricated using the micro-end-milling process. Fibroblasts were seeded and cultured to examine the viability of the developed micropatterned scaffolds and their absorbed cell adhesion. The results confirmed that the fabricated micro-patterns functioned successfully as scaffolds.

Abstract: Twenty implants of 3.75mm in diameter(Neoplant, Neobiotech, Korea) were used to evaluate the correlation between the resonance frequency analysis (RFA) and the radiographic method for periimplant bone change under in vitro conditions. To simulate peri-implant bone change, 2mm-deep 45° range horizontal defect and 2mm-deep 90° range horizontal defect area were serially prepared perpendicular to the X-ray beam after conventional implant insertion. ISQ values and gray values inside threads were measured before and after peri-implant bone defect preparation. ISQ value of resonance frequency analysis was changed according to peri-implant bone change and gray value of radiographic method was changed according to peri-implant bone change. In horizontal defect condition, relatively positive correlation were between ISQ and gray values(r=0.663).

Abstract: Clinical applications of expanded polytetrafluoroethylene (ePTFE) as a small diameter graft have been limited due to its limited patency rates, even though its demands are high. After fabricating the biodegradable PLGA layers on both the inside and outside of ePTFE, long-term in vitro smooth muscle cell culture was performed on the luminal scaffold surface. The fabricated hybrid ePTFE scaffolds were designed to have three distinctive layers and porous structures in the biodegradable layers generated by gas-foaming of the ammonium bicarbonate porogens, i.e. two layers of poly(lactide-co-glycolide) (PLGA) as biodegradable layers for tissue engineering and an ePTFE layer in the middle as a non-biodegradable layer. We evaluated the regenerated vascular tissues after applying either static or pulstile flow on a smooth muscle cells-seeded hybrid scaffold. Analysis of the engineered tissues was performed with SEM for morphological observation and H&E staining for observation of tissue development dependent upon a mode of culture system, flow patterns and scaffold species.

Abstract: This study is to develop a novel method for preparation of the chitosan scaffold having interconnected open pore structure and controlled pore distribution. For this, the effects of addition of non-solvent on chitosan solution were estimated. The porous scaffolds were typically prepared by solid-liquid separation and subsequent sublimation of solvent. Alcohol was used as non-solvent for chitosan. The difference of freezing temperature of each of the components induced the liquidliquid and the liquid-solid phase separation via demixing solution (solvent/non-solvent/chitosan). The morphology, heterogeneous pore distribution and mechanical properties of the scaffolds were examined. The addition of non-solvent in chitosan solution was to make the controlled homogeneous micropores and improved interconnectivity between pores without any surface skin layer. For control chitosan scaffold, the pore size was mainly about 80~100 μm. On the contrary, Pore diameters could be controlled mainly within the range 30~100 μm, with a variation of solvent/non-solvent ratio. The number of minute pore (4~25 μm) over chitosan scaffold increased with increasing ratio of non-solvent. New prepared scaffold exhibited larger value of breaking elongation, more elasticity, but less tensile strength than that of control scaffold.

Abstract: To develop a wound dressing that can be removed from the injured skin without the damage and supporting rapid healing, we made hybrid dressing of small intestinal submucosa (SIS) and hydrogels. Alginate and gelatin used as a dressing material in hydrogels were selected to coat SIS sheets. Characteristics and tendency of wound healing of prepared sheets were investigated. Water uptake ability was greater when the sheets were coated with gelatin than alginate although both showed higher water absorption than the native SIS sheets, but the degradation rate of alginate/gelatin coated SIS was slower than that of native SIS because both polymers may delay contact time of enzyme to the SIS surface in solution. It was observed that less of fibroblasts attached to the natural polymer coated SIS sheets. This property will make easy for the detachment of the sheet from the defected tissue. Wound closure examination showed that prepared sheets enhanced wound healing. It was concluded that prepared alginate/gelatin coated SIS sheets are positively regarded as an appropriate biodegradable wound dressing that is reducing patient’s pain during change of the dressing.