Translocation of a looped polymer threading through a nanopore.

Recent experiments reported that the complicated translocation dynamics of a looped DNA chain through a nanopore can be detected by ionic current blockade profiles. Inspired by the experimental results, we systematically study the translocation dynamics of a looped polymer, formed by three building blocks of a loop in the middle and two tails of the same length connected with the loop, by using Langevin dynamics simulations. Based on two entering modes (tail-leading and loop-leading) and three translocation orders (loop-tail-tail, tail-loop-tail, and tail-tail-loop), the translocation of the looped polymer is classified into six translocation pathways, corresponding to different current blockade profiles. The probabilities of the six translocation pathways are dependent on the loop length, polymer length, and pore radius. Moreover, the translocation times of the entire polymer and the loop are investigated. We find that the two translocation times show different dependencies on the translocation pathways and on the lengths of the loop and the entire polymer.

In Situ Visualization of Concentration Polarization during Membrane Ultrafiltration Using Microscopic Laser-Induced Fluorescence.

A novel noninvasive technique-microscopic laser-induced fluorescence (micro-LIF)-has been applied to achieve in situ visualization of concentration polarization (CP) of nanoparticles during cross-flow ultrafiltration at high resolutions. The reversible, highly dynamic nature of CP and its sensitive response to the filtration conditions were investigated and validated by direct visualization of the CP layer and the well depicted concentration profile near the membrane surface. Using micro-LIF, the formation of a CP layer during filtration and its back-diffusion after the filtration ceased can be directly observed. The dynamic variation of the CP layer with the cross-flow velocity and transmembrane pressure (TMP) change has also been demonstrated. The results showed that CP reached the steady state approximately 1 min after the filtration condition change. A higher cross-flow velocity and/or a lower TMP decrease the CP concentration and thickness. Further quantitative analysis of the filtration test results using the film theory model helps to obtain the particle concentration at the membrane surface and the thickness of the CP layer (30-50 µm). Accordingly, the nature of CP dynamics was characterized and the deficiency of the traditional CP model was explored.

Microanatomical changes and biomolecular expression at the PDL-entheses during experimental tooth movement.

The novel aspect of this study was to contextualize the co-localization of biomolecular expression in widened and narrowed periodontal ligament (PDL)-space within a mechanically activated periodontal complex. The PDL is unique as it is the only ligament with both innervation and vascularization. Maxillary molars in 6-week-old male C57BL/6 mice (N = 5) were experimentally translated for 2 weeks using an elastic spacer. Contralateral teeth were used as controls. Mechanical testing of the periodontal complex of a mouse in situ and imaging using X-ray micro-computed tomography (micro-XCT) illustrated deformations within blood vessels (BV) of the PDL. PDL-bone and PDL-cementum entheses at the widened and narrowed PDL-spaces following experimental tooth movement (ETM) illustrated osterix (OSX), bone sialoprotein (BSP), cluster of differentiation 146 (CD146), and protein gene product 9.5 (PGP9.5), indicating active remodeling at these sites. PGP9.5 positive nerve bundles (NBs) were co-localized with multinucleated cells (MCs), Howship's resorption lacunae, and CD146 positive BVs. Association between nerves and MC was complemented by visualizing the proximity of osmium tetroxide stained NBs with the ultrastructure of MCs by performing scanning transmission electron microscopy. Spatial association of NB with BV, and NB with MC, provided insights into the plausible co-activation of NBs to initiate osteoclastic activity. Resorption of mineral occurred as an attempt to restore PDL-space of the load-bearing complex, specifically at the PDL-entheses. Mapping of anatomy-specific structural elements and their association with regenerative molecules by correlating light and electron micrographs provided insights into the use of these extracellular matrix molecules as plausible targets for pharmacological interventions related to tooth movement. Within the realm of tissue regeneration, modulation of load can reverse naturally occurring mineral formation to experimentally induced resorption, and naturally occurring mineral resorption to experimentally induced formation at the enthesial sites to permit tooth translation.

The Role of Epithelial Stat3 in Amelogenesis during Mouse Incisor Renewal.

The aim of this study was to evaluate the role of epithelial signal transducer and activator of transcription 3 (STAT3) in mouse incisor amelogenesis. Since Stat3 is expressed in the epithelial component of developing and adult mouse teeth, we generated and analyzed Krt14Cre/+;Stat3fl/fl mutant mice in which Stat3 was inactivated in epithelia including ameloblast progenitors and ameloblasts, the cells responsible for enamel formation. Histological analysis showed little enamel matrix in mutant incisors compared to controls. Delayed incisor enamel mineralization was demonstrated using micro-computed X-ray tomography analysis and was supported by an increase in the pre-expression distance of enamel-enriched proteins such as amelogenin, ameloblastin, and kallikrein-4. Lastly, scanning electron microscopy analysis showed little enamel mineralization in mutant incisors underneath the mesial root of the 1st molar; however, the micro-architecture of enamel mineralization was similar in the erupted portion of control and mutant incisors. Taken together, our findings demonstrate for the first time that the absence of epithelial Stat3 in mice leads to delayed incisor amelogenesis.

A simulation study on the self-assembly of rod-coil-rod triblock copolymers within nanoslits.

Self-assembly of rod-coil-rod R4C12R4 triblock copolymers within a nanoslit is investigated by using dissipative particle dynamics simulations. Perpendicular lamellae (L⊥) in nonselective or weak selective slits and parallel lamellae (L∥) in coil-selective slits are observed, and both are almost independent of the slit thickness. However, in the rod-selective slits, the assembled structures are strongly dependent on the slit thickness. With an increase in the slit thickness, we sequentially observe hexagonally packed cylinders (HC) of rod blocks perpendicular to surfaces in thin slits, parallel wavy lamellae, orderly packed alternating cylinders in moderate slits, a mixture structure of HC near surfaces and L⊥ in the interior region, and finally L∥ in wide slits. Our simulation results reveal that the rod block and surface properties play an important role in the assembly of confined rod-coil-rod triblock copolymers. Results also illustrate the competition between the slit thickness and the length scale of lamellae in bulk for the confined copolymers in nanoslits.

Study on the polymer diffusion in a media with periodically distributed nano-sized fillers.

The effect of nano-sized fillers on the equilibrium and dynamical properties of a linear polymer is studied by using off-lattice Monte Carlo simulation. Fillers are arranged periodically in the system with period d and Lennard-Jones interaction between polymer and fillers is considered. Results show that the statistical dimension and dynamical diffusion of the polymer are dependent on the polymer-filler interaction strength ɛ(pf) and the relative size between R(G0) and d, here R(G0) is the radius of gyration of polymer in dilute solution. Normal diffusion of polymer is always observed in the regime 2R(G0) > d. And the diffusion coefficient D is scaled with chain length N as D ~ N(-α), where the exponent α increases with ɛ(pf). Whereas in the regime 2R(G0) < d ≪ Nl0 with l0 the mean bond length of polymer, normal diffusion is observed only at ɛ(pf) < 2, but the polymer will be adsorbed on the fillers and cannot diffuse at ɛ(pf) > 2. In addition, we find that there is a critical interaction strength ɛ*(pf) = 2 in our model system.

Separating different polymers using an interacting nanopore: a Monte Carlo study.

Translocation of a multi-polymer system containing two kinds of polymers, polymer A and polymer B, through an interacting nanopore is studied using dynamic Monte Carlo method. Polymer A and polymer B have different polymer-pore interactions. The probability of one kind of polymer first translocating through a nanopore is dependent on the polymer-pore interactions and the magnitude of driving force for monomers inside the nanopore. At weak driving, there are separation regions where one kind of polymer translocates through the pore always before another kind of polymer. A phase diagram containing separation regions and mixed region is presented. At last, the first-in first-out rule for the polymer translocation is investigated.

Polymer translocation through a gradient channel.

The translocation of polymer through a channel with a gradient interaction between the polymer and the channel is studied. The interaction is expressed by E = E0 + kx, where E0 is the initial potential energy at the entrance, x is the position of the monomer inside the channel, and k is the energy gradient. The mean first passage time τ is calculated by using Fokker-Planck equation for two cases (1) N > L and (2) N < L under the assumption that the diffusion rate D is a constant, here N is the polymer length and L is the length of channel. Results show that there is a minimum of τ at k = k(c) for both cases, and the value kc is dependent on E0 and driving force f. At large f, the scaling relation τ ∼ N is observed for long polymer chains. But the scaling relation is dependent on the energy gradient k for an unforced driving translocation.

Investigation of excipients impact on polysorbate 80 degradation in biopharmaceutical formulation buffers.

A study on the polysorbate 80 stability in various formulation buffers commonly used in biopharmaceuticals was performed, to investigate the excipients influence on polysorbate 80 degradation. Polysorbate 80 is a common excipient in biopharmaceutical products. However, its degradation will potentially impact the drug product quality, and may trigger protein aggregation and particles formation. Due to the heterogeneity of the polysorbates and the mutual effects with other formulation compositions, the study of polysorbate degradation is challenging. Herein, a real-time stability study was designed and performed. The polysorbate 80 degradation trend was monitored by fluorescence micelle-based assay (FMA), reversed-phase-ultra-performance liquid chromatography-evaporative light scattering detector (RP-UPLC-ELSD) assay, and LC-MS assay. These assays provide orthogonal results to reveal both the micelle-forming capability and the compositional changes of polysorbate 80 in different buffer systems. The degradation occurred after a period of storage under 25 °C in different trend, which indicates the excipients could impact the degradation kinetics. Upon comparison, the degradation is prone to happen in histidine buffer than in acetate, phosphate or citrate buffers. LC-MS confirms oxidation as an independent degradation pathway with detection of the oxidative aldehyde. Thus, it is necessary to pay more attention to the excipients selection and their potential impact on polysorbate 80 stability to achieve longer shelf life for the biopharmaceuticals. Besides, the protective roles of several additives were figured out, which could be applied as potential industrial solutions to the polysorbate 80 degradation issues.

Simulation study on the translocation of a partially charged polymer through a nanopore.

The translocation of a partially charged polymer through a neutral nanopore under external electrical field is studied by using dynamic Monte Carlo method on a simple cubic lattice. One monomer in the polymer is charged and it suffers a driving force when it locates inside the pore. Two time scales, mean first passage time τ(FP) with the first monomer restricted to never draw back into cis side and translocation time τ for polymer continuously threading through nanopore, are calculated. The first passage time τ(FP) decreases with the increase in the driving force f, and the dependence of τ(FP) on the position of charged monomer M is in agreement with the theoretical results using Fokker-Planck equation [A. Mohan, A. B. Kolomeisky, and M. Pasquali, J. Chem. Phys. 128, 125104 (2008)]. But the dependence of τ on M shows a different behavior: It increases with f for M < N/2 with N the polymer length. The novel behavior of τ is explained qualitatively from dynamics of polymer during the translocation process and from the free energy landscape.

Latex Microsphere-Based Bicolor Immunochromatography for Qualitative Detection of Neutralizing Antibody against SARS-CoV-2.

Neutralizing antibody (NAb) is a family of antibodies with special functions, which afford a degree of protection against infection and/or reduce the risk of clinically severe infection. Receptor binding domain (RBD) in the spike protein of SARS-CoV-2, a portion of the S1 subunit, can stimulate the immune system to produce NAb after infection and vaccination. The detection of NAb against SARS-CoV-2 is a simple and direct approach for evaluating a vaccine's effectiveness. In this study, a direct, rapid, and point-of-care bicolor lateral flow immunoassay (LFIA) was developed for NAb against SARS-CoV-2 detection without sample pretreatment, and which was based on the principle of NAb-mediated blockage of the interaction between RBD and angiotensin-converting enzyme 2. In the bicolor LFIA, red and blue latex microspheres (LMs) were used to locate the test and control lines, leading to avoidance of erroneous interpretations of one-colored line results. Under the optimal conditions, NAb against SARS-CoV-2 detection carried out using the bicolor LFIA could be completed within 9 min, and the visible limit of detection was about 48 ng/mL. Thirteen serum samples were analyzed, and the results showed that the NAb levels in three positive serum samples were equal to, or higher than, 736 ng/mL. The LM-based bicolor LFIA allows one-step, rapid, convenient, inexpensive, and user-friendly determination of NAb against SARS-CoV-2 in serum.

Robot Versus Fluoroscopy-Assisted Vertebroplasty and Kyphoplasty for Osteoporotic Vertebral Compression Fractures: A Systematic Review and Meta-analysis.

OBJECTIVE: This study aimed to conduct a systematic review and meta-analysis to compare the clinical results and complications of robot-assisted (RA) versus fluoroscopy-assisted (FA) percutaneous vertebral augmentation (PVA) in the treatment of osteoporotic vertebral compression fractures (OVCFs). METHODS: A comprehensive search of online databases including PubMed, Embase, Cochrane Library, web of science, and core journals of China National Knowledge Infrastructure were performed to identify related studies reporting the clinical results and complications of RA versus FA-assisted PVA in the treatment of OVCFs. The rate of bone cement leakage was used to assess the complications. After the surgery, the clinical findings were analyzed using the Visual Analog Scale scores and the Oswestry Disability Index scores. The surgical time, intraoperative fluoroscopy frequency, and x-ray exposure duration were used to evaluate the perioperative results. Forest plots were constructed to investigate the results. RESULTS: RA-PVA had a significantly lower bone cement leakage rate, shorter fluoroscopy frequency, and shorter radiation exposure time of doctors compared with FA-PVA. However, no significant differences were found between RA-PVA and FA-PVA in operative time and radiation exposure time of patients. Furthermore, no statistically differences were found between the 2 groups in Visual Analog Scale and Oswestry Disability Index scores after surgery. CONCLUSIONS: This meta-analysis showed that RA-PVA can reduce bone cement leakage rate, fluoroscopy frequency, and doctors' radiation exposure time. With the advancement of RA technology, we anticipate more high-quality randomized controlled trials of RA versus FA-PVA in the future to validate and update the results of this analysis.

Escape of polymer chains from an attractive channel under electrical force.

The escape of polymer chains from an attractive channel under external electrical field is studied using dynamical Monte Carlo method. Though the escaping process is nonequilibrium in nature, results show that the one-dimensional diffusion theoretical model based on the equilibrium assumption can describe the dependence of the average escaping time (τ(0)) on the polymer-channel interaction (ɛ), the electrical field (E), the chain length (n), and the channel length (L), qualitatively. Results indicate that both ɛ and E play very important roles in the escaping dynamics. For small ɛ, the polymer chain moves out of the channel continuously and quickly. While for large ɛ, the polymer chain is difficult to move out of long channels as it is trapped for a long time (τ(trap)) when the end segment is near the critical point x(C). These results are consistent with the theoretical results for the free energy profiles at small ɛ and large ɛ, respectively. The dependence of x(C) and τ(trap) on ɛ and E are discussed, and specific relations are obtained. The configurational properties of polymer chain are also investigated during the escaping process.

Monte Carlo simulation on polymer translocation in crowded environment.

The effect of crowded environment with static obstacles on the translocation of a three-dimensional self-avoiding polymer through a small pore is studied using dynamic Monte Carlo simulation. The translocation time τ is dependent on polymer-obstacle interaction and obstacle concentration. The influence of obstacles on the polymer translocation is explained qualitatively by the free energy landscape. There exists a special polymer-obstacle interaction at which the translocation time is roughly independent of the obstacle concentration at low obstacle concentration, and the strength of the special interaction is roughly independent of chain length N. Scaling relation τ ~ N(1.25) is observed for strong driving translocations. The diffusion property of polymer chain is also influenced by obstacles. Normal diffusion is only observed in dilute solution without obstacles or in a crowded environment with weak polymer-obstacle attraction. Otherwise, subdiffusion behavior of polymer is observed.

Simulation study on the translocation of diblock copolymer A(n)B(n) through interacting nanopores.

Translocation of diblock copolymer A(n)B(n) through an interacting nanopore is studied using a dynamic Monte Carlo method on a simple three-dimensional cubic lattice. The probabilities and translocation times of two translocation orientations of copolymer, orientation A with block A translocating first and orientation B with block B first, are mainly dependent on the segment-pore interactions ε(A) and ε(B). We find that both the probability and the translocation time are larger for the orientation with stronger attraction. The dynamic behaviors of copolymer translocation at different ε(A) and ε(B) can be explained based on the free energy landscapes of homopolymer at different polymer-pore interaction. The results reveal a complicated free energy landscape for copolymer translocation.

Biodegradable urethral stents seeded with autologous urethral epithelial cells in the treatment of post-traumatic urethral stricture: a feasibility study in a rabbit model.

OBJECTIVE: To evaluate the adhesion and growth of rabbit urethral epithelial cells (UECs) on a biodegradable unbraided mesh urethral stent, and to assess the feasibility and effect of the cell-seeded urethral stent for treating post-traumatic urethral stricture (PTUS) in a rabbit model. MATERIALS AND METHODS: Rabbit UECs were collected by biopsy from adult rabbit urethra and seeded onto the outer layer of a mesh biodegradable urethral stent. The growth of UECs in cell-scaffolds was assessed by scanning electron microscopy, immunohistochemical and fluorescence staining. In all, 32 male New Zealand rabbits were used, with either PTUS or uninjured, as a control group. Cell-seeded stents were implanted into the rabbits strictured urethra. The histological and immunohistochemical findings were assessed after death at 1, 2, 8, 12 and 24 weeks, respectively. The reconstruction and function were evaluated by urethroscopy and retrograde urethrography. RESULTS: The cultured UECs adhered to the stent and grew well. Immunohistochemistry showed that the cells were stained positively for cytokeratin. At 4 weeks, vs 2 weeks, the thickness of the papillary projections of the epithelium decreased and inflammatory cell infiltration diminished. At 24 weeks the injured urethra was completely covered by integrated regeneration of three to five layers of urothelium. There was no evidence of voiding difficulty, stricture recurrence or other complications. CONCLUSIONS: The unbraided mesh biodegradable urethral stent with autologous UECs seemed to be feasible for treating PTUS in the rabbit urethra, and provides a hopeful avenue for clinical application allowing reconstruction of PTUS.

Effect of attractive polymer-pore interactions on translocation dynamics.

The effect of attractive polymer-pore interaction on the translocation of polymer chain through a nanopore under electric field is studied by using dynamical Monte Carlo method. The translocation dynamics is remarkably influenced by the interaction. The translocation time for chain moving through nanopore is strongly dependent on the interaction. It reaches minimum at a moderate interaction which is found to be roughly independent of electric field as well as chain length. At weak interaction region, chain spends long time to overcome the barrier of the pore entrance, i.e., the chain is trapped at the entrance. While at strong interaction region, chain is difficult to leave the nanopore, that is, the chain is trapped at the exit of nanopore. The phenomenon is discussed from the view of free energy landscape.

The effect of titanium particles on rat bone marrow stem cells in vitro.

In arthroplasty prostheses and dental implant, titanium is an excellent biocompatible material for its advanced physical qualities and better biocompatibility. However, it was reported that high ratios of titanium particles can be liberated due to the continual loading or articulation cycles of the implant. Because bone marrow stem cells (BMSCs) located adjacent to the implant are critical contributors to osseous tissue integrity, this study researched the influence of titanium particles on BMSCs' viability, proliferation, and cell skeleton. In addition, the phagocytosis of titanium particles by BMSCs and expression of tumor suppressor protein p53 were also examined. It was found that exposure of BMSCs to titanium particles disrupted their viability and proliferation in vitro, which may due to the phagocytosis of titanium particles by BMSCs. Moreover, cell skeleton was destroyed and the p53 protein level increased as the titanium particles were added. For these results, it was concluded that titanium particles had a cytotoxic effect on BMSCs in vitro and would inhibit the bone formation around the implant.

Ligature-Induced Peri-implant Bone Loss Around Loaded Zirconia and Titanium Implants.

PURPOSE: To radiographically investigate ligature-induced peri-implant bone loss around loaded titanium (Ti-SLA) and zirconia (ZrO2-ZLA) implants using a canine model. MATERIALS AND METHODS: Forty sandblasted and acid-etched titanium and zirconia implants were alternately placed in the mandibles of five canines (20 Ti-SLA, 20 ZrO2-ZLA). Implants were restored after 6 weeks of unloaded healing. After 4 weeks of functional loading, oral hygiene procedures were stopped and experimental peri-implant bone loss was initiated by placing cotton ligatures. After 8 weeks of active progression, ligatures were removed and plaque was allowed to accumulate for another 16 weeks of spontaneous progression (without ligatures). Standardized radiographs were taken at implant placement, at functional loading, and every 2 weeks during active and spontaneous progression of bone loss. RESULTS: Before ligature placement, all implants were successfully osseointegrated and no clinical or radiographic signs of peri-implant infections were detectable. Two weeks after ligature removal, one titanium implant was lost; however, no zirconia implant failures were observed during the study. Radiographically, zirconia implants revealed statistically significantly less crestal peri-implant bone loss compared to titanium implants at the end of the active progression period (Ti-SLA: 3.92 mm; ZrO2-ZLA: 2.65 mm; P < .01); however, no significant differences occurred after the spontaneous progression period (P = .6). Combining the active and spontaneous progression periods together, zirconia implants demonstrated significantly reduced peri-implant bone loss compared to titanium implants (Ti-SLA: 3.76 mm; ZrO2-ZLA: 2.42 mm; P < .01). CONCLUSION: These results demonstrate a significantly reduced ligature-induced inflammation and bone loss for ZrO2-ZLA implants compared to Ti-SLA implants in the canine model.

Bioinspired Shear-Flow-Driven Layer-by-Layer in Situ Self-Assembly.

Layer-by-layer (LbL) assembly is widely applied as a coating technique for the nanoscale control of architecture and related properties. However, its translational applications are limited by the time-consuming and laborious nature of the process. Inspired by the blood-clotting process, herein, we develop a shear-flow-driven LbL (SF-LbL) self-assembly approach that accelerates the adsorption rate of macromolecules by mechanically configuring the polymer chain via a coil-stretch transition, which effectively simplifies and speeds the diffusion-controlled assembly process. The structural characteristics and surface homogeneity of the SF-LbL films are improved, and diverse three-dimensional structures can be achieved. Functional SF-LbL-assembled surfaces for corneal modification are successfully fabricated, and the surface of wounded rat corneas and skin can be directly decorated in situ with SF-LbL nanofilms due to the advantages of this approach. Furthermore, in situ SF-LbL self-assembly has promise as a simple approach for the wound dressing for interventional therapeutics in the clinic, as illustrated by the successful in situ fabrication of drug-free layers consisting of chitosan and heparin on the dorsal skin of diabetic mice to rescue defective wound healing. This bioinspired self-assembly approach is expected to provide a robust and versatile platform with which to explore the surface engineering of nanofilms in science, engineering, and medicine.