What do insects and geckos have in common? The answer, from the recent Royal Society conference on cell adhesion, is that their climbing mechanism depends on van der Waals forces (as well as friction and shear stress). However, at a structural and molecular level, the way they attach to surfaces is different. This was the focus of the conference – to understand the forces involved in cell adhesion, how geometry is important, and what we understand about adhesion at a molecular level.
Kevin Kendall (the main conference organiser) introduced the meeting by reminding everyone that it was 100 years since Ross Granville Harrison demonstrated that embryonic cells could be grown in culture outside of an organism – and that cell adhesion was important for this discovery.
A theme throughout the conference was to explore how various problems in adhesion have been tackled in nature – ranging from the attachment of organisms to surfaces or pathogens evading an organisms’ inbuilt defence systems – to give more insight into how such understanding could be mimicked in tissue engineering and give rise to new technologies.
To start the discussions, how organisms bind to various surfaces was explored. Geckos have “amazing feet” according to speaker Kellar Autumn, who has visualised billions of tiny hairs on gecko feet (setae) that enable them to bind to vertical surfaces.
Insects use adhesion pads to bind and climb on surfaces – but several secrete liquids to enable them to ’stick’ (as discussed by Walter Federle and Stanislav Gorb). Organisms need to deal with the fact that in nature, surfaces are not smooth and flat – and this is something that we have now taken into account in the cell culture environment. Indeed, we are using 3D cultures and different types of surface to grow cells.
Florian Rehfeldt talked about the importance of the mechano-chemical environment for cells and how to mimic a “bioenvironment”. Stiffness is essential for inducing differentiation in mesenchymal stem cells. A related problem was also discussed at a larger scale by Otto-Wilhelm Merten – multi-culturing of cells. Whilst adhesion cultures have been less fashionable (apart from growing vaccine cultures) this is now being reconsidered – as adhesion and the right environment is extremely important to maintain the pluripotent properties of stem cells in large-scale production.
Later in the conference, speakers discussed how our technologies can exploit how pathogens invade cells. Stephen Hart talked about liquid-particle nanotechnologies – where the biggest problem is to prevent degradation via endosome-linked pathways. The answer is coming from anionic liposomes, which act in a similar way to viral envelopes, and the hope is to use such technologies for synthetic gene delivery or removal of gene expression through siRNA.
Hart is currently working on deleting genes linked to neurodegenerative disease in rats using this technique. Another discussion focused on mesoporous silica nanoparticles – slightly larger structures that are hoped to bring larger drug volumes as well as siRNA to cells (as discussed by Andre Nel). The aim is to treat various cancers, for example, breast cancer. But safety is of course a concern for this second type of ‘hard’ nanoparticle – much discussion focused on the need to prevent revisiting previous problems of fibrous aggregates, as seen in asbestosis.
Another conundrum throughout the conference – as first raised by George Whitesides – was the role of water in all biological systems. Do we consider water enough in all our models and systems? Not enough according to Whitesides, who went on to comment that this could be the reason why some drug modelling is wrong – as forces and spatial predictions do not take water into account. Note also that the answer to the first question about geckos and insects only holds in the dry – they tend to fall off wet surfaces!
What does the future hold? Whitesides presented gentle ‘soft’ robots – that he hopes will be able to hold delicate objects, such as a liver during surgery. Whilst such ‘humanised’ robots should not replace the need for scientists, he did argue that one of the most important challenges will be to think beyond your own research problem, and he encouraged all to unite as interdisciplinary communities to solve further questions in adhesion over the next 100 years. As an interdisciplinary journal, BMC Biology of course welcomes papers that meet the challenge.