![]() ![]() The researchers aren’t yet sure exactly why the membrane-enclosed blob of PA solution can be so readily transformed into a tube. ‘A major advantage of this system is the possibility to manipulate the tube in real time and with spatiotemporal control, which means that diameter, length, membrane elasticity and even branching may be controlled.’ He notes that the membranes are chemically distinct on the inside and outside, which raises the possibility of giving the two sides different receptiveness to different types of cell, which could be of particular use for growing nerve conduits and blood vessels. ![]() The tubes ‘may be useful as blood vessels or neuronal conduits to guide nerve cell growth’, says Rein Ulijn of the City University of New York. They are stable for months under cell culture conditions, and flexible and relatively strong for a self-assembling material – slightly more so once coated with cells. This means that the ‘shapeable’ tube networks might be used to make complex scaffolds, perhaps even acting as a vascular network, without the need for moulds or templates. They found that mouse stem cells and human endothelial cells from umbilical tissue will successfully colonise the structures in a few weeks. Given the biocompatibility of elastin, Mata and colleagues figured their tubular scaffolds might be good hosts for growing living cells. And as the tube is extruded, it can quickly self-heal any ruptures in the membrane. ‘If we were to inject the peptide drop into a swimming pool of the ELP, and then inside touch it with say your five fingers, you will open five openings around the blob, each the diameter of your fingertips.’ The researchers have extruded tubes as narrow as 800µm, but Mata says he is confident that they could be made narrower still. The extrusion process looks rather like nylon threads being pulled from the interface of the two polymerising liquids.Īny touch will open the membrane, says Mata. In much the same way, if a glass rod touches the wall of the tube, a new tube forms there which can be gently pulled out like a branch. If it is touched top and bottom, it opens into a tube that eventually bridges the top and bottom of the solution, still with the PA solution inside. If the membrane is touched – by a glass rod, a finger, more or less anything – it changes shape over the course of a few minutes, forming an opening where the touch occurred. Electron microscopy showed that this has a multilayered structure, like lasagne, with each layer just a few nanometers thick. The ELP-PA complex may then aggregate to form a membrane. But when the PAs bind to them through non-covalent interactions such as hydrogen bonds and electrostatic interactions, they can be opened up in a manner akin to protein denaturation, as the PAs solubilise hydrophobic parts of the polypeptide. On their own, the elastin molecules collapse into compact blobs in water. When Mata and colleagues added the PA solution to the elastin-like protein (ELP), the PA formed a roughly spherical blob enclosed in a soft membrane, which is composed of an ELP-PA complex. Such peptide amphiphiles (PAs) have been shown previously to be capable of self-assembling in water into structures such as nanofibres and gels, which have themselves been explored as potential scaffolds for cell growth. The basic fabric is a composite of a synthetic polypeptide based on elastin – a stretchy protein found in connective tissue – with a small amphiphilic peptide that has water-soluble head and a fatty, insoluble tail. The structure is self-healing and bioactive, and can support the growth of human cells for tissue engineering.Īlvaro Mata of Queen Mary University of London and collaborators in Israel, Portugal and Spain combined molecular self-assembly with direct physical manipulation to draw out the tubes from a protein-based membrane. An international team of researchers has made tubular protein-based structures that can be shaped into a network by manually pulling out new branches from existing tubes. ![]()
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