The effect of geometry and material properties on the performance of a small hydraulic McKibben muscle system

Fluidic McKibben artificial muscles are one of the most popular biomimetic actuators, showing similar static and dynamic performance to skeletal muscles. In particular, their pneumatic version offers high-generated force, high speed and high strain in comparison to other actuators. This paper investigates the development of a small-size, fully enclosed, hydraulic McKibben muscle powered by a low voltage pump. Hydraulic McKibben muscles with an outside diameter of 6 mm and a length ranging from 35 mm to 80 mm were investigated. These muscles are able to generate forces up to 26 N, strains up to 23%, power to mass of 30 W/kg and tension intensity of 1.78 N/mm2 at supply water pressure of 2.5 bar. The effects of injected pressure and inner tube stiffness on the actuation strain and force generation were studied and a simple model introduced to quantitatively estimate force and stroke generated for a given input pressure. This unique actuation system is lightweight and can be easily modified to be employed in small robotic systems where large movements in short time are required

Biopolymeric Coatings for Local Release of Therapeutics from Biomedical Implants

Funding Information: S.T., B.M., and J.C. contributed equally to this work. The authors are grateful for funding received from the Australian Research Council Centre of Excellence program (Project Number CE 140100012). J.C. acknowledges the European Research Council Starting Grant (ERC‐StG‐2019‐848325). S.N. and F.D. acknowledge the financial support of Australian Research Council through DP200102164. Publisher Copyright: © 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.The deployment of structures that enable localized release of bioactive molecules can result in more efficacious treatment of disease and better integration of implantable bionic devices. The strategic design of a biopolymeric coating can be used to engineer the optimal release profile depending on the task at hand. As illustrative examples, here advances in delivery of drugs from bone, brain, ocular, and cardiovascular implants are reviewed. These areas are focused to highlight that both hard and soft tissue implants can benefit from controlled localized delivery. The composition of biopolymers used to achieve appropriate delivery to the selected tissue types, and their corresponding outcomes are brought to the fore. To conclude, key factors in designing drug-loaded biopolymeric coatings for biomedical implants are highlighted.publishersversionepub_ahead_of_prin

Simple and strong: twisted silver painted nylon artificial muscle actuated by Joule heating

Highly oriented nylon and polyethylene fibres shrink in length when heated and expand in diameter. By twisting and then coiling monofilaments of these materials to form helical springs, the anisotropic thermal expansion has recently been shown to enable tensile actuation of up to 49% upon heating. Joule heating, by passing a current through a conductive coating on the surface of the filament, is a convenient method of controlling actuation. In previously reported work this has been done using highly flexible carbon nanotube sheets or commercially available silver coated fibres. In this work silver paint is used as the Joule heating element at the surface of the muscle. Up to 29% linear actuation is observed with energy and power densities reaching 840 kJ m[superscript -3] (528 J kg[superscript -1]) and 1.1 kW kg[superscript -1] (operating at 0.1 Hz, 4% strain, 1.4 kg load). This simple coating method is readily accessible and can be applied to any polymer filament. Effective use of this technique relies on uniform coating to avoid temperature gradients

Conductive tough hydrogels

The aim of this thesis was to develop a hydrogel system with enhanced mechanical performance. This hydrogel system has to be preferentially electrically conductive to facilitate possible controlled drug release. To fabricate a tough hydrogel system, a double network (DN) approach was employed by forming two polymer networks interpenetrated in each other with considerably different crosslinking ratios. The new developments in tough hydrogel materials are highlighted in Chapter 1, and their enhanced mechanical performance and corresponding toughening mechanisms are discussed. These tough hydrogels have been mainly developed over the past ten years with many now showing mechanical properties comparable with those of natural tissues. The possibility of employing a conductive hydrogel system for controlled drug release purposes was investigated by studying chitosan hydrogel films containing carbon nanotubes in Chapter 2. A modulated release behaviour was demonstrated by tuning the strength and polarity of the applied voltage, ranging from -0.8 to +0.15 V. Attempts to make stronger hydrogels based on chitosan and other synthetic hydrogel networks resulted in fabricating chitosan-poly(acrylamide) fibres in Chapter 3, with up to, respectively, 11 and 8 times enhancement in modulus and tensile strength compared to PAAm hydrogel. Furthermore, to combine the strengthening mechanisms of hydrogen-bonding and double network hydrogels in forming a toughened hydrogel system, a double network system based on poly(acrylic acid) and a bottlebrush network made of poly(ethylene glycol) methyl ether methacrylates oligomers was made and characterized in Chapter 4. Mechanical properties (tensile, compression) and swelling behaviour of this system at various pHs were studied systematically, along with other physical properties such as transparency and surface contact angle. The results indicated that this system is strongly pH sensitive, with all of the mechanical and physical properties affected by the pH. Finally, a conducting polymer (PEDOT) and carbon nanotubes were employed to introduce conductivity to the aforementioned hydrogel network, and the results are presented in, respectively, Chapter 5 and Chapter 6. Conductivity of hydrogels at various pHs was studied in Chapter 5, showing the DN-PEDOT hydrogels have remained pH sensitive with a conductivity up to 4.3 S/cm at acidic pH. In Chapter 6 the formation of a carbon nanotube-rich sheath around a tough double network hydrogel core via a phase segregation process is described. This phenomenon was observed in various double network hydrogel structures, regardless of the nature and composition of the networks. The obtained hydrogels are potentially applicable in the field of controlled drug release. The conclusion chapter (Chapter 7) summarises the thesis, with a few suggestions for future studies in this field

Effect of tensile load on the actuation performance of pH-sensitive hydrogels

pH-responsive hydrogels are capable of converting chemical energy to mechanical work. To optimize their use as actuators, their response when operating against an external load must be fully characterized. Here, the actuation strain of a model pH-sensitive hydrogel as a function of different constant loads is studied. The experimental actuation strain, produced by switching the pH from 2 to 12, decreases significantly and monotonically with increasing initial tensile load. Two models are developed to predict the actuation strain as a function of applied stress. Simple mechanical models based on the change in hydrogel modulus and cross sectional area due to the change in pH are unsatisfactory as they predict only a small change in actuation strain with increasing external stress. However, the model based on the elastic and mixing free energy functions derived from the Flory-Huggins theory is found to accurately account for the actuation strain as a function of stress

Thermally activated paraffin-filled McKibben muscles

McKibben artificial muscles are one of the most pragmatic contractile actuators, offering performances similar to skeletal muscles. The McKibben muscles operate by pumping pressurized fluid into a bladder constrained by a stiff braid so that tensile force generated is amplified in comparison to a conventional hydraulic ram. The need for heavy and bulky compressors/ pumps makes pneumatic or hydraulic McKibben muscles unsuitable for microactuators, where a highly compact design is required. In an alternative approach, this article describes a new type of McKibben muscle using an expandable guest fill material, such as temperature-sensitive paraffin, to achieve a more compact and lightweight actuation system. Two different types of paraffin-filled McKibben muscles are introduced and compared. In the first system, the paraffinfilled McKibben muscle is simply immersed in a hot water bath and generates isometric forces up to 850 mN and a free contraction strain of 8.3% at 95C. In the second system, paraffin is heated directly by embedded heating elements and exhibits the maximum isometric force of 2 N and 9% contraction strain. A quantitative model is also developed to predict the actuation performance of these temperature sensitive McKibben muscles as a function of temperature

Drug Delivery Based on Stimuli-Responsive Injectable Hydrogels for Breast Cancer Therapy: A Review

Breast cancer is the most common and biggest health threat for women. There is an urgent need to develop novel breast cancer therapies to overcome the shortcomings of conventional surgery and chemotherapy, which include poor drug efficiency, damage to normal tissues, and increased side effects. Drug delivery systems based on injectable hydrogels have recently gained remarkable attention, as they offer encouraging solutions for localized, targeted, and controlled drug release to the tumor site. Such systems have great potential for improving drug efficiency and reducing the side effects caused by long-term exposure to chemotherapy. The present review aims to provide a critical analysis of the latest developments in the application of drug delivery systems using stimuli-responsive injectable hydrogels for breast cancer treatment. The focus is on discussing how such hydrogel systems enhance treatment efficacy and incorporate multiple breast cancer therapies into one system, in response to multiple stimuli, including temperature, pH, photo-, magnetic field, and glutathione. The present work also features a brief outline of the recent progress in the use of tough hydrogels. As the breast undergoes significant physical stress and movement during sporting and daily activities, it is important for drug delivery hydrogels to have sufficient mechanical toughness to maintain structural integrity for a desired period of time