Construction Of Natural Polymer Powder Adhesive And Development Of Medical Dressing

In the event of a serious skin injury,the wound needs to be dressed quickly to prevent infection and promote healing.Wound healing goes through four main stages:hemostasis,inflammation,proliferation,and remodeling.In clinical practice,bioadhesives have partially replaced sutures and tissue fixation staples to join tissues together and promote healing and control or prevent bleeding.However,adhesion in a wet environment remains a great challenge for bioadhesives.In the presence of liquids,the hydrated layer on the surface of the adherent material can prevent adhesives from forming interactions on the surface or cause swelling stresses that can lead to adhesion failure.Most medical adhesives have low adhesion strength to blood or adipose tissue,and improving the wet adhesion of adhesives is a hot topic of a great deal of research.The research in this thesis selects natural polysaccharides and gelatin similar to extracellular matrix as materials,based on the construction mechanism and adhesion mechanism of medical dressings,and prepares a series of new natural polymer composite adhesives that combine the functions of absorbing exudate,moisturizing,hemostasis and promoting healing,etc.The innovative application form of powder dressing can adapt to irregularly shaped wounds,rapidly absorb blood and wound exudate to form hydrogel,and It forms a stable adhesion interface with the wound so that it can perform its function perfectly.The second chapter of this paper is based on the cross-linking of hyaluronic acid derivatives（OHA）and gelatin（Gel）to construct powdered adhesive dressings.In this part of the work,different formulations of powder adhesives were prepared by controlling factors such as molecular weight of hyaluronic acid（high,medium and low）,degree of aldolization（high,medium and low）,and the ratio of aldehyde and amino groups（1:2,1:1,2:1）.In industrial production,the adoption of different preparation processes also has an impact on the performance of the products.The preparation of powder binders in this part is divided into two methods:one is to mix OHA and Gel powder directly,i.e.,physical mixing,and the other is to pre-crosslink OHA and Gel and then lyophilize the powder,i.e.,secondary lyophilization.The adhesion mechanism was investigated by studying the differences in mechanical properties,swelling and adhesion of different formulations of binders with different preparation processes.Through the screening study of the formulations,it was elaborated that the products prepared by the secondary lyophilization process have excellent mechanical properties,certain swellability and strong adhesion,which can reach more than 20 k Pa.In addition,the cohesive energy of gelatin curing and powder binder forming hydrogel plays a major role in the rheology and adhesion of powder binder.The work in the third chapter of this paper is based on the single network powder binder prepared by OHA and Gel in the previous chapter,and further constructs a double network cross-linked（DN）powder binder by introducing sodium alginate（SA）and calcium chloride（Ca Cl₂）as the second heavy cross-linked network.The balance between the adhesion capacity and the intrinsic strength of the powder binder is sought by controlling the viscosity and the degree of ion chelation of SA and the mixing ratio（1:2,1:1,2:1）of these two cross-linked network systems.Through the comparative study of single and double cross-linked network powder adhesives in terms of physicochemical properties,swelling properties and adhesion strength,it was found that the addition of SA/Ca Cl₂ improved the mechanical properties and reduced the swelling rate of DN adhesives,and that DN adhesives could absorb more interfacial water than single network OHA/Gel adhesives,overcoming the effect of poor wet adhesion while keeping the adhesion properties unchanged.In addition,when the OHA/Gel system and SA/Ca Cl₂ system are mixed in a1+1 mass ratio,the cohesive energy and interfacial energy are balanced and the adhesion force is the strongest.In addition,the powder adhesive prepared in this topic is biocompatible,degradable in vivo,without obvious inflammatory reaction,and promising to develop into a new natural polymer composite adhesive integrating the functions of absorbing exudate,moisturizing,hemostasis and promoting healing.In summary,this paper addresses the shortcomings of current powder adhesives in clinical use,and through formulation screening and investigation of adhesion mechanisms,a series of powder adhesives based on natural polymers with both mechanical properties and adhesion are constructed,which can be adapted to different sites and different types of wound treatment.In addition,their lower production cost and environmentally friendly processing steps are promising to develop into new commercializable medical dressings.