Reversible Gelation of Blood Using Self-Assembling Biopolymers: Understanding the Mechanism for Reversible Self-Assembly

University Of Maryland, College Park, College Park MD

Investigators

Abstract

Non-Technical: This award by the Biomaterials program in the Division of Materials Research to University of Maryland at College Park is to study the interactions between two types of biopolymers and blood cells. Preliminary studies by this researcher have shown that these biopolymers convert blood into a gel. Such gelation of blood is reminiscent of the physical changes during blood clotting, which is used by the body to stop bleeding from an open wound. Accordingly, these blood-gelling polymers could be used as hemostatic agents, i.e., materials that can stop bleeding from serious wounds and injuries. The broader impacts of this project could include the use of these biopolymers as life-saving materials by emergency responders at accident sites or by soldiers in the battlefield. In addition, the discovery of a "clotting" mechanism that does not depend on the molecules present in normal blood of healthy people could prove to be significant for patients who suffer from clotting disorders such as hemophilia. With respect to teaching, training and outreach activities, the PI is active in training students (graduate and undergraduate) and outreach activities with active participation of underrepresented groups. YouTube videos to highlight the proposed studies are being developed. Technical: This project is based on the investigator's recent finding that a class of biopolymers are capable of converting blood into an elastic, self-supporting gel. These polymers are hydrophobically modified (hm) derivatives of chitosan (hmC) and alginate (hmA). This project is based on the hypothesis that the reversible gelation is due to: 1) binding of the hydrophobic group's interaction with red blood cell membranes during the gelation process; and 2) the degelation process is due to the interaction of the biopolymer hydrophobic groups with the inner hydrophobic pockets of cyclodextrins used in the degelation step. This proposal will study the mechanism to answer the question of why such gelation occurs, and how gelation is correlated to the structure of the polymers. This project will study the role of hydrophobic groups from hmC or hmA chains, their interactions with membranes of blood cells, and how these polymers interconnect the cells into a volume-filling network. A unique feature of this self-assembly-based mechanism is that blood gelling can be reversed by introduction of cyclodextrins, i.e., sugar-based supramolecules with an inner hydrophobic pocket. It is hypothesized that this reversal, i.e., ungelling, occurs because hydrophobic groups from hmC and hmA unbind from the cells and embed within the inner hydrphobic pockets of cyclodextrins. To test these mechanisms, studies will be carried out with a series of hmC and hmA derivatives varying in the length and fraction of hydrophobic units. These polymers will also be studied with heparinized or citrated bovine blood at various cell densities. Rheological techniques will be used to probe the viscoelasticity of the resulting gels; optical microscopy (bright field and confocal) will be used to study the structure of the resulting mixtures at the microscale; and scattering techniques will be used to understand the conformation of the polymer at the nanoscale. In addition, cyclodextrins of various types will be used to reverse the gelation process. Thus, the optimal compositions for both gelation and degelation of blood will be identified. Before the polymers could be used for such applications, a thorough fundamental understanding of the mechanism for this reversible gelation is necessary, which is the focus of this project. The broader impact activities included teaching and training of students (graduate and undergraduate) and outreach activities with active participation of underrepresented groups. In addition, YouTube videos to highlight of the proposed research are being developed.