Engineering of fibrin-specific biocompatible microgels for the use as hemostatic agents
Biomaterials
Polymer Materials
Preparatory and Physical Chemistry of Polymers
Final Report Abstract
The need of efficient hemostats to stem blood flow is clearly reflected by the high mortality rates reported among trauma patients resulting from excessive bleeding and severe complications concomitant with the injury. The research within this project focused on the development of plateletmimicking particles from microgels composed of biocompatible polymers carrying polyethylene glycol (PEG) sidechains and fibrin-targeting peptides. Noteworthy, the softness of the particles was demonstrated to be essential to enable multiple binding to fibrin, to form local areas with high fiber density, and finally to induce overall clot contraction. Therefore, particles were prepared via free radical polymerization from oligo ethylene glycol methacrylate (OEGMA) and methacrylic acid (MAA) in the absence of a cross-linking agent. At low reaction temperatures, self-crosslinking through chain transfer reactions at the sidechains result in the formation of microgels with enhanced deformability. This is shown, for instance, in the enhanced spreading of particles deposited onto solid surfaces as detected by AFM. Additionally, AFM nanoindentation experiments demonstrate that crosslinker-free microgels are characterized by elastic moduli that are significantly smaller than PEG-DA cross-linked microgels prepared at otherwise identical conditions. In the next step, cross-linker-free microgels were rendered fibrin-specific by chemoligation of variable domain-like recognition motifs (sdFvs) that show high affinity for nascent fibrin fibers in the nM range but minimal binding to the soluble abundant precursor fibrinogen. Associated with the strong adhesion between PEG-based platelet-like particles (PEG-PLPs) and nascent fibrin fibers regions of high fibrin density are formed throughout the fibrin clot. The results shown here strongly indicate fibrin-induced particle assembly which leads to a synergy effect between local fibrin network collapse and the increase of local particle number density. The alteration of the fibrin microstructure leads to a significant improvement of the robustness of microgel-enriched fibrin gels. This is demonstrated by the ~4 fold increase of the average Young´s modulus. Mechanical stabilization by PEG-PLPs is comparable to the stiffening effect observed in platelet-rich clots, although less pronounced. Moreover, it could be shown that PEG-PLPs stabilize the fibrin clot against plasmin-induced fibrinolysis. This finding is very promising, since administration of PEG-PLPs might lead to longer lifetimes of the fibrin clot in vivo without the use of antifibrinolytic therapies.[28,32] Additionally, the application of PEG-PLPs greatly diminishes the fluid flow through the fibrin clot without limiting the diffusion of biomolecules through the fibrin network. This is very important with regards to the active transport of molecules that are essential for the wound healing process. The overall goal of the research project was to design fibrin-specific microstructured material that aids the natural clotting cascade by supporting the formation of robust fibrin clots and by increasing the mechanical strength of the fibrin network. With regards to the observations shown in this work, we can conclude that the fibrin-specific particles developed in this study show platelet-mimetic activity and high potential to be used as synthetic hemostats with application in emergency medicine and other biomedical fields, such as tissue engineering.
Publications
- Ultrasoft, highly deformable microgels, Soft Matter, 2015, 11, 2018-2028
Bachman, H.; Brown, A. C.; Clarke, K. C.; Dhada, K. S.; Douglas, A.; Hansen, C. E.; Herman, E.; Hyatt, J. S.; Kodlekere, P.; Meng, Z.; Saxena, S.; Spears, M. W., Jr.; Welsch, N.; Lyon, L. A.
(See online at https://doi.org/10.1039/c5sm00047e)
