Japan_IPAP: Engineering synthetic neuromuscular junctions to drive the autonomous function of biohybrid robots

Bottom-up synthetic biology aims to reproduce the structures and behaviours of cellular organisms by combining molecules that mimic the structural, functional and information containing roles present in biology. These structures are known as synthetic cells, and they can act as a framework to study biological processes (such as movement or replication), as well as act as miniature test-tubes, within which chemical and biochemical reactions can be carried out.

Over the last 5-10 years, synthetic cells have been developed that can produce protein biomolecules, that if sensed by living cells, can result in a change in cell behaviour. The assembly of defined interfaces between synthetic and living cells could therefore act to control biological systems, mimicking the organisation found in biological synapses where one cell is positioned close to a second, facilitating controlled chemical signalling between the cells. Such structures are essential for communication between the nervous system and muscles, where synaptic communication at the neuromuscular junction (NMJ) controls the contraction of muscles in higher order animals.
In biology, muscle tissue enables animals to move and undertake complex tasks. This has led to the application of engineered muscle tissue in another nascent area of bioengineering - that of biohybrid robots. Biohybrids utilise biological components as a core part of the robot, for example controlling the contraction of muscle tissue to power a biohybrid robot capable of picking up and releasing an object. However, conventional approaches to activating the robot rely on using electrical signals to activate muscle contraction. Whilst this results in successful activation, this approach is damaging to the muscle tissue, limiting the lifetime of the robot and the implementation of this approach in larger biohybrid devices.

This project aims to assemble synthetic cell - muscle tissue interfaces, where expression and release of a communication protein, Agrin, from synthetic cells results in protein clustering in the muscle tissue essential for the eventual contraction of the muscle. In this way we will utilise a biochemical approach to control the contraction of muscle tissue, forming for the first time a synthetic neuromuscular junction. Such junctions could be utilised as a new model to study synapse organisation in biology, lead to new tissue engineering strategies utilising synthetic cell co-cultures, and integrated into biohybrid robots to create a new generation of advanced bioinspired robots with increased functional lifetime.

In order to achieve this we are bringing together world leading research expertise in the UK and Japan with a view to bringing together expertise not available in concert elsewhere in the word: namely Ces (synthetic cells) and Takeuchi (biohybrid systems).

Synthetic cells are biomimetic nano- and micro- constructs that are built from molecular components which are rationally combined to create compartmentalised systems capable of complex behaviours (e.g. motility, communication). These behaviours are observed in their living counterparts, and so synthetic cells can help unravel fundamental understanding of biological processes through a "learning by building" approach as well as underpin the creation of functional microsystems for therapeutics, regenerative medicine and biosynthesis. If integrated into biohybrid robots that exploit novel synthetic biointerfaces with improved functionality over traditionally used mechanical components (e.g. muscle tissues that apply pulling forces to mechanical components upon contraction), synthetic cells could be used to assemble higher order dynamic systems, for example cell-cell interfaces critical to the function of multicellular organisms. By replacing biological components with rationally engineered, simpler synthetic cells, new biointerfaces can be created that bypass the complexity restrictions afforded by tissue engineering approaches that rely on the use of real cells.

Here we propose to develop biohybrid robots that will exploit a new generation of synthetic cell - muscle tissue interfaces that mimic the function of the neuromuscular junction, a synaptic structure essential for the bioelectrical actuation of muscle tissue. In-situ expression and secretion of Agrin proteins from synthetic cells will result in clustering of acetylcholine receptors in muscle, necessary for bioelectrical contraction. The development and validation of a synthetic neuromuscular junction will facilitate the generation of new biohybrid skeletal muscle robots capable of user-independent actuation and pave the way for the integration of synthetic cells in tissue engineering and regenerative medicine.