Tzer Min Lee

Enhanced osteoblastic cell response on zirconia by bio-inspired surface modification.

Excellent esthetic properties and limited plaque adhesion make zirconia ceramics an ideal material for implants in the fields of dentistry and orthopedics. Unfortunately, the physicochemical stability of zirconia makes it difficult to improve biocompatibility through surface modification. The dopamine-derived residue, 3,4-dihydroxy-L-phenylalanine (L-DOPA), has been identified as an important molecule secreted by marine mussels for the formation of adhesive pads. This study coated zirconia with L-DOPA to improve the biocompatibility of ZrO2. As confirmed by contact angle and X-ray photoelectron spectroscopy (XPS), the formation of L-DOPA film can be controlled by varying the process temperature. Results from scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that the topography of the zirconia substrate was preserved after being coated with a film of L-DOPA. Specifically, the thickness of the coating and initial cell spreading ability were both enhanced by preparing samples at higher temperatures. L-DOPA coated zirconia demonstrated better cyto-compatibility than uncoated specimens, as indicated by cell responses such as cell spreading and proliferation. These preliminary results suggest that L-DOPA film could be used to improve the cyto-compatibility of zirconia and further has the potential to immobilize other biofunctional molecules in biomedical applications.

Comparison of osseointegration on various implant surfaces after bacterial contamination and cleaning: a rabbit study.

PURPOSE To examine the osseointegration of various implant surfaces after bacterial contamination and cleaning. MATERIALS AND METHODS Four types of implant surface were manufactured: machined (M); plasma-spray hydroxyapaptite (HA); sandblasted, large-grit, acid-etched (SA); and titanium anodic oxide (TAO) were manufactured. The surface characteristics of these implants were determined using a scanning electron microscope, an energy dispersive spectrometer, and a contact profilometer. Each surface was subdivided into control and test groups. Test implants were co-incubated with Prevotella intermedia for 2 weeks, then cleaned with cotton pellets, soaked in saline, and irrigated. Control implants underwent the same cleaning procedure, but without bacterial contamination. Four control or test implants with different surface types were randomly inserted into the tibia of 10 New Zealand white rabbits. After 6 weeks of healing, 5 rabbits were sacrificed for histomorphometry, and the rest for removal torque assay. RESULTS Bacterial contamination adversely influenced every implant surface in terms of bone-to-implant contact (BIC) ratio and required removal torque. The negative results reached significant levels for rougher surfaces (HA and SA). For both contaminated and uncontaminated samples, HA and SA implants required significantly higher removal torque than that required for M implants. CONCLUSION Bacterial contamination jeopardized osseointegration on every tested implant surface. A more negative effect on BIC was found for implants with rougher surfaces. However, contaminated rough-surfaced implants showed more removal torque resistance than contaminated smooth implants.

Engineering three-dimensional structures using bio-inspired dopamine and strontium on titanium for biomedical application

The excellent mechanical properties and chemical stability of titanium and its alloys have led to their wide use as a material for dental and orthopaedic implants. However, the bio-inert nature of these materials must be overcome to enhance cell affinity and cell function following implantation. Effective implants require strong interfacial bonding, mechanical stability, osteoblast attachment, enhanced spreading and growth during early stages, and induced differentiation and mineralization in later stages. This study developed an organic-inorganic multilayer coating process for the modification of titanium implants in order to improve cell responses. A three-dimensional structure comprising strontium and micro-arc oxidized (MAO) titanium was covered with a film of poly(dopamine) to form a multilayer coating. The titanium surface formed a uniform hydrophilic oxide coating, which was firmly adhered to the surface. The poly(dopamine) film facilitated the initial attachment and proliferation of cells. Cell differentiation was enhanced by the release of strontium from the coatings. Our results demonstrate the efficacy of the proposed coating process in enhancing the multi-biological function of implant surfaces.

Effects of nanometric roughness on surface properties and fibroblast's initial cytocompatibilities of Ti6AI4V

Titanium alloy (Ti6Al4V) has widespread medical applications because of its excellent biocompatibility. Its biological responses can further be enhanced by polishing and passivation. Unfortunately, preparing titanium alloy samples of nanometric roughness is by far much more difficult than preparing those of micrometric roughness, and numerous investigations on roughness induced effects are all focused on micrometric scales. For the remedy, we investigate, at nanometric scale, the influence of roughness on surface properties and biological responses. Six groups of Ti6Al4V with average roughness (R(a)) values of 2.75-30.34 nm are prepared. The results indicated that nanometric roughness of samples change the wettability and amphoteric OH groups. The contact angles monotonically decrease from 2.75 to 30.34 nm and the rougher surfaces lead to higher wettability. The in vitro cell-culture studies, using Murine NIH-3T3 fibroblasts, showed the spindle-shaped morphology on rougher surface compared to round∕spherical morphology on smoother surface. A cytodetacher is employed to quantitatively measure the initial adhesion force of fibroblasts to specimen. The adhesion strength of fibroblasts, ranging from 55 to 193 nN, is significantly influenced by the nanometric roughness while the surface is within the range of 2.75-30.34 nm R(a) roughness, and the adhesion strength appeared stronger for rougher surface. The cell number on the smoother surface is higher than on the rougher surface at 5-day culture. The studies indicated that nanometric roughness would alter the surface properties and further influence cell morphology, adhesion strength, and proliferation.

Effect of bracket bevel design and oral environmental factors on frictional resistance.

OBJECTIVE To investigate the effects of bracket bevel design and oral environmental factors (saliva, temperature) on frictional resistance. MATERIALS AND METHODS Five types of brackets, namely a conventional bracket (Omni-arch), an active self-ligating bracket (Clippy), and three passive self-ligating brackets (Carriere, Damon, and Tenbrook T1) coupled with a 0.014-inch austenitic nickel-titanium archwire were tested. In the experimental model, which used a group of five identical brackets, the center bracket was displaced 3 mm to mimic the binding effects. The friction experiments were performed at three temperatures (20°C, 37°C, 55°C) in a dry or a wet (artificial saliva) state. Finally, the surfaces of the bracket slots were observed using scanning electron microscopy (SEM) before and after the friction tests. RESULTS The sliding frictional force was significantly influenced by the bracket slot bevel and saliva whether in the active or passive configuration (P < .05). The frictional force significantly increased as the temperature increased in the active configuration (P < .01). Based on the SEM observations, a correlation was found among the level of frictional force, the bevel angle, and the depth of scratches on bracket bevels. CONCLUSION Frictional force can be reduced by increasing the bevel angle and by lowering the oral temperature, whereas the presence of saliva increases frictional resistance.

Cell response on the biomimetic scaffold of silicon nano- and micro-topography

Silicon scaffolds were synthesized in a low-pressure furnace via a vapor-liquid-solid (VLS) mechanism. Structural dimensions of silicon scaffolds were tunable in the synthesis to satisfy diverse requirements for cell culture applications. Cylindraceous SiNWs structurally resemble fibrous proteins in connective tissue and the extracellular matrix (ECM), which are main cell adhesion substrata in vivo. Hemispherical silicon microbroccolis (SiMBs) possess large contact area with microscale topology for cell contact and attachment. Mouse 3T3 fibroblasts were cultured on microscale and nanoscale silicon structures with different surface modifications. Silicon scaffolds were functionalized by several physical and chemical vapor deposition methods to modify scaffold surface physical and chemical properties. Metal-coated SiNWs and SiMBs had been demonstrated and compared for their ability to provide mechanical support sites for cell adhesion and promote cell proliferation and maintain normal cell functionality. Scanning electron microscopy (SEM) micrographs at high magnification show cell-scaffold interactions, and immunofluorescence images reveal nuclear DNAs and actin cytoskeleton distribution on nanostructure covered substrates and selected biomarker expression was analyzed by enzyme-linked immunosorbent assay (ELISA).

Design and development of solar power-assisted manual/electric wheelchair

Wheelchairs are an essential assistive device for many individuals with injury or disability. Manual wheelchairs provide a relatively low-cost solution to the mobility needs of such individuals. Furthermore, they provide an effective means of improving the users cardiopulmonary function and upper-limb muscle strength. However, manual wheelchairs have a loss gross mechanical efficiency, and thus the risk of user fatigue and upper-limb injury is increased. Electric-powered wheelchairs reduce the risk of injury and provide a more convenient means of transportation. However, they have a large physical size and are relatively expensive. Accordingly, the present study utilizes a quality function deployment method to develop a wheelchair with a user-selectable manual/electric propulsion mode and an auxiliary solar power supply system. The auxiliary solar power supply increased the travel range of the wheelchair by approximately 26% compared with that of a wheelchair powered by battery alone. Moreover, the wheelchair has a modular design and can be disassembled and folded for ease of transportation or storage. Overall, the present results suggest that the proposed wheelchair provides an effective and convenient means of meeting the mobility needs of individuals with mobility difficulties.

Effect of TiO2 addition on surface microstructure and bioactivity of fluorapatite coatings deposited using Nd: YAG laser

To study the effect of titania (TiO2) addition on the surface microstructure and bioactivity of fluorapatite coatings, fluorapatite was mixed with TiO2 in 1:0.5 (FA + 0.5TiO2), 1:0.8 (FA + 0.8TiO2), and 1:1 (FA + TiO2) ratios (wt%) and clad on Ti-6Al-4V substrates using an Nd:YAG laser system. The experimental results show that the penetration depth of the weld decreases with increasing TiO2 content. Moreover, the subgrain structure of the coating layer changes from a fine cellular-like structure to a cellular-dendrite-like structure as the amount of TiO2 increases. Consequently, as the proportion of TiO2 decreases (increase in fluorapatite content), the Ca/P ratio of the coating layer also decreases. The immersion of specimens into simulated body fluid resulted in the formation of individual apatite. With a lower Ca/P ratio before immersion, the growth of the apatite was faster and then the coating layer provided a better bioactivity. X-ray diffraction analysis results show that prior to simulated body fluid immersion, the coating layer in all three specimens was composed mainly of fluorapatite, CaTiO3, and Al2O3 phases. Following simulated body fluid immersion, a peak corresponding to hydroxycarbonated apatite appeared after 2 days in the FA + 0.5TiO2 and FA + 0.8TiO2 specimens and after 7 days in the FA + TiO2 specimen. Overall, the results show that although the bioactivity of the coating layer tended to decrease with increasing TiO2 content, in accordance with the above-mentioned ratios, the bioactivity of all three specimens remained generally good.

Surface modification of Direct-Current and radio-frequency oxygen plasma treatments enhance cell biocompatibility

The sand-blasting and acid etching (SLA) method can fabricate a rough topography for mechanical fixation and long-term stability of titanium implant, but can not achieve early bone healing. This study used two kinds of plasma treatments (Direct-Current and Radio-Frequency plasma) to modify the SLA-treated surface. The modification of plasma treatments creates respective power range and different content functional OH groups. The results show that the plasma treatments do not change the micron scale topography, and plasma-treated specimens presented super hydrophilicity. The X-ray photoelectron spectroscopy (XPS)-examined result showed that the functional OH content of the RF plasma-treated group was higher than the control (SLA) and DC treatment groups. The biological responses (protein adsorption, cell attachment, cell proliferation, and differentiation) promoted after plasma treatments, and the cell responses, have correlated to the total content of amphoteric OH groups. The experimental results indicated that plasma treatments can create functional OH groups on SLA-treated specimens, and the RF plasma-treated SLA implant thus has potential for achievement of bone healing in early stage of implantation.

A Disease Model of Muscle Necrosis Caused by Aeromonas dhakensis Infection in Caenorhabditis elegans

A variety of bacterial infections cause muscle necrosis in humans. Caenorhabditis elegans has epidermis and bands of muscle that resemble soft-tissue structures in mammals and humans. Here, we developed a muscle necrosis model caused by Aeromonas dhakensis infection in C. elegans. Our data showed that A. dhakensis infected and killed C. elegans rapidly. Characteristic muscle damage in C. elegans induced by A. dhakensis was demonstrated in vivo. Relative expression levels of host necrosis-associated genes, asp-3, asp-4, and crt-1 increased significantly after A. dhakensis infection. The RNAi sensitive NL2099 rrf-3 (pk1426) worms with knockdown of necrosis genes of crt-1 and asp-4 by RNAi showed prolonged survival after A. dhakensis infection. Specifically knockdown of crt-1 and asp-4 by RNAi in WM118 worms, which restricted RNAi only to the muscle cells, conferred significant resistance to A. dhakensis infection. In contrast, the severity of muscle damage and toxicity produced by the A. dhakensis hemolysin-deletion mutant is attenuated. In another example, shiga-like toxin-producing enterohemorrhagic E. coli (EHEC) known to elicit toxicity to C. elegans with concomitant enteropathogenicty, did not cause muscle necrosis as A. dhakensis did. Taken together, these results show that Aeromonas infection induces muscle necrosis and rapid death of infected C. elegans, which are similar to muscle necrosis in humans, and then validate the value of the C. elegans model with A. dhakensis infection in studying Aeromonas pathogenicity.