Facile Synthesis of Acid-Labile Polymers with Pendent Ortho Esters

Smart nanogels for cancer treatment from the perspective of functional groups

Introduction: Cancer remains a significant health challenge, with chemotherapy being a critical treatment modality. However, traditional chemotherapy faces limitations due to non-specificity and toxicity. Nanogels, as advanced drug carriers, offer potential for targeted and controlled drug release, improving therapeutic efficacy and reducing side effects. Methods: This review summarizes the latest developments in nanogel-based chemotherapy drug delivery systems, focusing on the role of functional groups in drug loading and the design of smart hydrogels with controlled release mechanisms. We discuss the preparation methods of various nanogels based on different functional groups and their application in cancer treatment. Results: Nanogels composed of natural and synthetic polymers, such as chitosan, alginate, and polyacrylic acid, have been developed for chemotherapy drug delivery. Functional groups like carboxyl, disulfide, and hydroxyl groups play crucial roles in drug encapsulation and release. Smart hydrogels have been engineered to respond to tumor microenvironmental cues, such as pH, redox potential, temperature, and external stimuli like light and ultrasound, enabling targeted drug release. Discussion: The use of functional groups in nanogel preparation allows for the creation of multifunctional nanogels with high drug loading capacity, controllable release, and good targeting. These nanogels have shown promising results in preclinical studies, with enhanced antitumor effects and reduced systemic toxicity compared to traditional chemotherapy. Conclusion: The development of smart nanogels with functional group-mediated drug delivery and controlled release strategies represents a promising direction in cancer therapy. These systems offer the potential for improved patient outcomes by enhancing drug targeting and minimizing adverse effects. Further research is needed to optimize nanogel design, evaluate their safety and efficacy in clinical trials, and explore their potential for personalized medicine.

High-Molecular-Weight and Light-Colored Disulfide-Bond-Embedded Polyesters: Accelerated Hydrolysis Triggered by Redox Responsiveness

Disulfide bonds have attracted considerable attention due to their reduction responsiveness, but it is crucial and challenging to prepare disulfide-bond-based polyesters by melt polycondensation. Herein, the inherently poor thermal stability of the S-S bond in melting polycondensation was overcome. Moreover, poly(butylene succinate-co-dithiodipropionate) (PBSDi) with a light color and high molecular weights (Mn values up to 84.7 kg/mol) was obtained. These polyesters can be applied via melt processing with Td,5% > 318 °C. PBSDi10-PBSDi40 shows good crystallizability (crystallinity 56-38%) and compact lamellar thickness (2.9-3.2 nm). Compared with commercial poly(butylene adipate-co-terephthalate) (PBAT), the elevated mechanical and barrier performances of PBSDi make them better packaging materials. For the degradation behavior, the disulfide monomer obviously accelerates the enzyme degradation but has a weaker effect on hydrolysis. In 0.1 mol/L or higher concentrations of H2O2 solutions, the oxidation of disulfide bonds to sulfoxide and sulfone groups can be realized. This process results in a stronger nucleophilic attack, as confirmed by the Fukui function and DFT calculations. Additionally, the greater polarity and hydrophilicity of oxidation products, proved by noncovalent interaction analysis, accelerate the hydrolysis of polyesters. Moreover, glutathione-responsive breakage, from polymers to oligomers, is confirmed by an accelerated decline in molecular weight. Our research offers fresh perspectives on the effective synthesis of the disulfide polyester and lays a solid basis for the creation of high-performance biodegradable polyesters that degrade on demand.

Enhanced drug delivery to cancer cells through a pH-sensitive polycarbonate platform

Polymer-drug conjugates are widely investigated to enhance the selectivity of therapeutic drugs to cancer cells, as well as increase circulation lifetime and solubility of poorly soluble drugs. In order to direct these structures selectively to cancer cells, targeting agents are often conjugated to the nanoparticle surface as a strategy to limit drug accumulation in non-cancerous cells and therefore reduce systemic toxicity. Here, we report a simple procedure to generate biodegradable polycarbonate graft copolymer nanoparticles that allows for highly efficient conjugation and intracellular release of S-(+)-camptothecin, a topoisomerase I inhibitor widely used in cancer therapy. The drug-polymer conjugate showed strong efficacy in inhibiting cell proliferation across a range of cancer cell lines over non-cancerous phenotypes, as a consequence of the increased intracellular accumulation and subsequent drug release specifically in cancer cells. The enhanced drug delivery towards cancer cells in vitro demonstrates the potential of this platform for selective treatments without the addition of targeting ligands.

Dynamic precise dual-drug-backboned nano-prodrugs for selective chemotherapy

To achieve an ideal drug delivery platform with precise composition and high tumor selectivity, the PEGylated dual-drug backboned prodrug was synthesized via the copolymerization between diamine monomer of ortho ester and cisplatin- demethylcantharidin conjugate (Pt(IV)-1), and then terminated by mPEG550-active ester. The amphipathic prodrug could self-assemble into nano-prodrugs, which endowed the precise structure and high drug loading. Moreover, the nano-prodrugs exhibited physicochemical stability at physiological pH (7.4) for stable blood circulation, DePEGylation and dynamic size change for selective tumor accumulation and enhanced cellular internalization at tumoral extracellular pH (6.8), and efficient drug release for synergetic apoptosis and cytotoxicity at tumoral intracellular pH (5.0)/glutathione. Thus, the precise dual-drug backboned nano-prodrugs with detachable PEGylation, dynamic size change and efficient drug release could be potentially translated for clinically selective cancer treatment. STATEMENT OF SIGNIFICANCE: Few nanomedicines have been clinically used for cancer treatment and little progress has been made in the last decades due to the unprecise composition and unsatisfactory tumor selectivity. Herein, the PEGylated dual-drug backboned nano-prodrugs were successfully constructed by rational design and endowed the defined structure, precise drug ratio, extraordinary high drug loading and reduction/pH dual sensitivity. The nano-prodrugs further exhibited the stable storage and blood circulation through PEGylation and low critical micelle concentration, enhanced tumor accumulation and cellular uptake via extracellular DePEGylation and dynamic size translation, and synergetic cytotoxicity via intracellular efficient drug release, respectively. This study can open a new avenue for easy industrial manufacture and quality control, and highly selective chemotherapy appealing for clinical translation. .

Bicomponent polymeric micelles for pH-controlled delivery of doxorubicin

Stimuli-responsive drug delivery systems (DDSs) are expected to realize site-specific drug release and kill cancer cells selectively. In this study, a pH-responsive micelle was designed utilizing the pH-sensitivity of borate bonds formed between dopamine and boronic acid. First, methyl (polyethylene glycol)-block-polycaprolactone (mPEG-PCL) was conjugated with 4-cyano-4-(thiobenzoylthio)pentanoic acid (CTP) to obtain a macroinitiator. Two different segments poly(dopamine methacrylamide) (PDMA) and poly(vinylphenylboronic acid) (PVBA) were then grafted to the end of mPEG-PCL. Two triblock copolymers, mPEG-PCL-PDMA and mPEG-PCL-PVBA, were then obtained by reversible addition-fragmentation transfer (RAFT) polymerization. These copolymers and their mixture self-assembled in aqueous solution to form micelles that were able to load hydrophobic anticancer drug doxorubicin (DOX). These two-component micelles were found to be pH-sensitive, in contrast to the one-component micelles. Furthermore, MTT studies showed that the micelles were almost nontoxic. The DOX-loaded micelles showed cytotoxicity equivalent to that of DOX at high concentration. In vivo antitumor experiments showed that this pH-sensitive polymeric micellar system had an enhanced therapeutic effect on tumors. These two-component boronate-based pH micelles are universally applicable to the delivery of anticancer drugs, showing great potential for cancer therapy.

pH-Sensitive Biomaterials for Drug Delivery

The development of precise and personalized medicine requires novel formulation strategies to deliver the therapeutic payloads to the pathological tissues, producing enhanced therapeutic outcome and reduced side effects. As many diseased tissues are feathered with acidic characteristics microenvironment, pH-sensitive biomaterials for drug delivery present great promise for the purpose, which could protect the therapeutic payloads from metabolism and degradation during in vivo circulation and exhibit responsive release of the therapeutics triggered by the acidic pathological tissues, especially for cancer treatment. In the past decades, many methodologies, such as acidic cleavage linkage, have been applied for fabrication of pH-responsive materials for both in vitro and in vivo applications. In this review, we will summarize some pH-sensitive drug delivery system for medical application, mainly focusing on the pH-sensitive linkage bonds and pH-sensitive biomaterials.

Bioresponsive drug delivery systems for the treatment of inflammatory diseases

Inflammation is intimately related to the pathogenesis of numerous acute and chronic diseases like cardiovascular disease, inflammatory bowel disease, rheumatoid arthritis, and neurodegenerative diseases. Therefore anti-inflammatory therapy is a very promising strategy for the prevention and treatment of these inflammatory diseases. To overcome the shortcomings of existing anti-inflammatory agents and their traditional formulations, such as nonspecific tissue distribution and uncontrolled drug release, bioresponsive drug delivery systems have received much attention in recent years. In this review, we first provide a brief introduction of the pathogenesis of inflammation, with an emphasis on representative inflammatory cells and mediators in inflammatory microenvironments that serve as pathological fundamentals for rational design of bioresponsive carriers. Then we discuss different materials and delivery systems responsive to inflammation-associated biochemical signals, such as pH, reactive oxygen species, and specific enzymes. Also, applications of various bioresponsive drug delivery systems in the treatment of typical acute and chronic inflammatory diseases are described. Finally, crucial challenges in the future development and clinical translation of bioresponsive anti-inflammatory drug delivery systems are highlighted.

Dynamic micelles with detachable PEGylation at tumoral extracellular pH for enhanced chemotherapy

Although surface PEGylation of nanomedicines can decrease serum protein adsorption in vivo, it also blocks uptake by tumor cells. This dilemma could be overcome by employing detachably PEGylated strategy at tumoral extracellular microenvironment to achieve improved cellular uptake while prolonged circulation times. Herein, the amphiphilic graft copolymers with pH-sensitive ortho ester-linked mPEG in side chains and polyurethanes in backbone, can self-assemble into the free and doxorubicin (DOX)-loaded micelles. The pH-sensitive micelles could undergo several characteristics as follows: (i) PEGylated shells for stability in sodium dodecyl sulfonate (SDS) solution; (ii) DePEGylation via degradation of ortho ester linkages at tumoral extracellular pH (6.5) for gradually dynamic size changes and effective release of DOX; and (iii) enhanced cellular uptake and cytotoxicity via positive DOX. Moreover, the dynamic micelles with detachable PEGylation could quickly penetrate the centers of SH-SY5Y multicellular spheroids (MCs) and strongly inhibit tumor growth in vitro and in vivo, and might be considered as promising and effective drug carriers in tumor therapy.

Fabrication of Acidic pH-Cleavable Polymer for Anticancer Drug Delivery Using a Dual Functional Monomer

The preparation of tumor acidic pH-cleavable polymers generally requires tedious postpolymerization modifications, leading to batch-to-batch variation and scale-up complexity. To develop a facile and universal strategy, we reported in this study design and successful synthesis of a dual functional monomer, a-OEGMA that bridges a methacrylate structure and oligo(ethylene glycol) (OEG) units via an acidic pH-cleavable acetal link. Therefore, a-OEGMA integrates (i) the merits of commercially available oligo(ethylene glycol) monomethyl ether methacrylate (OEGMA) monomer, i.e., hydrophilicity for extracellular stabilization of particulates and a polymerizable methacrylate for adopting controlled living radical polymerization (CLRP), and (ii) an acidic pH-cleavable acetal link for efficiently intracellular destabilization of polymeric carriers. To demonstrate the advantages of a-OEGMA ( M_n = 500 g/mol) relative to the commercially available OEGMA ( M_n = 300 g/mol) for drug delivery applications, we prepared both acidic pH-cleavable poly(ε-caprolactone)₂₁- b-poly( a-OEGMA)₁₁ (PCL₂₁- b-P( a-OEGMA)₁₁) and pH-insensitive analogues of PCL₂₁- b-P(OEGMA)₁₈ with an almost identical molecular weight (MW) of approximately 5.0 kDa for the hydrophilic blocks by a combination of ring-opening polymerization (ROP) of ε-CL and subsequent atom transfer radical polymerization (ATRP) of a-OEGMA or OEGMA. The pH-responsive micelles self-assembled from PCL₂₁- b-P( a-OEGMA)₁₁ showed sufficient salt stability, but efficient acidic pH-triggered aggregation that was confirmed by the DLS and TEM measurements as well as further characterizations of the products after degradation. In vitro drug release study revealed significantly promoted drug release at pH 5.0 relative to the release profile recorded at pH 7.4 due to the loss of colloidal stability and formation of micelle aggregates. The delivery efficacy evaluated by flow cytometry analyses and an in vitro cytotoxicity study in A549 cells further corroborated greater cellular uptake and cytotoxicity of Dox-loaded pH-sensitive micelles of PCL₂₁- b-P( a-OEGMA)₁₁ relative to the pH-insensitive analogues of PCL₂₁- b-P(OEGMA)₁₈. This study therefore presents a facile and robust means toward tumor acidic pH-responsive polymers as well as provides one solution to the trade-off between extracellular stability and intracellular high therapeutic efficacy of drug delivery systems using a novel monomer of a-OEGMA with dual functionalities.

pH-Responsive, Functionalizable Spyrocyclic Polycarbonate: A Versatile Platform for Biocompatible Nanoparticles

Polymeric nanoparticles are widely investigated to enhance the selectivity of therapeutics to targeted sites, as well as to increase circulation lifetime and water solubility of poorly soluble drugs. In contrast to the encapsulation of the cargo into the nanostructures, the conjugation directly to the polymer backbone allows better control on the loading and selective triggered release. In this work we report a simple procedure to create biodegradable polycarbonate graft copolymer nanoparticles via a ring opening polymerization and subsequent postpolymerization modification strategies. The polymer, designed with both pH-responsive acetal linkages and a norbornene group, allows for highly efficient postpolymerization modifications through a range of chemistries to conjugate imaging agents and solubilizing arms to direct self-assembly. To demonstrate the potential of this approach, polycarbonate-based nanoparticles were tested for biocompatibility and their ability to be internalized in A549 and IMR-90 cell lines.

pH-Responsive Nanoscale Covalent Organic Polymers as a Biodegradable Drug Carrier for Combined Photodynamic Chemotherapy of Cancer

Covalent organic polymers (COPs) are a promising class of cross-linked polymeric networks and porous structures composed of covalent organic molecules that attract extensive attention. Despite increasing interest in applying COPs for applications in nanomedicine, the pH-sensitive COPs that are able to sensitively respond to the slightly acidic tumor microenvironment for tumor-specific drug delivery and therapy remain to be explored to our best knowledge. Herein, a new style of pH-responsive COPs were prepared using acryloyl meso-tetra( p-hydroxyphenyl) porphine (acryloyl-THPP) to react with 4,4'-trimethylene dipiperidine to form the pH-responsive cross-linked biodegradable β-amino esters (BAEs). Amine-modified poly(ethylene glycol) (PEG) was then introduced to terminate the reaction and form the PEG shell. The formulated pH-responsive THPP-BAE-PEG COPs can be utilized to encapsulate anticancer drug doxorubicin (DOX) due to their porous structure. Upon intravenous injection, such DOX-loaded COPs show a prolonged blood circulation as well as an efficient tumor accumulation. Along with the pH-triggered drug release for chemotherapy, the singlet oxygen produced by THPP under light exposure for photodynamic therapy would further endow us a combined treatment strategy, which offers synergistic antitumor effects in our in vivo tumor model experiments. Our study illustrates that COPs fabricated with tumor microenvironment responsive linkers may be a promising type of materials for applications in cancer nanomedicine.

Acid-labile poly(ethylene glycol) shell of hydrazone-containing biodegradable polymeric micelles facilitating anticancer drug delivery

Biodegradable pH-sensitive amphiphilic block polymer (mPEG-Hyde-PLGA) was synthesized via ring-opening polymerization, initiated from a hydrazone-containing macro-initiator. In this way, a pH-sensitive hydrazone bond was inserted into the backbone of block copolymer, linking hydrophilic poly(ethylene glycol) segment and hydrophobic poly(lactic-co-glycolic acid) segment. The copolymer self-assembled to form stable micelles with mean diameters below 100 nm and served as a drug delivery system for doxorubicin, with drug loading content of 5.3%. pH sensitivity of the hydrazone-containing micelles was investigated by changes in diameter and size distribution observed by dynamic light scattering measurements when the micelles were encountered to acidic medium. Small pieces and larger aggregates were found by transmission electron microscopy resulting from the disassociation of the micelles in acidic conditions. It was also noted that doxorubicin release from the pH-sensitive micelles is significantly faster at pH 4.0 and pH 5.0 compared to pH 7.4, while almost no difference was detected in the case of pH non-sensitive micelles. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays on HepG-2 and MCF-7 cells revealed that doxorubicin-loaded pH-sensitive micelles had higher antitumor activity than pH-insensitive ones. This pH-sensitive drug delivery system based on hydrazone-containing block copolymer has been proved as a promising drug formulation for cancer therapy.

Hydrazone-Containing Triblock Copolymeric Micelles for pH-Controlled Drug Delivery

In this study, the structure-activity relationship of amphiphilic block copolymer micelles as nanosized drug delivery system was revealed. Firstly, a biodegradable triblock polymers PEG-DiHyd-PLA containing hydrazone bond was synthesized through the ring-opening polymerization. In this method, PEG-DiHyd-Phenol was used as the initiator and L-lactide as the monomer. Then, the polymeric micelles were formed and used as nano-drug carriers with pH sensitivity. The structure and composition of the polymer were characterized by infrared (IR), nuclear magnetic resonance (1H-NMR), and gel permeation chromatography (GPC), we characterized the self-assembling process of the triblock polymers and the pH sensitivity of the micelles by the means of transmission electron microscopy (TEM), dynamic light scattering method (DLS). Doxorubicin (DOX) acts as the model drug, and we researched the capacities of drug loading and release in vitro of the micelles. MTT experiments showed that the blank micelles of PEG-DiHyd-PLA were not cytotoxic to tumor cells (HepG-2, MCF-7) and normal cell (L-02 cells), but the DOX loaded ones displayed more toxicity than the ones without hydrazone, which was consistent to the further confocal laser scanning microscopy and flow cytometry study.

Unlocking the Potential of Poly(Ortho Ester)s: A General Catalytic Approach to the Synthesis of Surface-Erodible Materials

Poly(ortho ester)s (POEs) are well-known for their surface-eroding properties and hence present unique opportunities for controlled-release and tissue-engineering applications. Their development and wide-spread investigation has, however, been severely limited by challenging synthetic requirements that incorporate unstable intermediates and are therefore highly irreproducible. Herein, the first catalytic method for the synthesis of POEs using air- and moisture-stable vinyl acetal precursors is presented. The synthesis of a range of POE structures is demonstrated, including those that are extremely difficult to achieve by other synthetic methods. Furthermore, application of this chemistry permits efficient installation of functional groups through ortho ester linkages on an aliphatic polycarbonate.

pH-sensitive nanogels with ortho ester linkages prepared via thiol-ene click chemistry for efficient intracellular drug release

pH-sensitive nanogels with ortho ester linkages were conveniently prepared through reaction of thiol-ene click chemistry. Through adjusting feed reactant ratios and concentrations of ortho ester diacrylamide (OEAM), pentaerythritol tetra(3-mercaptopropionate) (PT), and methoxyl poly(ethyleneglycol) acrylate (mPEGA), the size of the nanogels could be controlled at 100-200nm with relatively narrow size distributions. The nanogels with size of 149.1±17.7nm (designed as NG) were verified by proton nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), dynamic laser scattering (DLS) and transmission electron microscopy (TEM). Doxorubicin (DOX) was loaded into NG with high drug loading efficiency up to 73.7%. In vitro drug release studies showed that up to 75.9% DOX from NG was released in 24h at pH 5.0 because of hydrolysis of ortho ester. Cellular uptake studies confirmed that DOX-loaded NG (NG/DOX) could be readily internalized by two-dimensional cells, resulting in efficient antitumor efficiency of cancer cells. Three-dimensional (3D) multicellular tumor spheroids (MCTS) as in vitro tumor model was used to further evaluate the antitumor effect of NG/DOX. The results demonstrated that NG/DOX showed a significantly enhanced penetration and growth inhibition in 3D multicellular tumor spheroids (MCTS), compared to free DOX.

Chemically modified inulin microparticles serving dual function as a protein antigen delivery vehicle and immunostimulatory adjuvant

To develop a new subunit vaccine adjuvant, we chemically modified a naturally-occurring, immunostimulatory inulin polysaccharide to produce an acid-sensitive biopolymer (acetalated inulin, Ace-IN). Various hydrophobic Ace-IN polymers were formed into microparticles (MPs) by oil-in-water emulsions followed by solvent evaporation These Ace-IN MPs possessed tunable degradation characteristics that, unlike polyesters used in FDA-approved microparticulate formulations, had only pH-neutral hydrolytic byproducts. Macrophages were passively targeted with cytocompatible Ace-IN MPs. TNF-α production by macrophages treated with Ace-IN MPs could be altered by adjusting the polymers' chemistry. Mice immunized with Ace-IN MPs encapsulating a model ovalbumin (OVA) antigen showed higher production of anti-OVA IgG antibody levels relative to soluble antigen. The antibody titers were also comparable to an alum-based formulation. This proof-of-concept establishes the potential for chemically-modified inulin MPs to simultaneously enable dual functionality as a stimuli-controlled antigen delivery vehicle and immunostimulatory adjuvant.

Tunable dynamic fluorinated poly(orthoester)-based drug carriers for greatly enhanced chemotherapeutic efficacy

Tunable dynamic fluorinated poly(orthoester)-based drug carriers were evaluatedin vitroandin vivoand showed greatly enhanced chemotherapeutic efficacy.

Mechanisms and biomaterials in pH-responsive tumour targeted drug delivery: A review

As the mainstay in the treatment of various cancers, chemotherapy plays a vital role, but still faces many challenges, such as poor tumour selectivity and multidrug resistance (MDR). Targeted drug delivery using nanotechnology has provided a new strategy for addressing the limitations of the conventional chemotherapy. In the last decade, the volume of research published in this area has increased tremendously, especially with functional nano drug delivery systems (nanocarriers). Coupling a specific stimuli-triggered drug release mechanism with these delivery systems is one of the most prevalent approaches for improving therapeutic outcomes. Among the various stimuli, pH triggered delivery is regarded as the most general strategy, targeting the acidic extracellular microenvironment and intracellular organelles of solid tumours. In this review, we discuss recent advances in the development of pH-sensitive nanocarriers for tumour-targeted drug delivery. The review focuses on the chemical design of pH-sensitive biomaterials, which are used to fabricate nanocarriers for extracellular and/or intracellular tumour site-specific drug release. The pH-responsive biomaterials bring forth conformational changes in these nanocarriers through various mechanisms such as protonation, charge reversal or cleavage of a chemical bond, facilitating tumour specific cell uptake or drug release. A greater understanding of these mechanisms will help to design more efficient drug delivery systems to address the challenges encountered in conventional chemotherapy.

Microparticles formulated from a family of novel silylated polysaccharides demonstrate inherent immunostimulatory properties and tunable hydrolytic degradability

Acid-degradable polymers are well-suited for drug delivery vehicles because numerous physiological sites are acidic.

Precise modular synthesis and a structure–property study of acid-cleavable star-block copolymers for pH-triggered drug delivery

A series of well-defined three-armed star-block copolymers (mPEG-a-PCL-a-)₃ linked with acid-cleavable acetal groups have been prepared and used for the pH-triggered delivery of doxorubicin.

Galactosylated reduction and pH dual-responsive triblock terpolymer Gal-PEEP-a-PCL-ss-PDMAEMA: a multifunctional carrier for the targeted and simultaneous delivery of doxorubicin and DNA

A multifunctional bioreducible system based on galactosamine-modified PEEP-a-PCL-ss-PDMAEMA has been prepared and used for the targeted co-delivery of doxorubicin and DNA.

Oxidation-Accelerated Hydrolysis of the Ortho Ester-Containing Acid-Labile Polymers

We report a versatile method to tune the hydrolysis of the ortho ester-containing block copolymers by covalently incorporating oxidation-sensitive phenylboronic ester units. A series of block copolymers which contain a polyethylene glycol (PEG) block and a hydrophobic segment composed of different amounts of pendent ortho ester and phenylboronic ester groups were synthesized. These copolymers can self-assemble into narrowly dispersed micelle-like nanoparticles in phosphate buffer. The kinetics of phenylboronic ester oxidation and ortho ester hydrolysis in the nanoparticles were studied at different pH and H₂O₂ concentration. The results indicated that the phenylboronic ester oxidation rate was faster than the ortho ester hydrolysis rate at neutral pH, and both processes were accelerated with increasing H₂O₂ concentration. Nanoparticles which are extremely sensitive to the biorelevant concentration of H₂O₂ (50 μM) at pH 7.4 were obtained, suggesting great promise for inflammation-specific drug delivery.