Hanjong Kim

Dynamic Response of Polyvinyl Alcohol(PVA)-Hydrogel With Different PVA Concentrations

Polyvinyl Alcohol-Hydrogel (PVA-H) is a biomaterial used for manufacturing contact lenses as well as for the medium of drug delivery. Previous studies have also showed that PVA-H exhibits superior biocompatibility with hydrophilic elastic nature. The aim of this study is to examine the possible usage of the PVA-H as cartilage replacement material by determining the static and dynamic mechanical properties of PVA-H with different ratios of polyvinyl alcohol (PVA) and phosphate buffered saline (PBS) compositions.Three different types of PVA-H specimens were made by changing the ratio of PVA (Sigma-Aldrich) and PBS (Sigma-Aldrich) compositions (PVA-H1: 10 wt% PVA and 90 wt% PBS; PVA-H2: 20 wt% PVA and 80 wt% PBS; PVA-H3: 25 wt% PVA, 45 wt% PBS and DMSO 30 wt%). Static and dynamic tensile tests under the loading frequencies of 0.001, 0.01, 0.1, and 1 Hz were carried out to measure the biomechanical properties of PVA-H1, -H2 within PBS solution and -H3 within PBS/ DMSO solution.The equilibrium Young’s moduli (EY) of PVA-H1, -H2 and -H3 evaluated from the static displacement control were 84.2±35.1 kPa (n=10), 254±32.2 kPa (n=10) and 588±38.9 kPa (n=5), respectively. The amplitudes of dynamic tensile moduli were varied from 86.3±33.4 kPa (n=10) at 0.001 Hz to 96.9±42.0 kPa (n=10) at 1 Hz for PVA-H1, from 282.7±26.4 kPa (n=10) at 0.001 Hz to 309.1±32.2 kPa (n=10) at 1 Hz for PVA-H2 and from 643.8±49.8 kPa (n=10) at 0.001 Hz to 747.7±67.7 kPa (n=5) at 1 Hz for PVA-H3. According to the current results, the frequency dependence of the magnitude of the dynamic modulus confirms the viscoelastic nature of PVA-H material. However, it can be noted that the dynamic modulus increases by up to a factor of 1.15 for PVA-H1, 1.22 for PVA-H2 and 1.27 for PVA-H3, showing insignificant viscoelasticity compared with that for cartilage. The result that static and dynamic moduli of PVA-H3 are larger than those of PVA-H1 and PVA-H2 also suggests that the amount of PVA composition in PVA-H plays an important role in improving both static and dynamic mechanical strengths of PVA-H material. The phase angle decreased from 5.2±2.1 ° at 0.001 Hz to −0.3±1.7 ° at 1 Hz for PVA-H1, from 5.6±0.6 ° at 0.001 Hz to −0.3±0.7 ° at 1 Hz for PVA-H2 and from 8.2±1.1 ° at 0.001 Hz to 0.7±0.7 ° at 1 Hz for PVA-H3.Copyright

Biomechanical Effects of Kaempferol Treatments on the Bone Healing Process of Murine Tibia

Kaempferol is a typical flavonol-type flavonoid and has a protective effect on postmenopausal bone loss, and previous studies have reported that kaempferol treated groups show an increase in the callus size and bone mineral density as well as improvement in biomechanical behaviors in comparison with untreated control groups in the bone healing process. The present study aims at investigating the effect of kaempferol treatments on fractured murine tibia, by measuring kaempferol dose-dependent mechanical properties in the bone healing process of murine tibia fracture models.A stabilized fracture was generated at tibia by minor modification of the Hiltunen method for 8 weeks old ICR mice weighting 29.0 ∼ 30.5 g. Experimental mice were divided into 4 groups. Kaempferol of 0.2, 1.0, 5.0 mg/kg (body weight) with 20 % ethanol was administered to 3 groups and the remaining one group was only treated with 20 % ethanol as a control group. Three-point bending fracture tests were conducted to measure the mechanical properties (fracture load, fracture energy, stiffness) of murine tibiae at non-fractured regions near fracture sites 21 days after kaempferol treatments, via a custom-made biomechanical testing system (BTS, KST Co., Korea).The 5.0 mg/kg kaempferol treated group shows higher fracture load (20.54 ±5.04 N) than the control group (17.82 ±5.94 N). Fracture energy, total energy applied to tibia up to bone fracture, exhibited no significant differences between the control group and any of the kampferol treated groups, although both the 1.0 mg/kg kaempferol treated and control groups showed a little higher fracture energy than the 0.2 and 5.0 mg/kg kaempferol treated groups. Bone stiffness also did not show statistically significant differences between the control group and any of the kaempferol treated groups, with the highest stiffness value observed in the 1.0 mg/kg kaempferol treated group.Copyright