Bamboo fiber reinforced poly (acrylonitrile-styrene-acrylic)/chlorinated polyethylene via compabilization

In the quest to enhance the performance of natural fiber-reinforced polymer composites, achieving optimal dispersion of fiber materials within a polymeric matrix has been identified as a key strategy. Traditional approaches, such as the surface modification of natural fibers, often necessitate the use of additional synthetic chemical processes, presenting a significant challenge. In this work, taking poly (acrylonitrile-styrene-acrylic) (ASA) and bamboo fiber (BF) as a model system, we attempt to use the elastomer-chlorinated polyethylene (CPE) as a compatibilizer to tailor the mechanical properties of ASA/CPE/BF ternary composites. It was found that increasing CPE content contributed to more remarkable reinforcing efficiency, where composite with 15 phr CPE exhibited a nearly four-fold increase in reinforcing efficiency of tensile strength (20 %) compared with that of composite system without CPE (4.1 %). Such improvement was ascribed to the compatibilizing effect exerted by CPE, which prevented the aggregation of BF within polymeric matrix. Surface properties suggested the stronger interface between CPE and BF compared to that between ASA and BF and thereby contributed to the compabilizing effect. Since no chemical process was involved, it is suggested that the introduction of elastomer to be a universal, green and sustainable approach to achieve the reinforcement.

Artificial Octopus-Limb-Like Adhesive Patches for Cupping-Driven Transdermal Delivery with Nanoscale Control of Stratum Corneum

Drug delivery through complex skin is currently being studied using various innovative structural and material strategies due to the low delivery efficiency of the multilayered stratum corneum as a barrier function. Existing microneedle-based or electrical stimulation methods have made considerable advances, but they still have technical limitations to reduce skin discomfort and increase user convenience. This work introduces the design, operation mechanism, and performance of noninvasive transdermal patch with dual-layered suction chamber cluster (d-SCC) mimicking octopus-limb capable of wet adhesion with enhanced adhesion hysteresis and physical stimulation. The d-SCC facilitates cupping-driven drug delivery through the skin with only finger pressure. Our device enables nanoscale deformation control of stratum corneum of the engaged skin, allowing for efficient transport of diverse drugs through the stratum corneum without causing skin discomfort. Compared without the cupping effect of d-SCC, applying negative pressure to the porcine, human cadaver, and artificial skin for 30 min significantly improved the penetration depth of liquid-formulated subnanoscale medicines up to 44, 56, and 139%. After removing the cups, an additional acceleration in delivery to the skin was observed. The feasibility of d-SCC was demonstrated in an atopic dermatitis-induced model with thickened stratum corneum, contributing to the normalization of immune response.

High-performance composite elastomers with abundant heterostructures for enhanced electromagnetic wave absorption with ultrabroad bandwidth

Two-dimensional (2D) MXene has attracted vast attention in electromagnetic wave absorption (EWA), but there remains a contradiction between maintaining impedance matching and enhancing dielectric loss. Herein, the multi-scale architectures of ecoflex/2D MXene (Ti3C2Tx)@zero-dimensional CoNi sphere@one-dimensional carbon nanotube composite elastomers were successfully constructed by simple liquid-phase reduction and thermo-curing method. The binding between the hybrids as fillers and ecoflex as a matrix greatly enhanced the EWA capability of the obtained composite elastomer and improved its mechanical properties. Owing to its good impedance matching, abundant heterostructures, and synergistic electrical and magnetic losses, this elastomer exhibited an excellent minimum reflection loss of -67 dB at 9.46 GHz under a thickness of 2.98 mm. In addition, its ultrabroad effective absorption bandwidth reached 6.07 GHz. This achievement will pave the way for the exploitation of multi-dimensional heterostructures as high-performance electromagnetic absorbers with superior EWA ability.

A self-unfolding proximity enabling device for oral delivery of macromolecules

Oral delivery of macromolecules remains highly challenging due to their rapid degradation in the gastrointestinal tract and poor absorption across the tight junctions of the epithelium. In the last decade, researchers have investigated several medical devices to overcome these challenges using various approaches, some of which involve piercing through the intestine using micro and macro needles. We have developed a new generation of medical devices called self-unfolding proximity enabling devices, which makes it possible to orally deliver macromolecules without perforating the intestine. These devices protect macromolecules from the harsh conditions in the stomach and release their active pharmaceutical ingredients in the vicinity of the intestinal epithelium. One device version is a self-unfolding foil that we have used to deliver insulin and nisin to rats and pigs respectively. In our study, this device has shown a great potential for delivering peptides, with a significant increase in the absorption of solid dosage of insulin by ∼12 times and nisin by ∼4 times in rats and pigs, respectively. With the ability to load solid dosage forms, our devices can facilitate enhanced absorption of minimally invasive oral macromolecule formulations.

The effect of surface roughening of orthodontic elastomers on hydrophobicity and in vitro adherence of Streptococcus gordonii

OBJECTIVES

Biofilm formation around orthodontic appliances causes gingivitis, enamel decalcification and caries. Bacteria adhere less readily to superhydrophobic surfaces. The aim of this study was to determine whether a superhydrophobic surface could be generated on orthodontic elastomers by surface modification in order to reduce bacterial adhesion.

MATERIALS AND METHODS

Orthodontic elastomers were modified with sandpapers of various grit sizes (80-600 grit). Surface roughness of the modified and unmodified surfaces was assessed qualitatively with scanning electron microscopy and quantitatively with confocal microscopy. Water contact angles were measured with a goniometer to quantify hydrophobicity. Measurements were performed on unextended elastomers (100% original length) and elastomers extended to 150%, and 200% of the original length. Adhesion of Streptococcus gordonii to saliva coated elastomers was measured by counting colony forming units on agar plates.

RESULTS

Abrasion with different sandpapers produced elastomers with surface roughness (Ra) ranging from 2 to 12 μm. Contact angles followed a quadratic trend with a maximum contact angle of 104° at an Ra of 7-9 μm. Average water contact angles, when viewed perpendicular to the direction of extension, decreased from 99° to 90° when the extension was increased from 100% to 200% and increased from 100° to 103° when viewed parallel to the direction of extension. Bacterial adhesion increased as roughness increased and this effect was more pronounced with elastomer extension.

CONCLUSION

The surface roughness of orthodontic elastomers influences both their hydrophobicity and bacterial adhesion. Superhydrophobicity of elastomers could not be achieved with sandpaper abrasion.

Grafting of proteins onto polymeric surfaces: A synthesis and characterization challenge

This review aims at answering the following question: how can a researcher be sure to succeed in grafting a protein onto a polymer surface? Even if protein immobilization on solid supports has been used industrially for a long time, hence enabling natural enzymes to serve as a powerful tool, emergence of new supports such as polymeric surfaces for the development of so-called intelligent materials requires new approaches. In this review, we introduce the challenges in grafting protein on synthetic polymers, mainly because compared to hard surfaces, polymers may be sensitive to various aqueous media, depending on the pH or reductive molecules, or may exhibit state transitions with temperature. Then, the specificity of grafting on synthetic polymers due to difference of chemical functions availability or difference of physical properties are summarized. We present next the various available routes to covalently bond the protein onto the polymeric substrates considering the functional groups coming from the monomers used during polymerization reaction or post-modification of the surfaces. We also focus our review on a major concern of grafting protein, which is avoiding the potential loss of function of the immobilized protein. Meanwhile, this review considers the different methods of characterization used to determine the grafting efficiency but also the behavior of enzymes once grafted. We finally dedicate the last part of this review to industrial application and future prospective, considering the sustainable processes based on green chemistry.

A Large-Diameter Vascular Graft Replacing Animal-Derived Sealants With an Elastomeric Polymer

INTRODUCTION

To assess the safety and efficacy of an experimental large-diameter vascular graft externally sealed with an elastomeric polymer when used as an interposition graft in the descending aorta of sheep.

METHODS

The experimental vascular grafts as well as control gelatin sealed interposition grafts were inserted into the descending aorta of juvenile sheep. The grafts were assessed by time to hemostasis and blood loss during surgery and hematology and biochemistry panels at distinct time points. Magnetic resonance imaging (MRI) was performed at 3 and at 6 mo after surgery, after which the animals were euthanized and necropsies were carried out including macroscopic and microscopic examination of the grafts, anastomoses, and distal organs.

RESULTS

All animals survived the study period. There was no perceivable difference in the surgical handling of the grafts. The median intraoperative blood loss was 27.5 mL (range 10.0-125.0 mL) in the experimental group and 50.0 mL (range 10.0-75.0 mL) in the control group. The median time to hemostasis was 5.0 min (range 2.0-16.0 min) minutes in the experimental group versus 6.0 min (range 4.0-6.0 min) in the control group. MRI showed normal flow and graft patency in both groups. Healing and perianastomotic endothelialization was similar in both groups.

CONCLUSIONS

The experimental graft has a similar safety and performance profile and largely comparable necropsy results, in comparison to a commonly used prosthetic vascular graft, with the experimental grafts eliciting a nonadherent external fibrous capsule as the major difference compared to the control grafts that were incorporated into the periadventitia. Survival, hemostatic sealing, and hematologic and radiologic results were comparable between the study groups.

Cellulose and lignin in place of EPDM and carbon black for automotive sealing profiles

This study aims at using microcrystalline cellulose (MCC) and lignin in place of EPDM and carbon black with specified amounts to investigate the chemical, thermal, rheometric, mechanical, thermo-aging and morphological properties of EPDM elastomers. At the end of the study, the introduction of the MCC and lignin enabled higher elastic modulus and tear strength unlike tensile strength by revealing minor chemical shifts and lower thermal stability. In addition, the MCC and lignin facilitated the vulcanization process with fewer torque values by dispersing mostly homogeneously in the matrix. It was shown that all of the mechanical values were found to be in the range of the specified standard after the replacement of the MCC and lignin.

Percutaneous delivery and degradation of a shape memory elastomer poly(glycerol dodecanedioate) in porcine pulmonary arteries

Shape memory biodegradable elastomers are an emergent class of biomaterials well-suited for percutaneous cardiovascular repair requiring nonlinear elastic materials with facile handling. We have previously developed a chemically crosslinked shape memory elastomer, poly (glycerol dodecanedioate) (PGD), exhibiting tunable transition temperatures around body temperature (34-38 °C), exhibiting nonlinear elastic properties approximating cardiac tissues, and favorable degradation rates in vitro. Degree of tissue coverage, degradation and consequent changes in polymer thermomechanical properties, and inflammatory response in preclinical animal models are unknown material attributes required for translating this material into cardiovascular devices. This study investigates changes in the polymer structure, tissue coverage, endothelialization, and inflammation of percutaneously implanted PGD patches (20 mm × 9 mm x 0.5 mm) into the branch pulmonary arteries of Yorkshire pigs for three months. After three months in vivo, 5/8 samples exhibited (100%) tissue coverage, 2/8 samples exhibited 85-95% tissue coverage, and 1/8 samples exhibited limited (<20%) tissue coverage with mild-moderate inflammation. PGD explants showed a (60-70%) volume loss and (25-30%) mass loss, and a reduction in polymer crosslinks. Lumenal and mural surfaces and the cross-section of the explant demonstrated evidence of degradation. This study validates PGD as an appropriate cardiovascular engineering material due to its propensity for rapid tissue coverage and uneventful inflammatory response in a preclinical animal model, establishing a precedent for consideration in cardiovascular repair applications.

Experimental data for the magnetic properties of vulcanized natural rubber nanocomposites using vibrating sample magnetometer (VSM)

Base isolation is a technique installed to absorb any movement or vibration on the structures. The incorporation of nanocomposites into elastomer as the interesting materials especially for the active stiffness and vibration control of structural systems. A base isolator is made up of alternate layers of steel and rubber. The performance of magnetic rubber device is dependent on mechanical and magnetic properties of composite rubber materials. A vibrating sample magnetometer (VSM) is an instrument to detect the magnetic properties. The article provides information on the magnetic properties corresponding to different carbon nanotubes loadings of 0%, 1%, 3% and 5% and different loading of microcarbonyl iron (MCI) i.e. 0% (B0), 10% (B10), 20% (B20) and 30% (B30) in natural rubber compound. The magnetic properties dataset described the data from compression test.

Transparent and self-healing elastomers for reconfigurable 3D materials

Transparent soft materials have been widely used in applications ranging from packaging to flexible displays, wearable devices, and optical lenses. Nevertheless, soft materials are susceptible to mechanical damages, leading to functional failure and premature disposal. Herein, we introduce a transparent self-healing elastomer that is able to repair the polymer network via exchange reactions of dynamic disulfide bonds. Due to its self-healing ability, the mechanical properties of the elastomer can be recovered, as well as its transparency after multiple cycles of abrasion and healing. The self-healing polymer is fabricated into three-dimensional (3D) structures by folding or modular origami assembly of planar self-healing polymer sheets. The 3D polymer objects are employed as storage containers of solid and liquid substances, reactors for photopolymerization, and cuvettes for optical measurements (exhibiting superior properties to those of commercial cuvettes). These dynamic polymers show outstanding mechanical, optical, and recycling properties that could potentially be further adapted in adaptive smart packaging, reconfigurable materials, optical devices, and recycling of elastomers. This article is protected by copyright. All rights reserved.

Dynamic Pattern Formation of Active Matters Triggered by Mechanical Stimuli

In vitro gliding assay of the filamentous protein microtubule (MT) on a kinesin motor protein coated surface has appeared as a classic platform for studying active matters. At high densities, the gliding MTs spontaneously align and self-organize into fascinating large-scale patterns. Application of mechanical stimuli e.g., stretching stimuli to the MTs gliding on a kinesin-coated surface can modulate their self-organization and patterns according to the boundary conditions. Depending on the mode of stretching, MT at high densities change their moving direction and exhibit various kinds of patterns such as stream, zigzag and vortex pattern. In this chapter, we discuss detail procedures on how to apply mechanical stimuli to the moving MTs on a kinesin coated substrate.

D-band strain underestimates fibril strain for twisted collagen fibrils at low strains

Collagen fibrils are the main structural component of load-bearing tissues such as tendons, ligaments, skin, the cornea of the eye, and the heart. The D-band of collagen fibrils is an axial periodic density modulation that can be easily characterized by tissue-level X-ray scattering. During mechanical testing, D-band strain is often used as a proxy for fibril strain. However, this approach ignores the coupling between strain and molecular tilt. We examine the validity of this approximation using an elastomeric collagen fibril model that includes both the D-band and a molecular tilt field. In the low strain regime, we show that the D-band strain substantially underestimates fibril strain for strongly twisted collagen fibrils - such as fibrils from skin or corneal tissue.

Improvement of mechanical properties of elastic materials by chemical methods

Elastomers such as gels and rubbers play various roles in our lives. Elastomers, which guarantee the safety of airplanes and automobiles and the stability of buildings, are materials that have made the lives of people in the twentieth century extremely convenient. The existence of macromolecules, that is, giant molecules, has been clarified; the development of synthetic macromolecules has progressed; and understanding of elastomers has progressed. By introducing new ideas, it has become possible to obtain tough and hard elastomers, which was difficult under conventional ideas. In this paper, we will explain the development from the classical theory of elastomers to current efforts.

Folding photopolymerized origami sheets by post-curing

The paper presents a novel manufacturing approach to fabricate origami based on 3D printing utilizing digital light processing. Specifically, we propose to leave part of the model uncured during the printing step, and then cure it in the post-processing step to set the shape in a folded configuration. While the cured regions in the first step try to regain their unfolded shape, the regions cured in the second step attempt to keep their folded shape. As a result, the final shape is obtained when both regions’ stresses reach equilibrium. Finite element analysis is performed in ANSYS to obtain the stress distribution on common hinge designs, demonstrating that the square-hinge has a lower maximum principal stress than elliptical and triangle hinges. Based on the square-hinge and rectangular cavity, two variables—the hinge width and the cavity height—are selected as principal variables to construct an empirical model with the final folding angle. In the end, experimental verification shows that the developed method is valid and reliable to realize the proposed deformation and 3D development of 2D hinges.

Visible implant elastomer (VIE) success in early larval stages of a tropical amphibian species

Animals are often difficult to distinguish at an individual level, and being able to identify individuals can be crucial in ecological or behavioral studies. In response to this challenge, biologists have developed a range of marking (tattoos, brands, toe-clips) and tagging (banding, collars, PIT, VIA, VIE) methods to identify individuals and cohorts. Animals with complex life cycles are notoriously hard to mark because of the distortion or loss of the tag across metamorphosis. In amphibians, few studies have attempted larval tagging and none have been conducted on a tropical species. Here, we present the first successful account of VIE tagging in early larval stages (Gosner stage 25) of the dyeing poison frog (Dendrobates tinctorius) coupled with a novel anesthetic (2-PHE) application for tadpoles that does not require buffering. Mean weight of individuals at time of tagging was 0.12 g, which is the smallest and developmentally youngest anuran larvae tagged to date. We report 81% tag detection over the first month of development, as well as the persistence of tags across metamorphosis in this species. Cumulative tag retention vs tag observation differed by approximately 15% across larval development demonstrating that "lost" tags can be found later in development. Tagging had no effect on tadpole growth rate or survival. Successful application of VIE tags on D. tinctorius tadpoles introduces a new method that can be applied to better understand early life development and dispersal in various tropical species.

Prevention of excessive scar formation using nanofibrous meshes made of biodegradable elastomer poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

To reduce excessive scarring in wound healing, electrospun nanofibrous meshes, composed of haloarchaea-produced biodegradable elastomer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), are fabricated for use as a wound dressing. Three PHBV polymers with different 3HV content are used to prepare either solution-cast films or electrospun nanofibrous meshes. As 3HV content increases, the crystallinity decreases and the scaffolds become more elastic. The nanofibrous meshes exhibit greater elasticity and elongation at break than films. When used to culture human dermal fibroblasts in vitro, PHBV meshes give better cell attachment and proliferation, less differentiation to myofibroblasts, and less substrate contraction. In a full-thickness mouse wound model, treatment with films or meshes enables regeneration of pale thin tissues without scabs, dehydration, or tubercular scar formation. The epidermis of wounds treated with meshes develop small invaginations in the dermis within 2 weeks, indicating hair follicle and sweat gland regeneration. Consistent with the in vitro results, meshes reduce myofibroblast differentiation in vivo through downregulation of α-SMA and TGF-β1, and upregulation of TGF-β3. The regenerated wounds treated with meshes are softer and more elastic than those treated with films. These results demonstrate that electrospun nanofibrous PHBV meshes mitigate excessive scar formation by regulating myofibroblast formation, showing their promise for use as wound dressings.

3D printing and characterization of a soft and biostable elastomer with high flexibility and strength for biomedical applications

Recent advancements in 3D printing have revolutionized biomedical engineering by enabling the manufacture of complex and functional devices in a low-cost, customizable, and small-batch fabrication manner. Soft elastomers are particularly important for biomedical applications because they can provide similar mechanical properties as tissues with improved biocompatibility. However, there are very few biocompatible elastomers with 3D printability, and little is known about the material properties of biocompatible 3D printable elastomers. Here, we report a new framework to 3D print a soft, biocompatible, and biostable polycarbonate-based urethane silicone (PCU-Sil) with minimal defects. We systematically characterize the rheological and thermal properties of the material to guide the 3D printing process and have determined a range of processing conditions. Optimal printing parameters such as printing speed, temperature, and layer height are determined via parametric studies aimed at minimizing porosity while maximizing the geometric accuracy of the 3D-printed samples as evaluated via micro-CT. We also characterize the mechanical properties of the 3D-printed structures under quasistatic and cyclic loading, degradation behavior and biocompatibility. The 3D-printed materials show a Young's modulus of 6.9 ± 0.85 MPa and a failure strain of 457 ± 37.7% while exhibiting good cell viability. Finally, compliant and free-standing structures including a patient-specific heart model and a bifurcating arterial structure are printed to demonstrate the versatility of the 3D-printed material. We anticipate that the 3D printing framework presented in this work will open up new possibilities not only for PCU-Sil, but also for other soft, biocompatible and thermoplastic polymers in various biomedical applications requiring high flexibility and strength combined with biocompatibility, such as vascular implants, heart valves, and catheters.

Ecotoxicology of micronized tire rubber: Past, present and future considerations

Micronized tire rubber has recently come into focus as black particles that are found in microplastic (MP) samples worldwide. These particles have been found in all environmental compartments with the most likely source being the abrasion of car tires on road surfaces. Thus, it is well founded that tires are a source of MPs and that tire abrasion is a primary source of anthropogenic particulates. Currently, the impact of tires has been viewed through the lens of particulate pollution together with MPs, but this is a relatively new direction for this topic. Previously ecotoxicological research into the environmental consequences of tires has primarily been related to the leached chemicals from tire particulates. This paper aims to (i) highlight similarities and differences of micronized rubber particles with the existing suite of polymer contaminants termed as 'microplastics' or 'plastic debris', (ii) survey the existing literature on environmental presence, fate, and interaction of micronized rubber particles with biota, and lastly (iii) present future research needs that require consideration in order to move this research area forward. Existing knowledge gaps that require attention include; determining the environmental presence and fate of micronized rubber within different environmental compartments, understanding the interaction of rubber particles with biota, particularly as potential impacts have so far been attributed solely to the leachate, and evaluating whether standard ecotoxicological protocols need to be adapted for particulate contaminants in general and specifically to suit rubber particulates and leachate.

Highly stretchable, transparent and room-temperature self-healable polydimethylsiloxane elastomer for bending sensor

Highly stretchable and self-healable elastomers are attractive for a variety of applications in the fields of electrical skin and wearable devices. Herein, we proposed a simple one-pot two-step approach to synthesize room-temperature self-healable polydimethylsiloxane (PDMS) elastomers. Excess aminopropyl terminated polydimethylsiloxane was firstly reacted with isophorone diisocyanate to synthesize amino-terminated PDMS with incorporated ureido groups, followed by further reaction with terephthalaldehyde as chain extender to yield self-healing PDMS elastomers. The obtained elastomer exhibited high stretchability of 1670% and transmittance of 92%. Owing to the dynamic intermolecular hydrogen bonds, reversible imine bonds and highly flexible SiO chains, the elastomer showed excellent self-healing capability with a healing efficiency of 95% after healing at room temperature for 24 h. Even in water and artificial sweat, the healing efficiencies also reached 89% and 78%, respectively. In addition, the elastomer supported triple-layer bending sensor was fabricated with a sandwiched hydroxylated multiwalled carbon nanotubes (MWCNTs-OH) film and successfully applied for detecting human motions. Interestingly, the cut sensor was able to be recovered for working after being irradiated under sunlight for only 10 min. Our method to synthesize highly stretchable, transparent and self-healing elastomers is simple and the reaction can be carried out at room temperature, which is beneficial for the large-scale production and the further practical application in functional electronics.

Fundamental Limits to the Electrochemical Impedance Stability of Dielectric Elastomers in Bioelectronics

Incorporation of elastomers into bioelectronics that reduces the mechanical mismatch between electronics and biological systems could potentially improve the long-term electronics-tissue interface. However, the chronic stability of elastomers in physiological conditions has not been systematically studied. Here, using electrochemical impedance spectrum we find that the electrochemical impedance of dielectric elastomers degrades over time in physiological environments. Both experimental and computational results reveal that this phenomenon is due to the diffusion of ions from the physiological solution into elastomers over time. Their conductivity increases by 6 orders of magnitude up to 10^-8 S/m. When the passivated conductors are also composed of intrinsically stretchable materials, higher leakage currents can be detected. Scaling analyses suggest fundamental limitations to the electrical performances of interconnects made of stretchable materials.

Biomimetic surgical mesh to replace fascia with tunable force-displacement

Here we mimic the mechanical properties of native fascia to design surgical mesh for fascia replacement. Despite the widespread acceptance of synthetic materials as tissue scaffolds for pelvic floor disorders, mechanical property mismatch between mesh and adjacent native tissue drives fibrosis and erosion, leading the FDA to remove several surgical meshes from the market. However, autologous tissue does not induce either fibrosis or adjacent tissue erosion, suggesting the potential for biomimetic surgical mesh. In this study, we determined the design rules for mesh that mimics native fascia by mathematically modeling multi-component polymer networks, composed of elastin-like and collagen-like fibers, using a spring-network model. To validate the model, we measured the stress-strain curves of native bovine and nonhuman primate (Macaca mulatta) abdominal fascia in both toe and linear regions. We find that the stiffer collagen-like fibers must remain limp until the elastin-like fibers extend to the initial length of spanning collagen-like fibers under uniaxial tension. Comparing model results to experiment determines the product of fiber volume fraction and elastic modulus, a critical design parameter. Dual fiber mesh with mechanical properties that mimic fascia are feasible. These results have broad application to a wide range of soft tissue replacements including ~200,000 surgeries/year for pelvic floor disorders, because standard-of-care mesh contain only stiffer polymers that behave more like collagen than native tissue.

Large area flexible pressure/strain sensors and arrays using nanomaterials and printing techniques

Sensors are becoming more demanding in all spheres of human activities for their advancement in terms of fabrication and cost. Several methods of fabrication and configurations exist which provide them myriad of applications. However, the advantage of fabrication for sensors lies with bulk fabrication and processing techniques. Exhaustive study for process advancement towards miniaturization from the advent of MEMS technology has been going on and progressing at high pace and has reached a highly advanced level wherein batch production and low cost alternatives provide a competitive performance. A look back to this advancement and thus understanding the route further is essential which is the core of this review in light of nanomaterials and printed technology based sensors. A subjective appraisal of these developments in sensor architecture from the advent of MEMS technology converging present date novel materials and process technologies through this article help us understand the path further.

In vitro study of effects of aging and processing conditions on colour change in maxillofacial silicone elastomers

Background

The inherent colour change in maxillofacial silicone elastomers becomes perceptible 6–12 months after fabrication. Determining the factors that accelerate the degradation of the prosthesis can help the clinicians increase its life span. Therefore, the aim of the study was to investigate the effect of time passage, processing temperature, and molding-stone colour on the colour change of maxillofacial silicone elastomers after darkroom storage for 6000 h.

Methods

A total of ten study molds, each incorporating ten specimen gaps were fabricated using five different colors of dental stones. The gaps were filled with coloured Cosmesil M511 maxillofacial silicone elastomer. Five of the study molds, one of each stone color, were processed at room temperature (25 °C) for 24 h while the remainder were vulcanized at 100 °C for 1 h. Two stainless-steel molds were also fabricated to obtain a total of twenty control-group specimens of the same dimensions that were processed under the same conditions as the study molds. Colour measurements of the vulcanized silicone samples were performed using a Konica Minolta spectrophotometer. Initial measurements were obtained after the blocks were removed from the molds and the final measurements were recorded 6000 h after storage in the dark at 25 °C and 40% relative humidity. The CIEDE2000 colour-difference formula was used to measure the changes in the colour. One-way and two-way ANOVA, and an independent-sample t-test were used for statistical assessments.

Results

For every group, the colour change exceeded the perceptible thresholds. Thus, either the vulcanization temperature or the colour of the molding stone has a significant effect on the colour change over time. Those samples vulcanized in green and white molding stones at 100 °C exhibited a significantly higher ∆L*, ∆a*, and ∆b* values relative to the samples vulcanized at room temperature.

Conclusion

The molding-stone colour and vulcanization temperature both affect the degree of colour change after storage in a dark environment. The L*, a*, and b* values for the maxillofacial silicone elastomers are influenced by the direction of the increase or decrease according to the selected colour. This effect varies as the temperature increases.

The Formation of a Modified Surface Layer on Elastomeric Materials

Surface modification of an elastomer may be formed during sliding contact with a rigid counter surface. This alteration leads to a change of mechanical properties at the surface and as a result a change in frictional behavior. Therefore, investigations related to the formation of a modified surface layer on elastomers and its effect on friction are of importance. In the present study, the formation of a modified surface layer on elastomer reinforced by silica is studied. Sliding friction is performed using a pin-on-disc tribometer. Several parameters are varied, namely contact pressure, velocity, and roughness of the counter surface. The existence of a modified surface layer is investigated by using a scanning electron microscope. The results show that the existence of a modified surface layer depends on the competition between the formation rate of the layer and the wear rate. The formation of the layer depends on the contact pressure, velocity, and sliding distance. A general formulation to calculate the volume of formation is proposed. Furthermore, a map of the formation of a modified surface layer is developed.

Assessment of Extractable Elements from Elastomers

Compendia methods have historically been used to assess heavy metals in both drug products and packaging material extracts. However, these methods have been found to be inadequate for elemental specificity and accurate measurements. The International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) has published the Q3D, Guideline for Elemental Impurities, to provide a risk-based approach that specifies elements to be considered in a drug product risk assessment and permitted daily exposures (PDEs) depending on toxicological concern and route of administration. Consistent with these efforts, the United States Pharmacopeia (USP) withdrew the <231> Heavy Metals test procedure as of January 2018. The USP published new methods consistent with ICH Q3D risk-based approaches, <232> Elemental Impurities - Limits and <233> Elemental Impurities - Procedures. These new tests are intended for evaluation of drug products, leaving a gap in the assessment of extractable elements for packaging components. This gap prompted the need for a better understanding of the potential for elements of concern to extract from packaging materials and contribute to drug product elemental impurities. The present study investigated multiple extraction conditions coupled with modern analytical techniques to understand the capacity for elements to extract from elastomeric components. Most elements of interest, based on ICH or their potential for occurrence in elastomers, were ultimately recovered at levels below designated thresholds, allowing for correlation to PDE. These results highlight that although extractable elements from elastomeric components have the potential to contribute elemental impurities to a drug product, the actual contribution to cumulative levels would need to be calculated among all other potential sources as part of the process of elemental impurities assessment.LAY ABSTRACT: Compendia methods have historically been used to assess heavy metals in final drug products and extracts from packaging materials. However, these methods were found to provide inadequate data to address the evolving risk concerns of elemental impurities in drug products and their potential toxic effects. The International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use member countries are working toward implementing a risk-based approach that specifies elements to be considered in a drug product safety assessment and permitted daily exposures. The United States Pharmacopeia is coordinating with this goal by withdrawing the traditional procedure and replacing it with the tests that can inform safety risk assessments. However, the new tests are intended for evaluation of only final drug products, leaving a gap in the assessment of extractable elements for packaging components. The present study addressed this gap by focusing on elastomeric components used in injectable packaging systems and exploring appropriate elastomeric extraction methods coupled with modern analytical techniques to better understand the full potential for elements to extract from elastomers and contribute to the elemental impurity profile of a drug product.

Citrate chemistry and biology for biomaterials design

Leveraging the multifunctional nature of citrate in chemistry and inspired by its important role in biological tissues, a class of highly versatile and functional citrate-based materials (CBBs) has been developed via facile and cost-effective polycondensation. CBBs exhibiting tunable mechanical properties and degradation rates, together with excellent biocompatibility and processability, have been successfully applied in vitro and in vivo for applications ranging from soft to hard tissue regeneration, as well as for nanomedicine designs. We summarize in the review, chemistry considerations for CBBs design to tune polymer properties and to introduce functionality with a focus on the most recent advances, biological functions of citrate in native tissues with the new notion of degradation products as cell modulator highlighted, and the applications of CBBs in wound healing, nanomedicine, orthopedic, cardiovascular, nerve and bladder tissue engineering. Given the expansive evidence for citrate's potential in biology and biomaterial science outlined in this review, it is expected that citrate based materials will continue to play an important role in regenerative engineering.

Mechanically dynamic PDMS substrates to investigate changing cell environments

Mechanics of the extracellular matrix (ECM) play a pivotal role in governing cell behavior, such as cell spreading and differentiation. ECM mechanics have been recapitulated primarily in elastic hydrogels, including with dynamic properties to mimic complex behaviors (e.g., fibrosis); however, these dynamic hydrogels fail to introduce the viscoelastic nature of many tissues. Here, we developed a two-step crosslinking strategy to first form (via platinum-catalyzed crosslinking) networks of polydimethylsiloxane (PDMS) and then to increase PDMS crosslinking (via thiol-ene click reaction) in a temporally-controlled manner. This photoinitiated reaction increased the compressive modulus of PDMS up to 10-fold within minutes and was conducted under cytocompatible conditions. With stiffening, cells displayed increased spreading, changing from ∼1300 to 1900 μm² and from ∼2700 to 4600 μm² for fibroblasts and mesenchymal stem cells, respectively. In addition, higher myofibroblast activation (from ∼2 to 20%) for cardiac fibroblasts was observed with increasing PDMS substrate stiffness. These results indicate a cellular response to changes in PDMS substrate mechanics, along with a demonstration of a mechanically dynamic and photoresponsive PDMS substrate platform to model the dynamic behavior of ECM.

Transient phase behavior of an elastomeric biomaterial applied to abdominal laparotomy closure

Secure closure of the fascial layers after entry into the peritoneal cavity is crucial to prevent incisional hernia, yet appropriate purchase of the tissue can be challenging due to the proximity of the underlying protuberant bowel which may become punctured by the surgical needle or strangulated by the suture itself. Devices currently employed to provide visceral protection during abdominal closure, such as the metal malleable retractor and Glassman Visceral Retainer, are unable to provide complete protection as they must be removed prior to complete closure. A puncture resistant, biocompatible, and degradable matrix that can be left in place without need for removal would facilitate rapid and safe abdominal closure. We describe a novel elastomer (CC-DHA) that undergoes a rapid but controlled solid-to-liquid phase transition through the application of a destabilized carbonate cross-linked network. The elastomer is comprised of a polycarbonate cross-linked network of dihydroxyacetone, glycerol ethoxylate, and tri(ethylene glycol). The ketone functionality of the dihydroxyacetone facilitates hydrolytic cleavage of the carbonate linkages resulting in a rapidly degrading barrier that can be left in situ to facilitate abdominal fascial closure. Using a murine laparotomy model we demonstrated rapid dissolution and metabolism of the elastomer without evidence of toxicity or intraabdominal scarring. Furthermore, needle puncture and mechanical properties demonstrated the material to be both compliant and sufficiently puncture resistant. These unique characteristics make the biomaterial extraordinarily useful as a physical barrier to prevent inadvertent bowel injury during fascial closure, with the potential for wider application across a variety of medical and surgical applications.

STATEMENT OF SIGNIFICANCE

Fascial closure after abdominal surgery requires delicate maneuvers to prevent incisional hernia while minimizing risk for inadvertent bowel injury. We describe a novel biocompatible and biodegradable polycarbonate elastomer (CC-DHA) comprised of dihydroxyacetone, glycerol ethoxylate, and tri(ethylene glycol), for use as a rapidly degrading protective visceral barrier to aid in abdominal closure. Rapid polymer dissolution and metabolism was demonstrated using a murine laparotomy model without evidence of toxicity or intraabdominal scarring. Furthermore, mechanical studies showed the material to be sufficiently puncture resistant and compliant. Overall, this new biomaterial is extraordinary useful as a physical barrier to prevent inadvertent bowel injury during fascial closure, with the potential for wider application across a variety of medical and surgical applications.

Rubber elastomeric nanocomposites with antimicrobial properties

In this paper we show an elastomeric nanocomposite that exhibits antibacterial and antifungal activity. It comprises a rubber blend matrix and a nanofiller, which is a modified bentonite clay (Nanobent® ZR2). We have developed innovative technology for the nanofiller incorporation into the rubber matrix. This new approach was successfully implemented in pilot production at the Polish chemical manufacturer Spoiwo (Spoldzielnia Pracy Chemiczno-Wytworczej 'Spoiwo', Radom, Poland). Here we reveal that addition of the functionalised bentonite affects the mechanical and thermal behaviour of elastomers. For example, by adding 1-3% of bentonite nanoparticles we strongly enhanced elongation and tensile stress at break, whereas stiffness remained unchanged. We observed improvement of the thermal properties of the nanocomposites yielded and extension of the temperature usage range (from -29 to 311°C). As a proof of concept we present the antimicrobial effect of elastomeric nanocomposites verified on a wide range of both pathogenic and opportunistic reference bacteria strains, as well as reference strains of yeasts. The proposed method of hydrophilic nanofiller introduction into the rubber elastomer is economically viable and enables fabrication of elastomeric elements with high added value. Their significant antibacterial and antifungal activity makes them desirable in medicine, biomedical engineering, and the food industry.

Moldable elastomeric polyester-carbon nanotube scaffolds for cardiac tissue engineering

Polymer biomaterials are used to construct scaffolds in tissue engineering applications to assist in mechanical support, organization, and maturation of tissues. Given the flexibility, electrical conductance, and contractility of native cardiac tissues, it is desirable that polymeric scaffolds for cardiac tissue regeneration exhibit elasticity and high electrical conductivity. Herein, we developed a facile approach to introduce carbon nanotubes (CNTs) into poly(octamethylene maleate (anhydride) 1,2,4-butanetricarboxylate) (124 polymer), and developed an elastomeric scaffold for cardiac tissue engineering that provides electrical conductivity and structural integrity to 124 polymer. 124 polymer-CNT materials were developed by first dispersing CNTs in poly(ethylene glycol) dimethyl ether porogen and mixing with 124 prepolymer for molding into shapes and crosslinking under ultraviolet light. 124 polymers with 0.5% and 0.1% CNT content (wt) exhibited improved conductivity against pristine 124 polymer. With increasing the CNT content, surface moduli of hybrid polymers were increased, while their bulk moduli were decreased. Furthermore, increased swelling of hybrid 124 polymer-CNT materials was observed, suggesting their improved structural support in an aqueous environment. Finally, functional characterization of engineered cardiac tissues using the 124 polymer-CNT scaffolds demonstrated improved excitation threshold in materials with 0.5% CNT content (3.6±0.8V/cm) compared to materials with 0% (5.1±0.8V/cm) and 0.1% (5.0±0.7V/cm), suggesting greater tissue maturity. 124 polymer-CNT materials build on the advantages of 124 polymer elastomer to give a versatile biomaterial for cardiac tissue engineering applications.

STATEMENT OF SIGNIFICANCE

Achieving a high elasticity and a high conductivity in a single cardiac tissue engineering material remains a challenge. We report the use of CNTs in making electrically conductive and mechanically strong polymeric scaffolds in cardiac tissue regeneration. CNTs were incorporated in elastomeric polymers in a facile and reproducible approach. Polymer-CNT materials were able to construct complicated scaffold structures by injecting the prepolymer into a mold and crosslinking the prepolymer under ultraviolet light. CNTs enhanced electrical conductivity and structural support of elastomeric polymers. Hybrid polymeric scaffolds containing 0.5wt% CNTs increased the maturation of cardiac tissues fabricated on them compared to pure polymeric scaffolds. The cardiac tissues on hybrid polymer-CNT scaffolds showed earlier beating than those on pure polymer scaffolds. In the future, fabricated polymer-CNT scaffolds could also be used to fabricate other electro-active tissues, such neural and skeletal muscle tissues. In the future, fabricated polymer-CNT scaffolds could also be used to fabricate other electro-active tissues, such as neural and skeletal muscle tissues.

Outpatient multimodal intravenous analgesia in patients undergoing day-case surgery: description of a three year experience

Background

The use of elastomeric devices for ambulatory intravenous pain treatment in Major Ambulatory Surgery (MAS) has been described to improve postoperative pain management. The objective of the study was to describe the first 3 years experience of the use of elastomeric devices for ambulatory intravenous pain treatment in MAS implemented at our site since 2010.

Methods

Data were retrieved from the medical records for all patients who, between January 2010 and March 2014, underwent surgical procedures at the ambulatory surgical centre at our hospital and were prescribed a home-based continuous intravenous analgesia.

Results

Data were retrieved from the medical records of 1128 patients. The most frequent surgical interventions included orthopedic and proctology surgeries. 80 % of patients were discharged home without pain; during the first 48 h after discharge roughly 40 % of subjects were completely free of pain, 50 % reported mild pain (VAS 1 to 3) and 9 % reported higher pain scores (4 and above). Peripheral nerve block was associated to better pain control in the immediate postoperative period. Vomiting in the first 24 h was 4.6 % before introducing haloperidol into the drug schemes, and 2.6 % thereafter. Complications related with the intravenous route required treatment withdrawal in 1.1 % cases. Only 3.5 % of patients returned to the hospital in the first 72 h, mainly for non-pain related reasons. Overall, 99.5 % of patients were satisfied with the treatment received at home.

Conclusion

Our initial experience suggest that outpatient multimodal intravenous analgesia in patients undergoing day-case surgery is a feasible alternative in our setting, that allows an effective management of postoperative pain with a small rate of adverse events and complications requiring readmission.

Starch composites with aconitic acid

The aim of this project is to examine the effectiveness of using aconitic acid (AcA), a tricarboxylic acid which contains a carbon/carbon double bond (CC), to enhance the properties of starch-based films. Starch/glycerol cast films were prepared with 0, 2, 5, 10 and 15wt% AcA (starch wt% basis) and the properties analysed. It was shown that AcA acted as both a cross-linking agent and also a strong plasticising agent. The 5wt% AcA derived starch films were the most effectively cross-linked having the lowest solubility (28wt%) and decreased swelling coefficient (35vol.%) by approximately 3 times and 2.4 times respectively compared to the control film submerged in water (23°C). There was also a significant increase in the film elongation at break by approximately 35 times (compared to the control) with the addition of 15wt% AcA, emphasising the plasticising effect of AcA. However, generally there was a reduced tensile strength, softening of the film, and reduced thermal stability with increased amounts of AcA.

Polymer chain flexibility-induced differences in fetuin A adsorption and its implications on cell attachment and proliferation

Tissue cells are known to respond to the stiffness of the polymer substrate on which they are grown. It has been suggested that material stiffness influences the composition of the protein layer that adsorbs to the material surface, which affects subsequent cell behavior. Previously, the stiffness of a biomaterial elastomer formed from an acrylated star-poly(d,l lactide-co-ε-caprolactone) was found to influence both fibroblast proliferation as well as the adsorption of certain proteins. However, it remained unresolved as to whether material stiffness influenced protein adsorption from serum supplemented environments and which protein(s) may have been responsible for the difference in fibroblast proliferation. Using quantitative proteomics, we show that polymer stiffness influenced the composition of the protein layers that adsorb from serum supplemented media. Fetuin A was identified as a protein that influenced fibroblast proliferation and, when combined with basic fibroblast growth factor as a medium supplement, improved fibroblast proliferation over 14days. This study is the first to correlate cell proliferation to surface adsorbed fetuin A and presents the potential new application for fetuin A as biomaterial coating or surface modifier. This work also demonstrates a novel application of quantitative proteomics for the investigation of competitive protein adsorption to biomaterial surfaces.

STATEMENT OF SIGNIFICANCE

Cells are able to respond to the stiffness of their material substrate, but the method by which they sense material stiffness is still under investigation. Previously, material stiffness was found to impact the individual adsorption of fibronectin, a protein associated with cell attachment; however, it was unclear if stiffness was able to affect protein adsorption in environments with multiple proteins. This study shows that material stiffness affects the compositions of protein layers adsorbed from supplemented media, and suggests that cells may sense material stiffness via the adsorbed protein layer. Interestingly, fetuin A was found to be affecting cell proliferation and not fibronectin. Finally, this research demonstrates the use of relative quantitation proteomics as a potentially powerful method to improve biomaterial compatibility.

Long-Term Functional Efficacy of a Novel Electrospun Poly(Glycerol Sebacate)-Based Arterial Graft in Mice

Many surgical interventions for cardiovascular disease are limited by the availability of autologous vessels or suboptimal performance of prosthetic materials. Tissue engineered vascular grafts show significant promise, but have yet to achieve clinical efficacy in small caliber (<5 mm) arterial applications. We previously designed cell-free elastomeric grafts containing solvent casted, particulate leached poly(glycerol sebacate) (PGS) that degraded rapidly and promoted neoartery development in a rat model over 3 months. Building on this success but motivated by the need to improve fabrication scale-up potential, we developed a novel method for electrospinning smaller grafts composed of a PGS microfibrous core enveloped by a thin poly(ε-caprolactone) (PCL) outer sheath. Electrospun PGS-PCL composites were implanted as infrarenal aortic interposition grafts in mice and remained patent up to the 12 month endpoint without thrombosis or stenosis. Many grafts experienced a progressive luminal enlargement up to 6 months, however, due largely to degradation of PGS without interstitial replacement by neotissue. Lack of rupture over 12 months confirmed sufficient long-term strength, due primarily to the persistent PCL sheath. Immunohistochemistry further revealed organized contractile smooth muscle cells and neotissue in the inner region of the graft, but a macrophage-driven inflammatory response to the residual polymer in the outer region of the graft that persisted up to 12 months. Overall, the improved surgical handling, long-term functional efficacy, and strength of this new graft strategy are promising, and straightforward modifications of the PGS core should hasten cellular infiltration and associated neotissue development and thereby lead to improved small vessel replacements.

Elastomeric and mechanically stiff nanocomposites from poly(glycerol sebacate) and bioactive nanosilicates

Poly(glycerol sebacate) (PGS) has been proposed for tissue engineering applications owing to its tough elastomeric mechanical properties, biocompatibility and controllable degradation. However, PGS shows limited bioactivity and thus constraining its utilization for musculoskeletal tissue engineering. To address this issue, we developed bioactive, highly elastomeric, and mechanically stiff nanocomposites by covalently reinforcing PGS network with two-dimensional (2D) nanosilicates. Nanosilicates are ultrathin nanomaterials and can induce osteogenic differentiation of human stem cells in the absence of any osteogenic factors such as dexamethasone or bone morphogenetic proteins-2 (BMP2). The addition of nanosilicate to PGS matrix significantly enhances the mechanical stiffness without affecting the elastomeric properties. Moreover, nanocomposites with higher amount of nanosilicates have higher in vitro stability as determined by degradation kinetics. The increase in mechanical stiffness and in vitro stability is mainly attributed to enhanced interactions between nanosilicates and PGS. We evaluated the in vitro bioactivity of nanocomposite using preosteoblast cells. The addition of nanosilicates significantly enhances the cell adhesion, support cell proliferation, upregulate alkaline phosphates and mineralized matrix production. Overall, the combination of high mechanically stiffness and elastomericity, tailorable degradation profile, and the ability to promote osteogenic differentiation of PGS-nanosilicate can be used for regeneration of bone.

Biomimetic poly(glycerol sebacate)/poly(l-lactic acid) blend scaffolds for adipose tissue engineering

Large three-dimensional poly(glycerol sebacate) (PGS)/poly(l-lactic acid) (PLLA) scaffolds with similar bulk mechanical properties to native low and high stress adapted adipose tissue were fabricated via a freeze-drying and a subsequent curing process. PGS/PLLA scaffolds containing 73vol.% PGS were prepared using two different organic solvents, resulting in highly interconnected open-pore structures with porosities and pore sizes in the range of 91-92% and 109-141μm, respectively. Scanning electron microscopic analysis indicated that the scaffolds featured different microstructure characteristics, depending on the organic solvent in use. The PGS/PLLA scaffolds had a tensile Young's modulus of 0.030MPa, tensile strength of 0.007MPa, elongation at the maximum stress of 25% and full shape recovery capability upon release of the compressive load. In vitro degradation tests presented mass losses of 11-16% and 54-55% without and with the presence of lipase enzyme in 31days, respectively. In vitro cell tests exhibited clear evidence that the PGS/PLLA scaffolds prepared with 1,4-dioxane as the solvent are suitable for culture of adipose derived stem cells. Compared to pristine PLLA scaffolds prepared with the same procedure, these scaffolds provided favourable porous microstructures, good hydrophilic characteristics, and appropriate mechanical properties for soft tissue applications, as well as enhanced scaffold cell penetration and tissue in-growth characteristics. This work demonstrates that the PGS/PLLA scaffolds have potential for applications in adipose tissue engineering.

Highly elastic and suturable electrospun poly(glycerol sebacate) fibrous scaffolds

Poly(glycerol sebacate) (PGS) is a thermally-crosslinked elastomer suitable for tissue regeneration due to its elasticity, degradability, and pro-regenerative inflammatory response. Pores in PGS scaffolds are typically introduced by porogen leaching, which compromises strength. Methods for producing fibrous PGS scaffolds are very limited. Electrospinning is the most widely used method for laboratory scale production of fibrous scaffolds. Electrospinning PGS by itself is challenging, necessitating a carrier polymer which can affect material properties if not removed. We report a simple electrospinning method to produce distinct PGS fibers while maintaining the desired mechanical and cytocompatibility properties of thermally crosslinked PGS. Fibrous PGS demonstrated 5 times higher tensile strength and increased suture retention compared to porous PGS foams. Additionally, similar modulus and elastic recovery were observed. A final advantage of fibrous PGS sheets is the ability to create multi-laminate constructs due to fiber bonding that occurs during thermal crosslinking. Taken together, these highly elastic fibrous PGS scaffolds will enable new approaches in tissue engineering and regenerative medicine.

Growth factor and small molecule influence on urological tissue regeneration utilizing cell seeded scaffolds

Regenerative medicine strategies combine various attributes from multiple disciplines including stem cell biology, chemistry, materials science and medicine. The junction at which these disciplines intersect provides a means to address unmet medical needs in an assortment of pathologies with the goal of creating sustainable, functional replacement tissues. Tissue damage caused by trauma for example, requires rapid responses in order to mitigate further tissue deterioration. Cell/scaffold composites have been utilized to initiate and stabilize regenerative responses in vivo with the hope that functional tissue can be attained. Along with the gross reconfiguration of regenerating tissues, small molecules and growth factors also play a pivotal role in tissue regeneration. Several regenerative studies targeting a variety of urological tissues demonstrate the utility of these small molecules or growth factors in an in vivo setting.

Feasibility of osteosynthesis of fractured cadaveric hips following preventive elastomer femoroplasty

BACKGROUND

In vitro cadaveric studies showed that elastomer femoroplasty prevents displacement of fracture parts after proximal hip fracture allowing for conservative treatment. In the event that secondary displacement does occur, the purpose of this present study was to determine the feasibility of performing osteosynthesis of a fractured hip after preventive treatment with elastomer femoroplasty.

METHODS

Ten pairs of human cadaveric femurs were fractured in a simulated fall configuration. From each pair, one femur was randomly selected for elastomer femoroplasty prior to fracture generation and the contralateral femur was used as control. Following hip fracture generation, osteosynthesis was performed in all femurs. The operative time per case, technical difficulties during the procedure, and postoperative energy-to-failure load were recorded.

RESULTS

The mean (SD) time to perform osteosynthesis was 20 (6) minutes in the control-group and 19 (5) minutes in the elastomer femoroplasty-group (P=0.69). During osteosynthesis of the fractured hip in the elastomer femoroplasty-group, no difficulties including the need for additional instruments to remove elastomer from the proximal femur were recorded. Postoperative energy-to-failure load was similar in the control-group and the elastomer femoroplasty-group.

CONCLUSION

Fixation with routine osteosynthesis of displaced cadaveric hip fractures is not hindered by the presence of previously injected elastomer.

Engineering biodegradable polyester elastomers with antioxidant properties to attenuate oxidative stress in tissues

Oxidative stress plays an important role in the limited biological compatibility of many biomaterials due to inflammation, as well as in various pathologies including atherosclerosis and restenosis as a result of vascular interventions. Engineering antioxidant properties into a material is therefore a potential avenue to improve the biocompatibility of materials, as well as to locally attenuate oxidative stress-related pathologies. Moreover, biodegradable polymers that have antioxidant properties built into their backbone structure have high relative antioxidant content and may provide prolonged, continuous attenuation of oxidative stress while the polymer or its degradation products are present. In this report, we describe the synthesis of poly(1,8-octanediol-co-citrate-co-ascorbate) (POCA), a citric-acid based biodegradable elastomer with native, intrinsic antioxidant properties. The in vitro antioxidant activity of POCA as well as its effects on vascular cells in vitro and in vivo were studied. Antioxidant properties investigated included scavenging of free radicals, iron chelation and the inhibition of lipid peroxidation. POCA reduced reactive oxygen species generation in cells after an oxidative challenge and protected cells from oxidative stress-induced cell death. Importantly, POCA antioxidant properties remained present upon degradation. Vascular cells cultured on POCA showed high viability, and POCA selectively inhibited smooth muscle cell proliferation, while supporting endothelial cell proliferation. Finally, preliminary data on POCA-coated ePTFE grafts showed reduced intimal hyperplasia when compared to standard ePTFE grafts. This biodegradable, intrinsically antioxidant polymer may be useful for tissue engineering application where oxidative stress is a concern.

Nerve regeneration and elastin formation within poly(glycerol sebacate)-based synthetic arterial grafts one-year post-implantation in a rat model

The objective of this study was to evaluate the long-term performance of cell-free vascular grafts made from a fast-degrading elastic polymer. We fabricated small arterial grafts from microporous tubes of poly(glycerol sebacate) (PGS) reinforced with polycaprolactone (PCL) nanofibers on the outer surface. Grafts were interpositioned in rat abdominal aortas and characterized at 1 year post-implant. Grafts remodeled into "neoarteries" (regenerated arteries) with similar gross appearance to native rat aortas. Neoarteries mimic arterial tissue architecture with a confluent endothelium and media and adventita-like layers. Patent vessels (80%) showed no significant stenosis, dilation, or calcification. Neoarteries contain nerves and have the same amount of mature elastin as native arteries. Despite some differences in matrix organization, regenerated arteries had similar dynamic mechanical compliance to native arteries in vivo. Neoarteries responded to vasomotor agents, albeit with different magnitude than native aortas. These data suggest that an elastic vascular graft that resorbs quickly has potential to improve the performance of vascular grafts used in small arteries. This design may also promote constructive remodeling in other soft tissues.

Soft machines that are resistant to puncture and that self seal

A soft machine composed of a composite of elastomer and fibers resists puncture from sharp objects, and continues to operate even if punctured.

Luminescent elastomeric Janus particles

We report on a low-cost and low-tech method for the preparation of luminescent micro- and millimeter elastomeric particles with asymmetric morphology. The method of fabrication consists in UV-irradiating soft urethane/urea fluorescent spheres, which are then extracted in toluene and dried. Wrinkles appear on the irradiated portions of the particles surfaces, and the spatial periodicity can be controlled with variation in UV irradiation time and the amount of the luminescent compound. The spheres are thus composed of an urethane/urea network in which the tris(8-hydroxyquinolinato)aluminum (Alq3) fluorescent compound was incorporated. The asymmetric morphology and the optical properties of the resultant particles have been confirmed by scanning electron microscopy, atomic force microscopy, optical microscopy, and UV-Vis spectrophotometry. The system shows negligible leaching, and the encapsulation of the Alq3 without recourse to covalent bonding to the polymeric matrix has the advantage of allowing the tuning of the spheres morphology and fluorescence.

The effect of polymer degradation time on functional outcomes of temporary elastic patch support in ischemic cardiomyopathy

Biodegradable polyurethane patches have been applied as temporary mechanical supports to positively alter the remodeling and functional loss following myocardial infarction. How long such materials need to remain in place is unclear. Our objective was to compare the efficacy of porous onlay support patches made from one of three types of biodegradable polyurethane with relatively fast (poly(ester urethane)urea; PEUU), moderate (poly(ester carbonate urethane)urea; PECUU), and slow (poly(carbonate urethane)urea; PCUU) degradation rates in a rat model of ischemic cardiomyopathy. Microporous PEUU, PECUU or PCUU (n = 10 each) patches were implanted over left ventricular lesions 2 wk following myocardial infarction in rat hearts. Infarcted rats without patching and age-matched healthy rats (n = 10 each) were controls. Echocardiography was performed every 4 wk up to 16 wk, at which time hemodynamic and histological assessments were performed. The end-diastolic area for the PEUU group at 12 and 16 wk was significantly larger than for the PECUU or PCUU groups. Histological analysis demonstrated greater vascular density in the infarct region for the PECUU or PCUU versus PEUU group at 16 wk. Improved left ventricular contractility and diastolic performance in the PECUU group was observed at 16 wk compared to infarction controls. The results indicate that the degradation rate of an applied elastic patch influences the functional benefits associated patch placement, with a moderately slow degrading PECUU patch providing improved outcomes.

The use of polyurethane as an elastomer in thermoplastic microfluidic devices and the study of its creep properties

We report using polyurethane (PU) as an elastomer in microvalves integrated with thermoplastic microfluidic devices. Elastomer-based microvalves have been used in a number of applications and the elastomer often used is PDMS. Although it is a convenient material for prototyping, PDMS has been recognized to possess shortcomings such as solvent incompatibility and unfavorable manufacturability. We investigated the use of PU as an elastomer to address the challenges. A reliable method was developed to bond hybrid materials such as PU and cyclic olefin copolymer. The film thickness from 3.5 to 24.5 μm was studied to identify an appropriate thickness of PU films for desirable elasticity in microvalves. We integrated PU with thermally actuated, elastomer-based microvalves in thermoplastic devices. Valve actuations were demonstrated, and the relationship between the valve actuation time and heater power was studied. We compared PU with PDMS in terms of their microvalve performance. Valves with PDMS failed to function after two weeks since the thermal-sensitive solution evaporated through porous PDMS membrane, whereas the same valve with PU functioned properly after eight months. In addition, we evaluated the creep and creep recovery of PU, which is a common phenomenon of viscoelastic materials and is related to the long-term elastic property of PU after prolonged use.

Mechanically tissue-like elastomeric polymers and their potential as a vehicle to deliver functional cardiomyocytes

One of the major challenges in the field of biomaterials engineering is the replication of the non-linear elasticity observed in soft tissues. In the present study, non-linearly elastic biomaterials were successfully fabricated from a chemically cross-linked elastomeric poly(glycerol sebacate) (PGS) and thermoplastic poly(L-lactic acid) (PLLA) using the core/shell electrospinning technique. The spun fibrous materials, containing a PGS core and PLLA shell, demonstrated J-shaped stress-strain curves, and having ultimate tensile strength, rupture elongation, and stiffness constants respectively comparable to muscle tissue properties. In vitro evaluations also showed that PGS/PLLA fibrous biomaterials possess excellent biocompatibility, capable of supporting human stem-cell-derived cardiomyocytes over several weeks in culture. Therefore, the core/shell electrospun elastomeric materials provide a new potential scaffold to support cells in the therapy of a wide range of soft tissues exposed to cyclic deformation, such as tendon, ligament, cardiac or smooth muscle and lung epithelium.

Progress and challenges in biomaterials used for bone tissue engineering: bioactive glasses and elastomeric composites

Driven by the increasing economic burden associated with bone injury and disease, biomaterial development for bone repair represents the most active research area in the field of tissue engineering. This article provides an update on recent advances in the development of bioactive biomaterials for bone regeneration. Special attention is paid to the recent developments of sintered Na-containing bioactive glasses, borate-based bioactive glasses, those doped with trace elements (such as Cu, Zn, and Sr), and novel elastomeric composites. Although bioactive glasses are not new to bone tissue engineering, their tunable mechanical properties, biodegradation rates, and ability to support bone and vascular tissue regeneration, as well as osteoblast differentiation from stem and progenitor cells, are superior to other bioceramics. Recent progresses on the development of borate bioactive glasses and trace element-doped bioactive glasses expand the repertoire of bioactive glasses. Although boride and other trace elements have beneficial effects on bone remodeling and/or associated angiogenesis, the risk of toxicity at high levels must be highly regarded in the design of new composition of bioactive biomaterials so that the release of these elements must be satisfactorily lower than their biologically safe levels. Elastomeric composites are superior to the more commonly used thermoplastic-matrix composites, owing to the well-defined elastic properties of elastomers which are ideal for the replacement of collagen, a key elastic protein within the bone tissue. Artificial bone matrix made from elastomeric composites can, therefore, offer both sound mechanical integrity and flexibility in the dynamic environment of injured bone.

Tribological concepts involved in slipping accident analysis

According to tribology science, the friction force produced at the sliding interface between a rubber piece and an inflexible surface presents three main components: the first is due to molecular adhesion between the two bodies, it occurs at the regions of real contact; the second is a hysteresis component resulting from the periodic excitation of the bulk of the rubber by surface roughness; the third is due to effects of product shape. The shape of the elastomer product and the conditions in which the friction occurs (lubricant, roughness of the inflexible surface, etc.) determine the appearance of each one of these components and its importance. Experimentations made by the French national research and safety Institute (INRS) revealed adhesion and hysteresis components in the lubricated friction of an elastomer over a representative sample of industrial floor surfaces. Measurements have been made by means of a portable friction tester (PFT) assessing sliding resistance of floor coverings. The sliding movement takes place between a braked test wheel and the floor covering. The effect of product shape is insignificant as the wheel is covered with smooth elastomer. The friction force produced at the sliding interface between the elastomer and the floor covering has been evaluated on smooth and rough floors, and under different lubrication conditions (flooded with water, large, medium and small quantities of mineral oil). Several test wheels, with different and sometimes used rubber coverings, have been employed. The friction force is altered when the elastomer composition or the state of the elastomer that is covering the test wheel changes. The differences pointed out depend also on floor covering roughness and lubrication. The importance of either the adhesion or hysteresis components of the friction force in accordance with the composition and the state of the elastomer that is covering the test wheel, the lubricant amount, and the floor covering roughness enable the interpretation of these differences. Some experimental results are explained from the squeeze lubricant film process. This experimental study permits a better understanding of phenomena produced at the sliding interface between a rubber sole and a floor covering when a pedestrian slips. It also plays a great part in bringing the portable friction tester into operation in order to carry out a measurement campaign of slipping resistance of industrial floors.