Study On Antibacterial Nano-Dialdehyde Microfibrillated Cellulose/Gelatin Composite Hydrogels

Antibacterial wound dressings play an important role in wound healing and infection treatment.When the skin is seriously injured,it will lead to damage of the epidermis and the whole dermis,rapid loss of body fluids,decreased immunity,and weakened self-repair ability.In order to protect the wound and promote healing,proper dressings are needed to replace the damaged skin.The excellent biocompatibility makes gelatin hydrogels the good choice for wound dressing.However,the most obvious disadvantages of gelatin hydrogels are low mechanical strength and poor antibacterial properties.In this paper,the mechanical strength was improved by incorporating a surface modified cellulose nanofibrils.Two different types of antimicrobial agents,carboxymethyl chitosan and single-walled carbon nanotubes,were introduced to enhance the antibacterial properties of the gelatin-based hydrogels.(l)Nano sized microfibrillated cellulose(MFC)was obtained by high pressure homogenization following an alkali pretreatment.MFC microfibrils were tangled with each other and presented a three-dimensional network structure.Then,MFC was surface oxidized into dialdehyde microfibrillated cellulose(DAMFC)by NaIO4.DAMFC crosslinked with carboxymethyl chitosan(CMCS)composite hydrogels were studied.SEM results showed that the composite hydrogels had continuous three-dimensional pore structure.FT-IR revealed that the aldehyde group on the molecular chain of DAMFC reacted with the amino group on CMCS to form a C=N covalent bond.With the content of DAMFC increased from 5 wt%to 15 wt%,the compression strength increased significantly from 53.6 kPa to 230.5 kPa.And with the increase of DAMFC content,the gel time was shortened from 5 minutes to 29 seconds.(2)The effect of natural antimicrobial agent carboxymethyl chitosan(CMCS)on nano-dialdehyde microfibrillated cellulose/gelatin(DAMFC/Gel)composite hydrogels was studied.The SEM images showed that a porous network structure was formed in the composite system,with a pore size 2-8 ?m.The highest compression strengtih reached 2.28 MPa,which was 16.3 times that of pure gelatin hydrogel.The swelling experiment showed that the composite hydrogels could maintain the shape in PBS(pH=7.4)buffer solution for at least 72 h without break down,and the swelling ratio reached 1220%.CMCS/DAMFC/Gel showed powerful antibacterial effect against E.coli and S.aureus.The antibacterial ratio against E.coli reached 99.91%and against S.aurens 98.77%.The addition of carboxymethyl chitosan can inhibit the growth of bacteria obviously.(3)The effect of single-walled carbon nanotubes(SWCNT)on the structure and properties of nano-dialdehyde microfibrillated cellulose/gelatin(DAMFC/Gel)composite hydrogels was studied.The SWCNTs were dispersed very evenly in the matrix.The composite hydrogels have uniform and continuous network structure.At high SWCNT content,SWCNT tends to accue ulate in the composite,and therefore,leads to a decreased average pore size.This is also consistent with the compressive strength test(compression results tend to increase first and then decrease).The swelling experiment shows that the hydrogel can absorb about 7 times of its own dry weight and maintain shape stability for 72 h.It was found that the addition SWCNT significantly improved the antibacterial properties of the gelatin hydrogel.In the range of dosage set in this experiment,the antibacterial ratio of the composite hydrogel against E.coli was up to 83.71%.The antibacterial ratio against S.aureus reached 98.51%.SWNCT/DAMFC/Gel composite hydrogels are expected to be applied in wound dressings to reduce the bacterial infection on the wound surface.