Custom 3D Printable Silicones with Tunable Stiffness

Electrostatic Dissipation in 3D-Printable Silicone

In this report, we describe the incorporation of single-walled carbon nanotubes (CNTs) into 3D printable siloxane elastomers for electrostatic dissipation. The composite was characterized, focusing on how rheological and mechanical properties of the siloxane are affected at various CNT loading levels. Electrical properties were also characterized to develop materials with effective electrostatic dissipation. We demonstrate that low loadings (<1 wt %) of CNTs can be sufficiently dispersed into silicone resins that can be 3D printed, and the resulting material shows a significant improvement in electrostatic dissipation through the reduction in electrical resistivity with minimal effect on its mechanical properties.

Recent Advances in Sources of Bio-Inspiration and Materials for Robotics and Actuators

Bionic robotics and actuators have made dramatic advancements in structural design, material preparation, and application owing to the richness of nature and innovative material design. Appropriate and ingenious sources of bio-inspiration can stimulate a large number of different bionic systems. After millennia of survival and evolutionary exploration, the mere existence of life confirms that nature is constantly moving in an evolutionary direction of optimization and improvement. To this end, bio-inspired robots and actuators can be constructed for the completion of a variety of artificial design instructions and requirements. In this article, the advances in bio-inspired materials for robotics and actuators with the sources of bio-inspiration are reviewed. The specific sources of inspiration in bionic systems and corresponding bio-inspired applications are summarized first. Then the basic functions of materials in bio-inspired robots and actuators is discussed. Moreover, a principle of matching biomaterials is creatively suggested. Furthermore, the implementation of biological information extraction is discussed, and the preparation methods of bionic materials are reclassified. Finally, the challenges and potential opportunities involved in finding sources of bio-inspiration and materials for robotics and actuators in the future is discussed.

3D Printing of High Viscosity Reinforced Silicone Elastomers

Recent advances in additive manufacturing, specifically direct ink writing (DIW) and ink-jetting, have enabled the production of elastomeric silicone parts with deterministic control over the structure, shape, and mechanical properties. These new technologies offer rapid prototyping advantages and find applications in various fields, including biomedical devices, prosthetics, metamaterials, and soft robotics. Stereolithography (SLA) is a complementary approach with the ability to print with finer features and potentially higher throughput. However, all high-performance silicone elastomers are composites of polysiloxane networks reinforced with particulate filler, and consequently, silicone resins tend to have high viscosities (gel- or paste-like), which complicates or completely inhibits the layer-by-layer recoating process central to most SLA technologies. Herein, the design and build of a digital light projection SLA printer suitable for handling high-viscosity resins is demonstrated. Further, a series of UV-curable silicone resins with thiol-ene crosslinking and reinforced by a combination of fumed silica and MQ resins are also described. The resulting silicone elastomers are shown to have tunable mechanical properties, with 100–350% elongation and ultimate tensile strength from 1 to 2.5 MPa. Three-dimensional printed features of 0.4 mm were achieved, and complexity is demonstrated by octet-truss lattices that display negative stiffness.

3D Printing of a Polydimethylsiloxane/Polytetrafluoroethylene Composite Elastomer and its Application in a Triboelectric Nanogenerator

Silicone rubber elastomers are broadly used in various fields, where the three-dimensional (3D) printing of silicone rubber elastomers is important for the free construction of complex structures. Herein, a series of polydimethylsiloxane/polytetrafluoroethylene composite inks for direct-ink-writing 3D printing are developed. The inks are prepared by directly mixing a silicone rubber liquid precursor with polytetrafluoroethylene micropowder. The polytetrafluoroethylene micropowder serves as a thixotropic agent to regulate the rheological properties of the polydimethylsiloxane precursor to fulfill the requirement of 3D printing and endow the composite material with high electron affinity. The printed polydimethylsiloxane/polytetrafluoroethylene composite elastomer exhibits excellent elasticity and cyclic stability. A high-performance triboelectric nanogenerator is constructed with the 3D-printed polydimethylsiloxane/polytetrafluoroethylene composite as the triboelectric layer and elastic structure. This work establishes a new method of 3D printing polydimethylsiloxane-based elastomers and thus provides a new technique for constructing complex structures in flexible devices.

Extrusion 3D Printing of Polymeric Materials with Advanced Properties

3D printing is a rapidly growing technology that has an enormous potential to impact a wide range of industries such as engineering, art, education, medicine, and aerospace. The flexibility in design provided by this technique offers many opportunities for manufacturing sophisticated 3D devices. The most widely utilized method is an extrusion-based solid-freeform fabrication approach, which is an extremely attractive additive manufacturing technology in both academic and industrial research communities. This method is versatile, with the ability to print a range of dimensions, multimaterial, and multifunctional 3D structures. It is also a very affordable technique in prototyping. However, the lack of variety in printable polymers with advanced material properties becomes the main bottleneck in further development of this technology. Herein, a comprehensive review is provided, focusing on material design strategies to achieve or enhance the 3D printability of a range of polymers including thermoplastics, thermosets, hydrogels, and other polymers by extrusion techniques. Moreover, diverse advanced properties exhibited by such printed polymers, such as mechanical strength, conductance, self-healing, as well as other integrated properties are highlighted. Lastly, the stimuli responsiveness of the 3D printed polymeric materials including shape morphing, degradability, and color changing is also discussed.

3D Printing for the Clinic: Examining Contemporary Polymeric Biomaterials and Their Clinical Utility

The advent of additive manufacturing offered the potential to revolutionize clinical medicine, particularly with patient-specific implants across a range of tissue types. However, to date, there are very few examples of polymers being used for additive processes in clinical settings. The state of the art with regards to 3D printable polymeric materials being exploited to produce novel clinically relevant implants is discussed here. We focus on the recent advances in the development of implantable, polymeric medical devices and tissue scaffolds without diverging extensively into bioprinting. By introducing the major 3D printing techniques along with current advancements in biomaterials, we hope to provide insight into how these fields may continue to advance while simultaneously reviewing the ongoing work in the field.

Digital dentistry: The new state of the art - Is it disruptive or destructive?

OBJECTIVE

Summarizing the new state of the art of digital dentistry, opens exploration of the type and extent of innovations and technological advances that have impacted - and improved - dentistry. The objective is to describe advances and innovations, the breadth of their impact, disruptions and advantages they produce, and opportunities created for material scientists.

METHODS

On-line data bases, web searches, and discussions with industry experts, clinicians, and dental researchers informed the content. Emphasis for inclusion was on most recent publications along with innovations presented at trade shows, in press releases, and discovered through discussions leading to web searches for new products.

RESULTS

Digital dentistry has caused disruption on many fronts, bringing new techniques, systems, and interactions that have improved dentistry. Innovation has spurred opportunities for material scientists' future research.

SIGNIFICANCE

With disruptions intrinsic in digital dentistry's new state of the art, patient experience has improved. More restoration options are available delivering longer lifetimes, and better esthetics. Fresh approaches are bringing greater efficiency and accuracy, capitalizing on the interest, capabilities, and skills of those involved. New ways for effective and efficient inter-professional and clinician-patient interactions have evolved. Data can be more efficiently mined for forensic and epidemiological uses. Students have fresh ways of learning. New, often unexpected, partnerships have formed bringing further disruption - and novel advantages. Yes, digital dentistry has been disruptive, but the abundance of positive outcomes argues strongly that it has not been destructive.

High Resolution Magic Angle Spinning (HRMAS) Pulse Field Gradient (PFG) NMR Diffusometry Studies of Swollen Polymers

In this chapter, the combination of high resolution magic angle spinning (HRMAS) NMR spectroscopy and pulse field gradient (PFG) NMR diffusometry techniques to study solvent transport in swollen polymers is presented. The MAS suppression of magnetic susceptibility differences that exist for liquids absorbed in heterogenous polymer materials is shown to provide significant improvements in the NMR spectral resolution, thereby allowing the use of PFG NMR diffusion experiments to probe multiple chemical environments simultaneously. Recent examples of using 1H HRMAS PFG NMR experiments to measure solvent diffusion in 3D-printed siloxane polymer composites are detailed, along with an example of characterizing diffusion in methanol fuel cell anion exchange polymer membranes. These results demonstrate the power of HRMAS PFG NMR diffusometry to obtain information for complex chemical mixtures absorbed in polymers.

Multimaterial 3D Printing of Highly Stretchable Silicone Elastomers

3D printing of silicone elastomers with the direct ink writing (DIW) process has demonstrated great potential in areas as diverse as flexible electronics, medical devices, and soft robotics. However, most of current silicones are not printable because of their low viscosity and long curing time. The lack of systematic research on materials, devices, and processes during printing makes it a huge challenge to apply the DIW process more deeply and widely. In this report, aiming at the dilemmas in materials, devices, and processes, we proposed a comprehensive guide for printing highly stretchable silicone. Specifically, to improve the printability of silicone elastomers, nanosilica was added as a rheology modifier without sacrificing any stretching ability. To effectively control print speed and accuracy, a theoretical model was built and verified. With this strategy, silicone elastomers with different mechanical properties can all be printed and can realize infinite time and high speed printing (>25 mm/s) while maintaining accuracy. Here, super-stretchable silicone that can be stretched to 2000% was printed for the first time, and complex structures can be printed with high quality. For further demonstration, prosthetic nose, data glove capable of detecting fingers' movement, and artificial muscle that can lift objects were printed directly. We believe that this work could provide a guide for further work using the DIW process to print soft matters in a wide range of application scenarios.

Mechanochromic Stretchable Electronics

Soft and stretchable electronics are promising for a variety of applications such as wearable electronics, human-machine interfaces, and soft robotics. These devices, which are often encased in elastomeric materials, maintain or adjust their functionality during deformation, but can fail catastrophically if extended too far. Here, we report new functional composites in which stretchable electronic properties are coupled to molecular mechanochromic function, enabling at-a-glance visual cues that inform user control. These properties are realized by covalently incorporating a spiropyran mechanophore within poly(dimethylsiloxane) to indicate with a visible color change that a strain threshold has been reached. The resulting colorimetric elastomers can be molded and patterned so that, for example, the word "STOP" appears when a critical strain is reached, indicating to the user that further strain risks device failure. We also show that the strain at color onset can be controlled by layering silicones with different moduli into a composite. As a demonstration, we show how color onset can be tailored to indicate a when a specified frequency of a stretchable liquid metal antenna has been reached. The multiscale combination of mechanochromism and soft electronics offers a new avenue to empower user control of strain-dependent properties for future stretchable devices.