Mechanically switchable polymer fibers for sensing in biological conditions

Abstract

Abstract. The area of in vivo sensing using optical fibers commonly uses materials such as silica and polymethyl methacrylate, both of which possess much higher modulus than human tissue. The mechanical mismatch between materials and living tissue has been seen to cause higher levels of glial encapsulation, scarring, and inflammation, leading to failure of the implanted medical device. We present the use of a fiber made from polyvinyl alcohol (PVA) for use as an implantable sensor as it is an easy to work with functionalized polymer that undergoes a transition from rigid to soft when introduced to water. This ability to switch from stiff to soft reduces the severity of the immune response. The fabricated PVA fibers labeled with fluorescein for sensing applications showed excellent response to various stimuli while exhibiting mechanical switchability. For the dry fibers, a tensile storage modulus of 4700 MPa was measured, which fell sharply to 145 MPa upon wetting. The fibers showed excellent response to changing pH levels, producing values that were detectable in a range consistent with those seen in the literature and in proposed applications. The results show that these mechanically switchable fibers are a viable option for future sensing applications.

Replication of annulus fibrosus through fabrication and characterization of polyurethane and cellulose nanocrystal composite scaffolds

“…The ability of the composites to retain the same equilibrium point of water absorption is crucial for maintaining ideal mechanical properties and sample dimensions throughout the entirety of its use. 40,58,59 Although the CNCs in the wet state act individually, there may still be small swollen aggregates of CNCs within the composite. Therefore, if the composites begin to dry out from loss of moisture, the swollen CNC aggregates within the matrix will start to bond together through hydrogen bonding, causing the scaffold to become stiffer and contain defects, as well as decrease in height and cross-sectional area.…”

Efficient one-step amide formation using amino porphyrins

“…This absence of thiocarbamates is notable, because the reaction conditions in Tables 1 and 2 (use of DMSO and amine base) are similar to those used for conjugating hydroxyls by FITC. [40][41][42][43][44][45][46][47] The only exception were traces of carbamate-linked adducts detected via mass spectroscopy, suggesting minor conjugation to hydroxyls.…”

Photolithographic Fabrication of Mechanically Adaptive Devices

“…Water-responsive polymers that offer large property changes upon swelling represent a subset of this class of materials . Their properties are, for example, useful to create actuators, sensors, adaptive membranes, and biomedical devices or implants that soften upon exposure to physiological conditions. , The latter concept has been used to devise adaptive neural implants, including cortical electrodes and optical probes. , Such devices are useful to treat a range of medical conditions, − but the long-term functionality of rigid cortical implants was shown to be impacted by the mechanical mismatch with the soft cortical tissue. − This problem can be mitigated by devices that are initially rigid and allow facile implantation but soften when exposed to physiological conditions. − Several materials have been developed for this purpose, including nanocomposites of polymers and cellulose nanocrystals, photopolymerizable poly­(acrylate)­s and poly­(methacrylate)­s, as well as thiol–ene-based shape-memory polymers. − These materials all change their stiffness upon water sorption by up to 3 orders of magnitude, which causes plasticization and in the case of nanocomposites also disassembly of the reinforcing hydrogen-bonded cellulose nanocrystal network. Improved neural integration of adaptive implants has been reported in several studies, but limited processing options have restricted the application of water-responsive polymers to simple device geometries and structures and stifled their exploitation in more intricate or complex devices, which are usually fabricated by microelectromechanical systems technology processes. , …”

“… 2 Their properties are, for example, useful to create actuators, 3 sensors, 4 adaptive membranes, 5 and biomedical devices or implants that soften upon exposure to physiological conditions. 6 , 7 The latter concept has been used to devise adaptive neural implants, including cortical electrodes and optical probes. 8 , 9 Such devices are useful to treat a range of medical conditions, 10 − 16 but the long-term functionality of rigid cortical implants was shown to be impacted by the mechanical mismatch with the soft cortical tissue.…”