Soft Polymer-Actuated Compliant Microgripper with Adaptive Vibration-Controlled Grasp and Release.

Microgrippers that incorporate soft actuators are appropriate for micromanipulation or microsurgery owing to their ability to grasp objects without causing damage. However, developing a microgripper with a large gripping range that can produce a large force with high speed remains challenging in soft actuation mechanisms. Herein, we introduce a compliant microgripper driven by a soft dielectric elastomer actuator (DEA) called a spiral flexure cone DEA (SFCDEA). The submillimeter-scale SFCDEA exhibited a controllable linear displacement over a high bandwidth and the capability of lifting 100.9 g, which was 670 times higher than its mass. Subsequently, we developed a compliant microgripper based on the SFCDEA using smart composite microstructure technology to fabricate three-dimensional gripper linkages. We demonstrated that the microgripper was able to grasp various millimeter-scale objects with different shapes, sizes, and weights without a complex feedback control owing to its compliance. We proved the versatility of our gripper in robotic manipulation by demonstrating adaptive grasping and releasing of small objects using vibrations owing to its high bandwidth.

Knee Measurement System with Osteoarthritis Levels Using Artificial Cartilage and Skeletons.

Knee osteoarthritis (OA), also known as degenerative arthritis, is a disease characterized by irreversible changes in the cartilage and bones comprising the joints, resulting in pain, impaired function, and deformity. Furthermore, independent of natural aging, the rate of change in joint cartilage has increased in recent years, which is mainly attributed to environmental factors. The rising incidence of knee-related disorders emphasizes the importance of analyzing the morphology and kinematics of knee structure. This study introduces a knee measurement system designed to replicate the motions of knee using 3D-printing technology, providing insights into knee mechanics with OA level. The research explores the stages of OA using the Kellgren-Lawrence (KL) grade scale, highlighting the variations in the force applied to the knee bone according to movement. The developed knee-simulation system, utilizing the four-bar-link theory, presents a novel approach to studying OA levels 0 to 4. As OA progresses, the cartilage deteriorates, affecting the movement of OA. The OA-based knee measurement system that incorporates soft tissues and skeletons can assist in developing a personalized diagnostic approach for knee disease. This will also help to enhance surgical effectiveness by facilitating the creation of personalized prosthetic joints for individual patients and offering a customized surgical simulation.

Soft Polymer-Based Technique for Cellular Force Sensing.

Soft polymers have emerged as a vital type of material adopted in biomedical engineering to perform various biomechanical characterisations such as sensing cellular forces. Distinct advantages of these materials used in cellular force sensing include maintaining normal functions of cells, resembling in vivo mechanical characteristics, and adapting to the customised functionality demanded in individual applications. A wide range of techniques has been developed with various designs and fabrication processes for the desired soft polymeric structures, as well as measurement methodologies in sensing cellular forces. This review highlights the merits and demerits of these soft polymer-based techniques for measuring cellular contraction force with emphasis on their quantitativeness and cell-friendliness. Moreover, how the viscoelastic properties of soft polymers influence the force measurement is addressed. More importantly, the future trends and advancements of soft polymer-based techniques, such as new designs and fabrication processes for cellular force sensing, are also addressed in this review.

The Dynamic Viscoelasticity of Dental Soft Polymer Material Containing Citrate Ester-Based Plasticizers.

The aim of this study was to investigate the dynamic viscoelasticity of dental soft polymer material containing citrate ester-based plasticizers. Three kinds of citrate ester-based plasticizer (Citroflex® C-2: TEC, Citroflex® A-2: ATEC, and Citroflex® A-4: ATBC), with the combination of 5 wt% ethyl alcohol, were used as the liquid phase. The dynamic viscoelastic properties of nine ethyl methacrylate polymers: (A, B, C, D, E, F, G, H, and I) were immersed in 37 °C distilled water for 0, 1, 3, 7, 14 and 30 days, respectively. The dynamic viscoelastic properties were measured at 37 °C with an automatic dynamic mechanical analyzer. The shear storage modulus (G'), shear loss modulus (G″), and loss tangent (tan δ) were determined at 1 Hz. These parameters were statistically analyzed by two-way and one-way ANOVA and Tukey's multiple comparison test at a predetermined significance level of 0.05. A significant difference was found among the materials in terms of the dynamic viscoelasticity. The materials containing citrate ester-based plasticizer ATBC showed the most stable dynamic viscoelasticity. Considering the limitations of this study, the results suggest that the inclusion of citrate ester-based plasticizer can improve the durability of dental soft polymer materials.

Waveguide Plasmon Resonance of Arrayed Metallic Nanostructures Patterned on a Soft Substrate by Direct Contact Printing Lithography.

This paper presents a direct contact printing method to obtain arrayed metallic nanostructures on a soft polymer substrate. It utilizes a polydimethylsiloxane (PDMS) mold replicated from silicon molds to transfer metallic nanopatterns onto a polymer substrate based on differences in interfacial bonding energy. Arrayed metallic nanodisks with a disk diameter down to 180 nm and a center-to-center pitch around 400 nm are experimentally patterned on a PET substrate. The patterned metallic nanostructures are then spin-coated with a polymer layer; which mechanically secures the patterned nanostructures and optically allows waveguide plasmon resonance being excited by incident EM waves. Both experimental works and theoretical modeling are given to illustrate the behaviors of different types of plasmon resonance. These arrayed metallic nanostructures patterned on a soft polymer substrate and their tunable optical characteristics open up many possibilities in future engineering applications.

The effect of crude drugs on the angiogenic property and dynamic viscoelasticity of PEMA-based soft polymer materials.

This study aimed to determine the effect of crude drugs on the dynamic viscoelasticity and angiogenic property of soft polymer materials, in vitro. Two kinds of polyethyl methacrylates, and crude drugs (Astragalus membranaceus Bunge [HQ] and Salvia miltiorrhiza Bunge [DS]) were used in their powdered forms. And, acetyl tributyl citrate and ethyl alcohol were used in the liquid form. The dynamic viscoelasticity of each specimen was measured after 0, 1, 3, 7, 14 and 28 days of immersion in distilled water. The CellPlayer angiogenesis PrimeKit assay was used to test angiogenesis. Significant differences in dynamic viscoelasticity were observed among the materials. Specimens containing 1 wt% HQ showed higher angiogenic activity than those containing 5 wt% and 10 wt% HQ, and DS. Our results suggest that the addition of low amounts of crude drugs to soft polymer materials may promote angiogenesis in human tissues.

Ramp-hold relaxation solutions for the KVFD model applied to soft viscoelastic media.

The standard step-hold load-relaxation profile can yield variable estimates of mechanical properties due to the difficulty in achieving a step strain experimentally. A ramp-hold profile overcomes this limitation if appropriate model functions can be derived. Utilizing Boltzmann hereditary integral operators for two indentation geometries, analytical ramp solutions for load-relaxation were developed based on the Kelvin-Voigt fractional derivative (KVFD) model. The results identify three model parameters for characterizing viscoelastic behavior from a single model curve fit to the data: the elastic modulus E0, fractional-order parameter α, and relaxation time constant τ. The quantitative nature of the analysis was validated through measurements on gelatin emulsion samples exhibiting viscoelastic behavior. KVFD-model-based solutions provide mathematically simple and experimentally flexible descriptions of load-relaxation behavior for a range of viscoelastic properties and experimental conditions; e.g. one closed-form solution can fit the ramp and the hold phases of the relaxation time series. Experiments show that the solution for a spherical indenter and plate compressor each fit well to the corresponding experimental relaxation curves with a coefficient of determination R2 > 0.98. Parameters obtained from the spherical-tip indentation and plate-compression geometries agree within one standard deviation, confirming that the ramp solution based KVFD model yields consistent measurements for characterizing viscoelastic materials.

Viability, morphology and function of primary endothelial cells on poly(n-butyl acrylate) networks having elastic moduli comparable to arteries.

Soft hydrophobic poly(n-butyl acrylate) networks (cPnBA) were developed as entropy elastic substrates for passive mechanical stimulation of cells, where the elastic modulus of the cPnBAs could be systematically adjusted by variation of the cross-link density. The networks were synthesized by thermally-induced radical polymerization from n-butyl acrylate, with poly(propylene glycol) dimethacrylate (PPGDMA) acting as cross-linker, whereby the purity of the cPnBAs was confirmed by(1) H-NMR spectroscopy and gas chromatography. In this work two cPnBA polymer networks with an elastic modulus around 200 kPa and 1 MPa were investigated having an elastic modulus similar to that of arteries. Both cPnBAs exhibited an almost smooth surface with a surface roughness (R q) in the wet state ranging from 17 to 37 nm and a similar zetapotential, indicating an almost identical chemical composition within the topmost surface layer in terms of functional groups. In contrast, wettability of the samples was found to be different with an advancing angle ( advancing) of 123 ± 3.8° for cPnBA0250, while for cPnBA1100 significantly lower values for advancing (111 ± 3.8°) were obtained. First in vitro tests were performed with primary endothelial cells (HUVEC) to study its effects on vascular cell functions. Within the time period of cultivation (72 h), the cells on the cPnBA samples reached subconfluence and showed a viability rate of almost 100%. Although cell density differed after 72 h with more cells on cPnBA0250 than on cPnBA1100, both materials showed no significant effect on the cell morphology, the cellular LDH-release, which was used as marker for the integrity of the cell membrane, and the organisation of the VE-cadherin. However, lower cell density and less actin stress fibre formation on cPnBA1100 might indicate that cell-material interaction was weaker on cPnBA1100 than on cPnBA0250. The secretion of the vasoactive cytokines prostacyclin (PGI2) and thromboxane A2 (TXA2) was low compared to previously reported values. However, the anti-thrombogenic ratio of PGI2/TXA2 - which is balanced under physiological conditions - with much higher PGI2 compared to TXA2 (up to 17.6-fold after 72 h for cPnBA1100) suggests that this material might be effective to preventing thrombosis.