Starch Nanofiber Mats:Preparation,Incorporation Of Silver Nanoparticles,and Application As Wound Dressings

Starch is one of the most abundant natural polymers.It has low cost,high hydrophilicity,excellent biodegradability and biocompatibility,and thus is a potential biomaterial.The nanofibers prepared by electrospinning have similar structure to the extracellular matrix,which can facilitate cell proliferation and wound healing.The high porosity and small pore size of the nanofiber mats are favorable for exudate absorbing,vapor evaporation and microbial invasion prevention.Therefore,starch nanofiber mats are ideal wound dressings.However,as-spun starch nanofibers immediately dissolve in the aqueous physiological environment and are in lack of biological functions,which prevent their biomedical applications.Our group has recently developed a “periodate oxidation – electrospinning – adipic acid dihydrazide crosslinking” strategy for the crosslinking of polysaccharide nanofibers,which worked well for polysaccharides including pectin,konjac glucomannan and pullulan.The polysaccharide nanofibers prepared by this strategy have good water resistance and cytocompatibility.In this work,we adopted this strategy to develop starch nanofibers with water resistance and biocompatibility for biomedical applications.We further incorporated silver nanoparticles into the starch nanofibers to introduce bacteriostatic function,for the application as dressings for the treatment of infectious wounds.The detailed work and results are as follows:In the first part,we utilized the “periodate oxidation – electrospinning – adipic acid dihydrazide crosslinking” strategy to prepare starch nanofiber mats.The physical and chemical structures of the mats were characterized,and their medical properties such as strength,water resistance,and cytocompatibility were evaluated and compared the starch nanofiber mats prepared with the traditional glutaraldehyde crosslinking method.The nanofiber mats prepared with glutaraldehyde crosslinking strategy show only 60 kPa Young's modulus at wet state,retain only 31.9% of their initial mass after 4 weeks in simulated body fluid,and cause toxicity to L929 fibroblast cells.The starch nanofiber mats prepared with the “periodate oxidation – electrospinning – adipic acid dihydrazide crosslinking” strategy exhibit Young's modulus up to 2.65 MPa,can maintain 91.0% of their initial mass after 4 weeks' incubation,and have no toxicity to cells.Therefore,the starch nanofiber mats prepared with the “periodate oxidation – electrospinning – adipic acid dihydrazide crosslinking” strategy have moderate mechanical strength,excellent water resistance and good cytocompatibility,and are promising for biomedical applications.This work solves the water solubility problem of starch nanofibers,and lays a foundation for their biomedical applications.In the second part,we incorporated AgNPs into the starch nanofibers with the in situ reduction method.By optimizing the conditions,we obtained the starch /(AgNPs)composite nanofiber mats with excellent antibacterial and cytocompatibility.The properties such as vapor permeability and absorption of the starch/(AgNPs)composite nanofiber mats were characterized and the dressing efficacy were evaluated.We found that size and content of the AgNPs are dominated by the concentration of the initial silver nitrate solution,which affects the silver release behavior.The cytotoxicity and antibacterial activity of the composite nanofiber mats are both controlled by the release behavior of silver.The cytotoxicity of the mats depends on the silver release rate at early stage,which is governed by both the size and content of the AgNPs.The antibacterial activity is more related to the silver release rate at later stage and is determined mainly by the content of AgNPs.By controlling the concentration of initial silver nitrate solution and optimizing the size and content of AgNPs,we obtained starch/AgNPs composite nanofiber mats with good antibacterial activity and excellent cytocompatibility as well.The composite nanofiber mats also showed moderate wet strength(1 ~ 2 MPa),high liquid absorption capability(19 ~ 34 times of their own weights)and suitable vapor permeability [0.22 ~ 0.26 g/(cm~2·24 h)].The starch/AgNPs composite nanofiber mats are suitable for the treatment of infected and exuding wounds.This work clarifies the relationship between the preparation – structure – properties of starch/AgNPs composite nanofiber mats,which provides an effective way to solve the cytotoxicity of silver-incorporated medical materials.In summary,we prepared non-toxic and water resistant starch nanofiber mats with the “periodate oxidation – electrospinning – adipic acid dihydrazide crosslinking” strategy.Silver nanoparticles were further incorporated into the starch nanofibers by in situ reduction method.By optimizing the conditions,we obtained starch/AgNPs composite nanofiber mats with good antibacterial property and excellent cytocompatibility.The composite nanofiber mats also have medium mechanical strength,high liquid absorption and suitable vapor permeability,and are ideal for treating infections and exuding wounds.