Effects of denaturation and association of collagen on adsorption behavior: two-dimensional nanostructure and its property

Surface Engineering for Mechanical Enhancement of Cell Sheet by Nano-Coatings

Cell sheet technology is becoming increasingly popular in tissue engineering and regenerative medicine, due to integrity into versatile organ and manageable cell and tissue type from the bank, and no needs of large volume organ for transplantation. Cell sheets have still a room to resolve the mechanical resistance under load-bearing occasion, easy translocation into organ, and prompt shape modulation for regular application in vivo. Herein, a layer-by-layer (LbL) assembly of nanometer scaled film coating method was introduced to inter-planar cell sheet for multilayered cell sheet (M1) and a single cell before sheet formation (M2). Nano-films with collagen and alginate increased mechanical property of cell sheets without altering cell functions, viability, and proliferation. The moduli of triple layered cell sheet (M1) and (M2) were critically enhanced to 109% and 104%, compared to uncoated cell sheet (CON) with mono-layer, while modulus of CON with triple-layers were increased to 43%. LbL assembly to cell sheets offers increased modulus allowing cell sheet engineering to become a potential strategy under load-bearing environment.

Hydrophobin can prevent secondary protein adsorption on hydrophobic substrates without exchange

By combining several surface analytical tools, we show that an adsorbed layer of the protein H*Protein B prevents the adsorption of secondary proteins bovine serum albumin, casein, or collagen at low-salinity conditions and at pH 8. H*Protein B is an industrially producible fusion protein of the hydrophobin family, known for its high interfacial activity. While applications of hydrophobin have been reported to facilitate adhesion of proteins under different pH conditions, careful analysis by quartz-crystal microbalance and ellipsometry prove that no additional adsorption can be found on top of the H*Protein B layer in this study. Surface analysis by X-ray photoelectron spectroscopy and secondary ion mass spectrometry proves that the hydrophobin layer stays intact even after hours of exposure to solutions of the secondary proteins and that no exchange of proteins can be detected.

Fig. 1

Network structure of collagen layers absorbed on LB film

Elucidating the assembly mechanism of the collagen at interfaces is important. In this work, the structures of type I collagen molecules adsorbed on bare mica and on LB films of propanediyl-bis(dimethyloctadecylammonium bromide) transferred onto mica at zero surface pressure was characterized by AFM. On mica, the granular morphologies randomly distributed as elongated structures were observed, which were resulted from the interlacement of the adsorbed collagen molecules. On the LB films, the topographical evolution of the adsorbed collagen layers upon the increasing adsorption time was investigated. After 30 s, the collagen assembled into network-like structure composed of the interwoven fibrils, called as the first adlayer, which was attributed to its adsorption on the LB film by means of a limited number of contact points followed by the lateral association. One minute later, the second adlayer was observed on the top of the first adlayer. Up to 5 min, collagen layers, formed by inter-twisted fibrils, were observed. Under the same conditions after 1 min adsorption on LB film, the AFM image of the layer obtained in the diluted hydrochloric acid solution is analogous to the result of the sample dried in air, indicating that it is the LB film that leads to the formation of the network structure of collagen and the formation of the network structures of collagen layers is tentatively ascribed to the self-assembly of type I collagen molecules on LB film, not to the dewetting of the collagen solution during drying.