Preparation and characterization of pH-responsive metal-polyphenol structure coated nanoparticles

In this paper,tannic acid(TA)and Fe~(3+)were added to form a layer of metal-polyphenol network structure on the surface of the nanoparticles which were fabricated by zein and carbon quantum dots(CQDs)encapsulating phlorotannins(PTN).pH-Responsive nanoparticles were prepared successfully(zein-PTN-CQDs-Fe-~Ⅲ).Further,the formation of composite nanoparticles was confirmed by a series of characterization methods.The zeta-potential and Fourier transform infrared spectroscopy data proved that electrostatic interaction and hydrogen bonding are dominant forces to form nanoparticles.The encapsulation efficiency(EE)revealed that metal-polyphenol network structure could improve the EE of PTN.Thermogravimetric analysis and differential scanning calorimetry experiment indicated the thermal stability of zein-PTN-CQDs-Fe~Ⅲnanoparticles increased because of metal-polyphenol network structure.The pH-responsive nanoparticles greatly increased the release rate of active substances and achieved targeted release.

Pharmacokinetics of a ternary conjugate based pH-responsive 10-HCPT prodrug nano-micelle delivery system

A pH-responsive conjugate based 10-hydroxycamptothecin-thiosemicarbazide-polyethene glycol 2000 (10-HCPT-hydro-PEG) nano-micelles were prepared in our previous study. In the present study, ultra-performance liquid chromatography (UPLC-MS) method is developed to investigate its pharmacokinetics and biodistribution in tumor bearing mice. The results demonstrated that the conjugate circulated for a much longer time in the blood circulation system than commercial 10-HCPT injection, and bioavailability was significantly improved compared with 10-HCPT. In vivo biodistribution study showed that the conjugate could enhance the targeting and residence time in tumor site.

CaCO3-Assisted Preparation of pH-Responsive Immune-Modulating Nanoparticles for Augmented Chemo-Immunotherapy

Due to the negative roles of tumor microenvironment(TME)in compromising therapeutic responses of various cancer therapies,it is expected that modulation of TME may be able to enhance the therapeutic responses during cancer treatment.Herein,we develop a concise strategy to prepare pH-responsive nanoparticles via the CaCO3-assisted double emulsion method,thereby enabling effective co-encapsulation of both doxorubicin(DOX),an immunogenic cell death(ICD)inducer,and alkylated NLG919(aNLG919),an inhibitor of indoleamine 2,3-dioxygenase 1(IDO1).The obtained DOX/aNLG919-loaded CaCO3 nanoparticles(DNCaNPs)are able to cause effective ICD of cancer cells and at the same time restrict the production of immunosuppressive kynurenine by inhibiting IDO1.Upon intravenous injection,such DNCaNPs show efficient tumor accumulation,improved tumor penetration of therapeutics and neutralization of acidic TME.As a result,those DNCaNPs can elicit effective anti-tumor immune responses featured in increased density of tumor-infiltrating CD8+cytotoxic T cells as well as depletion of immunosuppressive regulatory T cells(Tregs),thus effectively suppressing the growth of subcutaneous CT26 and orthotopic 4T1 tumors on the Balb/c mice through combined chemotherapy&immunotherapy.This study presents a compendious strategy for construction of pH-responsive nanoparticles,endowing significantly enhanced chemo-immunotherapy of cancer by overcoming the immunosuppressive TME.

Towards recycling purpose:Converting PET plastic waste back to terephthalic acid using pH-responsive phase transfer catalyst

Converting polyethylene terephthalate(PET)wastes to its monomer and valuable chemicals via ecofriendly chemical method is still a challenge task.Previously,phase transfer catalysts used for alkaline hydrolysis were soluble in reaction media and hardly separated after reaction.Here,we reported several pH-responsive catalysts combined alkyl quaternary ammonium units with heteropolyacid anion for achieving stepwise product/catalyst separation and catalyst recycling.The properties of homogeneous/heterogeneous transfer behavior allow catalyst to be easily separated from reaction media by adjusting of pH value.Among them,[C_(16)H_(33)N(CH_(3))_(3)]_(3)PW_(12)O_(40)(abbreviated as[CTA]_(3)PW)exhibits the highest activity and the most suitable pH responsive values.Such a pH triggered switchable catalytic system not only shows good performance for depolymerization of pure PET,but also some real PET wastes such as coloured trays and PE/PET complex films could be completely degraded into terephthalic acid.Additionally,the reaction kinetics and activation energy of PET alkaline hydrolysis also studied with and without pH-responsive[CTA]_(3)PW.

Preparation of Hollow-Porous Rosin-Based Polyurethane Microspheres with pH-Responsive Characteristics

Preparation of polymer microspheres from naturally occurring resource is a challenge.Here,a rosin-based polyol(RAG)was used to prepare polyurethane resin(RPU)firstly,and then act as both self-assembled precursor and emulsifier,rosin based polyurethane microspheres(RPUMs)were prepared.In the process of self-emulsification,the RPU formed vesicles by self-assembly.The outer shell of the vesicle consisted of hydrophilic segments,while the inner shell contained the hydrophobic phase.After cross-linking the RPU and removal of the solvent in the core,the porous-hollow microspheres with pH-sensitive were obtained.The microspheres were characterized by optical microscope(OM),scanning electron microscopy(SEM)and transmission electron microscope(TEM).The effect of type and amount of the hydrophilic chain extender,and solvent on the morphology,particle size and distribution,and buffer volume of the microspheres were determined.The best conditions for synthetic RPUMs were as follows:n_(NCO)/n_(OH)=1,n_(RAG):n_(1-(2-hydroxyethyl)piperazine)=4:6,with azodiisobutyronitrile level of 1.0 wt.%,based on reactive monomers,mixing speed of both emulsification and polymerization at 400 r·min-1,the RPUMs synthesized had porous-hollow structure with a buffer volume of 1.6 mL.

Ultrasmall pH-responsive silicon phthalocyanine micelle for selective photodynamic therapy against tumo

Targeted photodynamic therapy(TPDT)based on the photosensitizers responsive for tumor micr oenvironment is promising because of the better anti-tumor effect and less phototoxicity against normal tissue than the traditional PDT.Nanoparticle based stimuli responsive photo-sensitizers have been widely explored for TPDT.Based on the acidic microenvironments in solid tumors,an ultrasmall pH-responsive silicon phthalocyanine nanomicelle(PSN)(smaller than 10 nm)was designed for selective PDT of tumor.PSN had high drug loading efficacy(more than 28%)and exhibited morphological transitions,enhanced fuorescence and improved singlet∞x-ygen yield under acidic environments.PSN was renal dlearable and could rapidly accumulate and be retained at tumor sites,achieving a tumor-inhibiting ffect better than phthalocyanine micelle without pH response.Tumors of mice treated with PSN for PDT were completely ablated without recurrence.Thus,we have developed a phthalocyanine-based pH responsive micelle with excellent tumor targeting ability,which is expected to realize the selective PDT of tumor.

Preparation and Properties of pH-Responsive Intelligent Medical Dressing Based on Bacterial Cellulose/Polyacrylic Acid

Bacterial cellulose/polyacrylic acid (BC/PAA) pH-responsive hydrogels were prepared by free-radical polymerization (in situ) using BC as the raw material and AA as the monomer. The hydrogels were loaded with curcumin (Cur) to prepare pH-responsive intelligent medical dressings. The preparation process of the hydrogels was optimized by a single factor and response surface experiment using their swelling degree as an index. The structures of BC/PAA pH-responsive hydrogels were characterized by scanning electron microscope (SEM), Fourier Transform Infrared spectrometer (FTIR), X-ray diffraction (XRD), and tensile tester, and the swelling properties, mechanical properties, bacteriostatic properties, and drug release behavior were investigated. The results showed that the BC/PAA pH-responsive hydrogel has a three-dimensional network structure with the swelling rate up to 1600 g/g, compressive strength of up to 8 KPa, and good mechanical properties, and the drug release behavior was in line with the logistic dynamics model, and it has good inhibitory effects on common pathogens of wound infection: E. coli, S. aureus, and P. aeruginosa.

MOF-based magnetic microrobot swarms for pH-responsive targeted drug delivery

Metal-organic frameworks(MOFs)hold significant potential as vehicles for drug delivery due to their expansive specific surface area,biocompatibility,and versatile attributes.Concurrently,magnetically actuated micro/nano-robots(MNRs)offer distinct advantages,such as untethered and precise manipulation.The fusion of these technologies presents a promising avenue for achieving non-invasive targeted drug delivery.Here,we report a MOF-based magnetic microrobot swarm(MMRS)for targeted therapy.Our approach overcomes limitations associated with a single MNR,including limited drug loading and the risk of loss during manipulation.We select Zeolitic Imidazolate Framework-8(ZIF-8)as the drug vehicle for its superior loading potential and p H-sensitive decomposition.Our design incorporates magnetic responsive components into the one-pot synthesis of Fe@ZIF-8,enabling collective behaviors under actuation.Tuning the yaw angle of alternating magnetic fields and nanoparticles'amount,the MMRSs with controllable size achieve instantaneous transformation among different configurations,including vortex-like swarms,chain-like swarms,and elliptical swarms,facilitating adaptation to environmental variations.Transported to the subcutaneous T24 tumor site,the MMRSs with encapsulated doxorubicin(DOX)automatically degrade and release the drug,leading to a dramatic reduction of the tumor in vivo.Our investigation signifies a significant advancement in the integration of biodegradable MOFs into microrobot swarms,ushering in new avenues for accurate and non-invasive targeted drug delivery.

Carbon dots-enhanced pH-responsive lubricating hydrogel based on reversible dynamic covalent bondings

Due to the various pH liquid environment in nature,the pH-responsive lubricating hydrogel is widely investigated and developed for tissue interface substitute.However,the applied liquid environment will lead to poor mechanical property and weaken the pH-responsive capability.In this work,a carbon dotsenhanced pH-responsive lubricating hydrogel is developed by combining a pH-responsive section of dynamic PVA-borax network into a PAAm covalent polymer network.The formed hydrogel presents a partial gel-sol transition under controlled pH environments.At low pH environments(<6.0),the formed lubricating layer originated from dynamic disassembly of PVA-borax hydrogel,and brings the lubricating properties on the hydrogel surface.Moreover,the mechanical strength and lubrication properties are well promoted by introducing the carbon dots into the hydrogel,the blue sol layer can be observed more visually under the fluorescence microscope.The pH-response also exhibits well reversibility.The prepared hydrogel broadens the idea for designing pH-responsive soft materials for soft lubricating actuator or robot.

Antibacterial hydrogel with pH-responsive microcarriers of slow-release VEGF for bacterial infected wounds repair

Bacterial infection causes wound inflammation and makes angiogenesis difficult.It is urgent to develop effectively antibacterial and pro-vascularizing dressings for wound healing.The hydrogel is developed with pH-responsive drug-releasing microcarriers which were loaded with vascular endothelial growth factor(VEGF)that promotes angiogenesis and actively respond to wound pH for control and prolong VEGF release.The surfaces of the microcarriers were coated with polydopamine which can reduce the silver nanoparticles(AgNPs)in situ,and dynamically crosslink with the polyacrylamide,which forms a stable slow-release system with different release behavior for the VEGF and AgNPs.The hydrogel inhib-ited bacterial formation and accelerated wound healing.With the hydrogel dressing,83.3%±4.29%of the wound heals at day 7,which is 40.9%±8.5%higher than the non-treatment group in defect infected model.The antibacterial properties of hydrogel down-regulate early inflammation-related cytokines,and the release of VEGF in the middle and late phases of wound healing in response to pH changes pro-motes angiogenesis and up-regulate the expression of angiogenesis-associated cytokine.The sequential release of antibacterial agents and pro-vascularizing agents in response to the change in wound microen-vironmental cues facilitate temporally controlled therapy that suites the need of different wound healing phases.Collectively,the hydrogel loaded with multifunctional microcarriers that enable controlled release of AgNPs and VEGF is an effective system for treating infected wounds.

Antimicrobial hydrogel with multiple pH-responsiveness for infected burn wound healing

Burns are a common medical problem globally,and wound infection is one of the major causes of inducing related complications.Although antibiotics effectively prevent wound infections,the misuse of antibiotics has created a new problem of superbugs.Herein,we propose a new strategy to obtain pH-responsive antimicrobial P-ZIF(ZIF:zeolitic imidazolate framework)by loading polyhexamethylenebiguanide(PHMB)into the framework of ZIF-8 nanoparticles.This will enable PHMB to be released in the weak acid environment of an infected wound.To address burn infections,P-ZIF nanoparticles were loaded into a hydrogel system made of sodium alginate(SA)and 3-aminophenylboronic acid modified human-like collagen(H-A)through borate ester bonds.The resulting H-A/SA/P-ZIF(HASPZ)hydrogel dressing not only possesses antibacterial and wound healing properties but also has dual pH responsiveness to prevent the overuse of medication while effectively treat deep second-degree burns.Therefore,P-ZIF nanoparticles and the corresponding HASPZ hydrogel dressing are considered of significant importance in antimicrobial,drug delivery,and wound repair.

Facile Fabrication of Hyperbranched Polyacetal Quaternary Ammonium with pH-Responsive Curcumin Release for Synergistic Antibacterial Activity

In the current global crisis of antibiotic resistance,persuit of an effective multi-pathway collaborative approach to enhance antibacterial activity is urgently needed.Here,a kind of hyperbranched polyacetal quaternary ammonium(Hyper-ace-QA)with efficiently antibacterial function were synthesized by a succession of efficient click strategies.The high molecular weights can be obtained just after UV irradiation for 3 h,and the grafting ratio can be easily adjusted through controlling solvent system,molar ratio,and temperature.Cytotoxicity studies indicated that Hyper-ace-QA had good biocompatibility and can be used as a potential antibacterial dressing.More importantly,after in situ encapsulation of bioactive curcumin drugs into the hyperbranched intramolecular cavities,the acid-liable acetal linkers within the hyperbranched backbone made the loading antibacterial drugs rapidly release with pH-or bacterial-responsive behaviors since many bacteria can produce acids at the infection site by the combined actions of immune response and bacterial metabolism.Therefore,the integration of quaternary ammonium characteristics and pH-triggered curcumin release could facilitate the antibacterial activity against gram-positive Staphylococcus aureus.This work represents a synergistic strategy on offering important guidance to rational design of multifunctional antimicrobial vehicles,which would be promising therapeutic alternatives for first aid treatment of wound infection in critical situations.

A soluble pH-responsive host-guest-based nanosystem for homogeneous exosomes capture with high-efficiency

Exosomes offer ideal biomarkers for liquid biopsies.However,high-efficient capture of exosomes has been proven to be extreme challenging.Here,we report a soluble pH-responsive host-guest-based nanosystem(pH-HGN)for homogeneous isolation of exosomes around physiological pH.The pH-HGN consists of two specifically functionalized modules.First,a pH-responsive module,poly-dimethylaminoethyl methacrylate,provides homogeneous capture circumstances and sharp pH-triggered self-assembly separation in aqueous solution to improve capture efficiency and reduce nonspecific adsorption.Second,a host-guest module,poly-acrylamide azobenzene andβ-cyclodextrin linked with exosomes-specific antibody,could act as the"cleavable bridge"to specific capture and subsequent rapid release of captured exosomes through host-guest interaction betweenβ-cyclodextrin and AAAB moieties.The pH-HGN offered high capture efficiencies for exosomes from two different cell lines,which were 90.2%±0.28%and 87.0%±4.6%for H1299 and MCF-7 cell-derived exosomes,respectively.The purity of isolated exosomes was(1.49±0.71)×10^(11)particles/μg,which was 4.1 times higher compared with the gold standard ultracentrifugation(UC)method.Furthermore,the isolated exosomes via the pH-HGN can preserve well integrity and biological activity.The developed pH-HGN was further successfully applied to differentiate lung cancer patients from healthy persons.These findings indicated that pH-HGN is a promising strategy in exosomes-based research and downstream applications.

A pH-responsive TiO_2-based Pickering emulsion system for in situ catalyst recycling

Developing methods for efficient product/catalyst separation and catalyst recycling is meaningful in multi-phase catalytic reactions. Here, we reported a p H-responsive emulsion system stabilized by interfacially active TiO2 nanoparticles for achieving in situ product/catalyst separation and catalyst recycling. In this system, emulsification and demulsification process could be easily engineered through tuning the p H values. The emulsion droplets were destroyed completely at a p H value of 3–4, and the solid catalyst distributed in the aqueous phase could be used to the next reaction cycle after removal of the organic product and adjusting the p H to 7–8. Such a p H triggered switchable Pickering emulsion catalytic system not only shows good recyclability of the solid catalyst but also high catalytic efficiency,and could be recycled more than 10 cycles.

Multi-modal anti-counterfeiting and encryption enabled through silicon-based materials featuring pH-responsive fluorescence and room-temperature phosphorescence

Nano Research volume 13,pages1614–1619(2020)Cite this article 236 Accesses Metrics details Abstract Optical silicon(Si)-based materials are highly attractive due to their widespread applications ranging from electronics to biomedicine.It is worth noting that while extensive efforts have been devoted to developing fluorescent Si-based structures,there currently exist no examples of Si-based materials featuring phosphorescence emission,severely limiting Si-based wide-ranging optical applications.To address this critical issue,we herein introduce a kind of Si-based material,in which metal-organic frameworks(MOFs)are in-situ growing on the surface of Si nanoparticles(SiNPs)assisted by microwave irradiation.Of particular significance,the resultant materials,i.e.,MOFs-encapsulated SiNPs(MOFs@SiNPs)could exhibit pH-responsive fluorescence,whose maximum emission wavelength is red-shifted from 442 to 592 nm when the pH increases from 2 to 13.More importantly,distinct room-temperature phosphorescence(maximum emission wavelength:505 nm)could be observed in this system,with long lifetime of 215 ms.Taking advantages of above-mentioned unique optical properties,the MOFs@SiNPs are further employed as high-quality anti-counterfeiting inks for advanced encryption.In comparison to conventional fluorescence anti-counterfeiting techniques(static fluorescence outputs are generally used,thus being easily duplicated and leading to counterfeiting risk),pH-responsive fluorescence and room-temperature phosphorescence of the resultant MOFs@SiNPs-based ink could offer advanced multi-modal security,which is therefore capable of realizing higher-level information security against counterfeiting.

Bone-targeted pH-responsive cerium nanoparticles for anabolic therapy in osteoporosis

Antiresorptive drugs are widely used for treatment of osteoporosis and cancer bone metastasis,which function mainly through an overall inhibition of osteoclast.However,not all osteoclasts are“bone eaters”;preosteoclasts(pOCs)play anabolic roles in bone formation and angiogenesis through coupling with osteoblasts and secreting platelet derived growth factor-BB(PDGF-BB).In this study,a bone-targeted pH-responsive nanomaterial was designed for selectively eliminating mature osteoclasts(mOCs)without affecting pOCs.Biocompatible cerium nano-system(CNS)was guided to the acidic extracellular microenvironment created by mOCs and gained oxidative enzymatic activity.Oxidative CNS decreased the viability of mOCs through accumulating intracellular reactive oxygen species and enhancing calcium oscillation.Non-acid secreting anabolic pOCs were thus preserved and kept producing PDGF-BB,which lead to mesenchymal stem cell osteogenesis and endothelial progenitor cell angiogenesis via PI3K-Akt activated focal adhesion kinase.In treating osteoporotic ovariectomized mice,CNS showed better protective effects compare with the current first line antiresorptive drug due to the better anabolic effects marked by higher level of bone formation and vascularization.We provided a novel anabolic therapeutic strategy in treating bone disorders with excessive bone resorption.

Targeted pH-responsive polyion complex micelle for controlled intracellular drug delivery

Cancer the rapy with nanoscale drug formulations has made significant progress in the past few decades.However,the selective accumulation and release of therapeutic agents in the lesion sites are still great challenges.To this end,we developed a cRGD-decorated pH-responsive polyion complex(PIC)micelle for intracellular targeted delivery of doxorubicin(DOX)to upregulate tumor inhibition and reduce toxicity.The PIC micelle was self-assembled via the electrostatic interaction between the positively charged cRGD-modified poly(ethylene glycol)-block-poly(L-lysine)and the anionic acid-sensitive 2,3-dimethylmaleic anhydride-modified doxorubicin(DAD).The decoration of cRGD enhanced the cell internalization of PIC micelle through the specific recognition ofαvβ3 integrin on the membrane of tumor cells.The active DOX was released under intracellular acidic microenvironment after endocytosis following the decomposition of DAD.Moreover,the targeted PIC micelle exhibited enhanced inhibition efficacies toward hepatoma in vitro and in vivo compared with the insensitive controls.The smart multifunctional micelle provides a promising platform for target intracellular delivery of therapeutic agent in cancer therapy.

Co-delivery of Doxorubicin and Afatinib with pH-responsive Polymeric Nanovesicle for Enhanced Lung Cancer Therapy

Drug-resistance and drastic side effects are two major issues of traditional chemotherapy which may result in trail failure even death.Nanoparticle-mediated multidrug combination treatment has been proven to be a feasible strategy to overcome these challenges.In the present study,amphipathic block polymer of methoxyl poly(ethylene glycol)-poly(aspartyl(dibutylethylenediamine)-co-phenylalanine)(m PEG-P(Asp(DBA)-co-Phe))was synthesized and self-assembled into p H-responsive polymeric vesicle.The vesicle was utilized to co-deliver cancer-associated epidermal growth factor(EGFR)inhibitor of afatinib and DNA-damaging chemotherapeutic doxorubicin hydrochloride(DOX)for enhanced non-small-cell lung cancer(NSCLC)therapy.As evaluated in vitro,the p H-responsive design of nanovesicle resulted in a rapid release of encapsulated drugs into tumor cells and caused enhanced cell apoptosis.In addition,in vivo therapeutic studies were conducted and the results evidenced that the co-delevery of DOX and afatinib using p H-sensitive nanovector was a promising strategy for NSCLC treatment.

Dual pH-responsive “charge-reversal like” gold nanoparticles to enhance tumor retention for chemo-radiotherapy

The strategy of pH-responsive aggregation in tumor micro-environment(TME)provides an intriguing platform for enhancing tumor retention and exerting therapeutic effects sufficiently.In this work,we have designed an intelligent dual pH-responsive self-aggregating nano gold system(Au@PAH-Pt/DMMA)for the combined chemo-radiotherapy,in which a“charge-reversal like”strategy was utilized to realize irreversible stable aggregation and pH-specific release of cisplatin prodrug in TME.Responsive aggregation increases the cellular uptake of Au@PAH-Pt/DMMA by 55%–60%,and the cellular uptake of Pt after X-ray irradiation can be further enhanced by 80%.Additionally,responsive aggregation greatly slows down the rate of efflux from tumor in vivo.This system not only promotes B16 cell apoptosis as a chemotherapeutic agent(30.4%),it also enhances the effect of chemo-radiotheray(CRT)by promoting apoptosis as a radiosensitizer(55.3%).The colony formation assay results were fitted to cell survival curve of B16 cells and the sensitization enhancement ratio(SER)was calculated to be 1.29,which shows a good radiosensitizing ability.When exposed to X-ray,this nanoplatform reached the ideal therapeutic effect,and the tumor inhibition rate of Au@PAH-Pt/DMMA reached 91.6%with low drug administration frequency and dose of X-ray.Overall,the dual pH-responsive nanoparticles Au@PAH-Pt/DMMA could effectively enhance tumor therapeutic efficiency by combined chemo-radiotherapy,which provides a potential method for clinical transformation of cancer treatment.

Antibacterial and pH-responsive Quaternized Hydroxypropyl Cellulose-g-Poly(THF-co-epichlorohydrin)Graft Copolymer:Synthesis,Characterization and Properties

The novel quaternized hydroxypropyl cellulose-g-poly(THF-co-epichlorohydrin)graft copolymers,HPC-g-QCP(THF-co-ECH),have been successfully synthesized to combine the properties from hydrophilic hard HPC biomacromolecular backbone and hydrophobic flexible polyether branches.Firstly,the P(THF-co-ECH)living chains were synthesized by cationic ring-opening copolymerization of THF with ECH.Secondly,P(THF-co-ECH)living chains were grafted onto HPC backbone by reaction with-OH groups along HPC to produce HPC-g-P(THF-co-ECH)graft copolymers.Thirdly,the mentioned graft copolymers were quaternized by reaction with ternanyamine to generate functionalized HPC-g-QCP(THF-co-ECH).The HPC-g-QCP(THF-co-ECH)graft copolymers exhibited good antibacterial ability against S.aureus or E.coli bacteria.The ibuprofen(IBU)-loaded microparticles of HPC-g-(QC)P(THF-co-ECH)graft copolymers were prepared by electrospraying.The in vitro pH-responsive drug-release behavior of IBU reached up to 75%of drug-loaded at pH=7A.This quaternized graft copolymer was beneficial to solving the problems of a burst effect and fast release of HPC as drug carriers.