Structural Construction And Biomedical Applications Of Bacterial Cellulose Hydrogels With Nanofiber Self-Reinforced Network

As water-rich materials,hydrogels with high water content are widely used in biomedical applications,but they always have poor mechanical properties.High-strength hydrogels usually contain synthetic polymers and have low water content and poor biocompatibility.In addition,natural polysaccharide-based hydrogels with good biocompatibility are prone to uncontrollable deformation due to swelling,resulting in a sharp decline in their mechanical properties.Swelling may also cause compression and damage to surrounding tissues when they are used in vivo,causing safety concerns in biomedical applications.Therefore,the preparation of high-strength and low-swelling hydrogels with good biocompatibility remains a great challenge in the field of biomedical hydrogels.Bacterial cellulose（BC）hydrogels are derived from organisms and have excellent biocompatibility.However,due to the limitation of the biosynthesis method of BC hydrogels,the structure and properties of the preparation are limited.Here,for developing a non-swelling high-strength pure natural hydrogel with good ionic conductivity and biocompatibility that is suitable for biomedical application,we regulated the nanostructure and aggregated structure of BC,to establish and perfected the construction system of BC macroscopic multidimensional hydrogel materials.Its application in the biomedical field is also explored.Specifically,the research contents are as follows:（1）Inspired by the homogeneous reinforced materials,by regulating the ratio of Li OH/urea alkaline solvent to achieve controlled dissolution,following by the chemical-crosslinking and physical-crosslinking,the aggregation structure and nanostructure of hydrogels can be controlled,a unique nanofiber-network-self-reinforced（FNSR）structured BC hydrogel was constructed.The hydrogels had excellent mechanical properties at a high-water content（>91%）,and the compressive strength could reach 3.17 MPa which is 56 times that of native BC.At the same time,no swelling occurred for the hydrogel,and the mechanical strength still remained in excess of90%for 15 days in water.It also had good biocompatibility,and the internal nanofibers facilitated cell proliferation and adhesion.It opens up a new horizon for the preparation of self-reinforced hydrogels with good biocompatibility and excellent mechanical properties.（2）On the basis of constructing a tailor-made FNSR structure,we aligned them to an oriented structure via a confined-drying process under stretching after pre-crosslinking.Thus,a non-swelling and ionically conductive anisotropic bacterial cellulose hydrogel（ABCH）with tunable high mechanical properties was obtained.The maximum tensile strength of anisotropic hydrogel could reach 14.3 MPa with 70%water content.It would still not swell and maintained 93%tensile strength after 30 days in water.At the same time,the nanochannels inside and around nanofibers allowed effective ion transport in ABCH at low ion concentration,and it obtained good ion conductivity of 0.3 S m^-1 relying only on ions in body fluids（<300 m M）.This facile strategy provided a useful paradigm for fabricating high-strength,non-swelling,and bio-ion conductive hydrogels for application in next-generation bioelectronic interfacing and flexible implantable devices.（3）A pure natural bacterial cellulose hydrogel fiber（BCHF）was prepared by a continuous wet-spinning method without any additional crosslinking step,relying only on the water as a coagulation bath.The hydrogel fiber exhibited an excellent tensile strength of 3.74 MPa as well as a high-water content of 87%.It also had non-swelling properties and maintained 90%of its original strength after being soaked in water for 14 days.The hydrogel fiber also integrated good ion conductivity and light-guiding performance,and it could be directly used as a pure natural nanofluidic device without packaging for the detection of trace neurotransmitters.The strategy of constructing multifunctional hydrogel fibers with pure natural components will open up a new route for the development of next-generation neural interfaces.We proposed the FNSR structural construction methods of BC hydrogels,prepared macroscopic multidimensional BC hydrogels,and studied their structure and properties.We also carried out preliminary investigations in optoelectronic probing,bio-molecular detection and other bio-medical applications,which would provide ideas and information for the preparation of high-strength non-swelling hydrogels for biomedical applications.