Controllable Preparation Of MXene Nanocomposite Hydrogels And The Study On Their Performances In Wearable Smart Medical Diagnosis And Treatment

Flexible epidermal sensors featuring excellent portability and real-time sensing capability have gained rapid development in recent years for their great potential in wearable smart medical treatment.Compared with flexible matrix such as rubber and polyester,hydrogels possess unique tissue similarity,good biocompatibility,and remarkable biological properties,consequently affording a promising material candidate for the fabrication of flexible epidermal sensors.However,conventional hydrogel-based sensors generally exhibit inferior mechanical,electrical,and sensing properties,poor self-healing,self-adhesive and anti-swelling properties,as well as poor multifunctionality,which greatly restrict their real-world applications in the high-performance monitoring of full-scale human motions and tiny electrophysiological signals（e.g.,electrocardiographic（ECG）and electromyographic（EMG）signals）for smart medical diagnosis.Meanwhile,they are short of the effective therapeutic function for further timely treatment after medical diagnosis.Therefore,it is highly desirable to explore novel multifunctional hydrogel materials for high-performance wearable smart medical diagnosis and treatment.MXene is an emerging two-dimensional nanomaterial with abundant surface functional groups,high mechanical strength,high electrical conductivity,good hydrophilicity,and excellent photothermal properties.As a result,the incorporation of the MXene into the hydrogel network is expected to endow the hydrogel with various improved properties and multifunctionalities,thereby providing an ideal platform for wearable smart medical diagnosis and treatment.This thesis aims to develop various multifunctional MXene nanocomposite hydrogels via reasonable molecular design and chemical synthesis,and to study their performances in human motion monitoring and intelligent theranostics,ultimately opening up new ideas for the integration of medical diagnosis and treatment.（1）Hydrogel materials with poor self-healing properties are susceptible to various accidental mechanical damages under repeated deformation,thereby greatly reducing the service life of the hydrogel-based sensors;meanwhile,conventional hydrogel-based sensors have a single function and cannot be integrated for simultaneous wearable smart medical diagnosis and therapy.In this part,the phenylboronic acid grafted hyaluronic acid（HA-PBA）was synthesized via a delicate EDC/NHS activation reaction,and then was assembled with MXene and polyvinyl alcohol（PVA）to prepare a self-healing MXene/HA-PBA/PVA nanocomposite hydrogel based on the dynamic borate ester bonds.The as-prepared MXene hydrogel（MXene/HA-PBA/PVA）exhibits obviously enhanced mechanical properties,improved electrical conductivity,and admirable sensing performances.Meanwhile,the hydrogel possesses robust self-healing ability and can rapidly repair their mechanical,conductive,and sensing properties at room temperature without any external stimulus,which can effectively increase the service life of hydrogel-based sensors.The epidermal sensors based on this MXene nanocomposite hydrogel displays relatively high sensing sensitivity(S₁=0.679 kPa^-1,S₂=0.079 kPa^-1),wide detection range（0.1-15 kPa）and good cyclic stability,which can be exploited to monitor full-scale human motions and subtle ECG/EMG signals for smart health diagnosis.In addition,the hydrogel also exhibits excellent photothermal properties and can be rapidly heated to～54℃ after near-infrared light（NIR,808 nm,1.00 W/cm²）irradiation for 120 s.Therefore,the MXene hydrogel-based sensor integrates a reliable photothermal therapy capability,enabling the timely and effective photothermal therapy for diseases such as wrist or elbow arthritis through the NIR light-induced hyperthermia after the medical diagnosis.（2）Maintaining a good fit of the hydrogel to the skin tissue is one of the most important factors to ensure the high-performance epidermal sensing of hydrogel-based sensors.However,hydrogel with poor self-adhesive properties ordinarily requires additional tapes for leading to the complicated operation,along with the inability to keep reliable contact with human skin for high-quality signal detection in real time;meanwhile,human skin is susceptible to wound bleeding and infection,highlighting the importance of reliable antibacterial and hemostatic properties.Inspired by mussel adhesion chemistry,a self-healing,adhesive and antibacterial mussel-inspired MXene hydrogel was prepared by introducing the catechol-rich tea polyphenols（TP）and MXene nanosheet network into the hydrogel polymeric network of phenylboronic acid-grafted sodium alginate（Alg-PBA）and carboxymethyl chitosan（CMCS）.The as-prepared MXene hydrogel not only exhibits the enhanced mechanical,electrical,and sensing properties as well as excellent self-healing properties,injectability and degradability,but also possesses high-strength（plastic 32.76 kPa,rubber25.26 kPa,glass 23.83 kPa,metal 14.01 kPa and porcine skin 18.74 kPa）and reproducible adhesion to various organic/inorganic material surfaces.Meanwhile,this work demonstrates that the adhesion properties derived from TP facilitate the MXene hydrogel-based epidermal sensor to obtain higher quality human physiological and electrophysiological signals.Moreover,the hydrogel also displays good biocompatibility,strong antibacterial ability（the bactericidal rates against Staphylococcus aureus and Escherichia coli were93.06%and 96.30%,respectively）and effective hemostasis,which is capable of preventing wound bleeding and infection in human skin and shows bright prospects in wound treatment.（3）The mechanical strength and tensile properties of hydrogels also have an important influence on the sensing performance of hydrogel-based sensors;meanwhile,the obvious swelling behavior of hydrogels in wet environments will put additional pressure on the wound for leading to secondary damage and other serious side effects,which is not conducive to subsequent reliable treatment.In this part,a highly stretchable and anti-swelling MXene hydrogel（MXene/Agar/PVA）was prepared by inducing the physical cross-linking of the supramolecular assemblies of MXene,low melting point agarose（Agar）and PVA via freeze-thawing method.The mechanical properties of the MXene hydrogels could be effectively tailored by changing the freeze-thawing cycles.The influence of the mechanical properties of the hydrogel on its sensing performance was then deeply studied and it was confirmed that the excellent stretchability can effectively broaden the sensing range and the good elasticity is beneficial to the rapid sensing response.The flexible sensor assembled from this hydrogel exhibits high sensitivity,wide detection range,and reliable cycling stability,which can be exploited for the ultrasensitive healthcare monitoring and intelligent wearable human-machine interaction.At the same time,it also possesses good biocompatibility,brilliant anti-swelling capability（swelling rate:～4.24%after 24 h of immersion in PBS solution）,and excellent photothermal properties,which can achieve rapid photothermal heating under short-time NIR（808 nm）light irradiation and the desired temperature can be facilely adjusted by changing the NIR power density for smart photothermal treatment of various diseases（such as the wrist arthritis）after the medical sensing.Moreover,the MXene hydrogel based on the temperature-sensitive Agar network can be triggered to be softened and partially disassociated under prolonged NIR light irradiation to release the loaded drug in an on-demand manner,exhibiting strong synergistic bactericidal effects.As a result,the MXene hydrogel combined with NIR light and antibiotics can be used for photothermal/drug synergistic treatment of wound infection with effectively accelerated wound healing.