In Vitro Evaluation of Electrospun Chitosan Mats Crosslinked with Genipin as Guided Tissue Regeneration Barrier Membranes

Guided tissue regeneration (GTR) is a surgical technique commonly used to exclude bacteria and soft tissues from bone graft sites in oral/maxillofacial bone graft sites by using a barrier membrane to maintain the graft contour and space. Current clinical barrier membrane materials based on expanded polytetrafluoroethylene (ePTFE) and bovine type 1 collagen are non-ideal and experience a number of disadvantages including membrane exposure, bacterial colonization/biofilm formation and premature degradation, all of which result in increased surgical intervention and poor bone regeneration. These materials do not actively participate in tissue regeneration, however bioactive materials, such as chitosan, may provide advantages such as the ability to stimulate wound healing and de novo bone formation. Our hypothesis is that electrospun chitosan GTR membranes will support cell attachment and growth but prevent cell infiltration/penetration of membrane, demonstrate in vitro degradation predictive of 4-6 month in vivo functionality, and will deliver antibiotics locally to prevent/inhibit periopathogenic complications. To test this hypothesis a series of chitosan membranes were electrospun, in the presence or absence of genipin, a natural crosslinking agent, at concentrations of 5 and 10 mM. These membranes were characterized by scanning electron microscopy, tensile testing, suture pullout testing, Fourier transform infrared spectroscopy, X-ray diffraction, and gel permeation chromatography, and in vitro biodegradation for diameter/morphology of fibers, membrane strengths, degree of crosslinking, crystallinity, molecular weight, and degradation kinetics, respectively. Cytocompability of membranes was evaluated in osteoblastic, fibroblastic and monocyte cultures. The activity of minocycline loaded and released from the membranes was determined in zone of inhibition tests using P. gingivalis microbe. The results demonstrated that genipin crosslinking extended the in vitro degradation timeframe, extended the release of minocycline, and increased the tensile strength of the resultant membranes while cytocompatibility, swelling, and tear strength were unaffected. In conclusion, electrospun chitosan membranes crosslinked with genipin are a suitable material for guided tissue regeneration and may help reduce bacterial infection and bacteria-induced host inflammatory response

Biomaterial and antibiotic strategies for peri-implantitis

Dental implants have 89% plus survival rates at 10-15 years, but peri-implantitis or dental implant infections may be as high as 14%. Peri-implantitis can limit clinical success and impose health and financial burdens to patients and health providers. The pathogenic species associated with periodontitis (e.g., Fusobacterium ssp, A. actinomycetemcomitans, P. gingivalis) are also associated with peri-implantitis. Incidence of peri-implantitis is highest within the first 12 months after implantation, and is higher in patients who smoke or have poor oral health as well as with calcium-phosphate-coated or surface-roughened implants. Biomaterial therapies using fibers, gels, and beads to deliver antibiotics have been used in the treatment of Peri-implantitis though clinical efficacy is not well documented. Guided tissue regeneration membranes (e.g., collagen, poly-lactic/glycolic acid, chitosan, ePTFE) loaded with antimicrobials have shown success in reosseointegrating infected implants in animal models but have not been proven in humans. Experimental approaches include the development of anti-bioadhesion coatings, coating surfaces with antimicrobial agents (e.g., vancomycin, Ag, Zn) or antimicrobial releasing coatings (e.g., calcium phosphate, polylactic acid, chitosan). Future strategies include the development of surfaces that become antibacterial in response to infection, and improvements in the permucosal seal. Research is still needed to identify strategies to prevent bacterial attachment and enhance normal cell/tissue attachment to implant surfaces. © 2008 Wiley Periodicals, Inc

Stochastic thermal feedback in switching measurements of a superconducting nanobridge caused by overheated electrons and phonons

Funding Information: The work is supported by the Foundation for Polish Science project “Stochastic thermometry with Josephson junction down to nanosecond resolution” (First TEAM/2016-1/10). Publisher Copyright: ©2021 American Physical SocietyWe study correlated switchings of a superconducting nanobridge probed with a train of current pulses. For pulses with a low repetition rate each pulse transits the superconducting bridge to the normal state with probability independent of the outcomes in the preceding pulses. We show that with the reduction of the time interval between pulses long-range correlation between pulses occurs: stochastic switching in a single pulse raises the temperature of the bridge and affects the outcome of the probing for the next pulses. As a result, an artificial intricate stochastic process with an adjustable strength of correlation is produced. We identify the regime where apparent switching probability exhibits the thermal hysteresis with discontinuity at a critical current amplitude of the probing pulse. This engineered stochastic process can be viewed as an artificial phase transition and provides an interesting framework for studying correlated systems. The process resembles the familiar transition from the superconducting to normal state in the current-bias nanowire, proceeding through a phase slip avalanche. Due to its extreme sensitivity to the control parameter, i.e., electric current, temperature, or magnetic field, it offers the opportunity for ultrasensitive detection.Peer reviewe

Flipping-Coin Experiment to Study Switching in Josephson Junctions and Superconducting Wires

When probed with current pulses, Josephson junctions and superconducting wires exhibit stochastic switching from a superconducting to a stable nonzero-voltage state. The electrical current dependence of the switching probability (the so-called S curve) or the switching-current distribution is a fingerprint of the physics governing the escape process. This work addresses the criterion of the independent switching event, which is important for the credibility of the switching measurements of superconducting wires and various Josephson junctions involving superconductor-insulator-superconductor tunnel junctions, proximity junctions, and Dayem nanobridges. Treating the Josephson junction as an electrical coin with a current-tuned switching probability, we investigate the effect of correlation between switching events on the switching statistics. We show that such a correlation originates from the thermal dynamics of the superconducting wire.Peer reviewe

Heat Hunting in a Freezer

Propagation and relaxation of nonequilibrium quasiparticles in superconductors are fundamental for functioning of numerous nanoscale devices, enabling operation of some of them, and limiting the performance of others. The quasiparticles heated above lattice temperature may relax locally via phonon or photon-emission channels, or diffuse over appreciable distances in a nanostructure altering the functionality of their remote components. Tracing quasiparticles experimentally in real-time domain has remained a challenging task owing to their rapid dynamics. With electronic nanothermometry, based on probing of the temperature-dependent switching current of a superconducting nanobridge, we monitor heat pulse carried by a flux of nonequilibrium quasiparticles as it passes by our detector with a noise-equivalent temperature of 10 mK/N, where N is the number of pulses probing the bridge (typically N=10000), and temporal resolution of a single nanosecond. The measurement provides the picture of quasiparticle diffusionin a superconducting aluminum strip and direct determination of the diffusion constant D equal to 100 cm2/s with no energy dependence visible.Peer reviewe