Surface functionalization of silicone rubber for permanent adhesion improvement

In Situ Growth of Functional Hydrogel Coatings by a Reactive Polyurethane for Biomedical Devices

Surface modification of thermoplastic polyurethane (TPU) could significantly enhance its suitability for biomedical devices and public health products. Nevertheless, customized modification of polyurethane surfaces with robust interfacial bonding and diverse functions via a simple method remains an enormous challenge. Herein, a novel thermoplastic polyurethane with a photoinitiated benzophenone unit (BPTPU) is designed and synthesized, which can directly grow functional hydrogel coating on polyurethane (PU) in situ by initiating polymerization of diverse monomers under ultraviolet irradiation, without the involvement of organic solvent. The resulting coating not only exhibits tissue-like softness, controllable thickness, lubrication, and robust adhesion strength but also provides customized functions (i.e., antifouling, stimuli-responsive, antibacterial, and fluorescence emission) to the original passive polymer substrates. Importantly, BPTPU can be blended with commercial TPU to produce the BPTPU-based tube by an extruder. Only a trace amount of BPTPU can endow the tube with good photoinitiated capacity. As a proof of concept, the hydrophilic hydrogel-coated BPTPU is shown to mitigate foreign body response in vivo and prevent thrombus formation in rat blood circulation without anticoagulants in vitro. This work offers a new strategy to guide the design of functional polyurethane, an elastomer-hydrogel composite, and holds great prospects for clinical translation.

Surface Modification of Silicone by Dielectric Barrier Discharge Plasma

The objective of the study was to modify the surface of the silicone rubber, using dielectric barrier discharge (DBD) to improve its hydrophilic properties. The influence of the exposure time, discharge power, and gas composition-in which the dielectric barrier discharge was generated-on the properties of the silicone surface layer were examined. After the modification, the wetting angles of the surface were measured. Then, the value of surface free energy (SFE) and changes in the polar components of the modified silicone over time were determined using the Owens-Wendt method. The surfaces and morphology of the selected samples before and after plasma modification were examined by Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR), atomic force microscopy AFM, and X-ray photoelectron spectroscopy (XPS). Based on the research, it can be concluded that the silicone surface can be modified using a dielectric barrier discharge. Surface modification, regardless of the chosen method, is not permanent. The AFM and XPS study show that the structure's ratio of oxygen to carbon increases. However, after less than four weeks, it decreases and reaches the value of the unmodified silicone. It was found that the cause of the changes in the parameters of the modified silicone rubber is the disappearance of oxygen-containing groups on the surface and a decrease in the molar ratio of oxygen to carbon, causing the RMS surface roughness and the roughness factor to return to the initial values.

The Effect of Pre-Stretched Substrate on the Electrical Resistance of Printed Ag Nanowires

One-dimensional nanomaterials have drawn attention as an alternative electrode material for stretchable electronics. In particular, silver nanowires (Ag NWs) have been studied as stretchable electrodes for strain sensors, 3D electronics, and freeform-shaped electronic circuits. In this study, Ag NWs ink was printed on the pre-stretched silicone rubber film up to 40% in length using a drop-on-demand dispenser. After printing, silicone rubber film was released and stretched up to 20% as a cyclic test with 10-time repetition, and the ratios of the resistance of the stretched state to that of the released state (R_stretched/R_released) were measured at each cycle. For Ag NWs electrode printed on the pre-stretched silicone rubber at 30%, R_stretched/R_released at 10% and 20% strain was 1.05, and 1.57, respectively, which is significantly less than about 7 for Ag NWs at the 10% strain without pre-stretched substrate. In the case of 10% strain on the 30% pre-stretched substrate, the substrate is stretched and the contact points with Ag NWs were not changed much as the silicone rubber film stretched, which meant that Ag NWs may slide between other Ag NWs. Ag NWs electrode on the 40% pre-stretched substrate was stretched, strain was concentrated on the Ag NWs electrode and failure of electrode occurred, because cracks occurred at the surface of silicone rubber film when it was pre-stretched to 40%. We confirmed that printed Ag NWs on the pre-stretched film showed more contact points and less electric resistance compared to printed Ag NWs on the film without pre-stretching.

Tough Bonding of Liquid Metal-Elastomer Composites for Multifunctional Adhesives

Liquid metal (LM) composites, which consist of LM droplets dispersed in highly deformable elastomers, have recently gained interest as a multifunctional material for soft robotics and electronics. The incorporation of LM into elastic solids allows for unique combinations of material properties such as high stretchability with thermal and electrical conductivity comparable to metals. However, it is currently a challenge to incorporate LM composites into integrated systems consisting of diverse materials and components due to a lack of adhesion control. Here, a chemical anchoring methodology to increase adhesion of LM composites to diverse substrates is presented. The fracture energy increases up to 100× relative to untreated surfaces, with values reaching up to 7800 J m^-2 . Furthermore, the fracture energy, tensile modulus, and thermal conductivity can be tuned together by controlling the microstructure of LM composites. Finally, the bonding technique is used to integrate LM composites with functional electronic components without encapsulation or clamping, allowing for extreme deformations while maintaining exceptional thermal and electrical conductivity. These findings can accelerate the adoption of LM composites into complex soft robotic and electronic systems where strong, reliable bonding between diverse materials and components is required.

Binary Promoter Improving the Moderate-Temperature Adhesion of Addition-Cured Liquid Silicone Rubber for Thermally Conductive Potting

The strong adhesion of thermally conductive silicone encapsulants on highly integrated electronic devices can avoid external damages and lead to an improved long-term reliability, which is critical for their commercial application. However, due to their low surface energy and chemical reactivity, the self-adhesive ability of silicone encapsulants to substrates need to be explored further. Here, we developed epoxy and alkoxy groups-bifunctionalized tetramethylcyclotetrasiloxane (D4H-MSEP) and boron-modified polydimethylsiloxane (PDMS-B), which were synthesized and utilized as synergistic adhesion promoters to provide two-component addition-cured liquid silicone rubber (LSR) with a good self-adhesion ability for applications in electronic packaging at moderate temperatures. The chemical structures of D4H-MSEP and PDMS-B were characterized by Fourier transform infrared spectroscopy. The mass percentage of PDMS-B to D4H-MSEP, the adhesion promoters content and the curing temperature on the adhesion strength of LSR towards substrates were systematically investigated. In detail, the LSR with 2.0 wt% D4H-MSEP and 0.6 wt% PDMS-B exhibited a lap-shear strength of 1.12 MPa towards Al plates when curing at 80 °C, and the cohesive failure was also observed. The LSR presented a thermal conductivity of 1.59 W m−1 K−1 and good fluidity, which provided a sufficient heat dissipation ability and fluidity for potting applications with 85.7 wt% loading of spherical α-Al2O3. Importantly, 85 °C and 85% relative humidity durability testing demonstrated LSR with a good encapsulation capacity in long-term processes. This strategy endows LSR with a good self-adhesive ability at moderate temperatures, making it a promising material requiring long-term reliability in the encapsulation of temperature-sensitive electronic devices.

Probing Covalent Interactions at a Silicone Adhesive/Nylon Interface

Covalent bonding is one of the most robust forms of intramolecular interaction between adhesives and substrates. In contrast to most noncovalent interactions, covalent bonds can significantly enhance both the interfacial strength and durability. To utilize the advantages of covalent bonding, specific chemical reactions are designed to occur at interfaces. However, interfacial reactions are difficult to probe in situ, particularly at the buried interfaces found in well-bonded adhesive joints. In this work, sum frequency generational (SFG) vibrational spectroscopy was used to directly examine and analyze the interfacial chemical reactions and related molecular changes at buried nylon/silicone elastomer interfaces. For self-priming elastomeric silicone adhesives, silane coupling agents have been extensively used as adhesion promoters. Here with SFG, the interfacial chemical reactions between nylon and two alkoxysilane adhesion promoters with varied functionalities (maleic anhydride (MAH) and epoxy) formulated into the silicone were observed and investigated. Evidence of reactions between the organofunctional group of each silane and reactive groups on the polyamide was found at the buried interface between the cured silicone elastomer and nylon. The adhesion strength at the nylon/cured silicone interfaces was substantially enhanced with both silane additives. SFG results elucidated the mechanisms of organo-silane adhesion promotion for silicone at the molecular level. The ability to probe and analyze detailed interfacial reactions at buried nylon/silicone interfaces demonstrated that SFG is a powerful analytical technique to aid the design and optimization of materials with desired interfacial properties.

Pneumatic Bionic Hand with Rigid-Flexible Coupling Structure

This paper presents a rigid-flexible composite of bionic hand structure design scheme solution for solving the problem of low load on the soft gripping hand. The bionic hand was designed based on the Fast Pneumatic Network (FPN) approach, which can produce a soft finger bending drive mechanism. A soft finger bending driver was developed and assembled into a human-like soft gripping hand which includes a thumb for omnidirectional movement and four modular soft fingers. An experimental comparison of silicone rubber materials with different properties was conducted to determine suitable materials. The combination of 3D printing technology and mold pouring technology was adopted to complete the prototype preparation of the bionic hand. Based on the second-order Yeoh model, a soft bionic finger mathematical model was established, and ABAQUS simulation analysis software was used for correction to verify the feasibility of the soft finger bending. We adopted a pneumatic control scheme based on a motor micro-pump and developed a human-computer interface through LabView. A comparative experiment was carried out on the bending performance of the finger, and the experimental data were analyzed to verify the accuracy of the mathematical model and simulation. In this study, the control system was designed, and the human-like finger gesture and grasping experiments were carried out.

Proteins on the rack: Mechanistic studies on protein particle formation during peristaltic pumping

Peristaltic pumping can cause protein particle formation. The expected causes were unfolding by heat in the pump head, oxidative stress by cavitation generated during roller movement, interfacial adsorption to the tubing wall and mechanical stress by stretching of the tubing itself. The pump head reached 28°C during experiments stayed well below the onset of the melting point of the proteins. Thus, heat may only be a relevant root cause for proteins containing domains with very low unfolding temperature. Analysis by terephthalic acid dosimetry and protein oxidation via RP-HPLC ruled out major induction of reactive hydroxyl radicals by pumping, indicating that cavitation does not play a significant role in particle generation. Addition of surfactants suppresses protein adsorption to the tubing wall and drastically reduced protein particle formation. This indicates that interfacial protein adsorption is a key element. Repeated stretching of tubing filled with protein solution led to the formation of protein particles, demonstrating that expansion and compression of the protein film on the tubing surface is the second key component for particle formation. Thus, protein particle generation during peristaltic pumping originates from the formation of a protein film on the tubing surface which gets stretched and compressed, leading to film fragments entering the bulk solution. This interplay of protein film formation and its rupture has been also observed at liquid/liquid or liquid/air interfaces.

Promoters for Improved Adhesion Strength between Addition-Cured Liquid Silicone Rubber and Low-Melting-Point Thermoplastic Polyurethanes

A polydimethylsiloxane armed with epoxy, alkoxy and acrylate groups was synthesized from silanol terminated-PDMS and epoxy and acrylate groups functionalized silane coupling agents, and utilized as the adhesion promoter (AP) to prepare addition-cured liquid silicone rubber that exhibited self-adhesion ability (SA-LSR) with biocompatible thermoplastic polyurethanes (TPU) sheets. The structural characteristics of AP were characterized by Fourier transform infrared (FTIR) spectroscopy, which demonstrated the strong adhesion to polyester-based TPU sheets due to a sufficient amount of acrylate groups, epoxy groups and silanol groups obtained by the hydrolysis of alkoxy groups. In detail, the peel-off strength of SA-LSR and TPU joints reached up to 7.63 N mm⁻¹ after the optimization of adhesion promoter including type and content, and curing condition including time and temperature. The cohesive failure was achieved during the sample breakage process. Moreover, the SA-LSR showed a good storage stability under proper storage conditions. This design strategy provided the feasibility to combine the advantages of addition-cured liquid silicone rubber and plastics with low melting points, promoting the potential application range of those silicone-based materials.

Effect of N-(2-Aminoethyl)-3-Aminopropyltrimethoxysilane on the Adhesion of the Modified Silicone Tie-Coating to Epoxy Primer

In this work, modified silicone tie-paints were prepared in a simple way for securing adhesion between the epoxy anticorrosive primer and silicone fouling release coating. Hydroxy-terminated polydimethylsiloxane (PDMS) mixture containing fillers and accessory ingredient was prepared as base component. N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane (DAMO) was mechanically mixed with other functional additives as curing component. ATR-FTIR, XPS, SEM and tensile tests were used to investigate the chemical structure, morphology and mechanical properties of the tie-coatings. It was focused on the effect of the DAMO content on the adhesion of the tie-coating to epoxy primer. Peel off and shear tests were carried out to evaluate the adhesion. The results showed that introducing DAMO can significantly improve the properties of the tie-coating. The adhesion between the tie-coating and the epoxy primer increases with the increase of DAMO content, but the excessive DAMO content will decrease the fracture strength of the tie-coating and decrease the quality of the coating. When the DAMO content in tie-coating is 1.97 wt.%, the tie-coating performs excellent in the interlaminar adhesion, shear strength and mechanical properties.

A Novel Computer-Controlled Maskless Fabrication Process for Pneumatic Soft Actuators

Template-based and additive manufacturing techniques have demonstrated some fabrication routes for creating pneumatic soft actuators. However, as the complexity and capability of the actuators continue to develop, the limitations of these approaches are becoming evident. These include difficulties for design variations, process speed and resolution, material compatibility and scalability, which hinder and restrict both the possible capabilities of the technology and its transition from research to industry. This body of work presents a computer-controlled, maskless manufacturing process with a different approach to allow for high-speed, low-cost and flexible creation of pneumatic soft actuation networks comprising multi-material construction. This was investigated through a bespoke fabrication platform that provides computer-controlled localised plasma treatment to selectively modify the chemical behaviour on the surface of silicone and polyethylene terephthalate (PET) bodies. The altered surface chemistry facilitated selective bond formation between the treated parts of the surface and, consequently, greater design variation and control over the pneumatic chambers that were formed. Selective treatment patterns allowed nonlinear pneumatic chamber designs to be created, and the strength of bonded silicone structures was shown to facilitate large deformations in the actuators. Furthermore, the different interactions between the plasma and silicone were leveraged to achieve feature sizes of <1 mm and treatment speeds of 20 mm2 per second of exposure. Two multi-material pneumatic soft actuators were then fabricated to demonstrate the potential of the platform as an automated manufacturing route for soft actuators.

Surface Modification and Adhesion Mechanism of Isotactic Polypropylene with Low-Energy Electron-Beam Treatments

Recently, smaller-size electron-beam (EB) accelerators have offered EB irradiation in laboratory systems. Therefore, polymer surface treatments with low-energy EB have been developed in the past years. For high adhesion strength, low-energy EB treatment is also a promising method in comparison to plasma surface treatment. In the plasma treatment, the mechanism of the effect on the adhesion properties has been proved and the excess treatments led to the formation of a weak boundary layer and reduction of adhesion strength. In contrast, the low-energy EB possesses high penetration ability. In this work, we focused on the surface treatments of isotactic polypropylene (it.PP) with low-energy EB irradiation for adhesion. The dependence of adhesion strength on the absorbed dose of electron beam was evaluated, and the mechanism of electron beam on the adhesion properties was investigated from various perspectives of surface properties and morphology. Compared to that of plasma-treated it.PP, the adhesion strength of it.PP with electron-beam irradiation increased drastically. We proved that the radical was generated in the substrates after electron-beam treatments and would form covalent bonds between adhesives and substrates, which achieved higher adhesion than plasma treatments. In addition, the electron beam reached effectively a deep region from the top surface of the substrates and provided larger adhesion strength.

Antifouling silicone hydrogel contact lenses via densely grafted phosphorylcholine polymers

Silicone hydrogel contact lenses (CLs) permit increased oxygen permeability through their incorporation of siloxane functional groups. However, contact lens biofouling can be problematic with these materials; surface modification to increase lens compatibility is necessary for acceptable properties. This work focuses on the creation of an antifouling CL surface through a novel grafting method. A polymer incorporating 2-methacryloyloxyethyl phosphorylcholine (MPC), well known for its antifouling and biomimetic properties, was grafted to the model lens surfaces using surface-initiated atom transfer radical polymerization (SI-ATRP). The SI-ATRP modification generated a unique double-grafted polymeric architecture designed to resist protein adsorption through the presence of a surrounding hydration layer due to the PC groups and steric repulsion due to the density of the grafted chains. The polymer was grafted from model silicone hydrogel CL using a four-step SI-ATRP process. Attenuated total reflectance-Fourier transform infrared spectroscopy and XPS were used to confirm the surface chemical composition at each step of the synthesis. Both the surface wettability and equilibrium water content of the materials increased significantly upon polyMPC modification. The surface water contact angle was as low as 16.04 ± 2.37° for polyMPC-50 surfaces; complete wetting (∼0°) was observed for polyMPC-100 surfaces. A decrease in the protein adsorption by as much as 83% (p < 0.000 36) for lysozyme and 73% (p < 0.0076) for bovine serum albumin was observed, with no significant difference between different polyMPC chain lengths. The data demonstrate the potential of this novel modification process for the creation of extremely wettable and superior antifouling surfaces, useful for silicone hydrogel CL surfaces.

Surface Chemical Functionalization of Wrinkled Thiol-ene Elastomers for Promoting Cellular Alignment

Wrinkled polymer surfaces find broad applicability; however, the polymer substrates are often limited to poly(dimethylsiloxane) (PDMS), which limits spatial control over wrinkle features and surface chemistry. An approach to surface functionalization of wrinkled elastomer substrates is demonstrated through versatile, multistep thiol-ene click chemistry. The elastomer is formed using a thiol-Michael reaction of tetrathiol with excess diacrylates while wrinkle formation is induced through a second free radical UV polymerization of the acrylates on the surface of the elastomer. Due to oxygen inhibition of the free radical polymerization, pendant acrylates at the surface remain unreacted and are subsequently functionalized with a multi-functional thiol, which can be further reacted through a number of thiol-X 'click' reactions. As a demonstration, these thiol surfaces are further modified to either promote cell adhesion of human mesenchymal stem cells (hMSCs) through coupling with RGDS-containing peptides or surface passivation through reaction with hydrophilic hydroxyl ethyl acrylate moieties. Through engineering a combination of surface chemistry and surface topography, hMSCs exhibited increased spreading and cell density on RGDS-functionalized surfaces and a two-fold increase in cell alignment when cultured on wrinkled substrates. Gradient functionalized surfaces created by tuning the wrinkle wavelength with UV irradiation enabled rapid screening of the effect of topography on the hMSCs. Further, this novel application of click chemistry enables simultaneous tuning of wrinkle topology and surface chemistry towards targeted material applications.

A customizable microfluidic platform for medium-throughput modeling of neuromuscular circuits

Neuromuscular circuits (NMCs) are vital for voluntary movement, and effective models of NMCs are needed to understand the pathogenesis of, as well as to identify effective treatments for, multiple diseases, including Duchenne’s muscular dystrophy and amyotrophic lateral sclerosis. Microfluidics are ideal for recapitulating the central and peripheral compartments of NMCs, but myotubes often detach before functional NMCs are formed. In addition, microfluidic systems are often limited to a single experimental unit, which significantly limits their application in disease modeling and drug discovery. Here, we developed a microfluidic platform (MFP) containing over 100 experimental units, making it suitable for medium-throughput applications. To overcome detachment, we incorporated a reactive polymer surface allowing customization of the environment to culture different cell types. Using this approach, we identified conditions that enable long-term co-culture of human motor neurons and myotubes differentiated from human induced pluripotent stem cells inside our MFP. Optogenetics demonstrated the formation of functional NMCs. Furthermore, we developed a novel application of the rabies tracing assay to efficiently identify NMCs in our MFP. Therefore, our MFP enables large-scale generation and quantification of functional NMCs for disease modeling and pharmacological drug targeting.

Bioinspired Further Enhanced Dry Adhesive by the Combined Effect of the Microstructure and Surface Free-Energy Increase

Silicone elastomers are known for having low surface free energies generally leading to poor adhesive performances. This surface characteristic can be enhanced by plasma treatments. The microstructured silicone elastomer surfaces can demonstrate superior adhesive performance that is more than 10 times higher in terms of pull-off forces, compared to their unstructured counterpart. Here, we have demonstrated that the combination of these two methods further enhances adhesive performance, especially when the surfaces are biomimetic micro/nanopatterned with, e.g., beetle-inspired mushroom-shaped adhesive microstructure (MSAMS). The plasma treatment time and pressure parameters were varied for the unstructured and MSAMS poly(vinylsiloxane) surfaces to find optimum parameters for maximum adhesion performance. Air plasma treatment induced average adhesive enhancement forces up to 30% on the unstructured surface, but the MSAMS surface demonstrated an enhancement of adhesive forces up to 91% higher than that of an untreated, microstructured control, despite the plasma-treated surface area of the structured surface being only 50% of that of the unstructured surface. High-speed video-recordings of individual microstructures in contact with a glass surface shows that the origin of the adhesion enhancement is due to the special detachment mechanism of individual microstructures that allows sustaining a wider contact area at detachment. We believe that this integration of the plasma treatment with MSAMS suggests a versatile way of functionalization that can further advance the adhesive ability of low-surface-energy polymer surfaces.

Thin Film Composite Silicon Elastomers for Cell Culture and Skin Applications: Manufacturing and Characterization

In this protocol, we present methods to fabricate thin elastomer composite films for advanced cell culture applications and for the development of skin adhesives. Two different poly-(dimethyl siloxanes) (PDMS and soft skin adhesive (SSA)), have been used for in depth investigation of biological effects and adhesive characteristics. The composite films consist of a flexible backing layer and an adhesive top coating. Both layers have been manufactured by doctor blade application technique. In the present investigation, the adhesive behavior of the composite films has been investigated as a function of the layer thickness or a variation of the Young's modulus of the top layer. The Young's modulus of PDMS has been changed by varying the base to crosslinker mixing ratio. In addition, the thickness of SSA films has been varied from approx. 16 µm to approx. 320 µm. Scanning electron microscopy (SEM) and optical microscopy have been used for thickness measurements. The adhesive properties of elastomer films depend strongly on the film thickness, the Young's modulus of the polymers and surface characteristics. Therefore, normal adhesion of these films on glass substrates exhibiting smooth and rough surfaces has been investigated. Pull-off stress and work of separation are dependent on the mixing ratio of silicone elastomers.

Additionally, the thickness of the soft skin adhesive placed on top of a supportive backing layer has been varied in order to produce patches for skin applications. Cytotoxicity, proliferation and cellular adhesion of L929 murine fibroblasts on PDMS films (mixing ratio 10:1) and SSA films (mixing ratio 50:50) have been conducted. We have shown here, for the first time, the side by side comparison of thin composite films manufactured of both polymers and present the investigation of their biological- and adhesive properties.

An oxygen plasma treated poly(dimethylsiloxane) bioscaffold coated with polydopamine for stem cell therapy

In this study, 3D macroporous bioscaffolds were developed from poly(dimethylsiloxane) (PDMS) which is inert, biocompatible, non-biodegradable, retrievable and easily manufactured at low cost. PDMS bioscaffolds were synthesized using a solvent casting and particulate leaching (SCPL) technique and exhibited a macroporous interconnected architecture with 86 ± 3% porosity and 300 ± 100 µm pore size. As PDMS intrinsically has a hydrophobic surface, mainly due to the existence of methyl groups, its surface was modified by oxygen plasma treatment which, in turn, enabled us to apply a novel polydopamine coating onto the surface of the bioscaffold. The addition of a polydopamine coating to bioscaffolds was confirmed using composition analysis. Characterization of oxygen plasma treated-PDMS bioscaffolds coated with polydopamine (polydopamine coated-PDMS bioscaffolds) showed the presence of hydroxyl and secondary amines on their surface which resulted in a significant decrease in water contact angle when compared to uncoated-PDMS bioscaffolds (35 ± 3%, P < 0.05). Seeding adipose tissue-derived mesenchymal stem cells (AD-MSCs) into polydopamine coated-PDMS bioscaffolds resulted in cells demonstrating a 70 ± 6% increase in viability and 40 ± 5% increase in proliferation when compared to AD-MSCs seeded into uncoated-PDMS bioscaffolds (P < 0.05). In summary, this two-step method of oxygen plasma treatment followed by polydopamine coating improves the biocompatibility of PDMS bioscaffolds and only requires the use of simple reagents and mild reaction conditions. Hence, our novel polydopamine coated-PDMS bioscaffolds can represent an efficient and low-cost bioscaffold platform to support MSC therapies.

Laminin modification subretinal bio-scaffold remodels retinal pigment epithelium-driven microenvironment in vitro and in vivo

Advanced age-related macular degeneration (AMD) may lead to geographic atrophy or fibrovascular scar at macular, dysfunctional retinal microenvironment, and cause profound visual loss. Recent clinical trials have implied the potential application of pluripotent cell-differentiated retinal pigment epithelial cells (dRPEs) and membranous scaffolds implantation in repairing the degenerated retina in AMD. However, the efficacy of implanted membrane in immobilization and supporting the viability and functions of dRPEs, as well as maintaining the retinal microenvironment is still unclear. Herein we generated a biomimetic scaffold mimicking subretinal Bruch's basement from plasma modified polydimethylsiloxane (PDMS) sheet with laminin coating (PDMS-PmL), and investigated its potential functions to provide a subretinal environment for dRPE-monolayer grown on it. Firstly, compared to non-modified PDMS, PDMS-PmL enhanced the attachment, proliferation, polarization, and maturation of dRPEs. Second, PDMS-PmL increased the polarized tight junction, PEDF secretion, melanosome pigment deposit, and phagocytotic-ability of dRPEs. Third, PDMS-PmL was able to carry a dRPEs/photoreceptor-precursors multilayer retina tissue. Finally, the in vivo subretinal implantation of PDMS-PmL in porcine eyes showed well-biocompatibility up to 2-year follow-up. Notably, multifocal ERGs at 2-year follow-up revealed well preservation of macular function in PDMS-PmL, but not PDMS, transplanted porcine eyes. Trophic PEDF secretion of macular retina in PDMS-PmL group was also maintained to preserve retinal microenvironment in PDMS-PmL eyes at 2 year. Taken together, these data indicated that PDMS-PmL is able to sustain the physiological morphology and functions of polarized RPE monolayer, suggesting its potential of rescuing macular degeneration in vivo.

Suppression Effect and Mechanism of Amine-Containing MQ Silicone Resin on the Tracking and Erosion Resistance of Silicone Rubber

How to effectively enhance the antitracking performance of silicone rubber is a huge challenge in the field of high-voltage insulation. In this contribution, amine-containing MQ silicone resin (A-MQ) was prepared to enhance the tracking and erosion resistance of addition-cure liquid silicone rubber (ALSR). The results showed that A-MQ imparted ALSR with excellent tracking and erosion resistance. When A-MQ content was 4 phr, all test samples passed the inclined plane test at 4.5 kV, and the erosion mass decreased by 67.8%. In addition, the tensile strength and tear strength increased by 13.2 and 13.6%, respectively, compared with that of ALSR without A-MQ. The suppression mechanism was further investigated in the aspects of heat attack and plasma bombardment by laser Raman spectroscopy, thermogravimetry, thermogravimetry-Fourier transform infrared spectrometry, scanning electron microscopy, attenuated total reflection-Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. This revealed that at the elevated temperature caused by arc discharge, A-MQ promoted crosslinking of the polysiloxane molecules and suppressed the generation of cyclic oligomers, which reduced the intensity of the electrical arc. Moreover, when suffering from plasma bombardment, which was also produced by arc discharge, A-MQ protected the silicone chains from degradation and eliminated the carbon deposited on the surface.

A Highly Stretchable and Robust Non-fluorinated Superhydrophobic Surface

Superhydrophobic surface simultaneously possessing exceptional stretchability, robustness, and non-fluorination is highly desirable in applications ranging from wearable devices to artificial skins. While conventional superhydrophobic surfaces typically feature stretchability, robustness, or non-fluorination individually, co-existence of all these features still remains a great challenge. Here we report a multi-performance superhydrophobic surface achieved through incorporating hydrophilic micro-sized particles with pre-stretched silicone elastomer. The commercial silicone elastomer (Ecoflex) endowed the resulting surface with high stretchability; the densely packed micro-sized particles in multi-layers contributed to the preservation of the large surface roughness even under large strains; and the physical encapsulation of the microparticles by silicone elastomer due to the capillary dragging effect and the chemical interaction between the hydrophilic silica and the elastomer gave rise to the robust and non-fluorinated superhydrophobicity. It was demonstrated that the as-prepared fluorine-free surface could preserve the superhydrophobicity under repeated stretching-relaxing cycles. Most importantly, the surface's superhydrophobicity can be well maintained after severe rubbing process, indicating wear-resistance. Our novel superhydrophobic surface integrating multiple key properties, i.e. stretchability, robustness, and non-fluorination, is expected to provide unique advantages for a wide range of applications in biomedicine, energy, and electronics.

Development and characterization of a stable adhesive bond between a poly(dimethylsiloxane) catheter material and a bacterial biofilm resistant acrylate polymer coating

Catheter associated urinary tract infections are the most common health related infections worldwide, contributing significantly to patient morbidity and mortality and increased health care costs. To reduce the incidence of these infections, new materials that resist bacterial biofilm formation are needed. A composite catheter material, consisting of bulk poly(dimethylsiloxane) (PDMS) coated with a novel bacterial biofilm resistant polyacrylate [ethylene glycol dicyclopentenyl ether acrylate (EGDPEA)-co-di(ethyleneglycol) methyl ether methacrylate (DEGMA)], has been proposed. The coated material shows excellent bacterial resistance when compared to commercial catheter materials, but delamination of the EGDPEA-co-DEGMA coatings under mechanical stress presents a challenge. In this work, the use of oxygen plasma treatment to improve the wettability and reactivity of the PDMS catheter material and improve adhesion with the EGDPEA-co-DEGMA coating has been investigated. Argon cluster three dimensional-imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used to probe the buried adhesive interface between the EGDPEA-co-DEGMA coating and the treated PDMS. ToF-SIMS analysis was performed in both dry and frozen-hydrated states, and the results were compared to mechanical tests. From the ToF-SIMS data, the authors have been able to observe the presence of PDMS, silicates, salt particles, cracks, and water at the adhesive interface. In the dry catheters, low molecular weight PDMS oligomers at the interface were associated with poor adhesion. When hydrated, the hydrophilic silicates attracted water to the interface and led to easy delamination of the coating. The best adhesion results, under hydrated conditions, were obtained using a combination of 5 min O₂ plasma treatment and silane primers. Cryo-ToF-SIMS analysis of the hydrated catheter material showed that the bond between the primed PDMS catheter and the EGDPEA-co-DEGMA coating was stable in the presence of water. The resulting catheter material resisted Escherichia coli and Proteus mirabilis biofilm colonization by up to 95% compared with uncoated PDMS after 10 days of continuous bacterial exposure and had the mechanical properties necessary for use as a urinary catheter.

Hydrophilic Organic Electrodes on Flexible Hydrogels

Prompted by the rapidly developing field of wearable electronics, research into biocompatible substrates and coatings is intensifying. Acrylate-based hydrogel polymers have gained widespread use as biocompatible articles in applications such as contact and intraocular lenses. Surface treatments and/or coatings present one strategy to further enhance the performance of these hydrogels or even realize novel functionality. In this study, the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is deposited from the vapor phase onto hydrated hydrogel substrates and blended with biocompatibilizing coconstituents incorporating polyethylene glycol (PEG) and polydimethyl siloxane (PDMS) moieties. Plasma pretreatment of the dehydrated hydrogel substrate modifies its surface topography and chemical composition to facilitate the attachment of conductive PEDOT-based surface layers. Manipulating the vapor phase polymerization process and constituent composition, the PEDOT-based coating is engineered to be both hydrophilic (i.e. to promote biocompatibility) and highly conductive. The fabrication of this conductively coated hydrogel has implications for the future of wearable electronic devices.

Ultrafast diffusion-controlled thiol–ene based crosslinking of silicone elastomers with tailored mechanical properties for biomedical applications

Thiol-ene coupling enables the metal-free ultra-fast (seconds) crosslinking of polysiloxanes.

Silicone surface with drug nanodepots for medical devices

An ideal surface of poly(dimethylsiloxane) (PDMS) medical devices requires sustained drug release to combat various tissue responses and infection. At present, a noncovalent surface coating with drug molecules using binders possesses a detachment problem, while covalently linking drug molecules to the surface provides no releasable drug. Here, a platform that allows the deposition of diverse drugs onto the PDMS surface in an adequate quantity with reliable attachment and a sustained-release character is demonstrated. First, a PDMS surface with carboxyl functionality (PDMS-COOH) is generated by subjecting a PDMS piece to an oxygen plasma treatment to obtain silanol moieties on its surface, then condensing the silanols with (3-aminopropyl)triethoxysilane molecules to generate amino groups, and finally reacting the amino groups with succinic anhydride. The drug-loaded carriers with hydroxyl groups on their surface can then be esterified to PDMS-COOH, resulting in a PDMS surface covalently grafted with drug-filled nanocarriers so that the drugs inside the securely grafted carriers can be released. Demonstrated here is the covalent linking of the surface of a PDMS endotracheal tube with budesonide-loaded ethylcellulose nanoparticles. A secure and high drug accumulation at the surface of the tubes (0.025 mg/cm2) can be achieved without changes in its bulk property such as hardness (Shore-A), and sustained release of budesonide with a high release flux during the first week followed by a reduced release flux over the subsequent 3 weeks can be obtained. In addition, the grafted tube possesses more hydrophilic surface and thus is more tissue-compatible. The grafted PDMS pieces show a reduced in vitro inflammation in cell culture and a lower level of in vivo tissue responses, including a reduced level of inflammation, compared to the unmodified PDMS pieces, when implanted in rats. Although demonstrated with budesonide and a PDMS endotracheal tube, this platform of grafting a PDMS surface with drug-loaded particles can be applied to other drugs and other devices.

Osteopontin (OPN) is an important protein to mediate improvements in the biocompatibility of C ion-implanted silicone rubber

Medical device implants are drawing increasing amounts of interest from modern medical practitioners. However, this attention is not evenly spread across all such devices; most of these implantable devices can cause adverse reactions such as inflammation, fibrosis, thrombosis, and infection. In this work, the biocompatibility of silicone rubber (SR) was improved through carbon (C) ion implantation. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results confirmed that these newly generated carbon-implanted silicone rubbers (C-SRs) had large, irregular peaks and deep valleys on their surfaces. The water contact angle of the SR surface decreased significantly after C ion implantation. C ion implantation also changed the surface charge distribution, silicone oxygen rate, and chemical-element distribution of SR to favor cell attachment. The dermal fibroblasts cultured on the surface C-SR grew faster and showed more typical fibroblastic shapes. The expression levels of major adhesion proteins, including talin-1, zyxin, and vinculin, were significantly higher in dermal fibroblasts cultured on C-SR coated plates than in dermal fibroblasts cultured on SR. Those same dermal fibroblasts on C-SRs showed more pronounced adhesion and migration abilities. Osteopontin (OPN), a critical extracellular matrix (ECM) protein, was up-regulated and secreted from dermal fibroblasts cultured on C-SR. Matrix metalloproteinase-9 (MMP-9) activity was also increased. These cells were highly mobile and were able to adhere to surfaces, but these abilities were inhibited by the monoclonal antibody against OPN, or by shRNA-mediated MMP-9 knockdown. Together, these results suggest that C ion implantation significantly improves SR biocompatibility, and that OPN is important to promote cell adhesion to the C-SR surface.

Nonplanar conductive surfaces via "bottom-up" nanostructured gold coating

Development of technologies for the construction of bent, curved, and flexible conductive surfaces is among the most important albeit challenging goals in the promising field of "flexible electronics". We present a generic solution-based "bottom-up" approach for assembling conductive gold nanostructured layers on nonplanar polymer surfaces. The simple two-step experimental scheme is based upon incubation of an amine-displaying polymer [the abundantly used poly(dimethylsiloxane) (PDMS), selected here as a proof of concept] with Au(SCN)4(-), followed by a brief treatment with a conductive polymer [poly(3,4-thylenedioxythiophene)/poly(styrenesulfonate)] solution. Importantly, no reducing agent is co-added to the gold complex solution. The resultant surfaces are conductive and exhibit a unique "nanoribbon" gold morphology. The scheme yields conductive layers upon PDMS in varied configurations: planar, "wrinkled", and mechanically bent surfaces. The technology is simple, inexpensive, and easy to implement for varied polymer surfaces (and other substances), opening the way for practical applications in flexible electronics and related fields.

Modification of the adhesive properties of silicone-based coatings by block copolymers

The improvement of the (bio)adhesive properties of elastomeric polydimethylsiloxane (PDMS) coatings is reported. This is achieved by a surface modification consisting of the incorporation of block copolymers containing a PDMS block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) block in a PDMS matrix, followed by matrix cross-linking and immersion of the obtained materials in water. Contact angle measurements (CA), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) showed the presence of the PDMAEMA block at the surface, drastic morphology changes, and improved adhesion properties after immersion in water. Finally, underwater bioadhesion tests show that mussels adhere only to block copolymer-filled coatings and after immersion in water, i.e., when the PDMAEMA blocks have been brought to the coating surface. These observations highlight the significant role of hydrophilic groups in the surface modification of silicone coatings.

Macroporous three-dimensional PDMS scaffolds for extrahepatic islet transplantation

Clinical islet transplantation has demonstrated success in treating type 1 diabetes. A current limitation is the intrahepatic portal vein transplant site, which is prone to mechanical stress and inflammation. Transplantation of pancreatic islets into alternative sites is preferable, but challenging, as it may require a three-dimensional vehicle to confer mechanical protection and to confine islets to a well-defined, retrievable space where islet neovascularization can occur. We have fabricated biostable, macroporous scaffolds from poly(dimethylsiloxane) (PDMS) and investigated islet retention and distribution, metabolic function, and glucose-dependent insulin secretion within these scaffolds. Islets from multiple sources, including rodents, nonhuman primates, and humans, were tested in vitro. We observed high islet retention and distribution within PDMS scaffolds, with retention of small islets (< 100 µm) improved through the postloading addition of fibrin gel. Islets loaded within PDMS scaffolds exhibited viability and function comparable to standard culture conditions when incubated under normal oxygen tensions, but displayed improved viability compared to standard two-dimensional culture controls under low oxygen tensions. In vivo efficacy of scaffolds to support islet grafts was evaluated after transplantation in the omental pouch of chemically induced diabetic syngeneic rats, which promptly achieved normoglycemia. Collectively, these results are promising in that they indicate the potential for transplanting islets into a clinically relevant, extrahepatic site that provides spatial distribution of islets as well as intradevice vascularization.