Black Phosphorus Nanosheet-incorporated Hydrogel For Photothermal And Biomineralization Therapy Of Dentin Hypersensitivity

Background:Dentin hypersensitivity(DH)manifests as a sharp toothache on stimulation and resolves on stimulus removal.All temperatures(cold and hot),chemical material(sour and sweet),and mechanical action(friction and chewing)stimulate teeth and act as a transient toothache.41.9% of 18–35 years old Europeans reported toothache on dental stimuli.DH with dentin exposure is a common symptom of various dental diseases caused by the destruction of the enamel integrity.At present,more and more desensitizing strategies are proposed to occlude exposed dentinal tubules and eliminate toothache in DH patients,such as ion or protein precipitation,bionic remineralization,nerve blockade,or photo-biomodulation.However,currently desensitizing strategies with poor acid resistance,friction resistance,and stability cannot get satisfying therapeutic outcomes.Photo-biomodulation is mainly used to seal dentinal tubules with a low-level laser.Laser desensitization therapy with easy operation has an immediate desensitization effect.The laser can transmit light energy to heat and melt the dentin surface to form a double-layer tubule structure and reduce the diameter of exposed dentinal tubules,it also evaporates dentinal tubules fluid and deposits insoluble salt in dentinal tubules,thus reducing the movement of dentinal tubules fluid.However,the high temperature of the dentin surface will lead to dentin cracks,collagen fiber degradation,and oral soft tissue burns,which greatly limits laser application.In order to avoid the formation of dentin surface cracks and degradation of collagen fibers,laser combined with desensitizers to improve desensitization efficiency is the focus of researchers.In recent years,photothermal agents(PTAs)have attracted wide attention in dentistry,PTAs can absorb light energy and convert it into heat energy.Photothermal therapy(PTT)is considered a new therapeutic strategy to eradicate Streptococcus mutans colonies in the oral cavity,which is of great significance for the treatment of dental caries caused by various causes.In the process of treatment,PTT with minimally invasive,non-drug resistance and low systemic toxicity produces a photothermal effect only in the presence of near-infrared(NIR)laser and PTAs.Due to the good absorbance and biocompatibility of PTAs,more and more organic and inorganic PTAs have been proposed.Compared with inorganic preparations,organic preparations have the characteristics of good biodegradability and easy kidney clearance,even the characteristics of good reproducibility,synthetic modification,and controllable preparation.However,the low photothermal conversion efficiency of PTAs limits the therapeutic effect.Black phosphorus(BP)has good biocompatibility and high PTT conversion efficiency.Methacrylate gelatin(GelMA)with a porous structure is beneficial to the diffusion of drugs,nutrients,and gases,which is of great significance for drug and ions release.At the same time,GelMA has been widely reported in the fields of dental pulp stem cell regeneration and osteogenic differentiation.The ability of GelMA to induce calcium deposition will be conducive to the formation of inorganic hydroxyapatite(HA).The main component of dentin is HA.The application of GelMA in desensitization therapy is of great significance to promote the formation of mineralization on the dentin surface.Hence,we designed the BP loaded on GelMA to form GelMA/BP hydrogel.GelMA/BP hydrogel still maintains a stable PTT effect,converting light energy into heat energy to reduce the diameter of dentinal tubules.In addition,phosphorus ions are continuously released from hydrogel to form phosphate,which binds calcium ions from the environment to promote the formation of mineralization on the dentin surface.Through in situ administration,mineralization is specifically deposited in dentinal tubules and seal them stably.Therefore,the PTAs combined with GelMA and BP as a PTT and biomineralization platform will play an important role in the development of DH therapy and has potential clinical practicability.Objective:We formed a biohybrid hydrogel combined with GelMA and BP by photocrosslinking,as a dental tissue engineering application for a PTT and biodegradation platform.Furthermore,we systematically carried out in vitro and in vivo experiments to evaluate the efficacy of GelMA/BP hydrogel as a biodegradable and photothermal therapy platform in DH therapy under NIR laser(808 nm)irradiation.Methods:1.We synthesized BP Nanosheets by liquid stripping method.2.We formed GelMA/BP hydrogel by photo-crosslinking.3.We characterized BP Nanosheets and GelMA/BP hydrogel by Field Emission Scanning Electron Microscopy(FE-SEM),Transmission Electron Microscopy(TEM),Malvern Panalytical Zetasizer Nano ZS,Inductively Coupled Plasma Mass Spectrometry(ICP-MS),and high-resolution confocal Raman microscope.4.We tested the mechanical property of GelMA/BP hydrogel with a rheometer and universal testing machine.5.We irradiated BP Nanosheets and GelMA/BP hydrogel by NIR laser and evaluated the photothermic properties of BP Nanosheets and GelMA/BP hydrogel under the monitoring of an infrared thermal imager.6.We evaluated the DH therapeutic effect of GelMA/BP hydrogel through in vitro and in vivo experiments,and explored the desensitization mechanism,then,we evaluated the acid resistance,abrasion resistance,and stability of dentin slices desensitization treatment via resistant tests.7.We evaluated the desensitization effect of GelMA/BP hydrogel and dental pulp tissue response in the DH treatment process through in vivo rats’ experiments.Results:1.The BP Nanosheets with a particle size of about 190.10 nm and an electric potential of about –21.60 m V were obtained by the liquid stripping method.GelMA/BP hydrogel with pore structure,swelling and degradation properties,and phosphorus ion releasing obtained by photo-crosslinking.2.The GelMA/BP hydrogel with the best strength could be used in desensitization therapy through mechanical properties experiments.3.We confirmed the photothermal properties of BP nanosheets and GelMA/BP hydrogels by photothermal tests.4.GelMA/BP hydrogel could seal open dentinal tubules to some extent,and there was no obvious dental pulp tissue injury.Conclusions:We formed a biohybrid GelMA/BP hydrogel combined with GelMA and BP by photo-crosslinking,as a photothermal and biomineralization and degradation platform for DH therapy.Under the excitation of the NIR laser,the composite hydrogel promotes open dentinal tubules diameter reduction by converting light energy into heat energy on the dentin surface,at the same time,the hydrogel continues to degrade and ion diffusion,which promotes the synthesis of mineralization on the dentin surface.it provides an effective way for desensitization therapy.