Frontiers in the design and synthesis of advanced nanogels for nanomedicine

Sustainable and Surfactant-Free Synthesis of Negatively Charged Acrylamide Nanogels for Biomedical Applications

Nanogels offer unique advantages, like high surface-to-volume ratio, scalable synthetic methods, and easily tailored formulations, that allow us to control size and introduce stimuli-responsive properties. Their potential for drug delivery is significant due to their biocompatibility, high drug loading capacity, and controlled and sustained drug release. The development of greener and sustainable processes is essential for large-scale applications. We report the synthesis in water of covalently cross-linked acrylamide-based nanogels, both neutral and negatively charged, with varying amounts of acryloyl-l-proline, using high-dilution radical polymerization, without the need for surfactants. The use of a water-based synthesis resulted in nanogels with high monomer conversions and chemical yields, as well as lower polydispersity and smaller particle sizes for the negatively charged nanogels, leading to a more efficient synthetic methodology, with reduced loss of starting materials, higher potential for scalability, and reduction in costs. The suitability of these nanogels for biomedical applications was supported by cytotoxicity studies showing no significant reduction in viability on a human neuroblastoma cell line.

Poly(2-oxazoline)-based core cross-linked star polymers: synthesis and drug delivery applications

Poly(2-oxazoline)s (POxs) are promising platforms for drug delivery applications due to their biocompatibility and stealth properties. In addition, the use of core cross-linked star (CCS) polymers based on POxs is expected to enhance drug encapsulation and release performances. In this study, we employed the "arm-first" strategy to synthesize a series of amphiphilic CCS [poly(2-methyl-2-oxazoline)]_n-block-poly(2,2'-(1,4-phenylene)bis-2-oxazoline)-cross-link/copolymer-(2-n-butyl-2-oxazoline)s (PMeOx)_n-b-P(PhBisOx-cl/co-ButOx)s by using microwave-assisted cationic ring-opening polymerization (CROP). First, PMeOx, as the hydrophilic arm, was synthesized by CROP of MeOx using methyl tosylate as the initiator. Subsequently, the living PMeOx was used as the macroinitiator to initiate the copolymerization/core-crosslinking reaction of ButOx and PhBisOx to form CCS POxs having a hydrophobic core. The molecular structures of the resulting CCS POxs were characterized by size exclusion chromatography and nuclear magnetic resonance spectroscopy. The CCS POxs were loaded with the anti-cancer drug doxorubicin (DOX), and the loading was detected by UV-vis spectrometry, dynamic light scattering, and transmission electron microscopy. In vitro studies showed that DOX release at pH 5.2 was faster than that at pH 7.1. The in vitro cytotoxicity study using HeLa cells revealed that the neat CCS POxs are compatible with the cells. In contrast, the DOX-loaded CCS POxs exhibited a cytotoxic effect in a concentration-dependent manner in HeLa cells, which strongly supports that the CSS POxs are potential candidates for drug delivery applications.

Synthesis of Anionic Nanogels for Selective and Efficient Enzyme Encapsulation

Polyelectrolyte nanogels containing cross-linked ionic polymer networks feature both soft environment and intrinsic charges which are of great potential for enzyme encapsulation. In this work, well-defined poly(acrylic acid) (PAA) nanogels have been synthesized based on a facile strategy, namely, electrostatic assembly directed polymerization (EADP). Specifically, AA monomers are polymerized together with a cross-linker in the presence of a cationic-neutral diblock copolymer as the template. Effects of control factors including pH, salt concentration, and cross-linking degree have been investigated systematically, based on which the optimal preparation of PAA nanogels has been established. The obtained nanogel features not only compatible pocket for safely loading enzymes without disturbing their structures, but also abundant negative charges which enable selective and efficient encapsulation of cationic enzymes. The loading capacities of PAA nanogels for cytochrome (cyt c) and lysozyme are 100 and 125 μg/mg (enzyme/nanogel), respectively. More notably, the PAA network seems to modulate a favorable microenvironment for cyt c and induces 2-fold enhanced activity for the encapsulated enzymes, as indicated by the steady-state kinetic assay. Our study reveals the control factors of EADP for optimal synthesis of anionic nanogels and validates their distinctive advances with respect to efficient loading and activation of cationic enzymes.

Nanogels: A novel approach in antimicrobial delivery systems and antimicrobial coatings

The implementation of nanotechnology to develop efficient antimicrobial systems has a significant impact on the prospects of the biomedical field. Nanogels are soft polymeric particles with an internally cross-linked structure, which behave as hydrogels and can be reversibly hydrated/dehydrated (swollen/shrunken) by the dispersing solvent and external stimuli. Their excellent properties, such as biocompatibility, colloidal stability, high water content, desirable mechanical properties, tunable chemical functionalities, and interior gel-like network for the incorporation of biomolecules, make them fascinating in the field of biological/biomedical applications. In this review, various approaches will be discussed and compared to the newly developed nanogel technology in terms of efficiency and applicability for determining their potential role in combating infections in the biomedical area including implant-associated infections.

Rapid preparation of nanogels by photopolymerization at 532 nm

The strategy of laser beam expansion was used to rapidly prepare nanogels by photopolymerization at 532 nm under low monomer concentration. According to the unique micellar morphology formed by amphiphilic polyethylene glycol diacrylate (PEGDA) in water, the monomer concentration was largely decreased to increase the distance of micellar aggregates. In this case, the photo-crosslinking could prefer to occur inside the micelles instead of crosslinking between the micellar aggregates. The variations of double bond content with reaction time in different beam expansion experiments were investigated. Finally, nanogels with uniform size could be rapidly prepared by regulating the reaction parameters, including monomer concentration, reaction time and power density.

Coupled stochastic simulation of the chain length and particle size distribution in miniemulsion radical copolymerization of styrene and N-vinylcaprolactam

Kinetic Monte Carlo modeling is applied for the coupled simulation of the chain length and particle size distribution in isothermal batch miniemulsion copolymerization of styrene and N-vinylcaprolactam.

Application of radiation for the synthesis of poly(n-vinyl pyrrolidone) nanogels with controlled sizes from aqueous solutions

Controlling of sizes of nanogels is very important for any biomedical application. In the present study we report a facile and reproducible method of preparing biocompatible nanogels of poly(N-vinyl pyrrolidone) (PVP) which were synthesized by using either electron beam (e-beam) (NGEB) or gamma irradiation (NGG) of dilute aqueous solutions. Nanogels with different hydrodynamic sizes were obtained at the variance of the polymer molecular weight, concentration, type of radiation source hence dose rate and total absorbed dose. For the first time a comparative study of gamma and e-beam irradiation was made on the same polymer with the aim of controlling sizes of nanogels in the range of 30-250 nm. Moreover the stability of radiation-synthesized nanogels was followed up to 2 years in refrigerated solution and found to retain their original sizes and distributions enabling their long-term storage and use. The synthesized nanogels were characterized by using dynamic light scattering (DLS), gel permeation chromatography (GPC), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. This work provides a clue to the fundamental question of how to control sizes of nanogels without using any additives which are indispensable with the other techniques. The technique is applicable to any water soluble polymer.

A New Strategy for Intestinal Drug Delivery via pH-Responsive and Membrane-Active Nanogels

Oral administration of hydrophobic and poorly intestinal epithelium-permeable drugs is a significant challenge. Herein, we report a new strategy to overcome this problem by using novel, pH-responsive, and membrane-active nanogels as drug carriers. Prepared by simple physical cross-linking of amphiphilic pseudopeptidic polymers with pH-controlled membrane-activity, the size and hydrophobicity-hydrophilicity balance of the nanogels could be well-tuned. Furthermore, the amphiphilic nanogels could release hydrophobic payloads and destabilize cell membranes at duodenum and jejunum pH 5.0-6.0, which suggests their great potential for intestinal drug delivery.

Biodegradable Smart Nanogels: A New Platform for Targeting Drug Delivery and Biomedical Diagnostics

Nanogels (or nanohydrogels) have been extensively investigated as one of the most promising nanoparticulate biomedical platforms owing to their advantageous properties that combine the characteristics of hydrogel systems with nanoparticles. Among them, smart nanogels that have the ability to respond to external stimuli, such as pH, redox, temperature, enzymes, light, magnetic field and so forth, are most attractive in the area of drug delivery. Besides, numerous multifunctionalized nanogels with high sensitivity and specificity were designed for diagnostic applications. In this feature article, we have reviewed and discussed the recent progress of biodegradable nanogels as smart nanocarriers of anticancer drugs and biomedical diagnostic agents for cancer.

Stimuli-responsive nanogel composites and their application in nanomedicine

Nanogels are nanosized crosslinked polymer networks capable of absorbing large quantities of water. Specifically, smart nanogels are interesting because of their ability to respond to biomedically relevant changes like pH, temperature, etc. In the last few decades, hybrid nanogels or composites have been developed to overcome the ever increasing demand for new materials in this field. In this context, a hybrid refers to nanogels combined with different polymers and/or with nanoparticles such as plasmonic, magnetic, and carbonaceous nanoparticles, among others. Research activities are focused nowadays on using multifunctional hybrid nanogels in nanomedicine, not only as drug carriers but also as imaging and theranostic agents. In this review, we will describe nanogels, particularly in the form of composites or hybrids applied in nanomedicine.

Self-Assembled Gold Nanoclusters for Bright Fluorescence Imaging and Enhanced Drug Delivery

Nanoparticles combining enhanced cellular drug delivery with efficient fluorescence detection are important tools for the development of theranostic agents. Here, we demonstrate this concept by a simple, fast, and robust protocol of cationic polymer-mediated gold nanocluster (Au NCs) self-assembly into nanoparticles (NPs) of ca. 120 nm diameter. An extensive characterization of the monodisperse and positively charged NPs revealed pH-dependent swelling properties, strong fluorescence enhancement, and excellent colloidal and photostability in water, buffer, and culture medium. The versatility of the preparation is demonstrated by using different Au NC surface ligands and cationic polymers. Steady-state and time-resolved fluorescence measurements give insight into the aggregation-induced emission phenomenon (AIE) by tuning the Au NC interactions in the self-assembled nanoparticles using the pH-dependent swelling. In vitro studies in human monocytic cells indicate strongly enhanced uptake of the NPs compared to free Au NCs in endocytic compartments. The NPs keep their assembly structure with quite low cytotoxicity up to 500 μg Au/mL. Enhanced drug delivery is demonstrated by loading peptides or antibodies in the NPs using a one-pot synthesis. Fluorescence microscopy and flow cytometry confirmed intracellular colocalization of the biomolecules and the NP carriers with a respective 1.7-fold and 6.5-fold enhanced cellular uptake of peptides and antibodies compared to the free biomolecules.

Enzyme-mediated in situ formation of pH-sensitive nanogels for proteins delivery

pH-Sensitive (PEG-b-P(LGA-g-Tyr)) nanogels were fabricated through the enzyme-mediated crosslinking reaction and used to load FITC-BSA for intracellular protein delivery.

Templateless synthesis of polyacrylamide-based Nanogels via RAFT dispersion polymerization

This paper reports on the synthesis of well-defined polyacrylamide-based nanogels via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization, highlighting a templateless route for the efficient synthesis of nanogels based on water-soluble polymers. RAFT dispersion polymerization of acrylamide in co-nonsolvents of water-tert-butanol mixtures by chain extension from poly(dimethylacrylamide) shows well-controlled polymerization process, uniform nanogel size, and excellent colloidal stability. The versatility of this approach is further demonstrated by introducing a hydrophobic co-monomer (butyl acrylate) without disturbing the dispersion polymerization process.

Controlled release of sunitinib in targeted cancer therapy: smart magnetically responsive hydrogels as restricted access materials

A magnetic hydrogel prepared by precipitation polymerization, with restricted access material (RAM) characteristics through the introduction of glycidyl methacrylate, for sunitinib malate release.

Surfactant-free aqueous preparation from a star polymer of size-controlled nanoparticles with encapsulated functional molecules

A simple preparation method for size-controlled nanoparticles with encapsulated functional molecules in a surfactant-free aqueous condition.

Core cross-linked nanogels based on the self-assembly of double hydrophilic poly(2-oxazoline) block copolymers

The synthesis of poly(2-oxazoline)-based block copolymers consisting of a cationic and a hydrophilic segment is described.

Poly(2-oxazoline)-based nanogels as biocompatible pseudopolypeptide nanoparticles

Hydrophilic nanogels based on partially hydrolyzed poly(2-ethyl-2-oxazoline) were synthesized in dilute aqueous media in the presence of 1,6-hexanediol diglycidyl ether as a cross-linker. Nanogel formation was monitored by DLS and HSQC NMR spectroscopy, and the final nano-objects were characterized by DLS, TEM, AFM, and NanoSight analyses. Nanogels with a hydrodynamic radius of 78 nm exhibiting a slight positive surface charge were obtained. MTS assays (cell metabolic activity test) evidenced that nanogels were nontoxic in the investigated concentration range (i.e., 0.1 to 400 μg/mL) and that no specific interaction with bovine serum albumin was observed.

Real-time UV-visible spectroscopy analysis of purple membrane-polyacrylamide film formation taking into account Fano line shapes and scattering

We theoretically and experimentally analyze the formation of thick Purple Membrane (PM) polyacrylamide (PA) films by means of optical spectroscopy by considering the absorption of bacteriorhodopsin and scattering. We have applied semiclassical quantum mechanical techniques for the calculation of absorption spectra by taking into account the Fano effects on the ground state of bacteriorhodopsin. A model of the formation of PM-polyacrylamide films has been proposed based on the growth of polymeric chains around purple membrane. Experimentally, the temporal evolution of the polymerization process of acrylamide has been studied as function of the pH solution, obtaining a good correspondence to the proposed model. Thus, due to the formation of intermediate bacteriorhodopsin-doped nanogel, by controlling the polymerization process, an alternative methodology for the synthesis of bacteriorhodopsin-doped nanogels can be provided.

Coacervate delivery systems for proteins and small molecule drugs

Coacervates represent an exciting new class of drug delivery vehicles, developed in the past decade as carriers of small molecule drugs and proteins. This review summarizes several well-described coacervate systems, including: i) elastin-like peptides for delivery of anticancer therapeutics; ii) heparin-based coacervates with synthetic polycations for controlled growth factor delivery; iii) carboxymethyl chitosan aggregates for oral drug delivery; iv) Mussel adhesive protein and hyaluronic acid coacervates. Coacervates present advantages in their simple assembly and easy incorporation into tissue engineering scaffolds or as adjuncts to cell therapies. They are also amenable to functionalization such as for targeting or for enhancing the bioactivity of their cargo. These new drug carriers are anticipated to have broad applications and noteworthy impact in the near future.