Based on its involvement in hemostasis and wound repair fibrinogen has become a very promising biopolymer for tissue engineering scaffolds. Nanofibrous fibrinogen scaffolds are particularly attractive as they can mimic the native nanoarchitecture of fibrous blood clots and the extracellular matrix (ECM). To date, fibrinogen has primarily been processed into nanofibers using electrospinning. However, this process requires high protein concentrations up to 200 mg/ml and uses organic solvents and high electric fields, which can impede the biological functionality of the protein.
Here, we introduce a novel biofabrication technique to prepare 3D-fibrinogen scaffolds on a large scale using salt-induced self assembly. With scanning electron microscopy (SEM) we observed that different salt buffers including PBS and sodium phosphate reproducibly yielded fibrinogen nanofibers upon drying.(1) A pH regime between 7 and 9 resulted in the formation of nanofibers while acidic pH did not yield any fibers. We could induce fibrillogenesis on different hydrophilic and hydrophobic substrate materials with protein concentrations of only 2 mg/ml. Fiber diameters varied from 100 to 300 nm, which is in the range of native ECM and fibrin nanofibers. By adjusting the salt concentration we could already fabricate macroscopic nanofibrous fibrinogen scaffolds with dimensions in the centimeter range and a thickness of several micrometers.
When we added a customized fixation and washing step after the fiber assembly we could prepare either free-standing or immobilized fibrinogen scaffolds. This feature was controlled by the choice of underlying substrate material.(1) SEM analysis of the fibrous fibrinogen networks after the final washing step revealed that the fiber morphology of immobilized and free-standing scaffolds was preserved during this treatment.
In summary, our new self assembly process offers a simple and well adjustable platform to fabricate 3D-fibrinogen scaffolds under physiological conditions. In contrast to electrospinning our new method only requires very low protein concentrations. The unique possibility to choose between immobilized and free-standing scaffolds makes this biofabrication route highly attractive to prepare nanofibrous fibrinogen biomaterials for versatile tissue engineering and wound healing applications.
(1) Stapelfeldt, K., Mednikova, P., Brüggemann, D.: Fibrous, biocompatible 3D-fibrinogen scaffolds, patent application pending, 2018