Researcher’s led by Prof. Hongbo Sun at Tsinhua university, Beijing has put the protein bovine serum albumin (BSA) to use as a muscle in microstructures. Microstructures fabricated by two-photon laser direct writing constituted two different polymers. Major part of the strutcure was constructed from the epoxy bisphenol-A based photoresist SU8. Additional features of photo-crosslinked BSA were added over the SU8 cured structures. A graphic representation of a micro-sized spider structure designed for demonstrating multimaterial integration and actuation can be seen in Figure 1(a).
Figure 1. Two-polymer functional structure fabricated from the epoxy bisphenol-A based photoresists SU8 and a hyrogel structure
The structure of proteins is complex, it is characterized as primary, secondary, tertiary and quaternary structures. The primary structure constitutes the sequence of amino acids that link up to for the protein. The primary structure of bovine serum albumin (BSA) is seen in Figure 1. Primary structure governs the folding of the proteins and the intramolecular bonds that arise within the three-dimensional structure of proteins. Hydrogen bonding between spatially proximate amino groups and carboxyl groups lead to formation of helices which constitute the secondary structure of the protein. There are a number of folds in a single protein chain is called its tertiary structure. The quaternary structure of proteins is dictated by the combination of multiple polypeptide arrays giving specific shapes. Quaternary structure of BSA can be seen in Figure 1 where several polypeptide units blue helices orange helices or re-helices. The final aggregated shape of BSA is called its quaternary structure. An interactive 3D visualization of the quaternary structure of BSA can be seen in Figure 2. The 3dmpl visualization can be pinched, zoomed or rotated in the visualization window. Upon rotating it can be seen that the 3D visualization has the same heart shaped structure as seen in the cartoon given in Figure 2.
Figure 1. The amino acid sequence in BSA. Reproduced from: https://doi.org/10.1186/s13065-019-0581-z11
Figure 2. This is the crystal structure of Bovine Serum Albumin (BSA) . You can zoom and interact with the molecular structure within the molecule display window.
Figure 3. pH depended change in the charge amino acids in the BSA sequence. Positive and negative charges developed in various molecular positions are key to the actuation behavior of BSA structures.