Papers by Author: Sang Ok Ko

Abstract: "Osseo" refers to bone and "integration" refers to how a prosthesis can be integrated with the bone in residual limbs both arms and legs. Osseointegration(OI) was originally defined as a direct structural and functional connection between ordered living bone and the surface of a loadcarrying implant. 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 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 according to the point on behavior of SGP for the boneimplant composite. In this study, we used a multi-channel measurement system and investigated SGP according to the point. Four white New Zealand rabbits underwent pure titanium implant insertion surgery to tibia after amputation. After checking full OI at the end of the 5 weeks, experimental animals were euthanized and the amputated tibia-implants were harvested. Holes of 0.5mm in diameter were made on the tissue of the tibia and electrodes of 0.16mm in diameter were inserted to the holes. Then, the instrumented bone-implant composites were placed to a servo material testing machine to apply axial compressive displacement loadings. During the compression tests, SGPs were also measured. Magnitude of SGP was found to be significantly increased near bone and implant interface for the osseointegrated bone-implant composite.

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 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 implant-bone interface. SGP generation is known to require intraosseous fluid flow related with generations of pore pressure gradient in bone. Therefore, SGP would interact with properties determining interstitial fluid flow characteristics such as viscosity, velocity, flow path directions, and interstitial fluid flow boundary conditions. Since interstitial fluid flow characteristics in bone are governed by pore pressure gradient, it could be possible to predict SGP indirectly through the prediction of pore pressure generation in bone. The aim of this study is to predict the distribution of pore pressure in OI bone-implant composite representing a completely osseointegrated rabbit tibia-titanium implant composite. The theoretical background of this prediction is based on the poroelasticity of 2-phase material that grounds on fluid flow and behavior of cortical bone material. In this study, we constructed a finite element (FE) model of the composite from images of micro-CT scanning. In the next step, we examined analysis of the FE model about pore pressure by using ABAQUS. In this analysis, the constitutive behavior was externally computed by utilizing a user subroutine. The results showed the different spatial distributions of pore pressure in the composite. The magnitudes of pore pressure were found to be significantly increased when the position was approached for the interface of implant-bone. Further analytical study is required to fully understand relationships between SGP and pore pressure distributions in OI bone-implant composite materials.

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 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 implant-bone interface. Since no study was performed to understand SGP behavior as a function of position for the implant-bone composite, a one-dimensional map of SGP was constructed along the longitudinal direction of the composite. For the purpose, nine electrodes including one reference were instrumented on the wet composite for the one-dimensional mapping of SGP during compression tests. The peak magnitudes of SGP were found to be significantly increased when the measurement position was approached for the interface of implant-bone. The results could indicate that the spatial SGP behavior of osseointegrated implant-bone composite could be caused by the interface of the implant-bone.

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.