The Design And Properties Of Bacterial Cellulose-based Medical Hydrogels

With the development of life sciences,the exploitation of new green and renewable biomedical materials has attracted extensive attention from researchers.Bacterial cellulose(BC)is a natural nanofiber produced by the metabolism of microorganisms such as Bacillus cereus.Its fiber structure is formed by self-assembly through extracellular hydrogen bonding and has the advantages of high purity,high crystallinity,high polymerization,ultra-fine nanofiber structure,high mechanical properties and good biocompatibility,etc.It has been widely used in biomedical fields such as injury repair and drug carriers.The requirements for material properties in the biomedical field are diverse;however,BC hydrogels produced by bacteria have a single structure,resulting in non-tunable mechanical properties,and their antimicrobial properties,antioxidant properties,and environmental responsiveness are often difficult to meet the application requirements.Therefore,it is urgent to modulate the chemical structure of BC to improve its mechanical properties and enrich its biomedical functions to meet the requirements of different scenarios of biomedical applications.In this paper,the preparation of BC nanofibers and the modification strategies were fully investigated to achieve the controlled design of functional active groups on the surface of BC for the application needs in the fields of tissue repair and drug carriers,and a series of multifunctional BC-based composite hydrogels were constructed to explore their application effects in the fields of helical neuron growth,intestinal anastomosis wound repair,and drug delivery to inhibit intestinal tumors.The main research contents are as follows:(1)Study of bacterial cellulose-based hydrogels as neural tissue engineering scaffolds to induce spiral neuron growthBC nanofibers were used as raw materials to obtain TEMPO-oxidized BC nanofibers(TOBC)by selective oxidation of C6 hydroxyl groups on the BC surface by 2,2,6,6-tetramethylpiperidine oxide(TEMPO)oxidation,and were compounded with two-dimensional nanosheets of graphene oxide(GO)to form GO/TOBC composite hydrogels by hydrogen bonding self-assembly under acidic conditions.The physicochemical properties of the hydrogels,such as morphology,structure,oxidation degree,degradation properties,mechanical properties,and hydrophobicity,were investigated,and the biocompatibility of the hydrogels was evaluated by cell proliferation assay and hemolysis assay.The effect of different ratios of GO and TOBC on inducing the accelerated growth of spiral neuronal cells(SGNs)was investigated by immunofluorescence staining,and the intrinsic mechanism of hydrogel-induced SGNs cell growth was probed by real-time fluorescence quantitative PCR.The results showed that the hydrogels had excellent cytocompatibility and hemocompatibility.The mechanical properties of the produced GO5/TOBC hydrogel were best matched with SGNs cells when the initial GO doping concentration was 50 μg/m L.It promoted the growth of growth cones and filopodia by increasing the expression of filopodia markers diap3,fscn2 and integrin β1,and significantly promoted the elongation of SGNs axons.Therefore,this hydrogel has potential application as a scaffold material for neural tissue engineering.(2)Study of bacterial cellulose-based hydrogels as medical dressings to promote healing of intestinal anastomosesOxidized BC nanofibers loaded with selenium nanoparticles were prepared by in situ generation method and compounded with alginate with active carboxyl groups to prepare multifunctional BC-based composite hydrogels by complexation reaction under the action of calcium ions.The structural and physicochemical properties of the hydrogels were characterized,distribution of selenium nanoparticles in the hydrogels and release properties of selenium were analyzed,and the hydrogels were tested for their in vitro antibacterial,antioxidant,biocompatibility and cell migration-promoting abilities.A rat intestinal anastomosis model was constructed,and the protective,anti-inflammatory and wound healingpromoting abilities of this hydrogel on the anastomotic wound were investigated,and its mechanism of action of protecting the intestinal barrier was explored.The results showed that the multifunctional hydrogel has a stable three-dimensional double network structure,enhanced mechanical properties,good water absorption,excellent selenium loading capacity and longlasting sustainable release,as well as antibacterial,anti-inflammatory,antioxidant and cell migration-promoting abilities,and has good protection,infection prevention and accelerated healing effects on the constructed intestinal anastomosis.Among them,Se-4 hydrogel scavenged 1,1-diphenyl-2-picrylhydrazyl(DPPH)radicals with an efficiency of 90.9%,and the selenium complex hydrogel showed excellent antibacterial properties against both Escherichia coli and Staphylococcus aureus.The inflammatory factors in the selenium hydrogel group were significantly lower than those in the control group and fibrin glue group 14 days after intestinal anastomosis,which proved that it could alleviate the systemic inflammation caused by intestinal anastomosis.Moreover,the selenium hydrogel-protected intestinal anastomosis had the highest weight growth rate,the best bursting pressure,the lowest tissue adhesion score and no intestinal obstruction after 14 days,with intact myofiber alignment at the anastomosis site,significant collagen deposition and no inflammatory cell infiltration,showing the best anti-inflammatory properties and anastomosis repair effect.In addition,immunoprotein blotting and immunofluorescence analysis showed that selenium hydrogel reduces neutrophil production of neutrophil extracellular trap networks(NETs)by inhibiting the ROS/MAPK pathway,repairs the intestinal mucosal barrier and reduces the inflammatory response,which is expected to be a novel anastomotic protection material.(3)Bacterial cellulose-based hydrogels as drug carriers for the precise treatment of intestinal cancersBC-based hydrogels containing disulfide bonds(Sul BC hydrogels)were prepared by polymeric grafting of terminal sulfhydryl groups with silane coupling agents and hydroxyl groups on the surface of BC nanofibers,followed by further cross-linking of terminal sulfhydryl groups in an oxidizing environment,and physical adsorption of the anticancer drug cisplatin(CDDP).The in vitro drug release and cell proliferation assays were performed to test the drug loading capacity and redox responsive targeted controlled drug release of the hydrogels.The anti-tumor mechanism and sensitization effect of the drug-loaded hydrogel were evaluated by cell clone formation assay,cell cycle apoptosis and immunofluorescence staining assay.The therapeutic effect of the hydrogel in combination with radiotherapy on intestinal cancer,in vivo non-invasive CT tracking and regulation of intestinal flora balance were then evaluated by animal experiments.The results showed that Sul BC hydrogel has the ability to adsorb drugs efficiently and release drugs responsively under reducing conditions,which can increase the radiosensitivity of cancer cells by damaging the double-stranded DNA of intestinal cancer cells to induce G2/M phase and apoptosis,and improve the combined treatment effect of radiotherapy and chemotherapy for intestinal cancer.Sul BC gel also improves the effect of radiation therapy for intestinal cancer by restoring the homeostasis of intestinal flora and reducing the relative abundance of harmful bacteria that cause radiotherapy-associated enteritis.