•New stability criteria of stably stratified shear flow are discovered.•Our criteria substantially improve the Howard–Miles criterion (1961).•Our criteria also generalize Rayleigh's inflection point ...theorem.•The novel approach we found is also efficient as a numerical approach.
Linear stability of inviscid, parallel, and stably stratified shear flow is studied under the assumption of smooth strictly monotonic profiles of shear flow and density, so that the local Richardson number is positive everywhere. The marginally unstable modes are systematically found by solving a one-parameter family of regular Sturm–Liouville problems, which can determine the stability boundaries more efficiently than solving the Taylor–Goldstein equation directly. By arguing for the non-existence of a marginally unstable mode, we derive new sufficient conditions for stability, which generalize the Rayleigh–Fjørtoft criterion for unstratified shear flows.
Titanium micro-scale topography offers excellent osteoconductivity and bone-implant integration. However, the biological effects of sub-micron topography are unknown. We compared osteoblastic ...phenotypes and in vivo bone and implant integration abilities between titanium surfaces with micro- (1-5 µm) and sub-micro-scale (0.1-0.5 µm) compartmental structures and machined titanium. The calculated average roughness was 12.5 ± 0.65, 123 ± 6.15, and 24 ± 1.2 nm for machined, micro-rough, and sub-micro-rough surfaces, respectively. In culture studies using bone marrow-derived osteoblasts, the micro-rough surface showed the lowest proliferation and fewest cells attaching during the initial stage. Calcium deposition and expression of osteoblastic genes were highest on the sub-micro-rough surface. The bone-implant integration in the Sprague-Dawley male rat femur model was the strongest on the micro-rough surface. Thus, the biological effects of titanium surfaces are not necessarily proportional to the degree of roughness in osteoblastic cultures or in vivo. Sub-micro-rough titanium ameliorates the disadvantage of micro-rough titanium by restoring cell attachment and proliferation. However, bone integration and the ability to retain cells are compromised due to its lower interfacial mechanical locking. This is the first report on sub-micron topography on a titanium surface promoting osteoblast function with minimal osseointegration.
Titanium implants are the standard therapeutic option when restoring missing teeth and reconstructing fractured and/or diseased bone. However, in the 30 years since the advent of micro-rough ...surfaces, titanium's ability to integrate with bone has not improved significantly. We developed a method to create a unique titanium surface with distinct roughness features at meso-, micro-, and nano-scales. We sought to determine the biological ability of the surface and optimize it for better osseointegration. Commercially pure titanium was acid-etched with sulfuric acid at different temperatures (120, 130, 140, and 150 °C). Although only the typical micro-scale compartmental structure was formed during acid-etching at 120 and 130 °C, meso-scale spikes (20-50 μm wide) and nano-scale polymorphic structures as well as micro-scale compartmental structures formed exclusively at 140 and 150 °C. The average surface roughness (Ra) of the three-scale rough surface was 6-12 times greater than that with micro-roughness only, and did not compromise the initial attachment and spreading of osteoblasts despite its considerably increased surface roughness. The new surface promoted osteoblast differentiation and in vivo osseointegration significantly; regression analysis between osteoconductivity and surface variables revealed these effects were highly correlated with the size and density of meso-scale spikes. The overall strength of osseointegration was the greatest when the acid-etching was performed at 140 °C. Thus, we demonstrated that our meso-, micro-, and nano-scale rough titanium surface generates substantially increased osteoconductive and osseointegrative ability over the well-established micro-rough titanium surface. This novel surface is expected to be utilized in dental and various types of orthopedic surgical implants, as well as titanium-based bone engineering scaffolds.
This study retrospectively evaluated the effects of bone density, staging strategy, implant stability, healing process, implant length, surface type, and photofunctionalization on early implant ...failure.
Consecutive study samples at Yokohama City University Hospital were analyzed for their early implant failure potentially influenced by patient-, surgical protocol-, and implant-related factors. Through the screening process using univariate analysis for those factors, candidate influential factors such as bone density, staging strategy, the level of initial implant stability, postoperative wound breakdown, the length of implants, the surface type of implants, and use or nonuse of photofunctionalization were selected as independent variables in forward multivariate logistic regression analysis. The odds ratio (OR) for candidate factors was calculated.
A total of 563 implants placed in 219 patients from 2005 to 2017 were analyzed for their early implant failure. Stepwise logistic regression analysis finally identified postoperative wound breakdown (OR = 0.21) and the use of photofunctionalization (OR = 0.30) that significantly reduced the risk of early implant failure (P < .01 and P < .05, respectively). The implant failure rate was 10.0% with postoperative wound breakdown and 1.0% without it, whereas it was 4.3% without photofunctionalization and 1.3% with it.
Among various patient-, surgical protocol-, and implant-related factors, the absence of postoperative wound breakdown and use of photofunctionalization significantly reduced the risk of early implant failure. It was notable that photofunctionalization, a unique, chairside measure to improve implant surfaces, was effective exclusively among implant-related factors.
Peri-implantitis is an unsolved but critical problem with dental implants. It is postulated that creating a seal of gingival soft tissue around the implant neck is key to preventing peri-implantitis. ...The objective of this study was to determine the effect of UV surface treatment of titanium disks on the adhesion strength and retention time of oral connective tissues as well as on the adherence of mucosal fibroblasts. Titanium disks with a smooth machined surface were prepared and treated with UV light for 15 min. Keratinized mucosal tissue sections (3 × 3 mm) from rat palates were incubated for 24 h on the titanium disks. The adhered tissue sections were then mechanically detached by agitating the culture dishes. The tissue sections remained adherent for significantly longer (15.5 h) on the UV-treated disks than on the untreated control disks (7.5 h). A total of 94% of the tissue sections were adherent for 5 h or longer on the UV-treated disks, whereas only 50% of the sections remained on the control disks for 5 h. The adhesion strength of the tissue sections to the titanium disks, as measured by tensile testing, was six times greater after UV treatment. In the culture studies, mucosal fibroblasts extracted from rat palates were attached to titanium disks by incubating for 24, 48, or 96 h. The number of attached cells was consistently 15-30% greater on the UV-treated disks than on the control disks. The cells were then subjected to mechanical or chemical (trypsinization) detachment. After mechanical detachment, the residual cell rates on the UV-treated surfaces after 24 and 48 h of incubation were 35% and 25% higher, respectively, than those on the control surfaces. The remaining rate after chemical detachment was 74% on the control surface and 88% on the UV-treated surface for the cells cultured for 48 h. These trends were also confirmed in mouse embryonic fibroblasts, with an intense expression of vinculin, a focal adhesion protein, on the UV-treated disks even after detachment. The UV-treated titanium was superhydrophilic, whereas the control titanium was hydrophobic. X-ray photoelectron spectroscopy (XPS) chemical analysis revealed that the amount of carbon at the surface was significantly reduced after UV treatment, while the amount of TiOH molecules was increased. These ex vivo and in vitro results indicate that the UV treatment of titanium increases the adhesion and retention of oral mucosa connective tissue as a result of increased resistance of constituent fibroblasts against exogenous detachment, both mechanically and chemically, as well as UV-induced physicochemical changes of the titanium surface.
The exact mechanisms by which implant surface properties govern osseointegration are incompletely understood. To gain insights into this process, we examined alterations in protein and blood ...recruitment around screw implants with different surface topographies and wettability using a computational fluid dynamics (CFD) model. Compared with a smooth surface, a microrough implant surface reduced protein infiltration from the outer zone to the implant thread and interface zones by over two-fold. However, the microrough implant surface slowed blood flow in the interface zone by four-fold. As a result, compared with the smooth surface, the microrough surface doubled the protein recruitment/retention index, defined as the mass of proteins present in the area per unit time. Converting implant surfaces from hydrophobic to superhydrophilic increased the mass of protein infiltration 2–3 times and slowed down blood flow by up to two-fold in the implant vicinity for both smooth and microrough surfaces. The protein recruitment/retention index was highest at the implant interface when the implant surface was superhydrophilic and microrough. Thus, this study demonstrates distinct control of the mass and speed of protein and blood flow through implant surface topography, wettability, and their combination, significantly altering the efficiency of protein recruitment. Although microrough surfaces showed both positive and negative impacts on protein recruitment over smooth surfaces, superhydrophilicity was consistently positive regardless of surface topography.
Titanium materials are essential treatment modalities in the medical field and serve as a tissue engineering scaffold and coating material for medical devices. Thus, there is a significant demand to ...improve the bioactivity of titanium for therapeutic and experimental purposes. We showed that ultraviolet light (UV)-pre-treatment changed the protein-adsorption ability and subsequent osteoconductivity of titanium. Fibronectin (FN) adsorption on UV-treated titanium was 20% and 30% greater after 1-min and 1-h incubation, respectively, than that of control titanium. After 3-h incubation, FN adsorption on UV-treated titanium remained 30% higher than that on the control. Osteoblasts were cultured on titanium disks after 1-h FN adsorption with or without UV-pre-treatment and on titanium disks without FN adsorption. The number of attached osteoblasts during the early stage of culture was 80% greater on UV-treated and FN-adsorbed (UV/FN) titanium than on FN-adsorbed (FN) titanium; osteoblasts attachment on UV/FN titanium was 2.6- and 2.1-fold greater than that on control- and UV-treated titanium, respectively. The alkaline phosphatase activity of osteoblasts on UV/FN titanium was increased 1.8-, 1.8-, and 2.4-fold compared with that on FN-adsorbed, UV-treated, and control titanium, respectively. The UV/FN implants exhibited 25% and 150% greater in vivo biomechanical strength of bone integration than the FN- and control implants, respectively. Bone morphogenetic protein-2 (BMP-2) adsorption on UV-treated titanium was 4.5-fold greater than that on control titanium after 1-min incubation, resulting in a 4-fold increase in osteoblast attachment. Thus, UV-pre-treatment of titanium accelerated its protein adsorptivity and osteoconductivity, providing a novel strategy for enhancing its bioactivity.
The nonlinear phase of magnetic reconnection is investigated by numerically solving a gyrofluid model. The scaling law for the explosive reconnection rate, which has been recently derived for an ...ideal two-fluid model Hirota et al., Phys. Plasmas 22, 052114 (2015), is found to consistently hold when either the ion-sound gyroradius ρS or the ion gyroradius ρi is comparable to the electron skin depth de, even in the presence of finite resistivity η. In this explosive phase, a local X-shaped current layer is spontaneously generated, in which the reconnection speed is closely related to the macroscopic shape of the layer and is almost independent of the layer width. The reconnection speed is therefore insensitive to the size of the microscopic scales, ρS, ρi, de and η. On the other hand, in the cold plasma limit, where ρS = ρi = 0, the intermittent acceleration of the reconnection speed is caused by the plasmoid instability. This also seems to be explosive on average, but the rate always falls below the explosive scaling law. The reconnection time extrapolated from this scaling law is shown to be fast enough to explain the time scale of solar flares.
The objective of this study was to compare the rate of implant stability development of as-received and photofunctionalized dental implants in regular and complex cases.
Forty-nine implants (24 ...as-received and 25 photofunctionalized) placed in regular or complex cases (simultaneous guided bone regeneration, sinus elevation, or fresh extraction sockets) were studied. Photofunctionalization was performed by ultraviolet (UV) treatment of implants for 15 minutes using a photo device immediately prior to placement, and the generation of superhydrophilicity was confirmed. Implant stability was evaluated by measuring the implant stability quotient (ISQ) at placement (ISQ1) and at stage-two surgery (ISQ2). The rate of implant stability development was evaluated by calculating the osseointegration speed index (OSI), defined as the ISQ increase per month (ISQ2-ISQ1/healing time in months). The percentage of innate bone support at placement was evaluated clinically and radiographically.
The average OSI was considerably greater for photofunctionalized implants (3.7 ± 2.9) than for as-received implants (0.0 ± 1.0). The OSI in complex cases was 4.2 ± 3.2 for photofunctionalized implants and 0.2 ± 0.9 for as-received implants. The OSI in cases with simultaneous sinus elevation was 5.5 ± 3.5 for photofunctionalized implants and 0.2 ± 1.1 for as-received implants. Photofunctionalized implants showed significantly higher ISQ2 values than as-received implants. Photofunctionalized implant ISQ2 values were greater than 60, regardless of primary stability and innate bone support at placement. In multivariate analysis including the effects of photofunctionalization, age and sex of patients, and diameter and length of implants, photofunctionalization showed the strongest influence on the OSI for both regular and complex cases, while other factors influenced the OSI only in certain conditions.
Photofunctionalization accelerated the rate and enhanced the final level of implant stability development compared with as-received implants, particularly for implants placed into poor-quality bone and other complex cases. Photofunctionalization was a stronger determinant of implant stability than all the other tested implant- and host-related factors.
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