Influence of Polymer Structure and Architecture on Drug Loading and Redox-Triggered Release

Responsive Surfactant-Driven Morphology Transformation of Block Copolymer Microparticles

Block copolymer (BCP) microparticles, which exhibit rapid change of morphology and physicochemical property in response to external stimuli, represent a promising avenue for the development of programmable smart materials. Among the methods available for generating BCP microparticles with adjustable morphologies, the confined assembly of BCPs within emulsions has emerged as a particularly facile and versatile approach. This review provides a comprehensive overview of the role of responsive surfactants in modulating interfacial interactions at the oil-water interface, which facilitates controlled BCP microparticle morphology. We elucidate how variations in the properties of responsive surfactants, activated by external stimuli, influence BCP chain arrangement and interfacial selectivity. Additionally, this review explores the applications of shape-switchable microparticles in advanced technologies such as smart display, fluorescence modulation, magnetic resonance imaging, drug delivery, and photonic crystal. Finally, the challenges and prospective future directions in this rapidly evolving field are discussed.

Precise intracellular uptake and endosomal release of diverse functional mRNA payloads via glutathione-responsive nanogels

We present a novel, highly customizable glutathione-responsive nanogel (NG) platform for efficient mRNA delivery with precise mRNA payload release control. Optimization of various cationic monomers, including newly synthesized cationic polyarginine, polyhistidine, and acrylated guanidine monomers, allowed fine-tuning of NG properties for mRNA binding. By incorporating a poly(ethylene) glycol-based disulphide crosslinker, we achieved glutathione-triggered mRNA release, enabling targeted intracellular delivery. Our NGs demonstrated superior encapsulation (up to 89.3 %) and loading (10.7 %) efficiencies, with controlled mRNA release kinetics at intracellular glutathione concentrations. NGs outperformed commercial transfection reagents across multiple cell lines, including traditionally difficult-to-transfect lines. We demonstrate the platform's versatility by successfully delivering GFP mRNA, Mango II RNA aptamers, and functionally relevant β2-AMPK mRNA. Furthermore, we used TIRF microscopy to measure exact RNA copy number within the NGs. Notably, mechanistic cellular uptake studies revealed that disulphide-containing NGs exhibit enhanced cellular uptake and endosomal escape, potentially due to interactions with cell surface thiols. This work represents a highly tuneable, efficient, and biocompatible platform for mRNA delivery with relevance for gene therapy and vaccine development.

Therapeutic induction of ferroptosis in tumors using PD-L1 targeting antibody nanogel conjugates

Although programmed cell death ligand 1 (PD-L1) is best known for its role in immune suppression, tumor-intrinsic functions are emerging. Here, we report that tumor cells that express PD-L1 are sensitive to ferroptosis inducers such as imidazole ketone erastin (IKE). PD-L1 promotes ferroptosis sensitivity because it suppresses SLC7A11 expression and diminishes glutathione levels. Although the use of anti-PD-L1 antibody drug conjugates (ADCs) could be effective for the delivery of ferroptosis inducers to specific tumor populations, the chemistry of most ferroptosis inducers precludes their incorporation in ADCs. To overcome this challenge, we synthesized an antibody nanogel conjugate (ANC) comprised of an anti-PD-L1 antibody conjugated to a nanogel encapsulated with IKE. This ANC targets PD-L1-expressing cells in vitro and in vivo and induces ferroptosis, resulting in tumor suppression. Importantly, this approach is superior to systemic administration of IKE because it enables enhanced delivery of IKE specifically to tumor cells and it requires lower drug doses for efficacy.

Poly(vinyl alcohol)-Incorporated Core-Shell Polymer Nanogels Functionalized by Block Copolymer Installation for Cisplatin Delivery

The functionalization approach for nanomaterials is of great importance for their application in drug delivery systems. Herein, an approach based on block copolymer installation into polymer nanogels was newly developed. Poly(vinyl alcohol)-incorporated polymer nanogels were prepared by a two-step dispersion/precipitation polymerization. Poly(methacrylic acid)-block-poly(3-fluorophenylboronic acid methacrylamide) (PMAA-b-PFPBMA) prepared by two-step reversible addition-fragmentation chain transfer polymerization was installed into the polymer nanogels via boronate ester formation. Furthermore, cisplatin as a cancer therapeutic drug was successfully loaded on the block copolymer-installed polymer nanogels, and cell death was achieved by using the resulting cisplatin-loaded nanogels. We believe that the functionality of the nanogels can be changed by varying the installed block copolymer, leading to the functionalization approach of polymer nanogels based on block copolymer installation, which will be of great utility in many fields.

Intertumoral and intratumoral barriers as approaches for drug delivery and theranostics to solid tumors using stimuli-responsive materials

The solid tumors provide a series of biological barriers in cellular microenvironment for designing drug delivery methods based on advanced stimuli-responsive materials. These intertumoral and intratumoral barriers consist of perforated endotheliums, tumor cell crowding, vascularity, lymphatic drainage blocking effect, extracellular matrix (ECM) proteins, hypoxia, and acidosis. Triggering opportunities have been drawn for solid tumor therapies based on single and dual stimuli-responsive drug delivery systems (DDSs) that not only improved drug targeting in deeper sites of the tumor microenvironments, but also facilitated the antitumor drug release efficiency. Single and dual stimuli-responsive materials which are known for their lowest side effects can be categorized in 17 main groups which involve to internal and external stimuli anticancer drug carriers in proportion to microenvironments of targeted solid tumors. Development of such drug carriers can circumvent barriers in clinical trial studies based on their superior capabilities in penetrating into more inaccessible sites of the tumor tissues. In recent designs, key characteristics of these DDSs such as fast response to intracellular and extracellular factors, effective cytotoxicity with minimum side effect, efficient permeability, and rate and location of drug release have been discussed as core concerns of designing paradigms of these materials.

Degradable Polymer-Based Nanoassemblies for Precise Targeting and Drug Delivery to Breast Cancer Cells without Affecting Normal Healthy Cells

Stimuli-responsive amphiphilic polymers are known to be precursors to forming promising nanoarchitectonics with tunable properties for application in biomedical sciences. Currently, self-immolative polymers are widely recognized as an emerging class of responsive materials with excellent degradability, which is one of the crucial criteria for designing a robust drug delivery vehicle. Here, we design an amphiphilic polyurethane endowed with a redox-responsive self-immolative linker and a pH-responsive tertiary amine on the backbone, which forms entropy-driven nanoscale supramolecular assemblies (average hydrodynamic diameter ∼110 nm) and is programmed to disassemble in a redox environment (GSH) due to the degradation of the polymer in a self-immolative fashion. The nanoassembly shows efficient drug sequestration and release in a controlled manner in response to glutathione (10 mM). The tertiary amine residing on the surface of the nanoassembly becomes protonated in the tumor microenvironment (pH ∼ 6.4-6.8) and generates positively charged nanoassembly (ζ-potential = +36 mV), which enhances the cancer cell-selective cellular uptake. The biological evaluation of the drug-loaded nanoassembly revealed triple-negative breast cancer (MDAMB-231) selective internalization and cell death while shielding normal cells (RBCs or PBMCs) from off-targeting toxicity. We envision that polyurethane with a redox-responsive self-immolative linker might open up new opportunities for a completely degradable polyurethane-based nanocarrier for drug delivery and diagnosis applications.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Optimizing Conjugation Chemistry, Antibody Conjugation Site, and Surface Density in Antibody-Nanogel Conjugates (ANCs) for Cell-Specific Drug Delivery

Targeted delivery of therapeutics using antibody-nanogel conjugates (ANCs) with a high drug-to-antibody ratio has the potential to overcome some of the inherent limitations of antibody-drug conjugates (ADCs). ANC platforms with simple preparation methods and precise tunability to evaluate structure-activity relationships will greatly contribute to translating this promise into clinical reality. In this work, using trastuzumab as a model antibody, we demonstrate a block copolymer-based ANC platform that allows highly efficient antibody conjugation and formulation. In addition to showcasing the advantages of using an inverse electron-demand Diels-Alder (iEDDA)-based antibody conjugation, we evaluate the influence of antibody surface density and conjugation site on the nanogels upon the targeting capability of ANCs. We show that compared to traditional strain-promoted alkyne-azide cycloadditions, the preparation of ANCs using iEDDA provides significantly higher efficiency, which results in a shortened reaction time, simplified purification process, and enhanced targeting toward cancer cells. We also find that a site-specific disulfide-rebridging method in antibodies offers similar targeting abilities as the more indiscriminate lysine-based conjugation method. The more efficient bioconjugation using iEDDA allows us to optimize the avidity by fine-tuning the surface density of antibodies on the nanogel. Finally, with trastuzumab-mertansine (DM1) antibody-drug combination, our ANC demonstrates superior activities in vitro compared to the corresponding ADC, further highlighting the potential of ANCs in future clinical translation.

Redox-Responsive Core-Cross-Linked Micelles of Miktoarm Poly(ethylene oxide)-b-poly(furfuryl methacrylate) for Anticancer Drug Delivery

The physiological instability of nanocarriers, premature drug leakage during blood circulation, and associated severe side effects cause compromised therapeutic efficacy, which have significantly hampered the progress of nanomedicines. The cross-linking of nanocarriers while keeping the effectiveness of their degradation at the targeted site to release the drug has emerged as a potent strategy to overcome these flaws. Herein, we have designed novel (poly(ethylene oxide))₂-b-poly(furfuryl methacrylate) ((PEO_2K)₂-b-PFMA_nk) miktoarm amphiphilic block copolymers by coupling alkyne-functionalized PEO (PEO_2K-C≡H) and diazide-functionalized poly(furfuryl methacrylate) ((N₃)₂-PFMA_nk) via click chemistry. (PEO_2K)₂-b-PFMA_nk self-assembled to form nanosized micelles (mikUCL) with hydrodynamic radii in the range of 25∼33 nm. The hydrophobic core of mikUCL was cross-linked by a disulfide-containing cross-linker using the Diels-Alder reaction to avoid unwanted leakage and burst release of a payload. As expected, the resulting core-cross-linked (PEO_2K)₂-b-PFMA_nk micelles (mikCCL) exhibited superior stability under a normal physiological environment and were de-cross-linked to rapidly release doxorubicin (DOX) upon exposure to a reduction environment. The micelles were compatible with HEK-293 normal cells, while DOX-loaded micelles (mikUCL/DOX and mikCCL/DOX) induced high antitumor activity in HeLa and HT-29 cells. mikCCL/DOX preferentially accumulated at the tumor site and was more efficacious than free DOX and mikUCL/DOX for tumor inhibition in HT-29 tumor-bearing nude mice.

Targeted Drug Delivery Using a Plug-to-Direct Antibody-Nanogel Conjugate

Targeted drug delivery using antibody-drug conjugates has attracted great attention due to its enhanced therapeutic efficacy compared to traditional chemotherapy. However, the development has been limited due to a low drug-to-antibody ratio and laborious linker-payload optimization. Herein, we present a simple and efficient strategy to combine the favorable features of polymeric nanocarriers with antibodies to generate an antibody-nanogel conjugate (ANC) platform for targeted delivery of cytotoxic agents. Our nanogels stably encapsulate several chemotherapeutic agents with a wide range of mechanisms of action and solubility. We showcase the targetability of ANCs and their selective killing of cancer cells over-expressing disease-relevant antigens such as human epidermal growth factor receptor 2, epidermal growth factor receptor, and tumor-specific mucin 1, which cover a broad range of breast cancer cell types while maintaining low to no toxicity to non-targeted cells. Overall, our system represents a versatile approach that could impact next-generation nanomedicine in antibody-targeted therapeutics.

Opportunities and Challenges of Switchable Materials for Pharmaceutical Use

Switchable polymeric materials, which can respond to triggering signals through changes in their properties, have become a major research focus for parenteral controlled delivery systems. They may enable externally induced drug release or delivery that is adaptive to in vivo stimuli. Despite the promise of new functionalities using switchable materials, several of these concepts may need to face challenges associated with clinical use. Accordingly, this review provides an overview of various types of switchable polymers responsive to different types of stimuli and addresses opportunities and challenges that may arise from their application in biomedicine.

Multiplexed Analysis of the Cellular Uptake of Polymeric Nanocarriers

Polymeric nanocarriers (PNCs) are versatile drug delivery vehicles capable of delivering a variety of therapeutics. Quantitatively monitoring their uptake in biological systems is essential for realizing their potential as next-generation delivery systems; however, existing quantification strategies are limited due to the challenges of detecting polymeric materials in complex biological samples. Here, we describe a metal-coded mass tagging approach that enables the multiplexed quantification of the PNC uptake in cells using mass spectrometry (MS). In this approach, PNCs are conjugated with ligands that bind strongly to lanthanide ions, allowing the PNCs to be sensitively quantitated by inductively coupled plasma-MS. The metal-coded tags have little effect on the properties or toxicity of the PNCs, making them biocompatible. We demonstrate that the conjugation of different metals to the PNCs enables the multiplexed analysis of cellular uptake of multiple distinct PNCs at the same time. This multiplexing capability should improve the design and optimization of PNCs by minimizing biological variability and reducing analysis time, effort, and cost.

Dual Responsive poly(vinyl caprolactam)-Based Nanogels for Tunable Intracellular Doxorubicin Delivery in Cancer Cells

In this work, doxorubicin (Dox)-encapsulated poly(vinyl caprolactam) (PVCL)-based three-dimensional nanogel networks were developed and were crosslinked with disulfide linkages. The nanogels degrade rapidly to low molecular weight chains in the presence of the typical intracellular concentration of glutathione. Doxorubicin (Dox) was successfully encapsulated into these nanogels. The nanogels have a high drug loading of 49% and can be tailored to 182 nm to deliver themselves to the targeted cells and release Dox under dual stimuli conditions, such as redox and temperature. By evaluating cell viability in the HepG2 cell line, we observed that Dox-loaded nanogels effectively killed the cancer cell. Fluorescence microscopy results show that the nanogels could easily be internalized with HepG2 cells. The results confirm that the nanogels destabilized in intracellular cytosol via degradation of disulfide bonds in nanogels networks and release of the Dox nearby the nucleus. These carriers could be promising for cancer drug delivery.

Synthesis of Polyethylene Glycol Diacrylate/Acrylic Acid Nanoparticles as Nanocarriers for the Controlled Delivery of Doxorubicin to Colorectal Cancer Cells

Doxorubicin (Dox) is known for its potential to deliver desirable anticancer effects against various types of cancer including colorectal cancer. However, the adverse effects are serious. This study aimed to synthesize polyethylene glycol diacrylate (PEGDA)/acrylic acid (AA)-based nanoparticles (PEGDA/AA NPs) for Dox delivery to colorectal cancer cells. The NPs were synthesized using free-radical polymerization reaction using the monomers PEGDA and AA with their physical properties, drug loading and release, biocompatibility, and anticancer effect evaluated. The NPs were spherical with a size of around 230 nm, with a 48% Dox loading efficiency and with loading capacity of 150 µg/mg. Intriguingly, the NPs had the ability to prolong the release of Dox in vitro over 24 h and were non-toxic to intestinal epithelial cells. Dox-loaded PEGDA/AA NPs (Dox-NPs) were able to effectively kill the colorectal cancer cell line (HT-29) with the Dox-NPs accumulating inside the cell and killing the cell through the apoptosis pathway. Overall, the synthesized PEGDA/AA NPs exhibit considerable potential as a drug delivery carrier for colon cancer-directed, staged-release therapy.