Periodic Reporting for period 1 - SAM (Soft Artificial Muscles)
Période du rapport: 2021-03-01 au 2023-02-28
The development of bioinspired materials that can expand and contract like animal muscles is a key step in the advancement of several scientific fields, especially robotics and medicine. Muscles exhibit a unique combination of softness, mechanical resistance, adaptability and the ability to undergo large anisotropic deformations, which is so far unmatched in artificial materials. The aim of this fellowship is to develop a novel class of nanocomposite materials that mimic natural muscles by combining stimuli-responsive hydrogels (SRH) and colloidal liquid crystals (CLC). SRHs consist of a network of stimuli-responsive polymer chains and a high fraction of water. By changing the solubility of the polymer with stimuli such as temperature and light it is possible to control the amount of water in the network, thereby producing large volumetric variations. SRHs are soft and shape-compliant actuating materials like muscles, but they generally exhibit poor mechanical resistance and the volumetric expansion has no preferential direction. These limitations will be overcome by attaching the stimuli-responsive polymer chains to anisotropic colloidal particles and assembling these building blocks in a uniaxially oriented manner like CLCs. The resulting nanocomposites will be soft, yet strong, capable of actuation-like conventional SRHs, and their expansion/contraction will be directional, thanks to the preferred orientation of the colloidal particles. The proposed platform rely on a modular design and will use rod-like cellulose nanocrystals (CNCs) as model colloids. These materials are inexpensive, biocompatible and can be extracted from renewable resources. The combination of CNC with stimuli-responsive hydrogel polymers into odered and axially oriented structures will afford a novel class of soft actuators that will bring significant advancement to fields like robotics and medicine.
In the 10 months of the fellowship, most of the efforts have been focused on building a computational protocol for predicting the actuation properties of artificial muscles composed of aligned cylindrical colloids grafted with stimuli-responsive polymers. The simulation protocol was successfully developed using the Sheutjens-Fleer self-consistent field (SF-SCF) method. The protocol allows to predict stroke, force and several other parameters of the artificial muscles. The results illustrate the effect of various relevant parameters such as solubility of the polymers, polymer chain lenght, grafting density on the particle surface and background salt concentration, and suggest that the actuation properties of the proposed artificial muscles will match or even exceed those of animal muscles.
With the remaining time, we optimized a workflow based on depolarized dynamic light scattering (DDLS) and small-angle X-ray scattering (SAXS) to characterize the building blocks of the artificial muscles. We used commercial and well-characterized cellulose nano-crystals (CNC) to benchmark our characterization protocol. Finally, we assessed the colloidal stability of the CNC in solution by means of static light scattering (SLS).
With the remaining time, we optimized a workflow based on depolarized dynamic light scattering (DDLS) and small-angle X-ray scattering (SAXS) to characterize the building blocks of the artificial muscles. We used commercial and well-characterized cellulose nano-crystals (CNC) to benchmark our characterization protocol. Finally, we assessed the colloidal stability of the CNC in solution by means of static light scattering (SLS).
During the fellowship, a radically new type of soft actuator (artificial muscles) has been designed and theoretically investigated. A simulation protocol that is fast and allows predicting the properties of such materials has been developed and used to perform systematic investigations. The results show that the properties of the artificial muscles can be carefully modulated by playing on several system parameters to meet different types of demands, and confirm the potential of the technology proposed in this fellowship. The work will soon be published in the form of an open-access peer-reviewed publication that is expected to help the community developing a new generation of soft artificial muscles.
Furthermore, the computational workflow developed in the fellowship can be easily adapted to study the properties of soft actuators bearing spherical or plate-like colloidal particles or to study actuation by temperature-responsive neutral polymer chains.
Furthermore, the computational workflow developed in the fellowship can be easily adapted to study the properties of soft actuators bearing spherical or plate-like colloidal particles or to study actuation by temperature-responsive neutral polymer chains.