Chemomechanical Systems Research Articles

Control of nonlinear bulk deformation and large shear strain on first-order phase transformation kinetics

Phase transformations play a key role in numerous coupled natural processes, and they are important for many industrial applications. However, the kinetics of phase transformations in coupled chemo-mechanical systems undergoing large mechanical deformations still needs to be better quantified. Here, we study the phase transformation kinetics of a two-phase binary mixture using the diffuse interface approach. We couple a Cahn–Hilliard type model with a mechanical model for a compressible viscous flow. The bulk compressibility is a nonlinear function of the pressure, and the shear viscosity is a nonlinear function of the concentration. The mechanical coupling is achieved by employing a pressure-dependent mechanical mixing term in the equation for the Gibbs energy. We derive a dimensionless system of equations which we solve numerically with a pseudo-transient method using conservative finite differences for discretization. We perform numerical simulations in 1D and 2D model setups considering far-field simple shear and pure shear. For a chemo-mechanically coupled system, we show that the velocity of the phase boundary is a linear function of the degree of metastability and, hence, confirm the hypothesis of “normal growth.” A stronger mechanical coupling and a larger volumetric effect of the chemical reaction result in lower phase boundary velocities. The 2D results show a significant impact of the mechanical coupling and the far-field deformation on the orientation and kinetics of the phase transformations. Under far-field simple shear and pure shear in 2D, the phase transformations generate string-like patterns. The orientation of these patterns is controlled by the applied far-field deformation and orientations differ by 45 degrees between simple shear and pure shear.

Gas-phase microactuation using kinetically controlled surface states of ultrathin catalytic sheets

Biological systems convert chemical energy into mechanical work by using protein catalysts that assume kinetically controlled conformational states. Synthetic chemomechanical systems using chemical catalysis have been reported, but they are slow, require high temperatures to operate, or indirectly perform work by harnessing reaction products in liquids (e.g., heat or protons). Here, we introduce a bioinspired chemical strategy for gas-phase chemomechanical transduction that sequences the elementary steps of catalytic reactions on ultrathin (<10nm) platinum sheets to generate surface stresses that directly drive microactuation (bending radii of 700nm) at ambient conditions (T = 20°C; Ptotal = 1atm). When fueled by hydrogen gas and either oxygen or ozone gas, we show how kinetically controlled surface states of the catalyst can be exploited to achieve fast actuation (600ms/cycle) at 20°C. We also show that the approach can integrate photochemically controlled reactions and can be used to drive the reconfiguration of microhinges and complex origami- and kirigami-based microstructures.

Retreatability of calcium silicate-based root canal sealer using reciprocating instrumentation with different irrigation activation techniques in single-rooted canals.

This study analysed the bioceramic sealer cleaning ability of two chemo-mechanical systems in intact and restored teeth. Thirty-two single-rooted teeth were used, and half of them restored with a pre-endodontic composite restoration (PCR). All samples were instrumented with a size 40 Reciproc Blue file and filled with BioRoot RCS. Canals were retreated using the R40 and then R50 Reciproc Blue. The samples were divided into four experimental groups (n = 8): intact teeth/passive ultrasonic irrigation (PUI) (G1), intact teeth/shock wave-enhanced emission photoacoustic streaming (SWEEPS) (G2), PCR/PUI (G3) and PCR/SWEEPS (G4). The samples were scanned by micro-CT before and after retreatment, and the volume of remaining filling material was evaluated. The minor percentage of residues were observed in G2, with a volume of 0.447 ± 0.356% of the endodontic space (P < 0.001). The Reciproc/SWEEPS technique showed the better performance in intact teeth compared with PUI technique. Pre-endodontic restoration did not significantly affect the effectiveness of sealer removal.

Advances in Synthetic Polyampholytes for Biotechnology and Medicine

Polyampholytes are unique macromolecules containing acid/base or anionic/cationic groups in the main or side chains that mimic the behavior of proteins, polypeptides or polynucleotides. Water-soluble and water-swelling polyampholytes exhibit salt-tolerant, thermal-resistant, shear-stable, self-healing, anti-fouling, self-assembling, and stimuli-responsive properties that provide broad impact as structural biomaterials, drug delivery and chemo-mechanical systems, biosensors, energy storage devices, supercapacitors, actuators etc. In this review we mainly pay attention to fundamental and applied aspects of synthetic polyampholytes in the context of biotechnology and medicine. Among the outlined topics the role of linear and crosslinked amphoteric macromolecules as well as macromolecular complexes of polyampholytes with polyelectrolytes, DNA, proteins and drugs is highlighted. Cryoprotective behavior of synthetic polyampholytes is shown with respect to cell preservation and viability. Injectable, soft, flexible, stretchable, self-healing and stimuli-responsive physically or chemically crosslinked polyampholyte gels that are promising materials for fabrication of artificial tissue, wound dressing, cartilage, cardiovascular, bone defect repair, regenerative medicine and tissue engineering scaffolds, soft actuators and sensors, soft robotics are also in the eyeshot of this review. Hierarchically structured multi-responsive polyampholytic gels, multilayered films and membranes possessing encapsulation–release and “on–off” behaviors are considered as antibiofouling, anticoagulation, and drug delivery system.

Digital Maskless Photolithographic Patterning of DNA-Functionalized Poly(ethylene glycol) Diacrylate Hydrogels with Visible Light Enabling Photodirected Release of Oligonucleotides.

Soft biomaterials possessing structural hierarchy have growing applications in lab-on-chip devices, artificial tissues, and micromechanical and chemomechanical systems. The ability to integrate sets of biomolecules, specifically DNA, within hydrogel substrates at precise locations could offer the potential to form and modulate complex biochemical processes with DNA-based molecular switches in such materials and provide a means of creating dynamic spatial patterns, thus enabling spatiotemporal control of a wide array of reaction-diffusion phenomena prevalent in biological systems. Here we develop a means of photopatterning two-dimensional DNA-functionalized poly(ethylene glycol) diacrylate (PEGDA) hydrogel architectures with an aim toward these applications. While PEGDA photopatterning methods are well-established for the fabrication of hydrogels, including those containing oligonucleotides, the photoinitiators typically used have significant crosstalk with many UV-photoswitchable chemistries including nitrobenzyl derivatives. We demonstrate the digital photopatterning of PEGDA-co-DNA hydrogels using a blue light-absorbing (470 nm peak) photoinitiator system and macromer comprised of camphorquinone, triethanolamine, and poly(ethylene glycol) diacrylate (Mn = 575) that minimizes absorption in the UV-A wavelength range commonly used to trigger photoswitchable chemistries. We demonstrate this method using digital maskless photolithography within microfluidic devices that allows for the reliable construction of multidomain structures. The method achieves feature resolutions as small as 25 μm, and the resulting materials allow for lateral isotropic bulk diffusion of short single-stranded (ss) DNA oligonucleotides. Finally, we show how the use of these photoinitiators allows for orthogonal control of photopolymerization and UV-photoscission of acrylate-modified DNA containing a 1-(2-nitrophenyl) ethyl spacer to selectively cleave DNA from regions of a PEGDA substrate.

Tactile Chemomechanical Transduction Based on an Elastic Microstructured Array to Enhance the Sensitivity of Portable Biosensors

Tactile sensors capable of perceiving biophysical signals such as force, pressure, or strain have attracted extensive interest for versatile applications in electronic skin, noninvasive healthcare, and biomimetic prostheses. Despite these great achievements, they are still incapable of detecting bio/chemical signals that provide even more meaningful and precise health information due to the lack of efficient transduction principles. Herein, a tactile chemomechanical transduction strategy that enables the tactile sensor to perceive bio/chemical signals is proposed. In this methodology, pyramidal tactile sensors are linked with biomarker-induced gas-producing reactions, which transduce biomarker signals to electrical signals in real time. The method is advantageous as it enhances electrical signals by more than tenfold based on a triple-step signal amplification strategy, as compared to traditional electrical biosensors. It also constitutes a portable and general platform capable of quantifying a wide spectrum of targets including carcinoembryonic antigen, interferon-γ, and adenosine. Such tactile chemomechanical transduction would greatly broaden the application of tactile sensors toward bio/chemical signals perception which can be used in ultrasensitive portable biosensors and chemical-responsive chemomechanical systems.

Experimental evidence of explosive synchronization in mercury beating-heart oscillators.

We report experimental evidence of explosive synchronization in coupled chemo-mechanical systems, namely in mercury beating-heart (MBH) oscillators. Connecting four MBH oscillators in a star network configuration and setting natural frequencies of each oscillator in proportion to the number of its links, a gradual increase of the coupling strength results in an abrupt and irreversible (first-order-like) transition from the system's unordered to ordered phase. On its turn, such a transition indicates the emergence of a bistable regime wherein coexisting states can be experimentally revealed. Finally, we prove how such a regime allows an experimental implementation of magneticlike states of synchronization, by the use of an external signal.

CLINICAL EVALUATION OF CHEMO-BECHANICAL CARIES REMOVAL USING CARIE-CARE SYSTEM AMONG SCHOOL CHILDREN

AbstractDental caries is considered as one of the most serious dental diseases that results in localized dissolution and destruction of the calcified tooth tissues. As possible alternatives to conventional techniques of caries removal, chemo mechanical caries removal systems have emerged. AIM: To clinically observe the advantages of Chemo-mechanical method of caries removal over Conventional technique. MATERIALS AND METHODS: A total of 64 teeth of 32children with class 1 open carious lesions were selected for the study from the school dental clinic after taking written consent. They were divided into two equal groups according to method of caries removal (32 chemomechanical and 32 conventional from both primary and permanent teeth respectively). In Group I, caries was removed using the carie-care system and in Group II, with the conventional drill and were restored equally with amalgam and ketac molar respectively. The restored teeth were followed up after 1 week, 1 month, 6 months and 1 year respectively for its clinical success. RESULTS: The results were subjected to statistical analysis using students paired t-test and chi-square tests. It showed that though Chemomechanical technique took a marginal increase in time compared to the conventional technique, it was found to be more comfortable for all the children. Amalgam restorations showed better retention compared to ketac molar restorations in both the techniques. CONCLUSION: Chemomechanical technique though time consuming is definitely superior compared to conventional technique in pediatric dentistry, provided we use a less technique sensitive restorative material which retains in the oral cavity for longer period of time. It is definitely a better treatment protocol in school based dental treatment compared to conventional technique

Extraordinarily large swelling energy of iodine-treated poly(vinyl alcohol) demonstrated by jump of a film.

Organic material characteristics of volume change and stress generation have attracted the attention of many researchers aiming to develop chemomechanical systems such as artificial muscles and polymer engines having the advantages of high energy density and silent operation. Although polymer gels offer a relatively large actuator stroke, their mechanical properties are relatively poor and the working temperature is relatively low, often limited by the evaporation of liquid if contained. We have developed an iodine-treated poly(vinyl alcohol) having extraordinarily large vapor-induced deswelling stress reaching 59 MPa, which is one to two orders of magnitude greater than those of ordinary polymer gels. Furthermore, this material has extremely large volumetric and gravimetric energy densities reaching 1.3 × 106 J m−3 and 9.6 × 102 J kg−1, respectively, and an elastic modulus of a few GPa and is heat-resistant to at least 200 °C. The high performance of this material can be demonstrated by a jump of a film. © 2014 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1357–1365

Stimuli-Responsive Chemomechanical Actuation: A Hybrid Materials Approach

Dynamic materials that can sense changes in their surroundings and functionally respond by altering many of their physical characteristics are primed to be integral components of future "smart" technologies. A fundamental reason for the adaptability of biological organisms is their innate ability to convert environmental or chemical cues into mechanical motion and reconfiguration on both the molecular and macroscale. However, design and engineering of robust chemomechanical behavior in artificial materials has proven a challenge. Such systems can be quite complex and often require intricate coordination between both chemical and mechanical inputs and outputs, as well as the combination of multiple materials working cooperatively to achieve the proper functionality. It is critical to not only understand the fundamental behaviors of existing dynamic chemomechanical systems but also apply that knowledge and explore new avenues for design of novel materials platforms that could provide a basis for future adaptive technologies. In this Account, we explore the chemomechanical behavior, properties, and applications of hybrid-material surfaces consisting of environmentally sensitive hydrogels integrated within arrays of high-aspect-ratio nano- or microstructures. This bio-inspired approach, in which the volume-changing hydrogel acts as the "muscle" that reversibly actuates the microstructured "bones", is highly tunable and customizable. Although straightforward in concept, the combination of just these two materials (structures and hydrogel) has given rise to a far more complex set of actuation mechanisms and behaviors. Variations in how the hydrogel is physically integrated within the structure array provide the basis for three fundamental mechanisms of actuation, each with its own set of responsive properties and chemomechanical behavior. Further control over how the chemical stimulus is applied to the surface, such as with microfluidics, allows for generation of more precise and varied patterns of actuation. We also discuss the possible applications of these hybrid surfaces for chemomechanical manipulation of reactions, including the generation of chemomechanical feedback loops. Comparing and contrasting these many approaches and techniques, we aim to put into perspective their highly tunable and diverse capabilities but also their future challenges and impacts.

Light induced fluorescence evaluation: A novel concept for caries diagnosis and excavation

In the era of minimal invasive dentistry, every effort should be directed to preserve the maximum tooth structure during cavity preparation. However, while making cavities, clinicians usually get indecisive at what point caries excavation should be stopped, so as to involve only the infected dentin. Apparent lack of valid clinical markers, difficulties with the use of caries detector dyes and chemo mechanical caries removal systems carve out a need for an improved system, which would be helpful to differentiate between the healthy and infected dentin during caries excavation. Light induced fluorescence evaluation is a novel concept implicated for caries detection and for making decisions while cavity preparation. This paper describes a few cases that explain the clinical applicability of this concept, using the SoproLife camera that works on this principle. Autofluorescence masking effect was found to be helpful for caries detection and the red fluorescence in the treatment mode was found helpful in deciding ‘when to stop the excavation process.’ Light induced fluorescence evaluation – Diagnosis - Treatment concept concept can be used as a guide for caries detection and excavation. It also facilitates decision making for stopping the caries excavation so as to involve infected dentin only.

An in vitro evaluation of microtensile bond strengths of two adhesive bonding agents to residual dentine after caries removal using three excavation techniques

To assess amounts of residual dentine retained after using three excavation techniques; the microtensile bond strengths (microTBS) to residual dentine, comparing etch-rinse vs. self-etching adhesives. 42 carious molars were subdivided (N=21) dependent upon adhesive/composite system (Adper Scotchbond 1XT and Filtek Supreme vs. Filtek Silorane adhesive and composite). Dividing into three (N=7), dependent upon caries excavation technique employed (hand vs. chemo-mechanical: Carisolv gel vs. experimental enzymatic gel (SFC-V)), caries removal was assessed using visual/tactile criteria and in situ autofluorescence (AF) confocal fibre-optic micro-endoscopy (CFOME). Post-restoration/four-week hydrated storage, four 0.9 mm(2) beams per tooth underwent microTBS testing/microscopic analysis of fractured surfaces. Three cavities from each excavation group were analysed using SEM. SEM revealed surface roughness with smear layer occluding tubule orifices in hand-excavated samples and a reduced, variable smear layer for both chemo-mechanical systems. CFOME AF assessment indicated hand excavation left sound dentine, Carisolv left affected dentine and SFC-V slightly under-prepared clinically. Mean microTBS values from etch-rinse samples (27 MPa (SD 3.9), hand; 22 MPa (SD 5.1), Carisolv; 26 MPa (SD 4.4), SFC-V) showed statistical differences between hand and Carisolv groups. Mean microTBS data for self-etch samples (22 MPa (SD 3.3), hand; 27 MPa (SD 6.1), Carisolv; 25 MPa (SD 4.7), SFC-V) showed significant differences between hand and Carisolv, and hand vs. SFC-V. Failure loci distribution in etch-rinse samples was between dentine-adhesive, within adhesive and within composite whereas self-etch samples exhibited failure predominantly between adhesive and composite. Data indicated that all null hypotheses were disproved.

Pick-and-Place Using Chemically Actuated Microgrippers

In this communication, we demonstrate the concept of single-use, chemically triggered, reversible tools in the form of mobile grippers that can be used to manipulate micro-objects. Both the closing and opening of the mobile grippers are triggered by chemicals, namely acetic acid (CH(3)COOH) and hydrogen peroxide (H(2)O(2)), respectively. The grippers close and open en masse based on chemically triggered, mechanical property changes within trilayer joints patterned within the gripper, and no external power is needed for operation. We describe the actuation of the gripper using a multilayer thin film model and demonstrate the utility of the gripper by picking-and-placing 200 microm diameter tubes and beads. Our pick-and-place microgripper is a first step toward the development of functional Micro Chemo-Mechanical Systems (MCMS), which are actuated by chemistry as opposed to electricity [as in Micro Electro-Mechanical Systems (MEMS)].

Fluorescence of primary dentine after chemomechanical and conventional rotary excavation

This was to compare fluorescence values of dentine remaining after caries removal using chemomechanical systems and conventional rotary methods. In vitro study. 30 extracted primary teeth with proximal carious cavities were divided into three groups according to caries removal method: Carisolv, Papacarie and conventional low speed rotary burs. Carious (initial) and remaining (final) dentine evaluations were assessed by visual-tactile examination and DIAGNOdent. Transversal microhardness (TMH) of remaining dentine was evaluated. Fluorescence and TMH values were submitted to two-way ANOVA and the post hoc Tukey test (alpha = 0.05) and Pearson's linear correlation. Two-way ANOVA revealed that fluorescence values were similar between conventional rotary excavation, Carisolv and Papacarie groups (p = 0.0542). No statistically significant differences (p = 0.1147) were found to TMH values. No correlation was found between fluorescence and TMH values (r = -0.0273). All caries excavation methods resulted in similar remaining dentine fluorescence values. No correlation was found between fluorescence values and TMH of remaining dentine.

Emerging challenges to structural integrity technology for high-temperature applications

Structural integrity technology has been widely used with great success for the design, manufacture and failure prevention of modern constructions such as chemical and petrochemical plants, power generation and energy conversion systems, as well as space and oceanic exploration. The modern needs of structural integrity technology are largely attributed to the increase of service temperature of the structures that results in the efficiency improvement in energy conversion and chemical processing technologies. Besides the needs arising from large-scale high-temperature plants, the high tech developments, such as micro chemo-mechanical systems and high-power electronics, provide new challenges to structural integrity technology. The present paper summarizes the recent technical progresses in large process plants and the aviation industry, micro chemo-mechanical systems, fuel cells, high-temperature electronics, and packaging and coating technologies. The state-of-the-art of structural integrity technology for high temperature applications is reviewed. Suggestions are provided for the improvement of current design and assessment methods.

Polymer gels as soft and wet chemomechanical systems—an approach to artificial muscles

Polymer gels as soft and wet chemomechanical systems—an approach to artificial muscles

Chemomechanical Systems: Study of Contraction and Mechanical Work of Poly(Acrylonitrile) Gel Fibers

Poly(acrylonim1e) fibers were preoxidated under stress, in the presence of air, then saponified by boiling in alkaline solutions. The chemomechani-cal behavior of these fibers, expressed as contraction and mechanical work, under different loads and in different solvent-nonsolvent and/or base-acid systems were investigated. Total nitrogen content, carboxyl groups content, tensile strength, and cross-link density were determined. Both contraction and mechanical work were expressed as functions of applied load in every studied system. The results of chemomechanical measurements were connected to those of chemical and physical investigations. Significant differences in chemomechanical behavior were found to be the result of different stress conditions during the preoxidation stage.

Chemomechanical Systems: Study of Contraction and Mechanical Work of Poly(Acrylonitrile) Gel Fibers

A fully predictive computer model SSEM (Single-Screw Extrusion Model) has been developed for the single-screw plasticating extruders (with conventional and mixing screws). The model takes into account five zones of the extruder (hopper, solids conveying, delay zone, melting zone, and melt conveying) and the die, and it describes an operation of the extruder-die system, making it possible to predict the mass flow rate of the polymer, the pressure and temperature profiles along the screw channel and in the die, the solid-bed profile, and power consumption. Moreover, the mixing degree, the temperature fluctuation, and the viscoelastic characteristic of the polymer are evaluated. The model also makes it possible to predict the morphological changes of the polymer blend during the compounding process in the single-screw extruder. The simulation parameters are the material and rheological properties of the polymer, the screw, hopper, and die geometry, and the operating conditions (screw speed and barrel temperature profile). Such a comprehensive approach to the modeling of extrusion creates a possibility of optimizing the process, for example, from the point of view of the quality of extrusion. The model has been verified experimentally on a 45-mm-diameter single-screw extruder.

Chemomechanical transformations of gels: artificial muscles and chemomechanical actuators

The needs for actuators with improved performances (in accuracy, speed of motion, power, response rate, compactness, compliance ...) in medical, spatial, marine areas have motivated the research on the study and the construction of new actuation systems having some characteristics of the human or animal muscle (natural muscle).The natural muscles are based on chemical to mechanical conversions (mechanoche- mical). These transformations can be obtained artificially by using chemomechanical materials : polymeric gels, ion exchange polymers, collagens and kitines. All these materials (natural or synthetic) consist of polymeric chains cross-linked in networks.The purpose of the work is the design of a muscle that has a similar structure derived from the original contractile pneumatic McKibben muscle. Some artificial muscles are conceived with chemomechanical power generation (by swelling and shrinking of materials inside the muscle) in the GARI Laboratory of DGE-INSAT. So these muscles with a contractile covering are rather similar to natural muscles due to their power supply and their covering.The first part of this paper gives a brief review of chemomechanical transformations of “soft gels” (hydrogels and organogels) and “hard gels” (ion exchange polymers). The soft gels are obtained either by an irreversible chemical reaction between preexisting linear chains (chain cross-linking) or by polymerisation of monomers, some of which having more than 2 reacting groups. They are able to retain a liquid in their tridimensional network. Factors (solvent, pH, temperature, electric field) provoking a modification of the network/liquid equilibrium can induce drastic volume changes. In the case of ion exchangers with weak basic groups, chemomechanic transformations result from an effect of the solvation in aqueous phase. For such polymers which have a granular morphology, addition of acidic or alkaline solutions provokes a swelling-deswelling cycle which can be controlled by the reaction stoechiometry.The second part is devoted to artificial muscles using these materials. At first, the ideal artificial muscle relative to the natural muscle performances is defined. Then, some chemomechanical muscle systems are presented including the robotic fish, worm-like muscle, gel fish, gel finger found in literature and our muscle constructed in the DGE-INSAT, in collaboration with GPI-INSAT and ENSIGC.The third part shows the chemomechanical actuators and the actuator function. Then the main characteristics of usual drive systems (electric, hydraulic and pneumatic actuators) are reviewed. The chemical actuator projects are presented : gel finger micro robot, gel motor, gel arm, robotic gripper abroad, our chemomechanical actuator using polymeric gels or ion exchange polymer in an adapted structure of the McKibben muscle type in Toulouse. The identification of the dynamic behavior (isotonic and isometric) has been achieved (using the MATLAB toolbox) for the ion exchange polymer muscle. This modelling is necessary for the computer control of the actuator using two chemomechanical muscles.It is now possible to consider how mechatronic actuation systems to drive a robot joint can be constructed, based on the performance range of the natural muscle : power/weight ratio, light, durability, flexibility, easy control in stabilisation and tracking of trajectory, low cost and low sensitivity to radiations.

特集：エネルギー変換 人工筋肉モデル ケモメカニカル高分子が生みだすもの

The isothermal conversion of chemical energy into mechanical work underlies the motility of living organisms. Chemomechanical systems based on the synthetic polymer gels are the only artificial systems able to convert chemical energy directly into mechanical work. They may have potential uses where power supply is limited, and actually some chemomechanical devices were developed. This brief article describes the principles, fundamental behaviors and potential applications of these systems.