Long-Term Thermal Aging of Modified Sylgard 184 Formulations

Norbornene Dicarboximide: A Green Alternative for Thiol-Norbornene Photopolymers

Carbic anhydride is an underappreciated starting material for 3D-printable, non-hydrogel photopolymers. Compared with other norbornene precursors, carbic anhydride is cheaper and reactive via aminolysis. As a result, the generalized and efficient functionalization with carbic anhydride can increase the utilization of thiol-norbornene photopolymers. Here, we report carbic anhydride's catalyst-free condensation with two commodity polymers: amine-functionalized polypropylene glycol and polydimethylsiloxane. The reaction completes in 1 h, produces water as the only byproduct, and does not require purification. It is therefore affordable, facile, and green. Mixing the product with thiol cross-linkers and the appropriate photoadditives produces photopolymers that are printable via Digital Light Processing. The photopolymers exhibit tunable tensile properties and a functional surface by varying the polymer backbone and thiol stoichiometry. Moreover, the photopolymers are 3D-printed into true-to-scale human aorta models and porous scaffolds with high resolution. The simple yet versatile platform will benefit additive manufacturing of soft materials and beyond.

Reversibly-bonded microfluidic devices for stable cell culture and rapid, gentle cell extraction

Microfluidic chips have emerged as significant tools in cell culture due to their capacity for supporting cells to adopt more physiologically relevant morphologies in 3D compared with traditional cell culture in 2D. Currently, irreversible bonding methods, where chips cannot be detached from their substrates without destroying the structure, are commonly used in fabrication, making it challenging to conduct further analysis on cells that have been cultured on-chip. Although some reversible bonding techniques have been developed, they are either restricted to certain materials such as glass, or require complex processing procedures. Here, we demonstrate a simple and reversible polydimethylsiloxane (PDMS)-polystyrene (PS) bonding technique that allows devices to withstand extended operations while pressurized, and supports long-term stable cell cultures. More importantly, it allows rapid and gentle live cell extraction for downstream manipulation and characterization after long-term on-chip culturing, and even further subculturing. Our new approach could greatly facilitate microfluidic chip-based cell and tissue cultures, overcoming current analytical limitations and opening up new avenues for downstream uses of on-chip cultures, including 3D-engineered tissue structures for biomedical applications.

Potential use of polydimethylsiloxane phantom in acupuncture manipulation practice

Objectives

Sufficient trials of acupuncture manipulations should be practiced to obtain proficiency. However, there is not an adequate quantitative methodology for selecting a tissue-mimicking phantom that effectively reproduces the mechanical behavior that occurs during acupuncture. The objective of this study was to determine the proper mixing ratio of polydimethylsiloxane (PDMS) to obtain tissue phantom that is the most similar to porcine phantoms.

Design

An automatic needle manipulator equipped with a six-degrees-of-freedom force/torque sensor was installed to monitor the interaction force that occurred when the acupuncture needle performed lifting-thrusting and twirling manipulations. Four types of PDMS phantoms, composed of two silicone elastomers with different hardener ratios, were studied alongside four control groups consisting of different porcine sites. A Visual Analog Scale was used to quantify the similarity of the PDMS phantoms to the controls by 11 Korean medical doctors.

Results

Using the lifting-thrusting method, PDMS D (mixing ratio of 1:4.5) and control 2 (porcine blade shoulder) revealed no significant difference in the dynamic friction coefficients or maximum and minimum friction force values (P < 0.001). Using the twirling method, PDMS D showed no significant difference from all controls in the viscosity coefficient or maximum and minimum torque values (P ≤ 0.001). By practitioners, PDMS D showed the greatest score.

Conclusion

PDMS D delivered a haptic sensation that is most similar to that of biological tissues in the case of acu-needle lifting-thrusting and twirling methods. This finding guides the preparation of tissue phantoms for acu-needle studies and acupuncture training.

Characterization of Temperature and Humidity Dependence in Soft Elastomer Behavior

Soft robots are predicted to operate well in unstructured environments due to their resilience to impacts, embodied intelligence, and potential ability to adapt to uncertain circumstances. Soft robots are of further interest for space and extraterrestrial missions, owing to their lightweight and compressible construction. Most soft robots in the literature to-date are made of elastomer bodies. However, limited data are available on the material characteristics of commonly used elastomers in extreme environments. In this study, we characterize four commonly used elastomers in the soft robotics literature-EcoFlex 00-30, Dragon Skin 10, Smooth-Sil 950, and Sylgard 184-in a temperature range of -40°C to 80°C and humidity range of 5-95% RH. We perform pull-to-failure, stiffness, and stress-relaxation tests. Furthermore, we perform a case study on soft elastomers used in stretchable capacitive sensors to evaluate the implications of the constituent material behavior on component performance. We find that all elastomers show temperature-dependent behavior, with typical stiffening of the material and a lower strain at failure with increasing temperature. The stress-relaxation response to temperature depends on the type of elastomer. Limited material effects are observed in response to different humidity conditions. The mechanical properties of the capacitive sensors are only dependent on temperature, but the measured capacitance shows changes related to both humidity and temperature changes, indicating that component-specific properties need to be considered in tandem with the mechanical design. This study provides essential insights into elastomer behavior for the design and successful operation of soft robots in varied environmental conditions.

Room temperature roll-to-roll additive manufacturing of polydimethylsiloxane-based centrifugal microfluidic device for on-site isolation of ribonucleic acid from whole blood

Polymer-based lab-on-a-disc (LoaD) devices for isolating ribonucleic acid (RNA) from whole blood samples have gained considerable attention for accurate biomedical analysis and point-of-care diagnostics. However, the mass production of these devices remains challenging in manufacturing cost and sustainability, primarily due to the utilization of a laser cutter or router computer numerical control (CNC) machine for engraving and cutting plastics in the conventional prototyping process. Herein, we reported the first energy-efficient room-temperature printing-imprinting integrated roll-to-roll manufacturing platform for mass production of a polydimethylsiloxane (PDMS)-based LoaD to on-site isolate ribonucleic acid (RNA) from undiluted blood samples. We significantly reduced energy consumption and eliminated thermal expansion variations between the mold, substrate, and resists by accelerating the PDMS curing time to less than 10 min at room temperature without using heat or ultraviolet radiation. The additive manufacturing technology was applied to fabricate a multi-depth flexible polymer mold that integrated macro (2 mm) and micro-sized (500 μm) features, which overcomes the economic and environmental challenges of conventional molding techniques. Our integrated R2R platform was enabled to print adhesion-promoting films at the first printing unit and continuously in-line imprint with a high replication accuracy (99%) for high-volume manufacturing of a new centrifugal microfluidic chip with an enhancement of mixing performance by integrating an efficient mixing chamber and serpentine micromixer. This research paved the way for scalable green manufacturing of large-volume polymer-based microfluidic devices, often required in real-world sample-driven analytical systems for clinical bioanalysis.

Synthesis and photochemical modification of monolayer thin MOF flakes for incorporation in defect free polymer composites

Metal-organic frameworks (MOFs) with benzophenone linker molecules are characterized by their ability to undergo photochemical postsynthetic modification. While this approach opens up almost unlimited possibilities for tailoring materials to specific applications, the processability of the large particles is still lacking. In this work, we present a new approach to fabricate micro flakes of the stable Zr-bzpdc-MOF (bzpdc = benzophenone-4-4'-dicarboxylate) with a thickness of only a few monolayers. The crystalline and nanoporous flakes form dispersions in acetone that are stable for months. Embedding the flakes in polymer composites was investigated as one of many possible applications. Zr-bzpdc-MOF micro flakes were decorated with poly(dimethylsiloxane) (PDMS) via a photochemical postsynthetic modification and incorporated into silicon elastomers. The PDMS functionalization allows covalent cross-linking between the MOF and the polymer while maintaining the porosity of the MOF. The resulting hybrid materials provide defect-free interfaces and show preferential adsorption of CO2 over CH4, making them attractive for gas separation or sensing applications. The work should serve as a basis for bringing bzpdc-MOFs into real-world applications - in polymeric membranes, but also beyond.

Self-Assembled, Hierarchical Structured Surfaces for Applications in (Super)hydrophobic Antiviral Coatings

A versatile method for the creation of multitier hierarchical structured surfaces is reported, which optimizes both antiviral and hydrophobic (easy-clean) properties. The methodology exploits the availability of surface-active chemical groups while also manipulating both the surface micro- and nanostructure to control the way the surface coating interacts with virus particles within a liquid droplet. This methodology has significant advantages over single-tier structured surfaces, including the ability to overcome the droplet-pinning effect and in delivering surfaces with high static contact angles (>130°) and good antiviral efficacy (log kill >2). In addition, the methodology highlights a valuable approach for the creation of mechanically robust, nanostructured surfaces which can be prepared by spray application using nonspecialized equipment.