A new water absorbable mechanical Epidermal skin equivalent: The combination of hydrophobic PDMS and hydrophilic PVA hydrogel

In vitro 3D skin culture and its sustainability in toxicology: a narrative review

In current toxicological research, 2D cell cultures and animal models are well- accepted and commonly employed methods. However, these approaches have many drawbacks and are distant from the actual environment in human. To embrace this, great efforts have been made to provide alternative methods for non-animal skin models in toxicology studies with the need for more mechanistically informative methods. This review focuses on the current state of knowledge regarding the in vitro 3D skin model methods, with different functional states that correspond to the sustainability in the field of toxicology testing. We discuss existing toxicology testing methods using in vitro 3D skin models which provide a better understanding of the testing requirements that are needed. The challenges and future landscape in using the in vitro 3D skin models in toxicology testing are also discussed. We are confident that the in vitro 3D skin models application may become an important tool in toxicology in the context of risk assessment.

Soft Materials by Design: Unconventional Polymer Networks Give Extreme Properties

Hydrogels are polymer networks infiltrated with water. Many biological hydrogels in animal bodies such as muscles, heart valves, cartilages, and tendons possess extreme mechanical properties including being extremely tough, strong, resilient, adhesive, and fatigue-resistant. These mechanical properties are also critical for hydrogels' diverse applications ranging from drug delivery, tissue engineering, medical implants, wound dressings, and contact lenses to sensors, actuators, electronic devices, optical devices, batteries, water harvesters, and soft robots. Whereas numerous hydrogels have been developed over the last few decades, a set of general principles that can rationally guide the design of hydrogels using different materials and fabrication methods for various applications remain a central need in the field of soft materials. This review is aimed at synergistically reporting: (i) general design principles for hydrogels to achieve extreme mechanical and physical properties, (ii) implementation strategies for the design principles using unconventional polymer networks, and (iii) future directions for the orthogonal design of hydrogels to achieve multiple combined mechanical, physical, chemical, and biological properties. Because these design principles and implementation strategies are based on generic polymer networks, they are also applicable to other soft materials including elastomers and organogels. Overall, the review will not only provide comprehensive and systematic guidelines on the rational design of soft materials, but also provoke interdisciplinary discussions on a fundamental question: why does nature select soft materials with unconventional polymer networks to constitute the major parts of animal bodies?

Probing gels and emulsions using large-amplitude oscillatory shear and frictional studies with soft substrate skin surrogates

Water swellable crosslinked polymers are widely used in oil-in-water emulsions for the healthcare and cosmetic industries due to their thickening properties. In this study, we investigate the rheological and lubrication behavior of a microgel-forming polymer, a lightly-crosslinked hydrophobically modified polyacrylic acid (HMPAA), in an aqueous medium and in an emulsion. Hydrogenated phosphatidylcholine, a class of phospholipids, is used as a surfactant in the emulsions composed of different oil content. Rheological behavior is probed both in the linear and non-linear regimes using small strain amplitude and large amplitude oscillatory shear (LAOS) experiments, respectively. We observe all systems to exhibit gel-like behavior with the elastic modulus (G') dominating and being frequency independent. Lissajous-Bowditch plots and nonlinear parameters obtained under large deformation show that the emulsions can resist greater deformations with smaller increase in the viscous dissipation when compared to a HMPAA gel. For tribology experiments, friction curves in a range of entrainment speeds are examined using substrates to mimic the skin surface (PDMS and Bioskin®). The role of polymer hydrophobicity on the different substrates are also explored by comparing the behavior of HMPAA to that of its hydrophilic analog, a polyacrylic acid highly crosslinked. We find the friction coefficient to be dependent on the hydrophobicity of the substrate and the polymer as well as the substrate roughness. These results taken together provide insights in the formulation of skincare products with efficient lubrication properties for different skin characteristics.

Guidelines for designing a realistic peripheral venous catheter insertion simulator: A literature review

A literature review was conducted to develop more realistic medical simulators that better prepare aspiring health professionals to perform a medical procedure in vivo. Thus, this review proposes an approach that might assist researchers design improved medical simulators, particularly new materials that would enhance the sensation of touch for skin substitutes. By targeting the current needs in the field of simulation learning, we concluded that peripheral venous catheter insertion simulators lack realistic haptic feedback. Enhanced peripheral venous catheter insertion simulators will accelerate the mastery of the medical procedure, thus decreasing the number of failures in patients and costs related to this procedure.

Evaluation of PVA/dextran/chitosan hydrogel for wound dressing

Developing a multiple functional wound dressing suitable for different stages of wound healing is important for patients with special wound such as burn or decubital ulcers. In this study, poly (vinyl alcohol) (PVA), dextran, and chitosan are integrated to produce ideal wound dressing where glutaraldehyde (GA) is used as the cross-linker. The result demonstrated that 6% PVA hydrogel with 0.25% chitosan was found to provide antimicrobial ability. The PVA/chitosan hydrogel combined with 4% dextran utilizing GA cross-linking also presents the high cell proliferation ability, which suggests that the hydrogel is potential as a wound dressing. In the following physical analyses, the addition of chitosan and dextran appeared to promote the thermostability, mechanical properties, water retention, and moisturizing ability in the PVA hydrogel. In conclusion, the PVA/chitosan/dextran hydrogel has promising potential such as high water content, antimicrobial property, and well cell proliferation, which can be applied to wound healing application.

The development of an artificial skin model and its frictional interaction with wound dressings

Human skin interacts with various materials in our daily life. The interaction between human skin and contacting materials is very important for the development of skin contacting products. Owing to the ethic and different testing results because of the using of in vivo or ex vivo skin, it is important to develop an artificial skin model (ASM) for the study. Therefore, an ASM mimicking the deformation and friction behavior of in vivo human skin was designed based on the evaluation of in vivo human skin behavior, and its frictional interaction with wound dressings was studied. The ASM was prepared by the combination of hydrophilic network carboxyl chitosan (CC) and hydrophobic network polydimethylsiloxane (PDMS). The influence of ingredient ratio, including PDMS/CC and curing agent/PDMS ratio, on the mechanical property of ASM was determined firstly. By adjusting the curing agent/PDMS ratio, the water absorption swelling rate (WASR) of ASM could be controlled to mimic different hydration status of human skin. With the changing of ingredient ratio and hydration level, the elastic modulus and viscoelasticity of ASM can be tailored to be similar to that of in vivo human skin. When the PDMS/CC ratio was 7:3, and PDMS/curing agent ratio was smaller than 1:30, the elastic modulus of ASM was in the range of in vivo inner forearm, and with the increasing of indentation depth, the elastic modulus decreased. Based on the ASM, the frictional interaction between skin/wound dressing/mattress was studied. It was found that although the friction using ASM was slightly higher than that using in vivo inner forearm, but the friction decreasing trend was the same for different kinds of wound dressings. In addition, the friction tested with ASM was less fluctuation, more reliable and reproducible than that tested with in vivo skin, indicating that the ASM was suitable to be used for the studying of frictional interaction between skin and product, such as wound dressings.

A highly printable and biocompatible hydrogel composite for direct printing of soft and perfusable vasculature-like structures

Vascularization is one major obstacle in bioprinting and tissue engineering. In order to create thick tissues or organs that can function like original body parts, the presence of a perfusable vascular system is essential. However, it is challenging to bioprint a hydrogel-based three-dimensional vasculature-like structure in a single step. In this paper, we report a new hydrogel-based composite that offers impressive printability, shape integrity, and biocompatibility for 3D bioprinting of a perfusable complex vasculature-like structure. The hydrogel composite can be used on a non-liquid platform and is printable at human body temperature. Moreover, the hydrogel composite supports both cell proliferation and cell differentiation. Our results represent a potentially new vascularization strategy for 3D bioprinting and tissue engineering.

Preparation of polyurethane/polyvinyl alcohol hydrogel and its performance enhancement via compositing with silver particles

Polyurethane/polyvinyl alcohol/silver composite hydrogel, showing enhanced mechanical and antibacterial properties, was fabricated.

A tribo-mechanical analysis of PVA-based building-blocks for implementation in a 2-layered skin model

Poly(vinyl) alcohol hydrogel (PVA) is a well-known polymer widely used in the medical field due to its biocompatibility properties and easy manufacturing. In this work, the tribo-mechanical properties of PVA-based blocks are studied to evaluate their suitability as a part of a structure simulating the length scale dependence of human skin. Thus, blocks of pure PVA and PVA mixed with Cellulose (PVA-Cel) were synthesised via freezing/thawing cycles and their mechanical properties were determined by Dynamic Mechanical Analysis (DMA) and creep tests. The dynamic tests addressed to elastic moduli between 38 and 50kPa for the PVA and PVA-Cel, respectively. The fitting of the creep compliance tests in the SLS model confirmed the viscoelastic behaviour of the samples with retardation times of 23 and 16 seconds for the PVA and PVA-Cel, respectively. Micro indentation tests were also achieved and the results indicated elastic moduli in the same range of the dynamic tests. Specifically, values between 45-55 and 56-81kPa were obtained for the PVA and PVA-Cel samples, respectively. The tribological results indicated values of 0.55 at low forces for the PVA decreasing to 0.13 at higher forces. The PVA-Cel blocks showed lower friction even at low forces with values between 0.2 and 0.07. The implementation of these building blocks in the design of a 2-layered skin model (2LSM) is also presented in this work. The 2LSM was stamped with four different textures and their surface properties were evaluated. The hydration of the 2LSM was also evaluated with a corneometer and the results indicated a gradient of hydration comparable to the human skin.