Spontaneous co-assembly of molecularly designed building blocks into hierarchically ordered, dynamic, hybrid macrotubes

A major limitation in generating materials using bottom-up strategies is the lack of order at the macroscale. In this work, we show that two self-assembling molecules, an elastin-like polymer (ELP) and a peptide amphiphile (PA), can interact to spontaneously to form hierarchically ordered, dynamic, bioactive, macrotubes. An RGD-containing ELP and a PA (C16V3A3K3) were synthesised using standard methods. The addition of PA solution into ELP instigated the formation of a hollow tube that expanded from the lower surface up to the air-liquid inter- face. The tubes were prepared at different pH values, and tempera- tures. Tubular macrostructures were formed when the zeta potential of the ELP was negative, i.e., above pH 5.5, indicating that an electrostatic interaction is involved in the assembly of the two molecules. When tubes prepared at RT were placed at 4 °C, they became less opaque, suggesting that there is also a temperature-dependent interaction between the two molecules. Continuous assembly for 48 h enabled the formation of strong structures that could easily be manipulated with tweezers and were stable in PBS at 37 °C. SEM images of the tubular structures showed that they were composed of a nanofibrous mem- brane, about 20 lm thick. When two tubes were assembled next to each other, they spontaneously fused into a larger tube. These self- assembled tubes, which show dynamic and temperature-dependent behavior have great potential for use in regenerative medicine applications.