Abstract: Accurate measurement of the mechanical properties of artificial or cultivated cartilage is a major factor for determining successive regeneration of defective soft tissues. In this study, we developed a novel method that enabled the bulk modulus (k-modulus) to be measured nondestructively using the relationship between volume and pressure of living soft tissues. In order to validate this method we estimated the bulk modulus of soft silicone rubbers using our new method and a conventional method. The results showed a 5 ~ 10% difference between the results obtained with the two methods. Our method was used subsequently to measure the mechanical properties of cultivated cartilage samples (collagen gel type), that had been incubated for four weeks in the presence or absence of human articular chondrocytes (HACs). Our experiments showed that cultivated cartilage tissues grown in the presence of HACs had a higher bulk modulus (120 ± 20 kPa) than samples grown without HACs (90 ± 15 kPa). The results indicated that our novel method offered an effective method for measurement of volume changes in minute living soft tissues, with the measurements having a high degree of accuracy and precision. Furthermore, this method has significant advantages over conventional approaches as it can be used to rapidly and accurately evaluate the strength of soft tissues during cultivation without causing damage to the specimen.

Abstract: Stabilization of the fibrous protein collagen is important in biomedical applications. This study investigated the efficacy of degradation control of collagen using (-)-epigallocatechin-3-Ogallate (EGCG). EGCG treatment of collagen in solid state was carried out and collagen sponges produced were characterized by measuring the physicochemical properties such as gel fraction, the enzymatic degradability and cytocompatibility. According to gel fraction, EGCG-treated sponges showed the increase of insolubility compared to intact sponges. It showed that EGCG played a role in a crosslinker of collagen. Through in vitro enzymatic degradation test, EGCG-treated collagen sponges showed significant enhancement of resistance to collagenase in comparison with 25 mM EDC-treated collagen sponges. Also, cell proliferation assays showed that 40 mM EGCG-treated collagen sponges exhibited similar cytocompatibility properties compared with tissue culture plate. In summary, EGCG treatment of collagen sponges increased the stability of collagen. Therefore, crosslinking of collagen based scaffold with EGCG imparted more desirable properties, making it more applicable for use as a scaffold in tissue engineering applications.

Abstract: There are still some existing problems that are common to all absorbable materials; 1) It cannot be subjected to radiosterilization, 2) Sufficient strength cannot be maintained until the complete bone union is obtained. To solve these problems, PLLA and PLLA/HA were mixed with cross-bridge supplementary agent, Triallyl Isocyanurate (TAIC). Using these materials in vivo, we created and tested γ-ray radiosterilized absorbable bone fixation materials.

Abstract: In order to evaluate the mechanical properties of the human skeletal muscles, the elasticity and viscosity of the human calf muscles were measured with Magnetic Resonance Elastography (MRE). MRE is a novel method to measure the mechanical properties of living soft tissues in vivo quantitatively by observing the strain waves propagated in the object. In this study, the shear modulus and viscosity coefficient were measured with MRE. The shear modulus was 3.7 kPa in relaxed state, and increased with increasing the muscle forces. Interestingly, the viscosity was changed with the vibration frequency applied to the muscles, that was 4.5 Pa·s at 100Hz vibration and 2.4 Pa·s at 200Hz vibration. This shows clearly the visco-elastic property.

Abstract: Hydroxyapatite (HA)-granule-implanted cylindrical titanium composites, which uniformly have HA granules on the curved surface, were formed by a hot pressing using HA-granuleimplantation system under the conditions of 1023 K, 1 h, 1960 N in vacuo. Cracks were not observed in the HA granules. The HA-granule-implanted titanium samples were implanted in a mandible of a dog. After 1 year, new thin bones like pillars were selectively structured on the HA granules with bone induction ability. The HA-granule-implantation technique is expected to be useful for designing shape of bone around titanium implant in order to match living bones.

Abstract: To improve the conventional and commercially-available medical adhesives such as cyanoacrylate, aldehyde-based, and fibrin glue, new bioadhesive has been prepared using medical and food additives as starting materials. Aldehyde groups could be easily introduced in dextran in the presence of sodium periodate in aqueous media, and the extent of the introduction could also be controlled. In vitro degradation speed of the hydrogel prepared by mixing of aldehyded dextran with ε-poly(L-lysine) at 37oC significantly varied by acetic anhydride concentration added to ε-poly(L-lysine) from < 5h to > 5 weeks. Bonding strength of the glue was 4 times higher than that of commercial fibrin glue and almost no cytotoxicity was observed, suggesting the development of novel self-degradable bioadhesive.