Fast-Gelling Polyethylene Glycol/Polyethyleneimine Hydrogels Degradable by Visible-Light

The treatment of burn wounds remains a clinical challenge due to the need for repeated dressings changes. Therefore, the development of a dressing system that can be atraumatically removed from the wound bed can be considered a breakthrough and improve treatment times. In this work, the development of an injectable, fast-gelling hydrogel is proposed that can change its mechanical properties when exposed to visible light. The hydrogels are prepared by a "click" amino-yne reaction between poly(ethylene glycol) (PEG) functionalized with propiolic acid and the amino groups of poly(ethyleneimine) (PEI). The hydrogels exhibit a fast gelation time, which can be adjusted by changing the weight percentage and molecular weight of the precursors. They also exhibit good swelling ability and adhesion to living tissues. More importantly, their mechanical properties changed upon irradiation with green light. This loss of properties is achieved by a 1 O2 -mediated mechanism, as confirmed by the degradation of the β-aminoacrylate linker. Moreover, the in vitro cell compatibility results of the hydrogels and their degradation products show good cytocompatibility. Therefore, it is believed that these hydrogels can be considered as materials with great potential for an innovative strategy for the treatment of burn wounds.

Nanotechnology-based techniques for hair follicle regeneration

The hair follicle (HF) is a multicellular complex structure of the skin that contains a reservoir of multipotent stem cells. Traditional hair repair methods such as drug therapies, hair transplantation, and stem cell therapy have limitations. Advances in nanotechnology offer new approaches for HF regeneration, including controlled drug release and HF-specific targeting. Until recently, embryogenesis was thought to be the only mechanism for forming hair follicles. However, in recent years, the phenomenon of wound-induced hair neogenesis (WIHN) or de novo HF regeneration has gained attention as it can occur under certain conditions in wound beds. This review covers HF-specific targeting strategies, with particular emphasis on currently used nanotechnology-based strategies for both hair loss-related diseases and HF regeneration. HF regeneration is discussed in several modalities: modulation of the hair cycle, stimulation of progenitor cells and signaling pathways, tissue engineering, WIHN, and gene therapy. The HF has been identified as an ideal target for nanotechnology-based strategies for hair regeneration. However, some regulatory challenges may delay the development of HF regeneration nanotechnology based-strategies, which will be lastly discussed.

Replacing Harmful Flame Retardants with Biodegradable Starch-Based Materials in Polyethylene Formulations

The addition of toxic flame retardants to commercially available polymers is often required for safety reasons due to the high flammability of these materials. In this work, the preparation and incorporation of efficient biodegradable starch-based flame retardants into a low-density polyethylene (LDPE) matrix was investigated. Thermoplastic starch was first obtained by plasticizing starch with glycerol/water or glycerol/water/choline phytate to obtain TPS-G and TPS-G-CPA, respectively. Various LDPE/TPS blends were prepared by means of melt blending using polyethylene graft maleic anhydride as a compatibilizer and by varying the content of TPS and a halogenated commercial flame retardant. By replacing 38% and 76% of the harmful commercial flame retardant with safe TPS-G-CPA and TPS-G, respectively, blends with promising fire behavior were obtained, while the limiting oxygen index (LOI ≈ 28%) remained the same. The presence of choline phytate improved both the charring ability and fire retardancy of starch and resulted in a 43% reduction in fire growth index compared to the blend with commercial flame retardant only, as confirmed by means of cone calorimetry. Standard UL 94 vertical tests showed that blends containing TPS exhibited dripping behavior (rated V2), while those with commercial flame retardant were rated V0. Overall, this work demonstrates the potential of starch as a natural flame retardant that could reduce the cost and increase the safety of polymer-based materials.

Facile Synthesis of Highly Stretchable, Tough, and Photodegradable Hydrogels

Recently, highly stretchable and tough hydrogels that are photodegradable on-demand have been reported. Unfortunately, the preparation procedure is complex due to the hydrophobic nature of the photocrosslinkers. Herein, a simple method is reported to prepare photodegradable double-network (DN) hydrogels that exhibit high stretchability, toughness, and biocompatibility. Hydrophilic ortho-nitrobenzyl (ONB) crosslinkers incorporating different poly(ethylene glycol) (PEG) backbones (600, 1000, and 2000 g mol-1 ) are synthesized. These photodegradable DN hydrogels are prepared by the irreversible crosslinking of chains by using such ONB crosslinkers, and the reversible ionic crosslinking between sodium alginate and divalent cations (Ca2+ ). Remarkable mechanical properties are obtained by combining ionic and covalent crosslinking and their synergistic effect, and by reducing the length of the PEG backbone. The rapid on-demand degradation of these hydrogels is also demonstrated by using cytocompatible light wavelength (λ = 365 nm) that degrades the photosensitive ONB units. The authors have successfully used these hydrogels as skin-worn sensors for monitoring human respiration and physical activities. A combination of excellent mechanical properties, facile fabrication, and on-demand degradation holds promise for their application as the next generation of substrates or active sensors eco-friendly for bioelectronics, biosensors, wearable computing, and stretchable electronics.

In Vitro Evaluation of Biphasic Calcium Phosphate Scaffolds Derived from Cuttlefish Bone Coated with Poly(ester urea) for Bone Tissue Regeneration

This study investigates the osteogenic differentiation of umbilical-cord-derived human mesenchymal stromal cells (hUC-MSCs) on biphasic calcium phosphate (BCP) scaffolds derived from cuttlefish bone doped with metal ions and coated with polymers. First, the in vitro cytocompatibility of the undoped and ion-doped (Sr²⁺, Mg²⁺ and/or Zn²⁺) BCP scaffolds was evaluated for 72 h using Live/Dead staining and viability assays. From these tests, the most promising composition was found to be the BCP scaffold doped with strontium (Sr²⁺), magnesium (Mg²⁺) and zinc (Zn²⁺) (BCP-6Sr2Mg2Zn). Then, samples from the BCP-6Sr2Mg2Zn were coated with poly(ԑ-caprolactone) (PCL) or poly(ester urea) (PEU). The results showed that hUC-MSCs can differentiate into osteoblasts, and hUC-MSCs seeded on the PEU-coated scaffolds proliferated well, adhered to the scaffold surfaces, and enhanced their differentiation capabilities without negative effects on cell proliferation under in vitro conditions. Overall, these results suggest that PEU-coated scaffolds are an alternative to PCL for use in bone regeneration, providing a suitable environment to maximally induce osteogenesis.

Targeted downregulation of MYC mediated by a highly efficient lactobionic acid-based glycoplex to enhance chemosensitivity in human hepatocellular carcinoma cells

The chemosensitization of tumor cells by gene therapy represents a promising strategy for hepatocellular carcinoma (HCC) treatment. In this regard, HCC-specific and highly efficient gene delivery nanocarriers are urgently needed. For this purpose, novel lactobionic acid-based gene delivery nanosystems were developed to downregulate c-MYC expression and sensitize tumor cells to low concentration of sorafenib (SF). A library of tailor-made cationic glycopolymers, based on poly(2-aminoethyl methacrylate hydrochloride) (PAMA) and poly(2-lactobionamidoethyl methacrylate) (PLAMA) were synthesized by a straightforward activators regenerated by electron transfer atom transfer radical polymerization. The nanocarriers prepared with PAMA₁₁₄-co-PLAMA₂₀ glycopolymer were the most efficient for gene delivery. These glycoplexes specifically bound to the asialoglycoprotein receptor and were internalized through the clathrin-coated pit endocytic pathway. c-MYC expression was significantly downregulated by MYC short-hairpin RNA (MYC shRNA), resulting in efficient inhibition of tumor cells proliferation and a high levels apoptosis in 2D and 3D HCC-tumor models. Moreover, c-MYC silencing increased the sensitivity of HCC cells to SF (IC₅₀ for MYC shRNA+ SF 1.9 μM compared to 6.9 μM for control shRNA + SF). Overall, the data obtained demonstrated the great potential of PAMA₁₁₄-co-PLAMA₂₀/MYC shRNA nanosystems combined with low doses of SF for the treatment of HCC.

Glycopolymers Mediate Suicide Gene Therapy in ASGPR-Expressing Hepatocellular Carcinoma Cells in Tandem with Docetaxel

Cationic glycopolymers stand out as gene delivery nanosystems due to their inherent biocompatibility and high binding affinity to the asialoglycoprotein receptor (ASGPR), a target receptor overexpressed in hepatocellular carcinoma (HCC) cells. However, their synthesis procedure remains laborious and complex, with problems of solubilization and the need for protection/deprotection steps. Here, a mini-library of well-defined poly(2-aminoethyl methacrylate hydrochloride-co-poly(2-lactobionamidoethyl methacrylate) (PAMA-co-PLAMA) glycopolymers was synthesized by activators regenerated by electron transfer (ARGET) ATRP to develop an efficient gene delivery nanosystem. The glycoplexes generated had suitable physicochemical properties and showed high ASGPR specificity and high transfection efficiency. Moreover, the HSV-TK/GCV suicide gene therapy strategy, mediated by PAMA₁₄₄-co-PLAMA₁₉-based nanocarriers, resulted in high antitumor activity in 2D and 3D culture models of HCC, which was significantly enhanced by the combination with small amounts of docetaxel. Overall, our results demonstrated the potential of primary-amine polymethacrylate-containing-glycopolymers as HCC-targeted suicide gene delivery nanosystems and highlight the importance of combined strategies for HCC treatment.

pH-responsive nanoparticles based on POEOMA-b-PDPA block copolymers for RNA encapsulation, protection and cell delivery

The use of gene-based products, such as DNA or RNA, is increasingly being explored for various innovative therapies. However, the success of these strategies is highly dependent on the effective delivery of these biomolecules to target cells. Therefore, the development of pH-responsive nanoparticles comprises the creation of intelligent delivery systems with high therapeutic efficiency. In this work, the pH-responsiveness of the poly(2-(diisopropylamino)ethyl methacrylate)) (PDPA) block was investigated for the encapsulation and delivery of small RNAs (sRNA) to cancer cells. The pH responsiveness was dependent on the protonation profile of the tertiary amines of PDPA, which directly affected the electrostatic interactions established with RNA. Thus, block copolymers based on poly(oligo(ethylene oxide) methyl ether methacrylate) (POEOMA) and PDPA, POEOMA-b-PDPA, were synthesized by supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP). The structure of the block copolymers was characterized by size exclusion chromatography and ¹H NMR spectroscopy. The copolymers allowed effective complexation of model sRNAs and a pre-miRNA with efficiencies of about 89 % and 91 %, respectively. The characterization by dynamic light scattering revealed that these systems had sizes between 76 and 1375 nm. It was also found that the morphology of the polyplexes depended on the pH, since the preparation at a pH lower than the pKa of the copolymers resulted in spherical but polydisperse particles, while higher pH values resulted in nanoparticles with more homogeneous size, but altered morphology. Moreover, due to pH-responsiveness, it was achieved the release of RNA at pH higher than the pKa of the copolymers, while maintaining its integrity. The polyplexes also showed a high potential to protect RNA from RNases. The transfection of a lung cancer model (A549) and fibroblast cell lines showed that these polyplexes did not cause cell toxicity. In addition, the polyplexes enabled the effective transfection of the A549 cell line with pre-miRNA-29b and miRNA-29b, resulting in a decrease of expression levels of the target DNMT3B gene by approximately 51 % and 47 %, respectively. Overall, the POEOMA-b-PDPA copolymers proved to be a promising strategy for developing responsive delivery systems, that can play a critical role in some diseases, such as cancer, where pH varies between the intra and extracellular environments.

Correction: Novel degradable amphiphilic 4-arm star PLA-b-POEOA and PLGA-b-POEOA block copolymers: synthesis, characterization and self-assembly

Correction for ‘Novel degradable amphiphilic 4-arm star PLA-b-POEOA and PLGA-b-POEOA block copolymers: synthesis, characterization and self-assembly’ by Andreia S. R. Oliveira et al., Polym. Chem., 2023, 14, 161–171, https://doi.org/10.1039/D2PY01216B.

Application of vinyl polymer-based materials as nucleic acids carriers in cancer therapy

Nucleic acid-based therapies have changed the paradigm of cancer treatment, where conventional treatment modalities still have several limitations in terms of efficacy and severe side effects. However, these biomolecules have a short half-life in vivo, requiring multiple administrations, resulting in severe suffering, discomfort, and poor patient compliance. In the early days of (nano)biotechnology, these problems caused concern in the medical community, but recently it has been recognized that these challenges can be overcome by developing innovative formulations. This review focuses on the use of vinyl polymer-based materials for the protection and delivery of nucleic acids in cancer. First, an overview of the properties of nucleic acids and their versatility as drugs is provided. Then, key information on the achievements to date, the most effective delivery methods, and the evaluation of functionalization approaches (stimulatory strategies) are critically discussed to highlight the importance of vinyl polymers in the new cancer treatment approaches. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures.

Photo-degradable, tough and highly stretchable hydrogels

We present for the first time highly stretchable and tough hydrogels with controlled light-triggered photodegradation. A double-network of alginate/polyacrylamide (PAAm) is formed by using covalently and ionically crosslinked subnetworks. The ionic Ca²⁺ alginate interpenetrates a PAAm network covalently crosslinked by a bifunctional acrylic crosslinker containing the photodegradable o-nitrobenzyl (ONB) core instead of the commonly used methylene bisacrylamide (MBAA). Remarkably, due to the developed protocol, the change of the crosslinker did not affect the hydrogel's mechanical properties. The incorporation of photosensitive components in hydrogels allows external temporal control of their properties and tuneable degradation. Cell viability and cell proliferation assays revealed that hydrogels and their photodegradation products are not cytotoxic to the NIH3T3 cell line. In one example of application, we used these hydrogels for bio-potential acquisition in wearable electrocardiography. Surprisingly, these hydrogels showed a lower skin-electrode impedance, compared to the common medical grade Ag/AgCl electrodes. This work lays the foundation for the next generation of tough and highly stretchable hydrogels that are environmentally friendly and can find applications in a variety of fields such as health, electronics, and energy, as they combine excellent mechanical properties with controlled degradation.

Dual electrochemical and chemical control in atom transfer radical polymerization with copper electrodes

In Atom Transfer Radical Polymerization (ATRP), Cu⁰ acts as a supplemental activator and reducing agent (SARA ATRP) by activating alkyl halides and (re)generating the Cu^I activator through a comproportionation reaction, respectively. Cu⁰ is also an unexplored, exciting metal that can act as a cathode in electrochemically mediated ATRP (eATRP). Contrary to conventional inert electrodes, a Cu cathode can trigger a dual catalyst regeneration, simultaneously driven by electrochemistry and comproportionation, if a free ligand is present in solution. The dual regeneration explored herein allowed for introducing the concept of pulsed galvanostatic electrolysis (PGE) in eATRP. During a PGE, the process alternates between a period of constant current electrolysis and a period with no applied current in which polymerization continues via SARA ATRP. The introduction of no electrolysis periods without compromising the overall polymerization rate and control is very attractive, if large current densities are needed. Moreover, it permits a drastic charge saving, which is of unique value for a future scale-up, as electrochemistry coupled to SARA ATRP saves energy, and shortens the equipment usage.

The use of a Cu cathode in eATRP allows exploiting the synergistic effect between electrochemical and chemical stimuli to halt or accelerate polymerizations, reduce energy consumption and achieve control in challenging systems.

Tosyl iodide – a new initiator for the photo-controlled iodine transfer polymerization of methacrylates under sunlight irradiation

A very simple photo-controlled iodine transfer polymerization system consisting only of methacrylate monomers, solvent (dimethylacetamide), and initiator (tosyl iodide) under violet and sunlight irradiation is reported.

Development of electrospun mats based on hydrophobic hydroxypropyl cellulose derivatives

In this work, hydroxypropyl cellulose esters (HPCE) with long aliphatic chains were prepared and innovatively used in electrospinning to obtain hydroxypropyl cellulose (HPC)-based mats with enhanced resistance to moist environments. The described approach is very simple and does not require any post-treatment (e.g. cross-linking step) to overcome a major problem concerning the premature loss of properties of cellulose-based materials when in contact with moisture. HPCE-based electrospun mats were characterized in terms of their morphology, swelling ability and in vitro hydrolytic degradation. The mats exhibited a swelling capacity of over 115%, depending on the degree of substitution. The in vitro hydrolytic degradation tests showed the high structural integrity of the mats (< 5% weight loss) over a period of 30 days. The in vitro cytotoxicity tests showed that the mats of HPC esters are cytocompatible and promote the adhesion, proliferation and spreading of NIH3T3 fibroblast cells. These data suggest that the HPCE mats may be interesting materials for wound dressings, as well as for other tissue engineering applications.

Development of light-degradable poly(urethane-urea) hydrogel films

Biocompatible hydrogels are exciting platforms that have stood out in recent years for their outstanding potential for biomedical applications. For these applications, the ability of the material to respond to an external stimulus can be a relevant addition. This responsiveness allows the material to modify its physical properties in such a way that it can deliver molecules that support the healing process or allow easy removal of the films from the tissue. Among the polymers used to produce these systems, polyurethane (PU) and polyurethane-urea (PUU) are some of the most cited examples. In this work, a new hydrogel-sensitive PUU film is proposed. These films are prepared from polyethylene glycol (PEG) and contain a ROS-responsive telechelic β-aminoacrylate bond. The hydrogel films showed interesting mechanical and thermal properties, good water uptake and low cytotoxicity, which makes them suitable for biomedical applications. More importantly, the hydrogel films exhibited a light-degradable profile through an innovative ROS-mediated cleavage process, as indicated by the loss of mechanical properties.

Process Development for Flexible Films of Industrial Cellulose Pulp Using Superbase Ionic Liquids

Due to environmental concerns, more attention has been given to the development of bio-based materials for substitution of fossil-based ones. Moreover, paper use is essential in daily routine and several applications of industrial pulp can be developed. In this study, transparent films were produced by industrial cellulose pulp solubilization in tetramethylguanidine based ionic liquids followed by its regeneration. Films were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), UV/Vis spectroscopy, proton nuclear magnetic resonance (¹H-NMR), dynamic scanning calorimetry (DSC), thermal analysis (TG), and X-ray diffraction (XRD). Mechanical tests showed that films have a good elongation property, up to 50%, depending on ionic liquid incorporation. The influence of the conjugated acid and dissolution temperature on mechanical properties were evaluated. These results revealed the potential of this methodology for the preparation of new biobased films.

Light-Activated Antimicrobial Surfaces Using Industrial Varnish Formulations to Mitigate the Incidence of Nosocomial Infections

Evidence has shown that hospital surfaces are one of the major vehicles of nosocomial infections caused by drug-resistant pathogens. Smart surface coatings presenting multiple antimicrobial activity mechanisms have emerged as an advanced approach to safely prevent this type of infection. In this work, industrial waterborne polyurethane varnish formulations containing for the first time cationic polymeric biocides (SPBs) combined with photosensitizer curcumin were developed to afford contact-active and light-responsive antimicrobial surfaces. SPBs were prepared by atom transfer radical polymerization, which allows control over the polymer features that influence antimicrobial efficiency (e.g., molecular weight), while natural curcumin was employed to impart photodynamic activity to the surface. Antibacterial testing against Gram-negative Escherichia coli revealed that glass surfaces coated with the new formulations displayed photokilling effect under white-light (42 mW/cm²) irradiation within only 15 min of exposure. In addition, it was observed a combined antimicrobial effect between the two biocides (cationic SPB and curcumin), with a higher reduction in the number of viable bacteria observed for the surfaces containing cationic SPB/curcumin mixtures in comparison with the one obtained for surfaces only with polymer or without biocides. The waterborne industrial varnish formulations allowed the formation of homogeneous films without the need for addition of a coalescing agent, which can be potentially applied in diverse surface substrates to reduce bacterial transmission infections in healthcare environments.

Catalytic Halogen Exchange in Supplementary Activator and Reducing Agent Atom Transfer Radical Polymerization for the Synthesis of Block Copolymers

Synthesis of block copolymers (BCPs) by catalytic halogen exchange (cHE) is reported, using supplemental activator and reducing agent Atom Transfer Radical Polymerization (SARA ATRP). The cHE mechanism is based on the use of a small amount of a copper catalyst in the presence of a suitable excess of halide ions, for the synthesis of block copolymers from macroinitiators with monomers of mismatching reactivity. cHE overcomes the problem of inefficient initiation in block copolymerizations in which the second monomer provides dormant species that are more reactive than the initiator. Model macroinitiators with low dispersity are prepared and extended to afford well-defined block copolymers of various compositions. Combined cHE/SARA ATRP is therefore a simple and potent polymerization tool for the copolymerization of a wide range of monomers allowing the production of tailored block copolymers.

Glycopolymer Brushes by Reversible Deactivation Radical Polymerization: Preparation, Applications, and Future Challenges

The cellular surface contains specific proteins, also known as lectins, that are carbohydrates receptors involved in different biological events, such as cell-cell adhesion, cell recognition and cell differentiation. The synthesis of well-defined polymers containing carbohydrate units, known as glycopolymers, by reversible deactivation radical polymerization (RDRP) methods allows the development of tailor-made materials with high affinity for lectins because of their multivalent interaction. These polymers are promising candidates for the biomedical field, namely as novel diagnostic disease markers, biosensors, or carriers for tumor-targeted therapy. Although linear glycopolymers are extensively studied for lectin recognition, branched glycopolymeric structures, such as polymer brushes can establish stronger interactions with lectins. This specific glycopolymer topology can be synthesized in a bottlebrush form or grafted to/from surfaces by using RDRP methods, allowing a precise control over molecular weight, grafting density, and brush thickness. Here, the preparation and application of glycopolymer brushes is critically discussed and future research directions on this topic are suggested.

Untethered Disposable Health Monitoring Electronic Patches with an Integrated Ag2O-Zn Battery, a AgInGa Current Collector, and Hydrogel Electrodes

Stretchable electronics stickers that adhere to the human skin and collect biopotentials are becoming increasingly popular for biomonitoring applications. Such stickers include electrodes, stretchable interconnects, silicon chips for processing and communication, and batteries. Here, we demonstrate a material architecture and fabrication technique for a multilayer, stretchable, low-cost, rapidly deployable, and disposable sticker that integrates skin-interfacing hydrogel electrodes, stretchable interconnects, and a Ag₂O-Zn (silver oxide-zinc) battery. In addition, the application of a printed biphasic current collector (AgInGa) for the Ag₂O-Zn battery is reported for the first time. Surprisingly, and unlike previously reported batteries, the battery capacity increases after being subjected to strain cycles and reaches a record-breaking areal capacity of 6.88 mAh cm^-2 post stretch. As a proof of concept, an application of heart rate monitoring is presented. The disposable patch is interfaced with a miniature battery-free electronics circuit for data acquisition, processing, and wireless transmission. A version of the patch partially covering the patient's chest can supply enough energy for continuous operation for ∼6 days.

Under pressure: electrochemically-mediated atom transfer radical polymerization of vinyl chloride

Electrochemically mediated ATRP (eATRP) of vinyl chloride (VC), a less activated monomer, was successfully achieved. It is the first report on eATRP of a gaseous monomer under pressure.

Use of recycled polypropylene/poly(ethylene terephthalate) blends to manufacture water pipes: An industrial scale study

Poly(ethylene terephthalate) (PET) and polypropylene (PP) are two major polymeric materials that constitute many single-use plastic products. A common strategy to reduce polymeric waste is via mechanical recycling, a low cost and efficient process. However, from an industrial point of view, the reliability of this process is more easily achieved by a downgrade in the final properties of these materials, which limits the usage of recycled-based materials to less demanding applications. Furthermore, due to the intrinsic heterogeneity of the PP or PET waste, the use of these materials in industrial processing, tuned and developed for virgin neat materials, poses serious integrity problems. This aspect is particularly relevant in the case of plastics originating from the food packaging industry. This work explores the possibility of incorporating either PP or PET originated from plastic solid waste (PSW), in pipe manufacturing, with competitive mechanical properties compared to those prepared from virgin materials. To achieve this industrial solution, a process was developed using PP/PET 70/30 wt% formulations and the impact of replacing the virgin material by the different PSW in the microstructure, thermal and mechanical properties of the final material was analyzed. The impact of using a compatibilizer able to counteract the natural immiscibility between the PP and PET domains was also assessed. The developed formulation with recycled PET is a good example of the applicability of work developed at a laboratory scale into industrial-scale production.

Poly(ethylene glycol)- block-poly(2-aminoethyl methacrylate hydrochloride)-Based Polyplexes as Serum-Tolerant Nanosystems for Enhanced Gene Delivery

Incorporation of poly(ethylene glycol) (PEG) into polyplexes has been used as a promising approach to enhance their stability and reduce unwanted interactions with biomolecules. However, this strategy generally has a negative influence on cellular uptake and, consequently, on transfection of target cells. In this work, we explore the effect of PEGylation on biological and physicochemical properties of poly(2-aminoethyl methacrylate) (PAMA)-based polyplexes. For this purpose, different tailor-made PEG- b-PAMA block copolymers, and the respective homopolymers, were synthesized using the controlled/"living" radical polymerization method based on activators regenerated by electron transfer atom transfer radical polymerization. The obtained data show that PEG- b-PAMA-based polyplexes exhibited a much better transfection activity/cytotoxicity relationship than the corresponding non-PEGylated nanocarriers. The best formulation, prepared with the largest block copolymer (PEG₄₅- b-PAMA₁₆₈) at a 25:1 N/P ratio, presented a 350-fold higher transfection activity in the presence of serum than that obtained with polyplexes generated with the gold standard bPEI. This higher transfection activity was associated to an improved capability to overcome the intracellular barriers, namely the release from the endolysosomal pathway and the vector unpacking and consequent DNA release from the nanosystem inside cells. Moreover, these nanocarriers exhibit suitable physicochemical properties for gene delivery, namely reduced sizes, high DNA protection, and colloidal stability. Overall, these findings demonstrate the high potential of the PEG₄₅- b-PAMA₁₆₈ block copolymer as a gene delivery system.

Thiourea Dioxide As a Green and Affordable Reducing Agent for the ARGET ATRP of Acrylates, Methacrylates, Styrene, Acrylonitrile, and Vinyl Chloride

Thiourea dioxide, a green and inexpensive compound used at industrial scale, was employed as reducing agent for the controlled polymerization of a wide range of monomer families, namely, acrylates (methyl acrylate, 2-hydroxyethyl acrylate, butyl acrylate, methacrylates (2-(dimethylamino)ethyl methacrylate, 2-aminoethyl methacrylate hydrochloride, and methyl methacrylate), styrene, acrylonitrile, and vinyl chloride (nonactivated monomer) by ATRP. Mechanistic studies confirmed that the polymerizations are ruled by the activators regenerated by electron transfer (ARGET) mechanism. It is worth noting that vinyl chloride has never been polymerized by ARGET ATRP. The system proved to be very versatile and robust, working in organic solvents, organic/water mixtures, and aqueous medium at near room temperature with low metal catalyst concentration. Chain extension experiments confirmed the high chain-end functionality of the polymers, allowing the preparation of several well-defined block copolymers.

Increasing the Antimicrobial Activity of Amphiphilic Cationic Copolymers by the Facile Synthesis of High Molecular Weight Stars by Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization

Infections caused by bacteria represent a great motif of concern in the health area. Therefore, there is a huge demand for more efficient antimicrobial agents. Antimicrobial polymers have attracted special attention as promising materials to prevent infectious diseases. In this study, a new polymeric system exhibiting antimicrobial activity against a range of Gram-positive and Gram-negative bacterial strains at micromolar concentrations (e.g., 0.8 μM) was developed. Controlled linear and star-shaped copolymers, comprising hydrophobic poly(butyl acrylate) (PBA) and cationic poly(3-acrylamidopropyl)trimethylammonium chloride) (PAMPTMA) segments, were obtained by supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) at 30 °C. The antibacterial activity of the polymers was studied by varying systematically the molecular weight (MW), hydrophilic/hydrophobic balance, and architecture. The MW was found to exert the greatest influence on the antimicrobial activity of the polymers, with minimum inhibitory concentration values decreasing with increasing MW. Live/dead membrane integrity assays and scanning electron microscopy analysis confirmed the bactericidal character of the synthesized PAMPTMA- (b)co-PBA polymers.

Cinnamic acid derivatives as promising building blocks for advanced polymers: synthesis, properties and applications

A global overview of the use of cinnamic acid derivatives in polymer science is given in this review paper.

Pushing the limits of robust and eco-friendly ATRP processes: untreated water as the solvent

ATRP can be performed in untreated water without addition of halide salts, with no deleterious effect on the polymerization control.

Liquid salts as eco-friendly solvents for atom transfer radical polymerization: a review

Liquid salts, comprising ionic liquids and eutectic mixtures, are organic compounds/mixtures characterized by a low melting point that have been emerging as a very promising eco-friendly solvent for atom transfer radical polymerization.

Guanidine as inexpensive dual function ligand and reducing agent for ATRP of methacrylates

N,N,N′,N′-Tetramethyl guanidine, an inexpensive and commercially available organic base, is used for the first time as ligand without any chemical modification for the supplemental activator and reducing agent atom transfer radical polymerization.

Preparation of well-defined brush-like block copolymers for gene delivery applications under biorelevant reaction conditions

Well-defined oligo(ethylene glycol) methyl ether methacrylate (OEOMA) based block copolymers with cationic segments composed by N,N-(dimethylamino) ethyl methacrylate (DMAEMA) and/or 2-(diisopropylamino) ethyl methacrylate (DPA) were developed under biorelevant reaction conditions. These brush-type copolymers were synthesized through supplemental activator and reducing agent (SARA) atom transfer radical polymerization (ATRP) using sodium dithionite as SARA agent. The synthesis was carried out using an eco-friendly solvent mixture, very low copper catalyst concentration, and mild reaction conditions. The structure of the block copolymers was characterized by size exclusion chromatography (SEC) analysis and ¹H nuclear magnetic resonance (NMR) spectroscopy. The pH-dependent protonation of these copolymers enables the efficient complexation with plasmid DNA (pDNA), yielding polyplexes with sizes ranging from 200 up to 700 nm, depending on the molecular weight of the copolymers, composition and concentration used. Agarose gel electrophoresis confirmed the successful pDNA encapsulation. No cytotoxicity effect was observed, even for N/P ratios higher than 50, for human fibroblasts and cervical cancer cell lines cells. The in vitro cellular uptake experiments demonstrated that the pDNA-loaded block copolymers were efficiently delivered into nucleus of cervical cancer cells. The polymerization approach, the unique structure of the block copolymers and the efficient DNA encapsulation presented can open new avenues for development of efficient tailor made gene delivery systems under biorelevant conditions.

Deep Eutectic Solvent Aqueous Solutions as Efficient Media for the Solubilization of Hardwood Xylans

This work contributes to the development of integrated lignocellulosic-based biorefineries by the pioneering exploitation of hardwood xylans by solubilization and extraction in deep eutectic solvents (DES). DES formed by choline chloride and urea or acetic acid were initially evaluated as solvents for commercial xylan as a model compound. The effects of temperature, molar ratio, and concentration of the DES aqueous solutions were evaluated and optimized by using a response surface methodology. The results obtained demonstrated the potential of these solvents, with 328.23 g L^-1 of xylan solubilization using 66.7 wt % DES in water at 80 °C. Furthermore, xylans could be recovered by precipitation from the DES aqueous media in yields above 90 %. The detailed characterization of the xylans recovered after solubilization in aqueous DES demonstrated that 4-O-methyl groups were eliminated from the 4-O-methylglucuronic acids moieties and uronic acids (15 %) were cleaved from the xylan backbone during this process. The similar M_w values of both pristine and recovered xylans confirmed the success of the reported procedure. DES recovery in four additional extraction cycles was also demonstrated. Finally, the successful extraction of xylans from Eucalyptus globulus wood by using aqueous solutions of DES was demonstrated.

Addressing the role of triphenylphosphine in copper catalyzed ATRP

A new Atom Transfer Radical Polymerization (ATRP) process with triphenylphosphine (PPh₃) and [Cu^IIMe₆TREN]²⁺ as the catalyst system is reported.

Mechanism of Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization Mediated by Inorganic Sulfites: Experimental Measurements and Kinetic Simulations

The mechanism of atom transfer radical polymerization (ATRP) mediated by sodium dithionite (Na2S2O4), with CuIIBr2/Me6TREN as catalyst (Me6TREN: tris[2-(dimethylamino)ethyl]amine)) in ethanol/water mixtures, was investigated experimentally and by kinetic simulations. A kinetic model was proposed and the rate coefficients of the relevant reactions were measured. The kinetic model was validated by the agreement between experimental and simulated results. The results indicated that the polymerization followed the SARA ATRP mechanism, with a SO2•- radical anion derived from Na2S2O4, acting as both supplemental activator (SA) of alkyl halides and reducing agent (RA) for CuII/L to regenerate the main activator CuI/L. This is similar to the reversible-deactivation radical polymerization (RDRP) procedure conducted in the presence of Cu0. The electron transfer from SO2•-, to either CuIIBr2/Me6TREN or R-Br initiator, appears to follow an outer sphere electron transfer (OSET) process. The developed kinetic model was used to study the influence of targeted degree of polymerization, concentration of CuIIBr2/Me6TREN and solubility of Na2S2O4 on the level of polymerization control. The presence of small amounts of water in the polymerization mixtures slightly increased the reactivity of the CuI/L complex, but markedly increased the reactivity of sulfites.

Retrospective Quality by Design (rQbD) applied to the optimization of orodispersible films

The study demonstrates the application of QbD based on historical data for a product at a later development stage - retrospective QbD (rQbD). More specifically, it is investigated the root-cause for the observed slower drug release in Orodispersible Films (ODFs) during storage. Risk assessment tools were used to identify parameters affecting ODFs critical quality attributes, namely percent drug release and residual water content. The parameters room temperature, room relative humidity, drying temperature and mixing equipment were used in the statistical modeling of the available data. The estimated models were then used to define the feasible working region. Statistical modeling indicates that initial residual water content of the ODFs is mainly affected by 2nd order interactions of room temperature, room relative humidity and drying temperature, while the stability of drug release profile is mostly influenced by room temperature and an interaction between room relative humidity and drying temperature. Depending on the drying temperature employed the effect of room temperature and room relative humidity change significantly. This work shows that it is possible to apply rQbD to achieve a greater understanding of the manufacturing process of ODFs and to define a proper design space.

Increasing the Bile Acid Sequestration Performance of Cationic Hydrogels by Using an Advanced/Controlled Polymerization Technique

PURPOSE

To investigate the influence of the polymerization technique and the content of hydroxyl groups on the performance of new bile acid sequestrants based on PAMPMTA-co-PHEA (PAMPTMA: poly((3-acrylamidopropyl)trimethylammonium chloride); PHEA: poly(2-hydroxyethyl acrylate)) hydrogels.

METHODS

PAMPMTA-co-PHEA hydrogels were prepared using either free radical polymerization or supplemental activator and reducing agent atom transfer radical polymerization. The chemical structure and composition of the hydrogels was confirmed by both FTIR and ssNMR. The binding of sodium cholate as the model bile salt was evaluated in simulated intestinal fluid using HPLC. The degradation of the polymers was evaluated in vitro in solutions mimicking the gastrointestinal tract environment.

RESULTS

The binding showed that an increase of the amount of HEA in the hydrogel lead to a decrease of the binding capacity. In addition, it was demonstrated for the first time that the hydrogels produced by SARA ATRP presented a higher binding capacity than similar ones produced by FRP. Finally, it was observed that copolymers of PAMPTMA-co-PHEA showed no sign of degradation in solutions mimicking both the stomach and the intestine environment.

CONCLUSIONS

The use of an advanced polymerization technique, such as the SARA ATRP, could be beneficial for the preparation of BAS with enhanced performance.

Aqueous SARA ATRP using Inorganic Sulfites

Aqueous supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) using inorganic sulfites was successfully carried out for the first time. Under optimized conditions, a well-controlled poly[oligo(ethylene oxide) methyl ether acrylate] (POEOA) was obtained with <30 ppm of soluble copper catalyst using tris(2-pyridylmethyl)amine (TPMA) ligand in the presence of an excess of halide salts (e.g. NaCl). Inorganic sulfites (e.g. Na2S2O4) were continuously fed into the reaction mixture. The mechanistic studies proved that these salts can activate alkyl halides directly and regenerate the activator complex. The effects of the feeding rate of the SARA agent (inorganic sulfites), ligand and its concentration, halide salt and its concentration, sulfite used, and copper concentration, were systematically studied to afford fast polymerizations rates while maintaining the control over polymerization. The kinetic data showed linear first-order kinetics, linear evolution of molecular weights with conversion, and polymers with narrow molecular weight distributions (Đ ~1.2) during polymerization even at relatively high monomer conversions (~80%). "One-pot" chain extension and "one-pot" block copolymerization experiments proved the high chain-end functionality. The polymerization could be directly regulated by starting or stopping the continuous feeding of the SARA agent. Under biologically relevant conditions, the aqueous SARA ATRP using inorganic sulfites was used to synthesize a well-defined protein-polymer hybrid by grafting of P(OEOA480) from BSA-O-[iBBr]30.

High transfection efficiency promoted by tailor-made cationic tri-block copolymer-based nanoparticles

Cationic polymer-based vectors have been considered a promising strategy in gene therapy area due to their inherent ability to condense genetic material and successfully transfect cells. However, they usually exhibit high cytotoxicity. In this work, it is proposed the use of a tailor-made gene carrier based on a tri-block copolymer of poly[2-(dimethylamino)ethyl methacrylate] and poly(β-amino ester) (PDMAEMA-b-PβAE-b-PDMAEMA), the influence of the PβAE length being assessed. For this purpose, three different block copolymers were prepared varying the molecular weight of this segment. The obtained materials were characterized by NMR and SEC analyzes. Different polyplexes formulations were prepared and evaluated in terms of physicochemical characterization (ethidium bromide intercalation assay, agarose gel electrophoresis assay, dynamic light scattering, zeta potential analyzes and atomic force microscopy) and biological activity (cytotoxicity, and luciferase and green fluorescent protein expression in Hela and COS-7 cell lines). Among the developed nanosystems, the best polyplex formulation revealed between 40- and 60-fold higher transgene expression, in HeLa and COS-7 cell lines, and much lower cytotoxicity than that observed with branched PEI and TurboFect™. Moreover, these nanosystems present suitable physicochemical properties for gene delivery namely reduced mean diameter and high DNA protection. The results reported here show the enormous potential of this block copolymer as gene carrier.

STATEMENT OF SIGNIFICANCE

Syntheses of PDMAEMA-b-PβAE-b-PDMAEMA block copolymers for an extremely effective non-viral vector. The block copolymer PDMAEMA₃₀₀₀-b-PβAE₁₂₀₀₀-b-PDMAEMA₃₀₀₀-based polyplexes at 100/1N/P ratio exhibits between 40- and 60-fold higher transgene expression in HeLa and COS-7 cell lines than commonly used polymeric non-viral vectors, namely branched PEI (known as the gold standard) and TurboFect™ (commercial available).

Peripheral Nerve Regeneration: Current Status and New Strategies Using Polymeric Materials

Experiments concerning peripheral nerve regeneration have been reported since the end of the 19^th century. The need to implement an effective surgical procedure in terms of functional recovery has resulted in the appearance of several approaches to solve this problem. Nerve autograft was the first approach studied and is still considered the gold standard. Since autografts require donor harvesting, other strategies involving the use of natural materials have also been studied. Nevertheless, the results were not very encouraging and attention has moved towards the use of nerve conduits made from polymers, whose properties can be easily tailored and which allow the nerve conduit to be easily processed into a variety of shapes and forms. Some of these materials are already approved by the US Food and Drug Administration (FDA), as is presented here. Furthermore, polymers with conductive properties have very recently been subject to intensive study in this field, since it is believed that such properties have a positive influence in the regeneration of the new axons. This manuscript intends to give a global view of the mechanisms involved in peripheral nerve regeneration and the main strategies used to recover motor and sensorial function of injured nerves.

Recent Developments in Antimicrobial Polymers: A Review

Antimicrobial polymers represent a very promising class of therapeutics with unique characteristics for fighting microbial infections. As the classic antibiotics exhibit an increasingly low capacity to effectively act on microorganisms, new solutions must be developed. The importance of this class of materials emerged from the uncontrolled use of antibiotics, which led to the advent of multidrug-resistant microbes, being nowadays one of the most serious public health problems. This review presents a critical discussion of the latest developments involving the use of different classes of antimicrobial polymers. The synthesis pathways used to afford macromolecules with antimicrobial properties, as well as the relationship between the structure and performance of these materials are discussed.