Stimuli-responsive gel based microfluidic switch

Elastic instabilities such as buckling, wrinkling and creasing of surfaces, and snapping transitions have historically represented mechanical failure in thin films. However, this does not have to be the case and elastic instabilities, particularly on soft polymer surfaces, can provide reversible control, sensing or actuation in response to well-defined signals or changes in their environment. In previous work, I have shown that surface instabilities can be electrically triggered on a gel surface supported by specifically designed underlying electrodes. The demonstrated actuation required a low voltage of 2 - 4 V. (Adv Mater. Vol 25, 2013) and a rapid actuation was also obtained with response times less than 1 second. This project uses the above insights together with my established understanding and experience in surface instability (mechanics) and materials science to produce a robust electric voltage controlled switch to regulate the liquid flow in a micro-channel.

Practically, the project will focus on understanding a hydrogel based micro-system that will allow quantitative determination of the following: i) the conditions under which buckling occurs and how the onset of buckling depends on the materials properties of the soft surface, the environmental parameters (Ionic values, temperature, pH values) and the electrode geometries; ii) how the morphology of buckling relates to the materials properties of the soft surface, the initial swelling state prior to the actuation, and the electrode geometries; iii) how to trim the buckled shape of the gel layer to effectively control the fluid flow in a micro-environment. Using the understanding from these experiments, a responsive gel based switch will be developed to dynamically regulate the liquid flow in a micro-channel.

The work of this project is cross disciplinary and includes mechanics, materials science and micro-engineering. A range of materials innovations will be used from lithographically produced structural electrodes to gel chemistry. The passive valve technology with an 'on-demand' actuation described in this project is situated in a broad scientific context (chemistry, applied physics, chemical-physics, micro-engineering, chemical engineering, and electro-chemistry). The project will provide the understanding needed to allow future development of novel micro-fluidic devices with high integratibility and automation of liquid flow.

1.Knowledge and Techniques
Using responsive materials-based passive valves to regulate fluid flow has the potential to bring a high degree of integration and automation to micro-fluidic device design, by reducing additional macroscopic moving parts and creating an easy-to-integrate platform with microelectrodes on a silicon substrate. The scientific and technical key to the proposed method is to electrically actuate an elastic buckling instability to translate in-plane strain energy into out-of-plane displacements/deformation of the gel. The project is based on an existing scientific phenomenon - surface instability, whose fundamental science has been understood during the last decade. New knowledge on the electro-actuation of surface buckling will lead to a better understanding of how to control surface instabilities, thus this approach will greatly accelerate translation to industrial products. From a wider technological perspective, the electro-buckling induced passive valve technique in this project can offer rapid switching to control flow in a micro-channel. It will provide a proof of concept for a high performance integrated microfluidic system as a key unit, in terms of the improved efficiency, low cost, and improved automation. Creating a method to integrate a passive valve by adopting electro-active materials is promising for controlling fluid flow within multifunctional chip devices, with potential development of the products in biology, tissue engineering, chemical engineering, etc.

2.Economic Impact (Direct and Indirect User Collaborations)
A key priority for the UK economy is the development of high-value and specialist manufacturing, underpinned by research which is often inherently multidisciplinary and disruptive. My industrial collaborator Reece Innovation, part of Reece Group Ltd (including Pearson Engineering, Responsive Engineering Group and Velocity UK Ltd), is focused on developing innovatively engineered products for new markets. The companies in the wider Reece Group have interests in subsea, oil and gas, and defence technologies, all of which have products related to the areas of materials science and micro-engineering in this project. Reece Innovation is based in Newcastle and develops long term engagements with Universities rather than single project collaborations. Our partners' global network of clients and suppliers will ensure the project has international reach and impact. Reece Innovation will bring industrial insight to the project and ensure benefits from any IPR can be quickly identified and exploited. They are also potential partners for future spin-off projects funded directly (under non-disclosure agreements), via Innovate UK/Technology Strategy Board (via KTPs or otherwise) or with other partners in, for example, EU Horizon 2020 projects. Where there are no concerns relating to IPR/NDAs, I will publicize and disseminate work via presentations at KTN events, publication of research, and presentation at national/international conferences.

3.People Pipeline and Public Engagement
The training of the postdoctoral researcher and a university funded PhD student with skills relevant to high value manufacturing will benefit both the individuals and UK industry. The experience gained will include (i) clean-room techniques, (ii) materials, (iii) measurement and instrumentation, (iv) microfluidics, (v) mechanics, and (vi) device design and fabrication. They will receive training in public understanding and engagement, and will be involved in exhibition and outreach work through Think Physics (https://www.northumbria.ac.uk/about-us/academic-departments/physics-and-electrical-engineering/thinkphysics/) from an early stage. This will benefit the individuals and also attract wider interest from the public by promoting the spirit of science and highlighting everyday impacts which arise from this research.