Biocompatible Elastomer Research Articles

In Silico Analysis of Elastomer-Coated Cerclage for Reducing Sternal Cut-Through in High-Risk Patients.

AISI 316 L stainless steel wire cerclage routinely used in sternotomy closure causes lateral cut-through damage and fracture, especially in cases of high-risk patients, which leads to postoperative complications. A biocompatible elastomer (Pellethane®) coating on the standard wire is proposed to mitigate the cut-through effect. Simplified peri-sternal and transsternal, sternum-cerclage contact models are created and statically analyzed in a finite element (FE) software to characterize the stress-reduction effect of the polymer coating for thicknesses between 0.5 and 1.125 mm. The performance of the polymer-coated cerclage in alleviating the detrimental cortical stresses is also compared to the standard steel cerclage in a full sternal closure FE model for the extreme cough loading scenario. It was observed via the simplified contact simulations that the cortical stresses can be substantially decreased by increasing the coating thickness. The full closure coughing simulation on the human sternum further corroborated the simplified contact results. The stress reduction effect was found to be more prominent in the transsternal contacts in comparison to peri-sternal contacts. Bearing in mind the promising numerical simulation results, it is put forth that a standard steel wire coated with Pellethane will majorly address the cut-through complication.

Unobtrusive, Cuffless Blood Pressure Monitoring Using a Soft Polymer Sensor Array With Flexible Hybrid Electronics

The state-of-the-art systems for blood pressure (BP) monitoring often use cuffed-based rigid sensory systems, bulky electronics, multiple measurement sites, and intermittent measurement. Here, we introduce a new type of epidermal electronics that were specifically designed for cuffless BP-monitoring system, named multiPANI. The proposed fully integrated wearable device is equipped with a wireless-flexible hybrid electronics, a personalized flexible sensor array, and encapsulated with a thin biocompatible elastomer layer for soft-conformal contact with the complex skin surface structure. In addition, a unique capability of multiPANI to monitor multiple local pulse wave velocity (PWV) enabling us to develop a novel hybrid BP estimation algorithm that combine a selective-local PWV and high-signal-to-noise-ratio-based pulse wave analysis (PWA) for robust-cuffless BP-monitoring system. Experimental results indicate that the proposed hybrid selective PWV-PWA BP model outperform the typical single-PWV BP model by ~30%, with an acceptable root-mean-square-error performance of 3.94 ± 0.5 and 1.88 ± 0.9 mmHg, for systolic BP and diastolic BP respectively. Collectively, this study demonstrated a unique solution of fully integrated epidermal electronics and hybrid BP estimation algorithm for a robust, cuffless, and long-term BP monitoring.

Biocompatible Elastomer with Adjustable Mechanical Properties and Degradation Rate as a Midline Segment of Bipartite Sling

Biocompatible Elastomer with Adjustable Mechanical Properties and Degradation Rate as a Midline Segment of Bipartite Sling

Development of physical, mechanical, antibacterial and cell growth properties of poly(glycerol sebacate urethane) (PGSU) with helping of curcumin and hydroxyapatite nanoparticles

Biocompatible and antimicrobial elastomers with controlled hydrophilicity and degradation rate, as well as appropriate stiffness and elasticity, are interesting for biomedical applications, such as regenerative medicine and tissue engineering.

Oxygen-Sensing Paramagnetic Probes for Clinical Oximetry.

Electron paramagnetic resonance (EPR) oximetry based on lithium naphthalocyanine paramagnetic crystals as oxygen sensors enables direct measurement of the partial pressure of oxygen (pO2) in tissues. The method uses topical or implantable forms of these oxygen-sensing crystals embedded in a biocompatible siloxane elastomer. This article presents a summary of these sensors for EPR oximetry and their applicability for tissue oxygen measurement in the clinic.

Three-Dimensional Printing of Poly(glycerol sebacate) Acrylate Scaffolds via Digital Light Processing.

Digital light processing (DLP)-based three-dimensional (3D) printing offers large improvements in fabrication throughput and spatial resolution when compared to various other additive manufacturing techniques. Both properties are highly desirable when fabricating biomaterial scaffolds that require design precision. Poly(glycerol sebacate) acrylate (PGSA) is a degradable, biocompatible, and photocurable elastomer. In this work, PGSA ink was developed for DLP 3D printing of porous tubular structures. Ink formulations with varying prepolymer concentrations (10-60 wt %), diluent (dimethyl sulfoxide (DMSO), 2-butoxyethyl acetate (EGBEA), and 1:1 DMSO/EGBEA), and degree of PGSA acrylation (17-75%) were studied to optimize printing efficiency and bulk properties of the printed scaffolds. Prepolymer inks with viscosity (<5 Pa·s) and photopolymerization kinetics (exposure time <10 s) appropriate for DLP were developed. Photocrosslinked PGSA scaffolds were further exposed to postfabrication treatments including additional UV exposure or thermal curing (150 °C) to demonstrate tunability in scaffold degradation kinetics and mechanical properties. Complementary to this effort, a 3D model-generation tool was developed to enable user-friendly customization of tubular scaffold design by controlling the pore and strut size of the volumetric mesh. The resulting DLP-printed PGSA scaffolds present high mimicry to complex 3D models with a minimum feature thickness of 80 μm. The tunable properties of PGSA coupled with enhanced precision in microstructure geometry provide a fabrication platform for a variety of tissue regeneration applications.

Characterizing the acoustic impedance and attenuation of biocompatible elastomers: An optimal design of experiments approach

Polymers have a range of densities and stiffnesses that can be further tuned with the addition of dopants to control their acoustic impedance and attenuation, important properties that impact acoustic transduction in underwater, medical, and other non-airborne applications. Previous research on impedance-matched polymers is limited in scope, focusing on a specific application and varying a limited number of variables independently. Here, we perform a more generalized study to model the relationship between multiple fabrication and characterization conditions on the acoustic impedance and attenuation of biocompatible elastomers with ceramic nanoparticle dopants. Following an I-optimal design of experiments approach, fifty samples were characterized with factors of polymer type (PDMS, Ecoflex, and Polyurethane), sample thickness, dopant density, concentration, and size, and characterization frequency and temperature. Statistical analysis revealed the main variables, as well as interactions between variables, that have a significant affect on the acoustic properties of the elastomers. The resulting statistical model specifies the conditions necessary to match the polymers to any acoustic impedance in the range of 1 to 2.5 MRayls. We demonstrate how the model is used to fabricate an elastomer with an acoustic impedance matched to skin and minimum attenuation.

Tough and Three-Dimensional-Printable Poly(2-methoxyethyl acrylate)-Silica Composite Elastomer with Antiplatelet Adhesion Property.

Poly(2-methoxyethyl acrylate) (PMEA) has attracted attention as a biocompatible polymer that is used as an antithrombotic coating agent for medical devices, such as during artificial heart and lung fabrication. However, PMEA is a viscous liquid polymer with low Tg, and its physical strength is poor even if a cross-linker is used, so it is difficult to make tough and freestanding objects from it. Here, we design and fabricate a biocompatible elastomer made of tough, self-supporting PMEA-silica composites. The toughness of the composite elastomer increases as a function of silica particle filling, and its stress at break is improved from 0.3 to 6.7 MPa. The fracture energy of the composite elastomer with 39.5 vol % silica particles is up to 15 times higher than that of the cross-linked PMEA with no silica particles and the material demonstrates stress-strain behavior that is similar to that of biological soft tissue, which exhibits nonlinear elasticity. In addition, the composite elastomer shows the potential to be an antithrombotic property, while the results of the platelet adhesion test of the composite elastomer show that the number of adhered platelets is not significantly affected by the silica addition. As the composite elastomer can be rapidly three-dimensional-printed into complex geometries with high-resolution features, it is expected to contribute to the development of medical devices from readily available materials.

Peptidoglycan-inspired autonomous ultrafast self-healing bio-friendly elastomers for bio-integrated electronics.

Elastomers are essential for stretchable electronics, which have become more and more important in bio-integrated devices. To ensure high compliance with the application environment, elastomers are expected to resist, and even self-repair, mechanical damage, while being friendly to the human body. Herein, inspired by peptidoglycan, we designed the first room-temperature autonomous self-healing biodegradable and biocompatible elastomers, poly(sebacoyl 1,6-hexamethylenedicarbamate diglyceride) (PSeHCD) elastomers. The unique structure including alternating ester-urethane moieties and bionic hybrid crosslinking endowed PSeHCD elastomers superior properties including ultrafast self-healing, tunable biomimetic mechanical properties, facile reprocessability, as well as good biocompatibility and biodegradability. The potential of the PSeHCD elastomers was demonstrated as a super-fast self-healing stretchable conductor (21 s) and motion sensor (2 min). This work provides a new design and synthetic principle of elastomers for applications in bio-integrated electronics.

Properties of Polydimethylsiloxane Modified by Blending with Polyvinylpyrrolidone and a Poly(ethylene oxide)-Poly(propylene oxide) Triblock Copolymer

Modification of biocompatible elastomers, especially polydimethylsiloxane (PDMS), through blending with hydrophilic excipients is sought in various biomedical applications to enhance the affinity o...

3D printing of a biocompatible double network elastomer with digital control of mechanical properties.

The majority of 3D-printed biodegradable biomaterials are brittle, limiting their potential application to compliant tissues. Poly (glycerol sebacate) acrylate (PGSA) is a synthetic biodegradable and biocompatible elastomer, compatible with light-based 3D printing. In this work we employed digital-light-processing (DLP)-based 3D printing to create a complex PGSA network structure. Nature-inspired double network (DN) structures with two geometrically interconnected segments with different mechanical properties were printed from the same material in a single shot. Such capability has not been demonstrated by any other fabrication technique. The biocompatibility of PGSA after 3D printing was confirmed via cell-viability analysis. We used a finite element analysis (FEA) model to predict the failure of the DN structure under uniaxial tension. FEA confirmed the soft segments act as sacrificial elements while the hard segments retain structural integrity. The simulation demonstrated that the DN design absorbs 100% more energy before rupture than the network structure made by single exposure condition (SN), doubling the toughness of the overall structure. Using the FEA-informed design, a new DN structure was printed and the FEA predicted tensile test results agreed with tensile testing of the printed structure. This work demonstrated how geometrically-optimized material design can be easily and rapidly achieved by using DLP-based 3D printing, where well-defined patterns of different stiffnesses can be simultaneously formed using the same elastic biomaterial, and overall mechanical properties can be specifically optimized for different biomedical applications.

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.

Fabrication and Characterization of Drug-Loaded Conductive Poly(glycerol sebacate)/Nanoparticle-Based Composite Patch for Myocardial Infarction Applications.

Heart tissue engineering is critical in the treatment of myocardial infarction, which may benefit from drug-releasing smart materials. In this study, we load a small molecule (3i-1000) in new biodegradable and conductive patches for application in infarcted myocardium. The composite patches consist of a biocompatible elastomer, poly(glycerol sebacate) (PGS), coupled with collagen type I, used to promote cell attachment. In addition, polypyrrole is incorporated because of its electrical conductivity and to induce cell signaling. Results from the in vitro experiments indicate a high density of cardiac myoblast cells attached on the patches, which stay viable for at least 1 month. The degradation of the patches does not show any cytotoxic effect, while 3i-1000 delivery induces cell proliferation. Conductive patches show high blood wettability and drug release, correlating with the rate of degradation of the PGS matrix. Together with the electrical conductivity and elongation characteristics, the developed biomaterial fits the mechanical, conductive, and biological demands required for cardiac treatment.

SEBS block copolymers as novel materials to design transdermal patches.

Styrene-block-(ethylene-co-butylene)-block-styrene (SEBS) copolymers are biocompatible elastomers with outstanding stability to UV radiation. This work addresses the potentialities of this class of elastomers for the development of transdermal patches. The influence of SEBS molecular weight, plasticizer and tackifier type on rheological pattern, debonding mechanisms, adhesive properties (i.e., tack, shear and peel adhesion) as well as on the in vitro biopharmaceutical performances (i.e., drug release and skin permeability) was investigated using ibuprofen as model drug. The relationships between the linear and non-linear rheological properties and the main adhesive and biopharmaceutical properties of the prepared patches have been demonstrated. The higher the viscous component of the matrix, the lower its cohesiveness and the faster the drug release rate. The in vitro skin permeability of ibuprofen was not limited by the polymeric matrix, even if compared to the commercial reference product. In conclusion, SEBS copolymers are suitable materials to design drug in-adhesive patches. In particular, SEBS-low molecular weight is the polymer worthy of consideration because of its favorable viscoelastic behavior.

One-pot preparation and applications of self-healing, self-adhesive PAA-PDMS elastomers

A new family of transparent, biocompatible, self-adhesive, and self-healing elastomer has been developed by a convenient and efficient one-pot reaction between poly(acrylic acid) (PAA) and hydroxyl-terminated polydimethylsiloxane (PDMS-OH). The condensation reaction between PAA and PDMS-OH has been confirmed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra. The prepared PAA-PDMS elastomers possess robust mechanical strength and strong adhesiveness to human skin, and they have fast self-healing ability at room temperature (in ~10 s with the efficiency of 98%). Specifically, strain sensors were fabricated by assembling PAA-PDMS as packaging layers and polyetherimide-reduced graphene oxide (PEI-rGO) as strain-sensing layers. The PAA-PDMS/PEI-rGO sensors are stably and reliably responsive to slight physical deformations, and they can be attached onto skin directly to monitor the body’s motions. Meanwhile, strain sensors can self-heal quickly and completely, and they can be reused for the motion detecting after shallowly scratching the surface. This work provides new opportunities to manufacture high performance self-adhesive and self-healing materials.

Biobased thermoplastic elastomer with seamless 3D-Printability and superior mechanical properties empowered by in-situ polymerization in the presence of nanocellulose

A biobased and biocompatible thermoplastic elastomer (TPE) with superior 3D printability was demonstrated with great potential for customized manufacturing technologies and fabrication of biointegrated devices. The inherent structural and stereochemical disadvantages of biobased monomers, such as 2,5-furandicarboxylic acid, in comparison with today used petroleum based monomers like terephthalic acid generally lead to lower mechanical performance for the biobased replacement polymers. This is additionally enhanced by poor interfacial adhesion and fusion commonly encountered during customized manufacturing technologies like 3D printing. Herein, we demonstrate that in-situ polymerization in the presence of trace amounts of cellulose nanocrystals (CNCs) can homogeneously distribute the nanofiller leading to dramatically strengthened thermally 3D-printable bio-furan-based TPE. This TPE exhibited a tensile strength of 67 MPa which is 1.5–7-fold higher than the values reported for silicone and thermoplastic urethane, which are widely used in biomedical applications. In addition, the TPE had an impressive extensibility of 860% and negligible in vivo cytotoxicity; such properties have not been reported to date for bio-based or petrochemical TPEs. While a petrochemical 3D printed TPE counterpart retained only half of the tensile strength compared to the hot-pressed analogue, the 3D-printed biobased TPE in-situ modified with nanocellulose maintained 70–80% of its strength under the same experimental conditions. This is explained by inter-diffusion between interfaces facilitated by the nanocellulose and the furan rings. Using the ergonomic shape of a wrist as a 3D-printable design, we successfully manufactured a wearable thermal therapeutic device from the nanocellulose modified biobased TPE, giving promise for wide variety of future applications.

Corrugation Enabled Asymmetrically Ultrastretchable (95%) Monocrystalline Silicon Solar Cells with High Efficiency (19%)

AbstractStretchable solar cells are of growing interest due their key role in realizing many applications such as wearables and biomedical devices. Ultrastretchability, high energy‐efficiency, biocompatibility, and mechanical resilience are essential characteristics of such energy harvesting devices. Here, the development of wafer‐scale monocrystalline silicon solar cells with world‐record ultrastretchability (95%) and efficiency (19%) is demonstrated using a laser‐patterning based corrugation technique. The demonstrated approach transforms interdigitated back contacts (IBC) based rigid solar cells into mechanically reliable but ultrastretchable cells with negligible degradation in the electric performance in terms of current density, open‐circuit voltage, and fill factor. The corrugation method is based on the creation of alternating grooves resulting in silicon islands with different shapes. The stretchability is achieved by orthogonally aligning the active silicon islands to the applied tensile stress and using a biocompatible elastomer (Ecoflex) as a stretchable substrate. The resulting mechanics ensure that the brittle silicon areas do not experience significant mechanical stresses upon asymmetrical stretching. Different patterns are studied including linear, diamond, and triangular patterns, each of which results in a different stretchability and loss of active silicon area. Finally, finite element method based simulation is conducted to study the generated deformation in the different patterned solar cells.

UV-curable, 3D printable and biocompatible silicone elastomers

A biocompatible silicone elastomer that can be UV-cured and 3D printed via thiol-ene photopolymerization between vinyl and thiol functionalized polysiloxanes is explored in this study. The in-situ photo-rheology demonstrates that the photo-crosslinking of silicone elastomer occurs instantaneously upon exposure to UV radiation and its gelation time is influenced synergically by thiol-ene molar ratio, photoinitiator dosage and UV irradiation intensity. Differential scanning photo-calorimeter results indicate that UV-initiated thiol-ene photoreaction preferably follows a second-order reaction kinetics and its activation energy is approximately 23.3 kJ/mol. Moreover, antibacterial assay shows thiol-ene UV-cured silicone elastomer can inhibit the growth of Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria to some extent. Cytotoxicity and biocompatibility results reveal that this silicone elastomer also has good biocompatibility, and it used as wound dressing is conducive to the recovery of wounds. Furthermore, due to excellent spatiotemporal controllability of thiol-ene photoreaction, various elaborate architectures are fabricated by photo-patterning. On the other hand, this UV-curable formulation can also be 3D printed into various structures with smooth surface and good accuracy. These results propose that thiol-ene UV-curable silicone elastomer will be a promising material in biomedical applications as wound dressings or customized soft tissue scaffolds through 3D printing.

Abstract 214: Effect of Matrix Stiffness on Adult Cardiomyocytes Using Dynamic, Tunable, and Reversible Magnetorheological PDMS Substrates

The physical properties of the extracellular matrix (ECM), including stiffness and viscoelasticity, play a key role in the development of hypertensive and hypertrophic cardiac diseases at the cellular level, affecting the morphology and function of heart tissue. The ECM is a dynamic structure that is continuously changing in both normal and diseased tissue. In an extension of prior studies examining how substrates of fixed stiffness affect cardiac cells, we introduce a novel experimental model that allows exploration of cardiomyocyte functional alterations in response to rapid and reversible matrix stiffness modulation. We fabricated a biocompatible magneto-rheological elastomer (MRE) culture substrate by adding iron particles to a PDMS elastomer. In the presence of an applied magnetic field, this substrate stiffens reversibly and nearly instantaneously from 10 kPa to 50 kPa: the range observed in normal and diseased myocardium, respectively. Adult cardiomyocytes isolated from non-failing human hearts (unused organ donors) or adult rats were cultured for 24 - 48 hours on the tunable MREs. Cardiomyocytes cultured on a stiffened MRE (~50 kPa) exhibited time-dependent reductions in cell shortening and peak Ca 2+ transient amplitude compared with cardiomyocytes cultured on a soft MRE (~10 kPa). Rates of cardiomyocyte shortening and re-lengthening were also slowed by culture on 50 kPa substrates. Using super-resolution imaging, we found that cardiomyocytes cultured on a stiffened MRE exhibited an increased microtubule network density and demonstrated increased cellular stiffness and viscoelasticity, as measured by nanoindentation. These studies indicate that adult human and rat cardiomyocytes are acutely sensitive to changes in extracellular stiffness within the pathophysiological range and tend to adapt their own stiffness to match that of their surroundings via dynamic changes in microtubule architecture. These mechanisms may contribute to the regulation of mechanical homogeneity within the myocardium. Our method provides a unique in vitro platform for studying mechanosensing, mechanotransduction and mechanical memory in isolated adult cardiomyocytes.

Effect of Polymer Binder on the Synthesis and Properties of 3D-Printable Particle-Based Liquid Materials and Resulting Structures.

Recent advances have demonstrated the ability to 3D-print, via extrusion, solvent-based liquid materials (previously named 3D-Paints) which solidify nearly instantaneously upon deposition and contain a majority by volume of solid particulate material. In prior work, the dissolved polymer binder which enables this process is a high molecular weight biocompatible elastomer, poly(lactic-co-glycolic) acid (PLGA). We demonstrate in this study an expansion of this solvent-based 3D-Paint system to two additional, less-expensive, and less-specialized polymers, polystyrene (PS) and polyethylene oxide (PEO). The polymer binder used within the 3D-Paint was shown to significantly affect the as-printed and thermal postprocessing behavior of printed structures. This development enables users to select one of several polymers to impart the most desirable properties for a given application. Additionally, 3D-Paints based on these new binders are not adversely affected by classes of particles that can chemically degrade PLGA, notably particles containing large quantities of alkali ions. This study demonstrates the ability to successfully use PS and PEO as binders in the 3D-Paint system and compares the rheological, mechanical, microstructural, and thermal properties of the modified 3D-Paints and resulting as-printed and thermally post-processed objects. These objects include, for the first time, structures resulting from 3D-Painting which mostly contain soda-lime glass and 45S5 bioactive glass.