Polymeric Devices Research Articles

Surface Immobilization of Nano-Silver on Polymeric Medical Devices to Prevent Bacterial Biofilm Formation.

Bacterial biofilm on medical devices is difficult to eradicate. Many have capitalized the anti-infective capability of silver ions (Ag+) by incorporating nano-silver (nAg) in a biodegradable coating, which is then laid on polymeric medical devices. However, such coating can be subjected to premature dissolution, particularly in harsh diseased tissue microenvironment, leading to rapid nAg clearance. It stands to reason that impregnating nAg directly onto the device, at the surface, is a more ideal solution. We tested this concept for a corneal prosthesis by immobilizing nAg and nano-hydroxyapatite (nHAp) on poly(methyl methacrylate), and tested its biocompatibility with human stromal cells and antimicrobial performance against biofilm-forming pathogens, Pseudomonas aeruginosa and Staphylococcus aureus. Three different dual-functionalized substrates—high Ag (referred to as 75:25 HAp:Ag); intermediate Ag (95:5 HAp:Ag); and low Ag (99:1 HAp:Ag) were studied. The 75:25 HAp:Ag was effective in inhibiting biofilm formation, but was cytotoxic. The 95:5 HAp:Ag showed the best selectivity among the three substrates; it prevented biofilm formation of both pathogens and had excellent biocompatibility. The coating was also effective in eliminating non-adherent bacteria in the culture media. However, a 28-day incubation in artificial tear fluid revealed a ~40% reduction in Ag+ release, compared to freshly-coated substrates. The reduction affected the inhibition of S. aureus growth, but not the P. aeruginosa. Our findings suggest that Ag+ released from surface-immobilized nAg diminishes over time and becomes less effective in suppressing biofilm formation of Gram-positive bacteria, such as S. aureus. This advocates the coating, more as a protection against perioperative and early postoperative infections, and less as a long-term preventive solution.

Electrospinning of Tough and Elastic Liquid Crystalline Polymer–Polyurethane Composite Fibers: Mechanical Properties and Fiber Alignment

AbstractTough and elastic microfiber composites composed of an elastic polyurethane (Hydrothane) and a liquid crystalline polymer (Vectran) are fabricated via electrospinning. The composite fibers (HVC) are examined as a function of the mixing ratio of the polymers and evaluated on the bases of fiber formation, morphology, thermal properties, mechanical performance, and fiber alignment. The fiber diameters of the HVCs decrease as the content of Vectran increases. When the fibers are aligned via a rotating target, they have even smaller diameters and increased uniformity than when a static target is employed. Surprisingly, the aligned fibers’ mechanical properties are different than those of random orientation; the HVC fibers of random orientation display increases in strength, toughness, and elastic modulii when increasing amounts of Vectran are incorporated in the fibers. The aforementioned mechanical properties of the aligned fibers decrease somewhat as the content of Vectran is increased. Further, the durability of the aligned fibers is examined by extensional durability tests over ten cycles. The tests indicate that the HVC fibers are very durable and can function as tunable, tough, and elastic fibrous polymer scaffolds and have potential applications in high‐performance composites, polymeric filtration devices, and fibrous bioengineering materials.

Photochemistry of Organic Retinal Prostheses.

Organic devices are attracting considerable attention as prostheses for the recovery of retinal light sensitivity lost to retinal degenerative disease. The biotic/abiotic interface created when light-sensitive polymers and living tissues are placed in contact allows excitation of a response in blind laboratory rats exposed to visual stimuli. Although polymer retinal prostheses have proved to be efficient, their working mechanism is far from being fully understood. In this review article, we discuss the results of the studies conducted on these kinds of polymer devices and compare them with the data found in the literature for inorganic retinal prostheses, where the working mechanisms are better comprehended. This comparison, which tries to set some reference values and figures of merit, is intended for use as a starting point to determine the direction for further investigation.

Reaction injection molding of hydrophilic-in-hydrophobic femtolitre-well arrays

Patterning of micro- and nanoscale topologies and surface properties of polymer devices is of particular importance for a broad range of life science applications, including cell-adhesion assays and highly sensitive bioassays. The manufacturing of such devices necessitates cumbersome multiple-step fabrication procedures and results in surface properties which degrade over time. This critically hinders their wide-spread dissemination. Here, we simultaneously mold and surface energy pattern microstructures in off-stoichiometric thiol-ene by area-selective monomer self-assembly in a rapid micro-reaction injection molding cycle. We replicated arrays of 1,843,650 hydrophilic-in-hydrophobic femtolitre-wells with long-term stable surface properties and magnetically trapped beads with 75% and 87.2% efficiency in single- and multiple-seeding events, respectively. These results form the basis for ultrasensitive digital biosensors, specifically, and for the fabrication of medical devices and life science research tools, generally.

Enhanced release of calcium phosphate additives from bioresorbable orthopaedic devices using irradiation technology is non-beneficial in a rabbit model: An animal study.

ObjectivesBioresorbable orthopaedic devices with calcium phosphate (CaP) fillers are commercially available on the assumption that increased calcium (Ca) locally drives new bone formation, but the clinical benefits are unknown. Electron beam (EB) irradiation of polymer devices has been shown to enhance the release of Ca. The aims of this study were to: 1) establish the biological safety of EB surface-modified bioresorbable devices; 2) test the release kinetics of CaP from a polymer device; and 3) establish any subsequent beneficial effects on bone repair in vivo.MethodsActivaScrew Interference (Bioretec Ltd, Tampere, Finland) and poly(L-lactide-co-glycolide) (PLGA) orthopaedic screws containing 10 wt% β-tricalcium phosphate (β-TCP) underwent EB treatment. In vitro degradation over 36 weeks was investigated by recording mass loss, pH change, and Ca release. Implant performance was investigated in vivo over 36 weeks using a lapine femoral condyle model. Bone growth and osteoclast activity were assessed by histology and enzyme histochemistry.ResultsCalcium release doubled in the EB-treated group before returning to a level seen in untreated samples at 28 weeks. Extensive bone growth was observed around the perimeter of all implant types, along with limited osteoclastic activity. No statistically significant differences between comparative groups was identified.ConclusionThe higher than normal dose of EB used for surface modification did not adversely affect tissue response around implants in vivo. Surprisingly, incorporation of β-TCP and the subsequent accelerated release of Ca had no significant effect on in vivo implant performance, calling into question the clinical evidence base for these commercially available devices.Cite this article: I. Palmer, S. A. Clarke, F. J Buchanan. Enhanced release of calcium phosphate additives from bioresorbable orthopaedic devices using irradiation technology is non-beneficial in a rabbit model: An animal study. Bone Joint Res 2019;8:266–274. DOI: 10.1302/2046-3758.86.BJR-2018-0224.R2.

Tough Responsive Polymer Hydrogels and Devices Crosslinked by Block Copolymer Micelles

Amphiphilic block copolymer Pluronic F127 is modified by acrylate groups on both ends, generating a functional triblock copolymer F127DA. The functional copolymer forms micelles in aqueous solution, with the hydrophilic PEO coronae containing reactive double bonds. The F127DA micelles are copolymerized with acrylamide, 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS), and methyl chloride quaternized N,N‐dimethylamino ethylacrylate (DMAEA‐Q) through free radical copolymerization, generating hydrogels with outstanding toughness, fatigue resistance, and responsiveness to pH, ion strength, and electric field. The polyelectrolyte hydrogels are assembled through electrostatic interactions into devices with periodic structures and property contrast, which enables shape transformations upon external stimuli.

Flexible, Stretchable and Healable Electronics

Organic electronics, based on semiconducting and conducting polymers, have been extensively investigated in the past two decades and have found commercial applications in lighting panels, smartphone and TV screens using OLEDs (organic light emitting diodes) technology. Many other applications are foreseen to reach the commercial maturity in future in areas such as transistors, sensors and photovoltaics. Organic electronic devices, apart from consumer applications, are paving the path for key applications at the interface between electronics and biology, such as in polymer electrodes for recording and stimulating neural activity in neurological diseases. In such applications, organic polymers are very attractive candidates due to their distinct property of mixed conduction: the ability to transport both electron/holes and ionic species. Additionally, conducting polymers offer the possibility to tune their surface properties (e.g., wettability or chemical reactivity) by changing their oxidation state, thus promoting or hindering the adhesion of biomolecules. This feature can be particularly useful for enhancing the biocompatibility of implantable electrodes. My talk will deal with processing and characterization of conducting polymer films and devices for flexible, stretchable and healable electronics. I will particularly focus on micro-patterning of conducting polymer films for flexible and stretchable devices and on healing of conducting polymer films.

Solar Energy Storage by Molecular Norbornadiene-Quadricyclane Photoswitches: Polymer Film Devices.

Devices that can capture and convert sunlight into stored chemical energy are attractive candidates for future energy technologies. A general challenge is to combine efficient solar energy capture with high energy densities and energy storage time into a processable composite for device application. Here, norbornadiene (NBD)–quadricyclane (QC) molecular photoswitches are embedded into polymer matrices, with possible applications in energy storing coatings. The NBD–QC photoswitches that are capable of absorbing sunlight with estimated solar energy storage efficiencies of up to 3.8% combined with attractive energy storage densities of up to 0.48 MJ kg−1. The combination of donor and acceptor units leads to an improved solar spectrum match with an onset of absorption of up to 529 nm and a lifetime (t 1/2) of up to 10 months. The NBD–QC systems with properties matched to a daily energy storage cycle are further investigated in the solid state by embedding the molecules into a series of polymer matrices revealing that polystyrene is the preferred choice of matrix. These polymer devices, which can absorb sunlight and over a daily cycle release the energy as heat, are investigated for their cyclability, showing multicycle reusability with limited degradation that might allow them to be applied as window laminates.

Structural and optical characterization of [(PVA:PVP)-Cu2+] composite films for promising semiconducting polymer devices

High quality semiconducting polymers of copper ions doped poly(vinyl alcohol) (PVA):poly(vinyl pyrrolidone) (50:50 wt%) [(PVA:PVP)-x wt % Cu2+] [x = 0,3,5,15 and 20 wt%] composite films were successfully prepared by the conventional solution casting method. The characterizations of the films were investigated by XRD scan, FT-IR and UV–Vis–NIR spectroscopic analysis. The obtained values of the d-spacing and crystallite length D parameters from Gaussian fitting of the broad XRD peaks of the virgin PVA, [(PVA:PVP)-x wt % Cu2+] polymer composite blend films indicate the miscibility and compatibility of the blend constituents and bonding of positively charged Cu2+ ions with negatively charged OH groups of the polymer chains. The optical energy gaps and the high frequency refractive indices are strongly affected by incorporation of Cu2+ ions in the (PVA:PVP) blend chains where the optical gap decreased from 4.68 eV for pure (PVA:PVP) polymer blend to 2.95 eV for [(PVA:PVP)-20 wt % Cu2+] and the high frequency refractive index increased from 2.42 to 2.78. Based on the collected results, the copper ions doped (PVA:PVP) polymer blend composite films can be considered as a promising, new and facile material for UV filters, semiconducting polymer devices, planar polymer waveguides and polymer solar cells designing.

Direct Digital Manufacturing of Nanocomposites

Additive manufacturing has surged in popularity as a route to designing and preparing functional parts. Depending on the parts function, certain attributes such as high mechanical performances may be desired. We develop a route for improving the mechanical properties of polymer devices, fabricated through additive manufacturing by combining electrospinning and stereo-lithography into one automated process. This process utilises the impressive mechanical properties of carbon nanotubes by encapsulating and aligning them in electrospun fibres. Composite fibres will be incorporated into polymer resins prepared with stereo-lithography, thereby providing resins that benefit from the composite fibres properties, enhancing their overall mechanical properties.

Nanocarriers and nonviral methods for delivering antiangiogenic factors for glioblastoma therapy: the story so far.

Angiogenesis, the formation of new blood vessels, is an essential component of glioblastoma (GB) progression. The development of angiogenesis inhibitor therapy, including treatments targeting vascular endothelial growth factor (VEGF) in particular, raised new hopes for the treatment of GB, but no Phase III clinical trial to date has reported survival benefits relative to standard treatment. There are several possible reasons for this limited efficacy, including VEGF-independent angiogenesis, induction of tumor invasion, and inefficient antiangiogenic factor delivery to the tumor. Efforts have been made to overcome these limitations by identifying new angiogenesis inhibitors that target angiogenesis through different mechanisms of action without inducing tumor invasion, and through the development of viral and nonviral delivery methods to improve antiangiogenic activity. Herein, we describe the nonviral methods, including convection-enhanced delivery devices, implantable polymer devices, nanocarriers, and cellular vehicles, to deliver antiangiogenic factors. We focus on those evaluated in intracranial (orthotopic) animal models of GB, the most relevant models of this disease, as they reproduce the clinical scenario of tumor progression and therapy response encountered in GB patients.

Conjugated Polymer Actuators and Devices: Progress and Opportunities.

Conjugated polymers (CPs), as exemplified by polypyrrole, are intrinsically conducting polymers with potential for development as soft actuators or "artificial muscles" for numerous applications. Significant progress has been made in the understanding of these materials and the actuation mechanisms, aided by the development of physical and electrochemical models. Current research is focused on developing applications utilizing the advantages that CP actuators have (e.g., low driving potential and easy to miniaturize) over other actuating materials and on developing ways of overcoming their inherent limitations. CP actuators are available as films, filaments/yarns, and textiles, operating in liquids as well as in air, ready for use by engineers. Here, the milestones made in understanding these unique materials and their development as actuators are highlighted. The primary focus is on the recent progress, developments, applications, and future opportunities for improvement and exploitation of these materials, which possess a wealth of multifunctional properties.

Energy transfer-enhanced external power conversion efficiency in blended polymeric thin film solar devices

In this paper, the spectral and electrical properties of a conjugated polymer poly [(9, 9-dioctyl-2, 7-divinylenefluorenylene)-alt-co-(1, 4-phenylene)] (PFO–MEH–PPV) with poly[3-(2-ethyl-isocyanato-octadecanyl) thiophene] (PECOD) in thin films have been studied. First, PFO–MEH–PPV and PECOD were dissolved in tetrahydrofuran and chloroform respectively for different concentrations. These solutions were deposited on glass substrates to form thin films with different thicknesses. The absorbance and photoluminescence spectra for each individual pure polymer were recorded and contrasted with those for blended conjugated polymer’s films to determine the effect of blending on the absorption and photoluminescence. Finally, we present a study on the processing and characterization of organic solar cells fabricated by spin coating pure PFO–MEH–PPV, PECOD and their blend as the organic active layer onto indium tin oxide layer (150 nm), followed by the evaporation of silver cathode (110 nm). The current–voltage characteristics of these cells were determined and external quantum efficiency. Upon blending the two polymers in solid forms, it could be seen that the efficiency (6.25%) for the cells based on a blend layer is higher than the ones without blending (4.4%). Finally, we demonstrated here that the combination/blending of conjugated polymers has resulted in optimized solar device function, with reasonably quantum efficiency higher than 10%.

Modeling and simulation of nonlinear electro-thermo-mechanical continua with application to shape memory polymeric medical devices

Shape memory materials have gained considerable attention thanks to their ability to change physical properties when subjected to external stimuli such as temperature, pH, humidity, electromagnetic fields, etc. These materials are increasingly used for a large number of biomedical applications. For applications inside the human body, contactless control can be achieved by the addition of electric and/or magnetic particles that can react to electromagnetic fields, thus leading to a composite biomaterial. The difficulty of developing accurate numerical models for smart materials results from their multiscale nature and from the multiphysics coupling of involved phenomena. This coupling involves electromagnetic, thermal and mechanical problems. This paper contributes to the multiphysics modeling of a shape memory polymer material used as a medical stent. The stent is excited by electromagnetic fields produced by a coil which can be wrapped around a failing organ. In this paper we develop large deformation formulations for the coupled electro-thermo-mechanical problem using the electric potential to solve the electric problem. The formulations are then discretized and solved using the finite element method. Results are validated by comparison with results in the literature.

Materials and Designs for Wearable Photodetectors.

Photodetectors (PDs), as an indispensable component in electronics, are highly desired to be flexible to meet the trend of next-generation wearable electronics. Unfortunately, no in-depth reviews on the design strategies, material exploration, and potential applications of wearable photodetectors are found in literature to date. Thus, this progress report first summarizes the fundamental design principles of turning "hard" photodetectors "soft," including 2D (polymer and paper substrate-based devices) and 1D PDs (fiber shaped devices). In short, the flexibility of PDs is realized through elaborate substrate modification, material selection, and device layout. More importantly, this report presents the current progress and specific requirements for wearable PDs according to the application: monitoring, imaging, and optical communication. Challenges and future research directions in these fields are proposed at the end. The purpose of this progress report is not only to shed light on the basic design principles of wearable PDs, but also serve as the roadmap for future exploration in wearable PDs in various applications, including health monitoring and Internet of Things.

Biomechanical characterization of a novel collagen-hyaluronan infused 3D-printed polymeric device for partial meniscus replacement.

The menisci transmit load by increasing the contact area and decreasing peak contact stresses on the articular surfaces. Meniscal lesions are among the most common orthopedic injuries, and resulting meniscectomies are associated with adverse polycaprolactone contact mechanics changes and, ultimately, an increased likelihood of osteoarthritis. Meniscus scaffolds were fabricated by 3D-printing a network of circumferential and radial filaments of resorbable polymer (poly(desaminotyrosyl-tyrosine dodecyl ester dodecanoate)) and infused with collagen-hyaluronan. The scaffold demonstrated an instantaneous compressive modulus (1.66 ± 0.44 MPa) comparable to native meniscus (1.52 ± 0.59 MPa). The scaffold aggregate modulus (1.33 ± 0.51 MPa) was within 2% of the native value (1.31 ± 0.36 MPa). In tension, the scaffold displayed a comparable stiffness to native tissue (127.6-97.1 N/mm) and an ultimate load of 33% of the native value. Suture pull-out load of scaffolds (83.1 ± 10.0 N) was within 10% of native values (91.5 ± 15.4 N). Contact stress analysis demonstrated the scaffold reduced peak contact stress by 60-67% and increased contact area by 38%, relative to partial meniscectomy. This is the first meniscal scaffold to match both the axial compressive properties and the circumferential tensile stiffness of the native meniscus. The improvement of joint contact mechanics, relative to partial meniscectomy alone, motivates further investigation using a large animal model. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2457-2465, 2019.

Redox gated polymer memristive processing memory unit

Memristors with enormous storage capacity and superior processing efficiency are of critical importance to overcome the Moore’s Law limitation and von Neumann bottleneck problems in the big data and artificial intelligence era. In particular, the integration of multifunctionalities into a single memristor promises an essential strategy of obtaining a high-performance electronic device that satisfies the nowadays increasing demands of data storage and processing. In this contribution, we report a proof-of-concept polymer memristive processing-memory unit that demonstrates programmable information storage and processing capabilities. By introducing redox active moieties of triphenylamine and ferrocene onto the pendants of fluorene skeletons, the conjugated polymer exhibits triple oxidation behavior and interesting memristive switching characteristics. Associated with the unique electrochemical and electrical behavior, the polymer device is capable of executing multilevel memory, decimal arithmetic operations of addition, subtraction, multiplication and division, as well as simple Boolean logic operations.

Evaluation of Magnesium-based Medical Devices in Preclinical Studies: Challenges and Points to Consider.

Absorbable metallic implants have been under investigation for more than a century. Animal and human studies have shown that magnesium (Mg) alloys can be safely used in bioresorbable scaffolds. Several cardiovascular and orthopedic biodegradable metallic devices have recently been approved for use in humans. Bioresorbable Mg implants present many advantages when compared to bioabsorbable polymer or nonabsorbable metallic implants, including similar strength and mechanical properties as existing implant-grade metals without the drawbacks of permanence or need for implant removal. Imaging visibility is also improved compared to polymeric devices. Additionally, with Mg-based cardiovascular stents, the risk of late stent thrombosis and need for long-term anti-platelet therapy may be reduced as the host tissue absorbs the Mg degradation products and the morphology of the vessel returns to a near-normal state. Absorbable Mg implants present challenges in the conduct of preclinical animal studies and interpretation of pathology data due to their particular degradation process associated with gas production and release of by-products. This article will review the different uses of Mg implants, the Mg alloys, the distinctive degradation features of Mg, and the challenges confronting pathologists at tissue collection, fixation, imaging, slide preparation, evaluation, and interpretation of Mg implants.

Retraction of "Single Polymeric Template-Based Full-Color Organic Electrochromic Device".

With low-cost and simple processing, organic electrochromic polymers have attracted considerable attention as a promising material platform for flexible and low-energy-consuming optoelectronic devices. However, typical electrochromic polymers can only be switched from natural-colored to oxidized-transparent states. As a result, the complexity of combining several distinct polymers to achieve a full-color gamut has significantly limited the niche applications of electrochromic polymers. Here we report an electrochromic polymer based on 4,7-di((3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine-3-yl)-3,4-ethylenedioxythiophene) (PEP), which exhibits fast full-color reversible tuning capability and good stability. Furthermore, a red-green-blue flexible electrochromic device just based on poly(PEP) was fabricated, which offers an effective approach to dynamically manipulate color and enables a variety of optoelectronic applications.

Propulsion and Mixing Generated by the Digitized Gait ofCaenorhabditis elegans

Nematodes have evolved to swim in highly viscous environments. Artificial mechanisms that mimic the locomotory functions of nematodes can be efficient viscous pumps. We experimentally simulate the motion of the head segment of Caenorhabditis elegans by introducing a reciprocating and rocking blade. We show that the bio-inspired blade's motion not only induces a flow structure similar to that of the worm, but also mixes the surrounding fluid by generating a circulatory flow. When confined between two parallel walls, the blade causes a steady Poiseuille flow through closed circuits. The pumping efficiency is comparable with the swimming efficiency of the worm. If implanted in a sealed chamber and actuated remotely, the blade can provide pumping and mixing functions for microprocessors cooled by polymeric flows and microfluidic devices.