Mechanochemical Drug Conjugation via pH-Responsive Imine Linkage for Polyether Prodrug Micelles

Polymeric Nanoparticles for Drug Delivery

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

Synthesis approaches of amphiphilic copolymers for spherical micelle preparation: application in drug delivery

The formation of polymeric micelles in aqueous environments through the self-assembly of amphiphilic polymers can provide a versatile platform to increase the solubility and permeability of hydrophobic drugs and pave the way for their administration. In comparison to various self-assembly-based vehicles, polymeric micelles commonly have a smaller size, spherical morphology, and simpler scale up process. The use of polymer-based micelles for the encapsulation and carrying of therapeutics to the site of action triggered a line of research on the synthesis of various amphiphilic polymers in the past few decades. The extended knowledge on polymers includes biocompatible smart amphiphilic copolymers for the formation of micelles, therapeutics loading and response to external stimuli, micelles with a tunable drug release pattern, etc. Different strategies such as ring-opening polymerization, atom transfer radical polymerization, reversible addition-fragmentation chain-transfer, nitroxide mediated polymerization, and a combination of these methods were employed to synthesize copolymers with diverse compositions and topologies with the proficiency of self-assembly into well-defined micellar structures. The current review provides a summary of the important polymerization techniques and recent achievements in the field of drug delivery using micellar systems. This review proposes new visions for the design and synthesis of innovative potent amphiphilic polymers in order to benefit from their application in drug delivery fields.

TM-Free and TM-Catalyzed Mechanosynthesis of Functional Polymers

Mechanochemically induced methods are commonly used for the depolymerization of polymers, including plastic and agricultural wastes. So far, these methods have rarely been used for polymer synthesis. Compared to conventional polymerization in solutions, mechanochemical polymerization offers numerous advantages such as less or no solvent consumption, the accessibility of novel structures, the inclusion of co-polymers and post-modified polymers, and, most importantly, the avoidance of problems posed by low monomer/oligomer solubility and fast precipitation during polymerization. Consequently, the development of new functional polymers and materials, including those based on mechanochemically synthesized polymers, has drawn much interest, particularly from the perspective of green chemistry. In this review, we tried to highlight the most representative examples of transition-metal (TM)-free and TM-catalyzed mechanosynthesis of some functional polymers, such as semiconductive polymers, porous polymeric materials, sensory materials, materials for photovoltaics, etc.

Cinnamaldehyde-Contained Polymers and Their Biomedical Applications

Cinnamaldehyde, a natural product that can be extracted from a variety of plants of the genus Cinnamomum, exhibits excellent biological activities including antibacterial, antifungal, anti-inflammatory, and anticancer properties. To overcome the disadvantages (e.g., poor water solubility and sensitivity to light) or enhance the advantages (e.g., high reactivity and promoting cellular reactive oxygen species production) of cinnamaldehyde, cinnamaldehyde can be loaded into or conjugated with polymers for sustained or controlled release, thereby prolonging the effective action time of its biological activities. Moreover, when cinnamaldehyde is conjugated with a polymer, it can also introduce environmental responsiveness to the polymer through the form of stimuli-sensitive linkages between its aldehyde group and various functional groups of polymers. The environmental responsiveness provides the great potential of cinnamaldehyde-conjugated polymers for applications in the biomedical field. In this review, the strategies for preparing cinnamaldehyde-contained polymers are summarized and their biomedical applications are also reviewed.

Mechanochemical Preparation of Protein : hydantoin Hybrids and Their Release Properties

Mechanochemistry is a versatile methodology that can be employed both for covalent bond formation in organic synthesis as well as a mediator to allow preparation novel colloidal dispersions for drug delivery. Herein, ball-milling was employed for the solid-state preparation of fluorescent hydrophobic hydantoins, followed by the unprecedented mechanochemically-mediated complexation of hydrophobic hydantoins within hydrophilic protein β-lactoglobulin (BLG) and BLG nanofibrils (BLGNFs). These hydantoin:protein materials were in turn incorporated into hydrogels. The effect of incorporation of hydantoins into proteins, as well as the effect of protein structure, on the release properties were then investigated. The conversion of BLG to BLGNFs led to a more sustained release demonstrating that heat treatment of BLG into BLGNFs could be employed to modify release properties. To the best of our knowledge, this is the first example where protein : hydantoin complexes were prepared by mechanochemical methodology and mechanochemistry was combined with self-assembly in order to prepare protein nanomaterials for drug-delivery applications. In addition, the use of the developed protein materials is not limited to delivery of drugs but can for example be employed as components of smart food (delivery of nutrients) or release systems of pesticides.

Self-Reporting Polysaccharide Polymersome for Doxorubicin and Cisplatin Delivery to Live Cancer Cells

We report self-reporting fluorescent polysaccharide polymersome nanoassemblies for enzyme-responsive intracellular delivery of two clinical anticancer drugs doxorubicin (DOX) and cisplatin to study the real-time drug-releasing aspects by fluorescent resonance energy transfer (FRET) bioimaging in live cancer cells. Fluorescent polymersomes were tailor-made by tagging an aggregation-induced emission (AIE) optical chromophore, tetraphenylethylene (TPE), and a plant-based vesicular directing hydrophobic unit through enzyme-biodegradable aliphatic ester chemical linkages in the polysaccharide dextran. The blue-luminescent polymersome self-assembled in water and exhibited excellent encapsulation capability for the red-luminescent anticancer drug DOX. FRET between the AIE polymersome host and DOX guest molecules resulted in a completely turn-off probe. At the intracellular level, the lysosomal enzymatic disassembly of the polymersome restored the dual fluorescent signals from DOX and TPE at the nucleus and the lysosomes, respectively. Live-cell confocal microscopy coupled with selective photoexcitation was employed to study the real-time polymersome disassembly by monitoring the turn-on fluorescent signals in human breast cancer cell lines. Alternatively, carboxylic acid-functionalized AIE polymersomes were also tailor-made for cisplatin stitching to directly monitor Pt drug delivery. The polymersome nanoassemblies exhibited excellent structural tolerance for the chemical conjugation of the Pt drugs, and the fluorescence signals were unaltered. An in vitro drug release study confirmed that the cisplatin-stitched fluorescent polymersomes were very stable under physiological conditions and underwent lysosomal enzymatic degradation to inhibit the cancer cell growth. A lysosomal colocalization experiment using confocal microscopy substantiates the enzyme-responsive degradation of these polymersomes to release both the encapsulated and conjugated drugs at the intracellular level. The present design provides a unique opportunity to deliver more than one anticancer drug from a single polymersome platform in cancer research.

Acid-sensitive charge-reversal co-assembled polyurethane nanomicelles as drug delivery carriers

In order to obtain drug delivery carriers with good stability in blood and high cellular uptake efficiency, carboxyl groups and tertiary amine groups were respectively introduced into polyurethane to synthesize two kinds of amphiphilic polyurethanes with opposite charges (PUC and PUN). Their structures were characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (¹H NMR) spectroscopy and gel permeation chromatography (GPC). PUC-PUN co-assembled nanomicelles were prepared by electrostatic interaction between PUC and PUN micelles, which showed acid-sensitive property. When the pH of the solution was decreased from 7.4 to 6.5, PUC-PUN-1 micelles showed negative-to-positive charge-reversal property among these micelles. The results of stability and cell experiments demonstrated that PUC-PUN-1 micelles not only had excellent stability in simulated normal physiological environment but also could obviously enhance the cellular uptake efficiency. PUC-PUN-1 micelles had low cytotoxicity against SGC-7901 and MGC-803 cells, whereas PUC-PUN-1/DOX micelles had higher cytotoxicity compared to pure DOX and PUN-1/DOX micelles. Moreover, the results of in vivo antitumor activity experiments showed that PUC-PUN-1/DOX micelles had better tumor inhibition ability and safety than pure DOX. In addition, the results of in vitro drug release experiments indicated that PUC-PUN-1/DOX micelles had almost no burst release or leakage of drugs in pH 7.4 environment. However, the drug release was accelerated in pH 5.0, which followed Fickian diffusion mechanism.

Solvent-Free Mechanochemical Post-Polymerization Modification of Ionic Polymers

Despite their superior stability and facile handling, ionic polymers have limited solubility in most organic solvents, restricting the range of substrates and reaction conditions to which they can be applied. To overcome this solubility issue, the present study presents a solvent-free mechanochemical reaction. Specifically, a post-polymerization modification of ammonium-functionalized polyether was demonstrated using a solvent-free vibrational ball-milling technique. The formation of imine bonds between the ionic polymer and an aromatic aldehyde led to the complete conversion to imine within 1 h without any bond breakage on the polymer backbone. The viability of this approach for a wide range of aldehydes was also evaluated, highlighting the potential of the mechanochemical post-polymerization modification of polymers that are inaccessible by conventional solution approaches.

Recent developments in selenium-containing polymeric micelles: prospective stimuli, drug-release behaviors, and intrinsic anticancer activity

Selenium is capable of forming a dynamic covalent bond with itself and other elements and can undergo metathesis and regeneration reactions under optimum conditions. Its dynamic nature endows selenium-containing polymers with striking sensitivity towards some environmental alterations. In the past decade, several selenium-containing polymers were synthesized and used for the preparation of oxidation-, reduction-, and radiation-responsive nanocarriers. Recently, thioredoxin reductase, sonication, and osmotic pressure triggered the cleavage of Se-Se bonds and swelling or disassembly of nanostructures. Moreover, some selenium-containing nanocarriers form oxidation products such as seleninic acids and acrylates with inherent anticancer activities. Thus, selenium-containing polymers hold promise for the fabrication of ultrasensitive and multifunctional nanocarriers of radiotherapeutic, chemotherapeutic, and immunotherapeutic significance. Herein, we discuss the most recent developments in selenium-containing polymeric micelles in light of their architecture, multiple stimuli-responsive properties, emerging immunomodulatory activities, and future perspectives in the delivery and controlled release of anticancer agents.