Biomimetic Actuation and Tissue Growth

Natural materials may change their shape and structure throughout their lifetime. Examples range from the development of organs during embryogenesis, the healing of damaged tissues, to passive humidity driven plant motion. Such examples are driven either through the formation of new tissue in particular locations or via the heterogeneous deformation of already existing tissues. The resultant macroscopic shape change is then controlled by geometry - the geometry of the constraining environment and the geometry of how the deforming tissues are arranged inside the material itself. In this group we investigate this general theme with a focus on two main directions using both theoretical and experimental techniques:

1. The materials design of natural and biomimetic actuators
2. The effect of geometry on collective cell behaviour or tissue growth

Finite element simulation of twisting induced by swelling. The motion is controlled by the geometric arrangement of the swellable elements (grey), for more information see (Turcaud et al 2011)	Tissue formation by pre-osteoblasts in a square pore (left) compared to a simple curvature driven growth simulation (right). see (Rumpler et al 2008)

Biomimetic Actuation

Our inspiration comes from plant systems (See also the groups of Michaela Eder and Ingo Burgert), which can show complex motion through the passive absorption of water, for example in the pine cone and wheat awns. These systems are particularly interesting in that the organs are both structure and motor in one, the motion being controlled by the geometric arrangement of constituent tissues with different swellabilities. Our main focus is here is to firstly develop mechanical models for simple biomimetic systems, and to apply these to natural plant systems. Furthermore, we are interested in exploring the design space of actuation driven by material architecture. We then aim to apply these design principles learnt to new biomimetic composites.

• Goswami, L., et al. (2008). Stress generation in the tension wood of poplar is based on the lateral swelling power of the G-layer. Plant Journal, 56(4), 531–538.
• Harrington, M. J., et al. (2011). Origami-like unfolding of hydro-actuated ice plant seed capsules. Nature Communications, 2, 337–7.
• Abraham, Y., et al. (2011) Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn. Journal of the Royal Society, Interface, online.
• Turcaud, S., et al. (2011). An excursion into the design space of biomimetic architectured biphasic actuators. International Journal of Materials Research, 102, 607–612.
• Stoychev, G., et al. (2012). Shape-Programmed Folding of Stimuli-Responsive Polymer Bilayers . ACS Nano, DOI: 10.1021/nn300079f

Tissue Growth

In addition to being controlled by biochemical factors, tissue growth is also effected by the physical properties of the local cell environment such as stiffness and shape. We are particularly interested in evidence that the local geometry, namely the surface curvature of the substrate, controls the rate of cell proliferation and resultant tissue growth. Our goal is to combine theoretical models for tissue growth with in-vitro cell-culture experiments in order to understand the observed dependence of growth behaviour on curvature. We then aim to use our models to better understand the role of geometry on processes such as bone healing and remodelling (See also the groups of Wolfgang Wagermaier and Richard Weinkamer).

• Rumpler, M., et al. (2008). The effect of geometry on three-dimensional tissue growth. Journal of The Royal Society, Interface, 5(27), 1173–1180.
• Dunlop, J. W. C., et al. (2010). A theoretical model for tissue growth in confined geometries. Journal of the Mechanics and Physics of Solids, 58(8), 1073–1087.
• Kommareddy, K. P., et al. (2010). Two stages in three-dimensional in vitro growth of tissue generated by osteoblastlike cells Biointerphases, 5(2), 45–52.
• Kollmannsberger, P., Bidan, C. M., Dunlop, J. W. C., & Fratzl, P. (2011). The physics of tissue patterning and extracellular matrix organisation: how cells join forces. Soft Matter, 7, 9549-9560.
• Bidan C. M. et al. (2012). How Linear Tension Converts to Curvature: Geometric Control of Bone Tissue Growth . PLoS ONE 7(5), e36336, doi:10.1371/journal.pone.0036336