Biomass-based nanofibers for hemostatic application
Creators: name: Mohamed, Elmira
Publisher: name: The Australian National University
Year: 2022

description: Hemorrhage accounts for a large number of deaths in trauma, childbirth and complex surgeries. A variety of nanomaterials, including oxidized cellulose nanofibers, has been studied as hemostatic materials to overcome the shortcomings of commercial hemostats. However, to date, the hemostatic properties of non-oxidized cellulose nanofibers and the influence of nanofibers structural characteristics on their hemostatic properties have not been elucidated. Also, non-green and costly production methods of nanomaterials have impeded their large scale use. The present thesis addresses the above-mentioned gaps by investigating (i) the synthesis of nanofibers from biomass-based sources using a green ball-milling method, (ii) the relationship between the morphology and pro-coagulant properties of nanofibers, (iii) the hemostatic properties and underlying hemostatic mechanisms of morphologically-optimized nanofibers comparing to benchmark commercial hemostats, and (iv) the biocompatibility and biodegradation of morphologically-optimized cellulose nanofibers. Firstly, non-oxidized cellulose nanofibers were synthesized by ball-milling of cellulose for 0 to 180 min. Nanofibers with a highest aspect ratio (166) and a highest specific surface area (17) were obtained after 90 min of milling without altering their chemical and crystalline structure. The systematic studies on the correlation of structural characteristics and hemostatic properties of non-oxidized cellulose nanofibers revealed a direct relationship between the aspect ratio and specific surface area of nanofibers in terms of their maximum contribution to platelet function and plasma coagulation. The morphologically-optimized cellulose nanofibers reduced the clotting time of human blood, by 68% and 88% in a gel and a sponge form, respectively, through contact activation of plasma coagulation and the entrapment of platelets, outperforming benchmark hemostats, Surgicel and Combat Gauze. The morphologically-optimized cellulose nanofibers induced effective hemostasis in the blood of platelet-deficient patients (reducing clotting time by 80%) and the blood treated with heparin (reducing clotting time by 54%). In an in vivo murine liver injury model, the morphologically-optimized non-oxidized cellulose nanofibers reduced blood loss by 38%, outperforming Surgicel (15%). The pH-neutral non-oxidized cellulose nanofibers did not damage isolated red blood cells nor impede the proliferation of cultured fibroblast or endothelial cells, in contrast to the Surgicel. In a murine model, subcutaneous implantation of cellulose nanofibers over 8 weeks showed histologically a resolving foreign body reaction with slow degradation of cellulose nanofibers. Tissue scarring was not evident in contrast to Surgicel. Finally, the new understanding of the structure-performance relationship was applied to produce nanofibers from chitin. Past research has focused on the hemostatic properties of chitosan (deacetylated chitin) nanofibers but not chitin. 5 h of ball-milling resulted in chitin nanofibers morphologically-optimized for hemostatic application. A correlation between morphology and hemostatic efficacy of nanofibers was observed. The morphologically-optimized chitin nanofibers shortened clotting time by 70% and 63% in a suspension and a dry form, respectively. The thesis has made multiple important contributions to the research field of hemostatic nanomaterials; (i) developing new techniques to synthesize nanofibers and to assess hemostatic properties of nanofibers, (ii) obtaining a new knowledge on the hemostatic performance of nanofibers and the role of structural characteristics, and (iii) introducing a new class of promising hemostatic materials with excellent hemostatic performance, minimal toxicity, and good in vivo biocompatibility and biodegradability. The above-mentioned achievements may lead to the development of more effective, economical and less toxic hemostatic materials.