Osmotic-driven plant movements are widely recognized as impressive examples of energy efficiency and low power consumption. These aspects motivate the interest in developing an original biomimetic concept of new actuators based on the osmotic principle exploited by plants. This study takes a preliminary step in this direction, by modelling the dynamic behaviour of two exemplificative yet relevant implementations of an osmotic actuator concept. In more detail, the considered implementations differ from each other in the way actuation energy storage is achieved (through a piston displacement in the former case, through membrane bulging in the latter). The dynamic problem is analytically solved for both cases; scaling laws for the actuation figures of merit (namely characteristic time, maximum force, maximum power, power density, cumulated work and energy density) as a function of model parameters are obtained for the bulging implementation. Starting from such performance indicators, a preliminary dimensioning of the envisaged osmotic actuator is exemplified, based on design targets/constraints (such as characteristic time and/or maximum force). Moreover, model assumptions and limitations are discussed towards effective prototypical development and experimental testing. Nonetheless, this study takes the first step towards the design of new actuators based on the natural osmotic principle, which holds potential for disruptive innovation in many fields, including biorobotics and ICT solutions.
This paper reports the chemical synthesis of methoxy poly(ethyleneglycol)-block-poly(ε-caprolactone-co-4-hydroxyvalerate) from ε-caprolactone and γ-valerolactone, a five-membered ring rarely used in chemical synthesis due to its low reactivity. This procedure enabled production of copolymers with controlled ratios of repeating units and molecular weights, as demonstrated by GPC, FT-IR and NMR characterization. Copolymer degradation rate was found to depend on macromolecular composition, and finely tuneable in a wide range of values. Similarly, hydrophilicity was dependent on γ-valerolactone content, and could be accurately controlled by varying the composition of the reaction feed. Importantly, this copolymer showed lower levels of acidic degradation products than other biodegradable polymers, thus resulting in improved biocompatibility. These encouraging results demonstrate the feasibility of the chemical synthesis of a novel and versatile material with interesting properties that fill a gap in the range of commercially available biodegradable polymers.
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