Papers by Author: Young Hwan Park

Abstract: The mechanical performance of cancellous bone is characterized using experimental measure of parameters (elastic moduli, permeability, etc.) which apply poroelasticity theory. Poroelastic investigations of bone are being extended to investigations of micro-mechanisms of remodeling processes and transport of metabolic product in bone. To understand physiological and pathological behavior of human skeletal system, the accurate measurement of biomechanical properties for bone is the one of important works. Particularly, the microscopic measurement is very important since the biomechanical behavior at the small scale of bone could be closely related to the remodeling of bone. But microscopic measurement of permeability coefficient which is one of important parameter of poroelasticity theory was never measured. In this study, a small scale permeability testing machine was developed to measure accurate coefficient of microscopic specimen permeability. Total of twenty one cylindrical cancellous specimens with a diameter of 500
from seven fresh male and female lumbar vertebrae (14, 39, 59, 61, 69, 75, and 77 years) were fabricated using a micro-milling machine having a resolution of 10
. To determine the directional permeability, bone coordinate was set to be x1 (longitudinal axis) and others were set as x2 (posteroanterior axis) and x3 (latero-medial axis). The measured mean permeability (± SD) values of each direction from x1 to x3 were 9 5.56 10− × (S.D. ± 10 7.10 10− × ), 9 6.66 10− × (S.D. ± 10 6.56 10− × ), and 9 7.04 10− × (S.D. ± 10 8.47 10− × ) m2/Pa/sec, respectively. Mean value in the x1 direction of specimens were the smallest (p<0.01) in comparison to x2 and x3 directions.

Abstract: Experimental measurement of pore pressure generation in lacunocanalicular network of trabeculae is never measured, although the characteristics could be important for bone remodeling. In this study, the pore pressure generation in micro-trabecular specimens within the elastic range was measured in vitro using a specially designed micro-experimental setup and a MEMS based micro-pressure transducer. Then, a quasi-static loading (9㎛/min) was applied up to the strain of 0.4 % with measuring pore pressure generations in the undrained and drained conditions. 49.2 ± 4.45 KPa of pore pressure generation at the 0.4% strain was found in the undrained condition. In contrast, no pore pressure generation was measured in the drained condition. The result could let us know the amount of a possible maximum pore pressure generation in lacunocanalicular network of trabeculae within the elastic range.

Abstract: Multi-directional mechanical properties of human cancellous bone tissue were never measured using a compressive test with microscopic cubic specimens. In this study, a small scale compressive testing machine with nano meter resolution and a measurement system for Poisson’s ratio with sub-nano meter resolution were developed to measure accurate microscopic mechanical properties of human CBT. The measured mean longitudinal (E1), postero-anterior (E2), and lateromedial (E3) elastic moduli were 3.47 GPa (S.D. ±0.41), 2.57 GPa (S.D. ±0.28), and 2.54 GPa (S.D. ±0.22), respectively. ANOVA showed that the longitudinal elastic modulus (E1) was significantly (p < 0.01) greater than the postero-anterior (E2) and latero-medial (E3) elastic moduli. For Poisson’s ratios, ν12 was significantly (p <0.01) higher than ν23 and ν31.

Abstract: Osseointegration (OI) could be described as the modality for stable fixation of titanium implant to bone structure. The OI has become a realized phenomenon of importance in the dental and rehabilitation sciences since recently developed dentures and artificial limbs are directly attached to human skeleton by using osseointegrated (OI) implants. Previously, a study showed that bone strain generated potential (SGP) that is an electrical potential and considered to be generated by fluid flow in bone could be used as a parameter to examine the amount of OI on bone-implant interface. Since no study was performed to understand effects of loading rate changes on behavior of SGP for the bone-implant composite, rate dependent behavior of SGP was investigated in this study. Four different displacement rates, 100, 200, 500, and 1000 mm per minute were applied to the bone-implant composites. During the compression tests, SGPs were also measured. Magnitude of SGP was found to be significantly increased as the rate increased for OI bone-implant composite. In contrast, the time duration of SGP was decreased as the rate increased. These results could imply that the temporal SGP behavior of bone-implant composite is significantly affected by the loading rate.

Abstract: In this study, a minimally invasive assessment using bone strain generated potential (SGP) was developed to examine the amount of osseointegration (OI) at bone-implant interface. SGP is generated by interstitial fluid flow in porous bone structure. Four experimental white New Zealand rabbits underwent pure titanium implant insertion surgery to tibia after amputation. After surgery, two animals were kept in small cages with minimal movement (Group 1). In contrast, the other rabbits were kept in a large cage that was large enough for jumping and walking (Group 2). At the end of the 5 weeks, all experimental animals were euthanized and the amputated tibia-implants were harvested. Then, a quasi-static force was applied to a bone site near the bone-implant interface for each tibia-implant specimen. Also, SGPs were measured near the interface using needle or probe electrodes. After the measurements, digital radiographs were taken to check the amount of OI for the interfaces. Full OI was observed for animals in Group 1. However, incomplete OI was found for animals in Group 2. Also, significant difference was found for mean SGP values between Group 1 and 2. The results could imply that SGP could be used as a minimally invasive assessment method to check the OI at the bone-implant interface.