Soft Silicone Research Articles

ESPRESS.0: Eustachian Tube-Inspired Tactile Sensor Exploiting Pneumatics for Range Extension and SenSitivity Tuning.

Optimising the sensitivity of a tactile sensor to a specific range of stimuli magnitude usually compromises the sensor's widespread usage. This paper presents a novel soft tactile sensor capable of dynamically tuning its stiffness for enhanced sensitivity across a range of applied forces, taking inspiration from the Eustachian tube in the mammalian ear. The sensor exploits an adjustable pneumatic back pressure to control the effective stiffness of its 20 mm diameter elastomer interface. An internally translocated fluid is coupled to the membrane and optically tracked to measure physical interactions at the interface. The sensor can be actuated by pneumatic pressure to dynamically adjust its stiffness. It is demonstrated to detect forces as small as 0.012 N, and to be sensitive to a difference of 0.006 N in the force range of 35 to 40 N. The sensor is demonstrated to be capable of detecting tactile cues on the surface of objects in the sub-millimetre scale. It is able to adapt its compliance to increase its ability for distinguishing between stimuli with similar stiffnesses (0.181 N/mm difference) over a large range (0.1 to 1.1 N/mm) from only a 0.6 mm deep palpation. The sensor is intended to interact comfortably with skin, and the feasibility of its use in palpating tissue in search of hard inclusions is demonstrated by locating and estimating the size of a synthetic hard node embedded 20 mm deep in a soft silicone sample. The results suggest that the sensor is a good candidate for tactile tasks involving unpredictable or unknown stimuli.

The Sandwich Technique for Quick and Efficient Application of Negative Pressure Wound Therapy to the Feet and Hands: A Case Report

Introduction. NPWT is a surgical dressing that combines polyurethane foam with the subsequent application of continuous or intermittent negative pressure. NPWT facilitates granulation tissue production by macrostrain, microstrain and, if desired, fluid instillation. Sealing the polyurethane foam over the wound bed is achieved using acrylic drapes; however, this can be difficult to use in some anatomic sites. Failure to achieve an effective seal can necessitate additional supplies, which has led to increased innovation in developing a more effective NPWT seal over the target wound bed. Obtaining an effective pressure seal on the feet or hands can be difficult because these anatomic sites have distinct curvature for each digit, with multiple interdigital web spaces and independent mobility. In this case report, the authors propose a technique to apply either an acrylic drape or combination acrylic and soft silicone drape utilizing the “sandwich technique” to seal NPWT foam quickly and efficiently to the feet or hands.

Kinematic Modeling of a Twisted-String Actuated Soft Robotic Finger as Part of an Anthropomorphic Gripper

Twisted string actuators (TSAs) generate high tendon-based (muscle-like) linear actuation and forces and have wide operational bandwidth. For these properties, TSAs are well-suited for advanced robotic and mechatronic applications, though their inclusion in soft robots has been limited. We recently employed TSAs to drive an anthropomorphic soft gripper which successfully demonstrated dexterous grasping and manipulation. While the gripper showed superior qualitative performance, the lack of modeling and control strategies limited its realization in a fully autonomous system that could generalize well to new grasping behaviors. As a first step toward this objective, this paper presents modeling strategies for a monolithic soft silicone finger driven by a TSA. A physics-based kinematic model is developed to predict the bending and velocity kinematics of the finger as a function of the TSA's twisting angle. An average error of 2.06° was obtained for the kinematic bending model across different actuation behaviors and an average error of 2.95°/s was measured for the angular velocity model.

Retracted: Application of Self-Adhesive Soft Silicone Common Foam Dressing in Reducing Intraoperative Pressure Ulcers in Elderly ICU Patients.

[This retracts the article DOI: 10.1155/2021/4482201.].

Effects of soft silicone polyurethane foam dressings for the prevention of pressure ulcers in high-risk patients: Factors associated with pressure injury

Effects of soft silicone polyurethane foam dressings for the prevention of pressure ulcers in high-risk patients: Factors associated with pressure injury

Soft and Rigid Integrated Durable Coating for Large-Scale Deicing

Soft silicone has been widely used for anti-icing coating, but the ice adhesion strength is usually scaled with the iced area at a relatively large thickness. On the other hand, a thin rigid poly(vinyl chloride) (PVC) film could be independent of the iced area and was named a low-interfacial-toughness material. Thus, a soft and rigid integrated (SRI) coating was prepared by doping PVC particles into a silicone matrix here. The introduction of PVC particles not only served as phase II to accelerate the stress concentration but also favored the formation of a wrinkle structure. After further introducing plasticizers, this SRI coating not only has a very low ice adhesion strength at a low iced length but also tends to a limit value irrespective of the iced length, which further leads to excellent large-area deicing behavior. Furthermore, the SRI coating demonstrated outstanding chemical stability, mechanical robustness, and on-field repairability.

Delayed Light‐Driven Actuations after Light Stopping

AbstractThe manipulation of light actuators benefits from the advantages of the immediacy of light response. However, the immediacy of light response leads to indispensability of light irradiation in the actuating processes. The actuation after light irradiation stops, i.e., a delayed actuation can execute actuation functions, which is free of direct light irradiation. Here are proposed several delayed actuation systems after light irradiation based on intrinsic delay properties of shape memory alloy materials and additional regulation of soft silicone layers. Continuous motions after light stopping have been realized such as linear and rotating motions. Moreover, the delayed actuation relatively separates the irradiation and actuation, where an operational window period is allowed for task execution in light‐preventing scenarios. The delay principle of light actuation overcomes the limitation of immediate response of light manipulation, and is also applicable to more materials and systems.

Metallic intraocular foreign body removal assisted through the extrusion line

AbstractPurpose: To describe an alternative vitreoretinal surgical manoeuvre, to remove metallic intraocular foreign bodies.Methods: Two patients, at different time lines, underwent vitrectomy to remove a metallic intraocular foreign body (IOFB). A 3‐port vitrectomy was performed, a 23‐G constellation vitrectomy equipment was used in both procedures, careful core vitrectomy was first done, vitreous adhesions and vitreous detachment was carefully done, retina was partially detached at the IOFB location, vitreous adhesions were cut and released gently not to increase the retinal detachment. Liquid prefluorocarbon was placed on the macula. As the vitreous adherences were cut, the IOFB was free from all potential tractional forces, the soft silicone tip cannula was held on to its surface, and at maximal vacuum aspiration, the IOFB was brought up to the anterior chamber, switching the light pipe for forceps in the other hand, and removed out of the eye. A complete as possible vitrectomy was performed, intraocular laser around the retinal brakes was performed, an intraocular lens was placed in the ciliary sulcus with the optic within the anterior capsule, and silicone oil was used as tamponade.Results: No signs of intraocular inflammation were recorded postoperatively. Intraocular silicone oil removal was done at the third post‐operative month in both cases, retina remained attached through follow up, both patients had over 9 months follow‐up visits, visual acuity improved from initial presentation, and also improved after the silicone oil tamponade removal.Conclusions: Active aspiration through the soft silicon tip cannula can be used to reach, and assist removal of metallic intraocular foreign bodies, being this manoeuvre safe, reproducible, possibly time‐saving, and also it could potentially avoid the risk of IOFB mobilization, avoiding further damage to the retina.

Extremely Soft, Stretchable, and Self-Adhesive Silicone Conductive Elastomer Composites Enabled by a Molecular Lubricating Effect

Softness, adhesion, stretchability, and fast recovery from large deformations are essential properties for conductive elastomers that play an important role in the development of high-performance soft electronics. However, it remains an ongoing challenge to obtain conductive elastomers that combine these properties. We have fabricated a super soft (Young's modulus 2.3-12 kPa), highly stretchable (up to 1500% strain), and underwater adhesive silicone conductive elastomer composite (SF-C-PDMS) by incorporating dimethyl silicone oil as a lubricating agent in a cross-linked molecular network. The resultant SF-C-PDMS not only exhibits superior softness but also can readily recover after a strain of 1000%. The initial resistance only decreases by 8% after 100000 cycles of tensile fatigue test (100% strain, 0.5 Hz, 15 mm/s). This multifunctional silicone conductive elastomer composite is obtained in a one-step preparation at room temperature using commercially available materials. Moreover, we illustrate the capabilities of this composite in motion sensing.

Investigation of High-Resolution Distributed Fiber Sensing System Embedded in Flexible Silicone Carpet for 2D Pressure Mapping.

Fiber-optic sensors are a powerful tool to investigate physical properties like temperature, strain, and pressure. Such properties make these sensors interesting for many applications including biomedical applications. Fiber sensors are also a great platform for distributed sensing by using the principles of optical frequency domain reflectometry. Distributed sensing is becoming more and more used to achieve high-resolution measurements and to map physical properties of biomaterials at small scale, thus obtaining 2D and 3D mapping of a particular area of interest. This work aims at building and investigating a 2D sensing carpet based on a distributed fiber sensing technique, to map local pressure applied to the carpet. The two-dimensional mapping is obtained by embedding a single-mode optical fiber inside a soft silicone carpet. The fiber has been bent and arranged in a specific configuration characterized by several parallel lines. Different fiber fixation methods have been investigated by means of a comparative analysis to perform better characterization and to achieve a more precise response of the carpet. The best pressure sensitivity coefficient (0.373 pm/kPa or considering our setup 1.165 nm/kg) was detected when the fiber was fully embedded inside the silicone carpet. This paper demonstrates the possibility of mapping a 2D distributed pressure over a surface with a resolution of 2 mm by 2 mm. The surface of investigation is 2 cm by 6 cm, containing 310 sensing points. The sensing carpet has been validated selecting several preferential positions, by testing the consistency of the results over different portions of the carpet.

Growth-Induced Wrinkles and Dotlike Patterns of a Swollen Fluoroalkylated Thin Film by the Reaction of Surface-Attached Polymethylhydrosiloxane.

The design of hydrophobic surfaces requires a material which has a low solid surface tension and a simple fabrication process for anchoring and controlling the surface morphology. A generic method for the spontaneous formation of robust instability patterns is proposed through the hydrosilylation of a fluoroalkene bearing dangling chains, Rf = C6F13(CH2)3-, with a soft polymethylhydrosiloxane (PMHS) spin-coated gel polymer (0.8 μm thick) using Karstedt catalyst. These patterns were easily formed by an irreversible swelling reaction due to the attachment of a layer to various substrates. The buckling instability was created by two different approaches for a gel layer bound to a rigid silicon wafer substrate (A) and to a soft nonswelling silicone elastomer foundation (B). The observations of grafted Rf-PMHS films in the swollen state by microscopy revealed two distinct permanent patterns on various substrates: dotlike of wavelength λ = 0.4-0.7 μm (A) or wrinkle of wavelength λ = 4-7 μm (B). The elastic moduli ratios of film/substrate were determined using PeakForce quantitative nanomechanical mapping. The characteristic wavelengths (λ) of the patterns for systems A and B were quantitatively estimated in relation to the thickness of the top layer. A diversity of wrinkle morphologies can be achieved by grafting different side chains on pristine PMHS films. The water contact angle (WCA) hysteresis of fluorinated chain (Rf) was enhanced upon roughening the surfaces, giving highly hydrophobic surface properties for water with static/hysteresis WCAs of 136°/74° in the resulting wrinkle (B) and 119°/41° in the dotlike of lower roughness (A). The hydrophobic properties of grafted films on A with various mixtures of hexyl/fluoroalkyl chains were characterized by static CA: WCA 104-119°, ethylene glycol CA 80-96°, and n-hexadecane CA 17-61°. A very low surface energy of 15 mN/m for Rf-PMHS was found on the smoother dotlike pattern.

Pneumatic soft phononic crystals with tunable band gap

Tuning the band gap by mechanically generating deformation of soft phononic crystals provides an effective means to manipulate the propagation of acoustic waves. In this paper, a pneumatic soft phononic crystal is computationally designed to realize tunable band gap. It consists of a line of soft inflatable silicone cylinders surrounded by air. In detail, there is no band gap in the soft phononic crystal when it is unpressurized. By applying the air pressure, the scatterer in the soft phononic crystal is deformed, then a new reversible band gap appears in the phononic crystal. By adjusting the air pressure, the opening and closing of the band gap can be controlled. In addition, the width of the band gap can be tuned by the application of air pressure. We obtained the mechanical parameters of the rubber-like material from the experimental data. On this basis, the variation of the band gap of phononic crystals with applied different air pressures to the soft scatterer is investigated numerically. The effect of scatterer geometry on the band gap evolution of phononic crystals is also parametrically studied. Compared with traditional mechanical deformation means, such as tension and compression, the pneumatic manipulation is low-cost, fast in response and easy to integrate. This work introduces a feasible design of tunable soft phononic crystals.

High-Sensitive Wearable Strain Sensors Based on the Carbon Nanotubes@Porous Soft Silicone Elastomer with Excellent Stretchability, Durability, and Biocompatibility.

Wearable strain sensors can transfer human physical motions into digital features and connect the real world to the virtual world. However, there is still a huge challenge to prepare breathable strain sensors with good sensitivity, stretchability, softness, durability, and biocompatibility, simultaneously. Herein, we employ the soft silicone elastomer as a highly stretchable substrate and propose a new strain sensor based on the carbon nanotubes@porous soft silicone elastomer (CNTs@PSSE) by salt-template-assisted and dip-coating methods. The CNTs (conductive fillers) are firmly embedded in the PSSE. The obtained sensors exhibit excellent sensitivity up to 2845.1 and a large sensing strain range of 186%. Notably, the CNTs@PSSE sensors also possess strong robustness, which can resist ultrasonic deterioration and carry out more than 10,000 high-frequency stretch-relax cycles in the presence of an obvious notch caused by the scissor. Moreover, the excellent biocompatibility indicates that the sensors can be safely attached to human skin for precisely detecting full-range human motions and being configured on smart wireless gloves for synchronous control of the bionic hand robot.

Enhancing iPSC-CM Maturation Using a Matrigel-Coated Micropatterned PDMS Substrate.

Cardiac myocytes isolated from adult heart tissue have a rod-like shape with highly organized intracellular structures. Cardiomyocytes derived from human pluripotent stem cells (iPSC-CMs), on the other hand, exhibit disorganized structure and contractile mechanics, reflecting their pronounced immaturity. These characteristics hamper research using iPSC-CMs. The protocol described here enhances iPSC-CM maturity and function by controlling the cellular shape and environment of the cultured cells. Microstructured silicone membranes function as a cell culture substrate that promotes cellular alignment. iPSC-CMs cultured on micropatterned membranes display an in-vivo-like rod-shaped morphology. This physiological cellular morphology along with the soft biocompatible silicone substrate, which has similar stiffness to the native cardiac matrix, promotes maturation of contractile function, calcium handling, and electrophysiology. Incorporating this technique for enhanced iPSC-CM maturation will help bridge the gap between animal models and clinical care, and ultimately improve personalized medicine for cardiovascular diseases. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Cardiomyocyte differentiation of iPSCs Basic Protocol 2: Purification of differentiated iPSC-CMs using MACS negative selection Basic Protocol 3: Micropatterning on PDMS.

A multi-module soft robotic arm with soft actuator for minimally invasive surgery.

Compared to traditional rigid robotic arms, soft robotic arms are flexible, environmentally adaptable and biocompatible. Recently, most minimally invasive cardiac procedures still rely on traditional rigid surgical tools. However, rigid tools lack sufficient bending angles, which are high-risk in terms of contact with tissues and organs. A soft robotic arm with multiple degrees of freedom was designed to repair atrial septal defects in cardiac surgery. The developed multi-module soft robotic arm consists of four different units, including a bending unit, a turning unit, a stretching unit and gripper units. The three movement units can reach the specified position, and the gripper units can hold a surgical tool stably, such as a suture needle in cardiac surgery. A cardiac surgery to repair an atrial septal defect has been completed, validating the reliability and functionality of the developed multi-module soft robotic arm. The multi-module flexible soft robotic arm for minimally invasive surgery proposed in this paper can reach the designated surgical area during surgery to repair Atrial Septal Defects. Meanwhile, the design of the actuator of the robot arm was used a completely soft silicone material replacing the rigid material, which releases the contact trauma of the organs during the surgery.

Wireless Flexible Magnetic Tactile Sensor with Super-Resolution in Large-Areas.

Tactile recognition is among the basic survival skills of human beings, and advances in tactile sensor technology have been adopted in various fields, bringing benefits such as outstanding performance in manipulating objects and general human-robot interactions. However, promoting enhanced perception of the existing tactile sensors is limited by their sensor array arrangement and wire-connected design. Here we present a wireless flexible magnetic tactile sensor (FMTS) consisting of a multidirection magnetized flexible film (perception module) and a contactless Hall sensor (signal receiving module). The flexible magnetic film is composed of NdFeB microparticles and soft silicone elastomer microparticles, and it transfers the unambiguous transduction of external force position and magnitude into magnetic signals. Benefiting from the specific magnetization arrangement and clustering algorithm, only one Hall sensor is needed in FMTS to perceive the magnitude and position of the contact spot simultaneously with super-resolution (2.1 mm average error) on a large area (3600 mm2), and the effective working distance is also greatly extended (∼30 mm), allowing for the full softness and adaptability to diverse conditions. We anticipate that this design will promote the development of soft tactile sensors and their integration into human-robot interaction and humanoid robot perception.

One‐Step Synthesis of Dynamically Shaped Stiff Nanorods Using Soft Silicone Materials to Control Water Repulsion and Collection (Small 40/2022)

Dynamically Shaped Stiff Nanorods In article number 2203820, Stefan Seeger and co-workers propose a dynamic droplet assisted growth and shaping (d-DAGS) synthesis strategy for the one-step synthesis and in-situ control of the shape of nanostructures. The obtained bamboo-shaped silicone nanorods exhibit highly-regular and tunable structure with ultra-high aspect ratio, present robust mechanical stiffness and chemical durability, and can be used for various practical applications.

Penile lenghthening original technique using a pubo-cavernous spacer. Long term results from a series of over 200 patients.

We report our long experience in the surgical treatment of patients requesting penile lengthening by suspensory ligament release and placement of a custom-made soft silicone pubo-cavernous spacer. The aim was to show that with this surgical technique the results obtained are maintained over time. It is crucial to achieve postoperative satisfaction of these patients who show fragility and self-esteem problems. From 1999 to 2020, we treated 245 patients with congenital or acquired penile brevity. We carefully analysed the preoperative and postoperative (at 6, 12, 24 and 48 months) penile size of the patients to evaluate whether this technique could allow the long-term maintenance of aesthetic results. We also assessed preoperative erectile function and we focused on the psychological aspects to avoid surgery in patients with dysmorphophobia. This original technique involves the section of the suspensory ligament and the implantation of a silicone spacer between the pubic symphysis and the corpora cavernosa. This spacer is conformed to the patient anatomy and maintains the relationship between the anatomical structures unchanged over time. Sexual self-esteem and patient satisfaction were assessed with the APPSSI questionnaire. The mean increase in penile length was about 2.5 cm in flaccid state and 1.9 cm in stretched state. There were no injuries of the neurovascular bundle or urethra, and no erectile dysfunction was noted. These results persisted at 6, 12, 24 and 48 months without significant differences. Over 80% of patients stated that they were completely satisfied with the results obtained. This satisfaction remained stable along follow up. The section of the suspensory ligament and the implant of the soft silicone spacer provide real penis elongation with satisfactory results that persist over time. This technique avoids the frequent complication of short-term shortening due to the scar adhesions of the edges of the dissected ligament. The high aesthetic satisfaction of patients is stable at controls at 6, 12, 24 and 48 months.

Study on soft hot embossing process for making microstructures in a cyclo-olefin polymeric (COP) film

Thermoplastic polymers are the primary materials for fabricating commercial microfluidic devices. Despite many excellent properties, the low thermal conductivity is a common limiting factor in speeding up temperature-dependent biological processes, particularly for polymerase chain reactions. There is a need to develop a fabrication process to create thin-film microfluidic devices that can have a small thermal mass and a short microchannel-to-surface distance. This type of device requires the depth of micropatterns to be very close to the film thickness, which can encounter serious fractures during the demolding process. To overcome this challenge, we develop a soft hot embossing process to create micropatterns in a 188 µm thick cyclo-olefin polymeric (COP) film with a high embossing-depth to film-thickness ratio. The advantage of using a soft master is it can easily be peeled off from the molded film without causing a fracture from micropatterns. Polydimethylsiloxane (PDMS) is used as the soft silicone master, and four different 110 µm high micropatterns are studied, including ribs, grooves, and circular columns and cavities. PDMS masters for creating a 110 µm deep microchannel with different arrays of 70 µm deep microwells are also investigated. The heights of these one-layer and two-layer PDMS masters are 58.8% and 95.7% of the film thickness. Experimental findings show that less than 3% height variation can be achieved using a single-layer PDMS master with a low aspect ratio. For the two-layer micropatterns, it was found that a dense array with a smaller gap between microwells can have a better pattern transfer. In summary, this study demonstrates the feasibility of using a soft master to create deep or tall micropatterns in a COP film. The possibility of using a soft hot embossing process to create micropatterns for thin-film microfluidic devices is verified.

Soft Molds with Micro-Machined Internal Skeletons Improve Robustness of Flapping-Wing Robots.

Mobile millimeter and centimeter scale robots often use smart composite manufacturing (SCM) for the construction of body components and mechanisms. The fabrication of SCM mechanisms requires laser machining and laminating flexible, adhesive, and structural materials into small-scale hinges, transmissions, and, ultimately, wings or legs. However, a fundamental limitation of SCM components is the plastic deformation and failure of flexures. In this work, we demonstrate that encasing SCM components in a soft silicone mold dramatically improves the durability of SCM flexure hinges and provides robustness to SCM components. We demonstrate this advance in the design of a flapping-wing robot that uses an underactuated compliant transmission fabricated with an inner SCM skeleton and exterior silicone mold. The transmission design is optimized to achieve desired wingstroke requirements and to allow for independent motion of each wing. We validate these design choices in bench-top tests, measuring transmission compliance, kinematics, and fatigue. We integrate the transmission with laminate wings and two types of actuation, demonstrating elastic energy exchange and limited lift-off capabilities. Lastly, we tested collision mitigation through flapping-wing experiments that obstructed the motion of a wing. These experiments demonstrate that an underactuated compliant transmission can provide resilience and robustness to flapping-wing robots.