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

非技术：该奖项由马里兰大学帕克分校材料研究部生物材料项目颁发，旨在研究两种生物聚合物与血细胞之间的相互作用。该研究人员的初步研究表明，这些生物聚合物可以将血液转化为凝胶。这种凝胶状的血液让人联想到血液凝固过程中的生理变化，血液凝固是人体用来止血的。因此，这些血液凝胶聚合物可以用作止血剂，即可以阻止严重伤口和损伤出血的材料。该项目的更广泛影响可能包括使用这些生物聚合物作为事故现场应急人员或战场上士兵的救生材料。此外，发现一种不依赖于健康人正常血液中存在的分子的“凝血”机制，可能对患有凝血障碍（如血友病）的患者具有重要意义。在教学、培训和外联活动方面，PI积极培训学生（研究生和本科生），并在代表性不足群体的积极参与下开展外联活动。正在制作YouTube视频，以突出拟议的研究。技术：这个项目是基于研究者最近的发现，一类生物聚合物能够将血液转化为有弹性的、自我支撑的凝胶。这些聚合物是壳聚糖（hmC）和海藻酸盐（hmA）的疏水改性（hm）衍生物。这个项目是基于这样的假设：可逆凝胶是由于：1)在凝胶过程中疏水基团与红细胞膜相互作用的结合；2)脱胶过程是由于生物聚合物疏水性基团与在脱胶步骤中使用的环糊精内部疏水袋的相互作用。本提案将研究机制，以回答为什么这种凝胶发生的问题，以及凝胶是如何与聚合物的结构相关联的。该项目将研究hmC或hmA链上的疏水性基团的作用，它们与血细胞膜的相互作用，以及这些聚合物如何将细胞连接成一个体积填充网络。这种基于自组装的机制的一个独特之处在于，血液凝胶化可以通过引入环糊精（即具有内部疏水袋的糖基超分子）来逆转。据推测，这种逆转，即不结胶的发生，是因为hmC和hmA的疏水基团从细胞中脱离并嵌入环糊精的疏水口袋内。为了测试这些机制，将对一系列长度和疏水单元分数不同的hmC和hmA衍生物进行研究。这些聚合物也将在不同细胞密度下用肝素化或柠檬酸化的牛血液进行研究。流变学技术将用于探测所得凝胶的粘弹性；光学显微镜（明场和共聚焦）将用于在微观尺度上研究所得混合物的结构；散射技术将用于了解纳米级聚合物的构象。此外，各种类型的环糊精将用于逆转凝胶化过程。因此，将确定用于血液凝胶化和脱胶的最佳组合物。在聚合物可用于此类应用之前，有必要对这种可逆凝胶的机制进行彻底的基本了解，这是本项目的重点。影响更广泛的活动包括对学生（研究生和本科生）的教学和培训以及有代表性不足群体积极参与的外联活动。此外，正在制作YouTube视频，以突出拟议的研究。

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.