Kwon-Yong Lee

Sterilization using a microwave-induced argon plasma system at atmospheric pressure

The use of microwave plasma for sterilization is relatively new. The advantages of this method are the relatively low temperature, time-savings and its nontoxic nature, in contrast to traditional methods such as heat and gas treatment, and radiation. This study investigated the sterilization effects of microwave-induced argon plasma at atmospheric pressure on materials contaminated with various microorganisms, such as bacteria and fungi. A low-cost and reliable 2.45 GHz, waveguide-based applicator was designed to generate microwave plasma at atmospheric pressure. This system consisted of a 1 kW magnetron power supply, a WR-284 copper waveguide, an applicator including a tuning section, and a nozzle section. Six bacterial and fungal strains were used for the sterilization test. The results showed that regardless of the strain, all the bacteria used in this study were fully sterilized within 20 seconds and all the fungi were sterilized within 1 second. These results show that this sterilization method is ea...

In situ contact analysis of the prosthesis components of Prodisc-L in lumbar spine following total disc replacement.

Study Design. A three-dimensional, nonlinear finite element analysis was performed to predict the in situ contact interaction of prosthesis components of the Prodisc-L in a multisegmental lumbar model following total disc replacement (TDR). Objective. Efforts were made to investigate how the TDR implant contact characteristics could affect the 3-dimensional kinematics, facet loads of the lumbar spine following TDR. Summary of Background Data. Although spinal motion analyses of human lumbar cadaveric models after Prodisc TDR have been widely studied, the interaction of the disc prosthesis, particularly its in situ contact mechanics, is never known. Methods. A validated intact multisegmental lumbar finite element model L2–L4 was altered to accommodate the TDR prosthesis through anterior approach. At L3–L4 disc space, the Prodisc-L of 6° lordosis angle was implanted centrally. The model was subjected to compressive preload and pure moments to create flexion, extension, lateral bending, and axial rotation motion in physiologic range. The contact interaction between the superior component of Prodisc-L and the UHMWPE inlay were assessed in terms of contact region (CR), contact area (CA), and contact pressure (CP). Parameters of range of motion (ROM) and facet loading transfer were simultaneously analyzed and compared with those of the intact model. Results. The predicted contact area was 3.5 times larger in flexion than that observed in extension, whereas the maximum contact pressure in the disc articulation was very similar with 15.1 MPa for flexion and 14.5 MPa for extension. Joint surface incongruence was developed in extension motion. The implanted model exhibited a 91.4% increase in ROM accompanied by a 150.6% rising in facet force during extension, while the flexion motion showed the least effects of TDR. In lateral bending and axial rotation, the abnormal joint “lift off” was not seen. Conclusion. The in situ function of the TDR prosthesis was highly dependent on how well the device could incorporate itself into the mechanical environment in the disc space, which has been determined by the rest of the spinal structures, including the retained disc anulus, articular facets, ligaments, vertebrae, and muscular stabilizers. The different contact interaction of the artificial disc components revealed here could be attributed to the violation of this mechanical environment which, in turn, may bring adverse effects to those spinal elements.

Effects of nonlinearity in the materials used for the semi-rigid pedicle screw systems on biomechanical behaviors of the lumbar spine after surgery*

Recently, various types of semi-rigid pedicle screw fixation systems have been developed for the surgical treatment of the lumbar spine. They were introduced to address the adverse issues commonly found in traditional rigid spinal fusion--abnormally large motion at the adjacent level and subsequent degeneration. The semi-rigid system uses more compliant materials (nitinol or polymers) and/or changes in rod design (coiled or twisted rods) as compared to the conventional rigid straight rods made of Ti alloys (E = 114 GPa, υ = 0.32). However, biomechanical studies on the semi-rigid pedicle screw systems were usually limited to linear modeling of the implant and anatomic elements, which may not be capable of reflecting realistic post-operative motions of the spine. In this study, we evaluated the effects of nonlinearity in materials used for semi-rigid pedicle screw fixation systems to evaluate the changes in biomechanical behaviors using finite element analysis. Changes in range of motion (ROM) and center of rotation (COR) were assessed at the operated and adjacent levels. Actual load-displacement results of the semi-rigid rod from mechanical test were carried out to reflect the nonlinearity of the implant. In addition, nonlinear material properties of various spinal ligaments studies were used for the finite element modeling. The post-operative models were constructed by modifying the previously validated intact model of the L1-S1 spine. Eight different post-operative models were made to address the effects of nonlinearity-with a traditional stiffness modulus rod (with linear ligaments, case 1; with nonlinear ligaments, case 5), with a rigid rod (with linear ligaments, case 2; with nonlinear ligaments, case 6), with a soft rod (with linear ligaments, case 3; with nonlinear ligaments, case 7), and with a nonlinear rod (with linear ligaments, case 4; with nonlinear ligaments, case 8). To simulate the load on the lumbar spine in a neutral posture, follower load (400 N) was applied and then the hybrid loading condition was applied to measure the ROM and COR in the sagittal plane. The more the nonlinearity was included in the model the closer the motion behavior of the device was to that of the intact spine. Furthermore, our results showed that the nonlinearity of the semi-rigid rod was a more sensitive factor than the nonlinearity of the spinal ligaments on biomechanical behavior of the lumbar spine after surgery. Therefore, for better understanding of the surgical effectiveness of the spinal device, more realistic material properties such as nonlinearity of the device and anatomic elements should be considered. In particular, the nonlinear properties of the semi-rigid rod were considered more than the nonlinearity of spinal ligaments.

Wear of UHMWPE against Zirconia/Alumina Composite

The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on a novel low temperature degradation-free zirconia/alumina composite material and on the conventional ceramics (alumina and zirconia) used for a femoral head in total hip joint replacement. The wear of UHMWPE pins against these ceramic disks was evaluated by performing linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in a bovine serum. The weight loss of polyethylene against the novel low temperature degradation-free zirconia/alumina composite disks was much less than conventional ceramics for all tests. The mean weight loss of the polyethylene pins was more in the linear reciprocal sliding test than in the repeat pass rotational sliding test for all kinds of disk materials. Neither the coherent transfer film nor the surface damage was observed on the surface of the novel zirconia/alumina composite disks during the test. In conclusion, the novel zirconia/alumina composite leads the least wear of polyethylene among the tested ceramics and demonstrates the potential as the alternative materials for femoral head in total hip joint replacement.

Protection of Human Fibroblasts from Reactive Oxygen Species by Green Tea Polyphenolic Compounds

The potential protective roles played by green tea compounds (GTPCs) against reactive oxygen species-induced oxidative stress in cultured fetal human dermal fibroblasts (fHDFs) were investigated according to cell viability measurement methods, such as fluorescence double staining followed by flow cytometry (FCM), MTT assay and crystal violet uptake. Oxidative stress was induced in the fHDFs, either by adding 50 mM H2O2 or by the action of 40 U/L xanthine oxidase (XO) in the presence of xanthine (250 µM). FCM analysis was the most suitable to show that both treatments produced a significant (p < 0.05) reduction in the fHDF viability, attributed to its high sensitivity. On the microscopic observations, the cell death with necrotic morphology was appreciably induced by both treatments. These oxidative stress-induced damages were significantly (p < 0.05) prevented by pre-incubating the fHDFs with 200 µg/ml GTPC for 1 h. These results suggest that GTPC can act as a biological antioxidant in a cell culture experimental model and prevent oxidative stress-induced cytotoxicity in cells.

Erratum: Regeneration of whole meniscus using meniscal cells and polymer scaffolds in a rabbit total meniscectomy model (Journal of Biomedical Materials Research Part A (2006) 77, 4 (659-671) DOI: 10.1002/jbm.a.30579)

The current treatments of meniscal lesion in knee joint are not perfect to prevent adverse effects of meniscus injury. Tissue engineering of meniscus using meniscal cells and polymer scaffolds could be an alternative option to treat meniscus injury. This study reports on the regeneration of whole medial meniscus in a rabbit total meniscectomy model using the tissue engineering technique. Biodegradable scaffolds in a meniscal shape were fabricated from polyglycolic acid (PGA) fiber meshes that were mechanically reinforced by bonding PGA fibers at cross points with 75:25 poly(lactic-co-glycolic acid). The compressive modulus of the bonded PGA scaffold was 28-fold higher than that of nonbonded scaffold. Allogeneic meniscal cells were isolated from rabbit meniscus biopsy and cultured in vitro. The expanded meniscal cells were seeded onto the polymer scaffolds, cultured in vitro for 1 week, and transplanted to rabbit knee joints from which medial menisci were removed. Ten or 36 weeks after transplantation, the implants formed neomenisci with the original scaffold shape maintained approximately. Hematoxylin and eosin staining of the sections of the neomenisci at 6 and 10 weeks revealed the regeneration of fibrocartilage. Safranin-O staining showed that abundant proteoglycan was present in the neomenisci at 10 weeks. Massons trichrome staining indicated the presence of collagen. Immunohistochemical analysis showed that the presence of type I and II collagen in neomenisci at 10 weeks was similar to that of normal meniscal tissue. Biochemical and biomechanical analyses of the tissue-engineered menisci at 36 weeks were performed to determine the quality of the tissue-engineered menisci. Tissue-engineered meniscus showed differences in collagen content and aggregate modulus in comparison with native meniscus. This study demonstrates, for the first time, the feasibility of regenerating whole meniscal cartilage in a rabbit total meniscectomy model using the tissue engineering method.

Neural Cells on Iridium Oxide

Iridium oxide was investigated as a material for the stimula ting neural electrode. Iridium oxide was formed by potential sweep of iridium film that was deposi ted on either Si wafer or silicone rubber with electron-beam evaporation. The rate of iridium oxide format ion was dependent on the upper and lower limits of potential sweep. The higher thickness of iri dium oxide produced the higher charge injection due to the reversible valence transition of iridium within oxide. Embryonic cortical neural cells formed neurofilament after 4-day culture on iridium oxi de, which indicated neural cells could adhere and survive on iridium oxide. Introduction Interaction between neurons and electrodes is very important for stim ulation or signal collection. The restoration of a variety of physiological functions by electricall y ctivating nerves serving paralyzed muscles has been of particular interest. The first application of functional electrical stimulation (FES) was by Liberson [1] who stimulated the peroneal nerve in adult hemipleg ia to correct drop foot during the swing phase of locomotion. For the rehabilitation of locomotion in parapl egics and hemiplegics, thirty-two electrodes are required and even more stimulations are demanded for the refined control [2]. A major problem limiting the widespread application FES has been the lack of stimulating electrodes that can be used for long-term precise multipoint stimulation of nerve s. Practical application requires miniaturized electrode geometry, which still demands high charge i njection capability over the suitable range in potential. Recently, iridium oxide was investigat ed s a candidate electrode material [3-6]. Iridium oxide shows electrochromic behavior, where a change of col r takes place between oxidative and reductive state of iridum. The color of iridium oxide st art changing from metallic to blue around 0.4 V (SHE) in 0.1 M H 2SO4, become darker and remains dark blue above near 0.9 V (SHE). The bleaching process occurrs during the cathodic sweep. The dar k blue became lightened around 1.0 V (SHE) and no blue color could be observed below 0.4 V (SHE). The double proton-electron injection mechanism has been proposed to explain the elect rochromism of the anodic iridium oxide film by Gottesfeld et al. [7]. They postulated the fol lowing reaction to describe the film conversion processes: Ir(OH)n Irx(OH)n-x + xH + + xe In this mechanism, during the coloration process, electrons are removed fr m the oxide across the metal-oxide interface by application of a suitable anodic potential to the metal substrate. Charge repulsion causes an equivalent amount of mobile positive charge carrier s (protons) to be ejected Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 805-808 doi:10.4028/www.scientific.net/KEM.254-256.805

An effective method of gait stability analysis using inertial sensors

This study aims to develop an effective measurement instrument and analysis method of gait stability, particularly focused on the motion of lower spine and pelvis during gait. Silicon micromechanical inertial instruments have been developed and body-attitude (pitch and roll) angles were estimated via closed-loop strapdown estimation filters, which results in improved accuracy of estimated attitude. Also, it is shown that the spectral analysis utilizing the Fast Fourier Transform (FFT) provides an efficient analysis method, which provides quantitative diagnoses for the gait stability. The results of experiments on various subjects suggest that the proposed system provides a simplified but an efficient tool for the evaluation of both gait stabilities and rehabilitation treatments effects.

Wear Behaviors of UHMWPE against LTD-Free Zirconia/Alumina Composites

The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on four different compositions of novel low temperature degradation-free zirconia/alumina (Z/A) composite material used for a femoral head in total hip joint replacement. The wear of UHMWPE pins against these Z/A composite disks were evaluated by performing the linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in a bovine serum. The novel low temperature degradation (LTD)-free tetragonal zirconia polycrystal (TZP)/alumina composite (90(5.3Y, 4.6Nb)-TZP/10Al2O3) induced the less wear amount of UHMWPE than the other Z/A composites. Linear reciprocal motion wore more the UHMWPE pin than did repeat pass rotational motion for all disk materials. It was observed that few transfer film on the sliding track of Z/A composite disks and the matching contact surfaces of pins had relatively less scratch. Getting rid of transfer film, there is no change of surface roughness on the sliding track of Z/A composite disks. This novel Z/A composite (90(5.3Y, 4.6Nb)-TZP/10 Al2O3) demonstrates the potential as an alternative material for the femoral head in total hip replacement.

Dynamic Compressive Creep of Extruded Ultra-High Molecular Weight Polyethylene

To estimate the true wear rate of polyethylene acetabular cups used in total hip arthroplasty, the dynamic compressive creep deformation of ultra-high molecular weight polyethylene (UHMWPE) was quantified as a function of time, load amplitude, and radial location of the specimen in the extruded rod stock. These data were also compared with the creep behavior of polyethylene observed under static loading. Total creep strains under dynamic loading were only 64%, 70%, and 61% of the total creep strains under static loading at the same maximum pressures of 2 MPa, 4 MPa, and 8 MPa, respectively. Specimens cut from the periphery of the rod stock demonstrated more creep than those cut from the center when they were compressed in a direction parallel to the extrusion direction (vertical loading), whereas the opposite was observed when specimens were compressed in a direction perpendicular to the extrusion direction (transverse loading). These findings show that creep deformation of UHMWPE depends upon the orientation of the crystalline lamellae.