Preparation And Exploration Of Multifunctional Collagen-Based Flexible Electronic Sensing Materials

As a basic device to capture dynamic signals in the Internet of Things era,flexible sensors such as pressure sensors,temperature sensors,humidity sensors,and sweat sensors are based on polymers.However,most of the current flexible sensors have defects such as single function,biological incompatibility,and battery power supply,which seriously limit their practical application in daily life.As an important component of renewable natural organic polymer materials,unique spatial conformation and chemical composition endow collagen with weak antigenic,chemically modifiable,degradable,and mechanical strength,thus showing great application potential in the field of flexible sensors.The shortcomings of collagen in mechanically stability,hydrophobicity,and conductivity limit its application.Based on this,collagen aggregates(CA)with multi-level aggregation,three-dimensional network,and a large number of active groups(-NH2,-COOH,and-OH)were selected as the base material.And,the power supply/self-powered flexible sensors with pressure,humidity,and temperature sensitivity were prepared by chemical cross-linking(schiff base,condensation and polymerization reaction),physical doping and structural design,using conductive materials with different functional properties as conductive building units.Through a comprehensive evaluation of the sensor’s key properties such as feature sensitivity,anti-interference,durability and degradation,it is confirmed that the sensor based on CA can be used in electronic skin(e-skin),wearable devices,and smart cartilage scaffolds.The research content and results are shown as follows:(1)Collagen-based externally powered multifunctional flexible sensors for detecting pressure and humidity are prepared by CA and functional conductive materials,which was "structural templates" and "conductive units".Polyaniline/H-MWNTs composites(PANI-MWNTs)were "bridged" with CA through intermolecular amide bonds and secondary bonds(hydrogen bonds)to prepare functional composites.The pressure-sensing layer(CA-P-M)and humidity-sensing layer(CA-M)are assembled into multi-functional sensors by cross finger electrode.The multi-layer space structure of natural skin bionic"multi-layer structure" and internal "three-dimensional structure" is prepared by water evaporation method and mechanical compression molding method.The pressure-sensing layer exhibited high sensitivity(GF=5.2)and short response and recovery times(110 ms and 130 ms)in the range of 0.028～100 kPa.At the same time,the humidity-sensing layer showed high humidity sensitivity(28%)and short response/recovery time(56 s and 55 s)in 0%～80%RM.More importantly,the sensor has anti-interference,stability,wearabilit and degradability in complex environments at the same time,which makes it have good application potential in the fields of bionic skin,health monitoring,and wearable devices.(2)CA-based self-powered flexible sensor for pressure,humidity and temperature detection based on the principle of TENG was prepared by electrostatic spinning.CA or aminosilane(KH-792)modified CA(CA-NH2)and polyvinylidene fluoride(PVDF)or polyvinyl alcohol(PVA)are the positive/negative friction layer materials of the self-powered(pressure sensitive)layer.H-MWNTs,poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)MWNTs(PEDOT:PSS-MWNTs)were used as conductive units of humidity and temperature-sensing layers.The self-powered(pressure-sensitive)layer of sensor can provide electricity to the temperature and humidity-sensing layers through interdigitated electrodes.In addition,the sensor exhibits self-powered,functional integration,comfortable wearing,non-toxic,and degradable.a)In this section,the self-powered multi-functional flexible sensor prepared with CA can detect pressure and transform mechanical energy into electricity for humidity and temperature detection.The positive and negative friction layers were collagen aggregate nanofibers(CA NFs)prepared,and the negative friction layers were PVA/PVDF nanofibers(B-C-N PVA/PVDF NFs)with spider web and beadchain structure,which ware prepared by electrostatic spinning.PEDOT:PSSMWNTs composite conductive material was doped into CA and electrospining to obtain a temperature-sensing layer(CA-PP-M NFs).And humidity-sensing layer(CA-M NFs)with ant antennae structure was prepared by doping H-MWNTs in CA.The pressure-sensing layer exhibits sensitivity and generating power up to 2.25 V · kPa-1 and 79.4 mW·m-2 in the range of 0～135 kPa.The temperature and humidity-sensing layers have excellent signals-stimuluses linearity and antiinterference in the range of 27～55℃ and 25%～85%RH,respectively.In addition,the biological non-toxicity,natural degradability,hydrophobicity(94.3°),and permeability(18 mm · s-1)demonstrate its promising application potential in electronic skin,health monitoring,wearable devices,and bionic robots.b)A skin-inspired all-nanofiber flexible multifunctional sensor was prepared by electrospinning with CA-NH2 as the substrate,which has the advantages of self-powered,multifunctional,wearable,and biocompatible,and can be used as a sleep quality detection device.The pressure-sensing layer assembled with CA-NH2 nanofibers(CA-NH2 NFs)as positive friction layer and PVDF NFs with bead chain structure as negative friction layer(Bead PVDF NFs)has excellent triboelectric charge density,sensitivity,hydrophobicity and durability.The CA-M nanofibers(CA-M NFs)were prepared as a humiditysensing layer and assembled with a triboelectric pressure-sensitive layer as a selfpowered multifunctional sensor.And humidity-sensing layer of self-powered multifunctional sensor is CA-M nanofibers(CA-M NFs).Scientific tests show that the sensitivity of the pressure-sensing layer can reach 0.32 V·kPa-1 in the range of 0～135 kPa.The humidity-sensing layer exhibited good linearity(R2=0.98)and response/recovery time(20 s and 33 s)in the range of 25%～85%RH.Furthermore,the sensor has the characteristics of biocompatibility,breathability,ultra-thin and light,and can be used in wearable devices and sleep environment and sleep quality monitoring.(3)A smart cartilage repair scaffold consisting of a self-powered pressure sensor and a cartilage repair scaffold was prepared.The double-sided microconvex structure CA,chitosan(CS)and hydroxyapatite(HA)composite(CA-CS-HA)was prepared by the template method as the positive friction layer.The polycaprolactone(PCL)and HA composite(PCL-HA)with double microconvex structure prepared by the template method was used as the negative friction layer,and the positive and negative friction layers were assembled into a negativepositive-negative sealing sandwich "sandwich" structure.The scaffold part was based on PCL,poly(lactic-co-glycolic acid)(PLGA)and HA composite(PCLPLGA-HA),and the cartilage scaffold with porous structure was prepared by washing-out method.The smart scaffold is excellent in cytotoxicity,in vivo degradability and sensing,and can be applied to the repair of human cartilage defects.The sensitivity of the sensor part in the range of 0.4～1.8 MPa is 4.6 V·MPa-1,and the power generation per unit area is 17.5 mW·m-2.The evaluation of cell proliferation demonstrated that electrical stimulation of chondrocytes by converting mechanical energy into electrical energy could promote their proliferation in PCL-PLGA-HA scaffolds.In addition,the intelligent stent can monitor the repair of cartilage defects in real time,breaking the "black box" state of cartilage defect repair,and has high practical application value.