Biomimetic stimulus-responsive star diblock gelators

Messenger RNA Delivery for Tissue Engineering and Regenerative Medicine Applications

The ability to control cellular processes and precisely direct cellular reprogramming has revolutionized regenerative medicine. Recent advances in in vitro transcribed (IVT) mRNA technology with chemical modifications have led to development of methods that control spatiotemporal gene expression. Additionally, there is a current thrust toward the development of safe, integration-free approaches to gene therapy for translational purposes. In this review, we describe strategies of synthetic IVT mRNA modifications and nonviral technologies for intracellular delivery. We provide insights into the current tissue engineering approaches that use a hydrogel scaffold with genetic material. Furthermore, we discuss the transformative potential of novel mRNA formulations that when embedded in hydrogels can trigger controlled genetic manipulation to regenerate tissues and organs in vitro and in vivo. The role of mRNA delivery in vascularization, cytoprotection, and Cas9-mediated xenotransplantation is additionally highlighted. Harmonizing mRNA delivery vehicle interactions with polymeric scaffolds can be used to present genetic cues that lead to precise command over cellular reprogramming, differentiation, and secretome activity of stem cells-an ultimate goal for tissue engineering.

Engineered Hydrogels for Local and Sustained Delivery of RNA-Interference Therapies

It has been nearly two decades since RNA-interference (RNAi) was first reported. While there are no approved clinical uses, several phase II and III clinical trials suggest the great promise of RNAi therapeutics. One challenge for RNAi therapies is the controlled localization and sustained presentation to target tissues, to both overcome systemic toxicity concerns and to enhance in vivo efficacy. One approach that is emerging to address these limitations is the entrapment of RNAi molecules within hydrogels for local and sustained release. In these systems, nucleic acids are either delivered as siRNA conjugates or within nanoparticles. A plethora of hydrogels has been implemented using these approaches, including both traditional hydrogels that have already been developed for other applications and new hydrogels developed specifically for RNAi delivery. These hydrogels have been applied to various applications in vivo, including cancer, bone regeneration, inflammation and cardiac repair. This review will examine the design and implementation of such hydrogel RNAi systems and will cover the most recent applications of these systems.

pH-Responsive polymers

This review summarizes pH-responsive monomers, polymers and their derivative nano- and micro-structures including micelles, cross-linked micelles, microgels and hydrogels.

Semibranched polyglycidols as “fillers” in polycarbonate hydrogels to tune hydrophobic drug release

We report on the synthesis of polycarbonate based hydrogels that contain semibranched polyglycidols entrapped into the polycarbonate-diethylene oxide matrix.

Amphiphilic star copolymer-based bimodal fluorogenic/magnetic resonance probes for concomitant bacteria detection and inhibition

Four-arm star-shaped copolymers, TPE-star-P(DMA-co-BMA-co-Gd), containing TPE cores with an aggregation-induced emission (AIE) feature, a T 1 -type magnetic resonance (MR) contrast agent, and amphiphilic cationic arms, are synthesized. By taking advantage of non-covalent interactions between star copolymers and bacteria surfaces, bimodal fluorometric/MR detection and concomitant inhibition of both Gram-positive and Gram-negative bacteria strains in aqueous media are explored.

Insight in the phase separation peculiarities of poly(dialkylaminoethyl methacrylate)s

The thermoresponsive and pH-sensitive behavior of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), poly(N,N-diethylaminoethyl methacrylate) (PDEAEMA), and poly(N,N-diisopropylaminoethyl methacrylate) (PDiPAEMA) is compared by use of different techniques. We employed temperature- and pH-dependent turbidimetry, fluorescence spectroscopy (of the polarity indicator 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran, 4HP, which is sometimes also abbreviated as DCM), and IR spectroscopy (of the carbonyl band). Within specific pH windows, all polymers showed phase separation at elevated temperatures (showing a lower critical solution temperature behavior, an LCST behavior). By increasing the hydrophobicity of the dialkylaminoethyl substituent, the phase separation is shifted to lower pH (at constant temperatures; pH(PDMAEMA) > pH(PDEAEMA) > pH(PDiPAEMA)) or to lower temperatures (at constant pH; T(PDMAEMA) > T(PDEAEMA) > T(PDiPAEMA)). While PDMAEMA does not exhibit pronounced changes in polarity upon phase separation (as seen by fluorescence spectroscopy), PDEAEMA and PDiPAEMA provide a nonpolar surrounding for the 4HP uptake above their collapse. In addition, PDiPAEMA causes the sharpest transition (as seen by the 4HP probe), although the carbonyl hydration experiences a more gradual (sigmoidal) transition for all polymers (as seen by IR). These observations allow a distinction of the phase separation mechanisms. While the LCST properties of PDMAEMA are mainly caused by backbone/carbonyl interactions, its rather polar dimethylaminoethyl group does not inflict pronounced hydrophobicity, but promotes a higher water content within the phase-separated polymer. In contrast, the phase separation of PDEAEMA and PDiPAEMA is mainly influenced by the less polar dialkylaminoethyl groups, leading to drastic changes in the hydrophobicity around the cloud points. Further, the IR data suggest that the diisopropylaminoethyl groups of PDiPAEMA tend to backfold to the carbonyl groups/backbone to minimize water-polymer contact already in its soluble state. Finally, this study might lead to advanced lasing applications of the laser dye 4HP.

Cell membrane-inspired phospholipid polymers for developing medical devices with excellent biointerfaces

This review article describes fundamental aspects of cell membrane-inspired phospholipid polymers and their usefulness in the development of medical devices. Since the early 1990s, polymers composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) units have been considered in the preparation of biomaterials. MPC polymers can provide an artificial cell membrane structure at the surface and serve as excellent biointerfaces between artificial and biological systems. They have also been applied in the surface modification of some medical devices including long-term implantable artificial organs. An MPC polymer biointerface can suppress unfavorable biological reactions such as protein adsorption and cell adhesion - in other words, specific biomolecules immobilized on an MPC polymer surface retain their original functions. MPC polymers are also being increasingly used for creating biointerfaces with artificial cell membrane structures.

Protein immobilization onto poly(acrylic acid) functional macroporous polyHIPE obtained by surface-initiated ARGET ATRP

Amino-functional macroporous monoliths from polymerized high internal phase emulsion (polyHIPE) were surface modified with initiators for atom transfer radical polymerization (ATRP). The ATRP initiator groups on the polyHIPE surface were successfully used to initiate activator regeneration by electron transfer (ARGET) ATRP of (meth)acrylic monomers, such as methyl methacrylate (MMA) or tert-butyl acrylate (tBA) resulting in a dense coating of polymers on the polyHIPE surface. Addition of sacrificial initiator permitted control of the amount of polymer grafted onto the monolith surface. Subsequent removal of the tert-butyl protecting groups yielded highly functional polyHIPE-g-poly(acrylic acid). The versatility to use the high density of carboxylic acid groups for secondary reactions was demonstrated by the successful conjugation of enhanced green fluorescent protein (eGFP) and coral derived red fluorescent protein (DsRed) using EDC/sulfo-NHS chemistry, on the polymer 3D-scaffold surface. The materials and methodologies presented here are simple and robust, thus, opening new possibilities for the bioconjugation of highly porous polyHIPE for bioseparation applications.

Double Responsive Hydrogels based on Tertiary Amine Methacrylate Star Block Copolymers

Double hydrophilic stimuli-responsive star block copolymers with poly(2-(dimethylamino)ethyl methacrylate) (PDMA) inner blocks and poly(2-(diethylamino)ethyl methacrylate) (PDEA) outer blocks were synthesized using ATRP. Different multifunctional initiators based on sugar scaffolds were employed in a core-first approach with sequential polymerization of both blocks yielding stars with 4 and 6 arms, respectively, and varying length of the PDEA outer block. The star block copolymers show pH- and temperature-responsive aggregation as revealed by dynamic light scattering and turbidimetry. The impact of pH, PDEA block length and arm number on the gelation behavior was investigated by tube inversion and rheology.

Physical hydrogels with self-assembled nanostructures as drug delivery systems

INTRODUCTION

As an essential complement to chemically crosslinked hydrogels, drug delivery systems based on physical hydrogels with self-assembled nanostructures are gaining increasing attention, owing to potential advantages of reduced toxicity, convenience of in situ gel formation, stimuli-responsiveness, reversible sol-gel transition, and improved drug loading and delivery profiles.

AREAS COVERED

In this review, drug delivery systems based on physical hydrogels are discussed according to their self-assembled nanostructures, such as micelles, layer-by-layer constructs, supramolecular inclusion complexes, polyelectrolyte complexes and crystalline structures. The driving forces of the self-assembly include hydrophobic interaction, hydrogen bonding, electrostatic interaction, π-π stacking and weak van der Waals forces. Stimuli-responsive properties of physical hydrogels, including thermo- and pH-sensitivity, are considered with particular focus on self-assembled nanostructures.

EXPERT OPINION

Fabricating self-assembled nanostructures in drug delivery hydrogels, via physical interactions between polymer-polymer and polymer-drug, requires accurately controlled macro- or small molecular architecture and a comprehensive knowledge of the physicochemical properties of the therapeutics. A variety of nanostructures within hydrogels, with which payloads may interact, provide useful means to stabilize the drug form and control its release kinetics.

A smart supramolecular hydrogel of N(alpha)-(4-n-alkyloxybenzoyl)-L-histidine exhibiting pH-modulated properties

Six L-histidine-based amphiphiles, N(alpha)-(4-n-alkyloxybenzoyl)-L-histidine of different hydrocarbon chain lengths, were designed, synthesized, and examined for their ability to gelate water. Four of members of this family of amphiphiles were observed to form thermoreversible hydrogels in a wide range of pH at room temperature. The structural variations were characterized by critical gelation concentration, gelation time, gel melting temperature (T(gs)), rheology, and electron microscopy. Among the amphiphiles, the n-octyl derivative showed better gelation ability in the studied pH range. The amphiphiles were found to have T(gs) higher than body temperature (37 degrees C) showing their stability. Also, relatively higher yield stress (>1000 Pa) values of the hydrogels show their higher strength. The effective gelator molecules self-assemble into fibrous structures. Scanning electron microscopic picture of the hydrogels revealed large ribbons with right-handed twist. Small-angle XRD and circular dichroism spectroscopy were also employed to characterize the hydrogels. It was observed that pi-pi stacking, hydrophobic interaction, amide hydrogen bonding, and solubility factor contribute to the stability and strength of the hydrogels.

Molecular recognition at the exterior surface of a zwitterionic telomer brush

3-Sulfo-N,N-dimethyl-N-(2'-methacryloyloxyethyl)propanaminium inner salt (SPB) was polymerized on a glass plate with a surface-confined initiator of atom transfer radical polymerization (ATRP) having a 2-bromoisobutyryl group. The glass plate modified with a brush of sulfobetaine telomer (PSPB) was highly hydrophilic and showed a strong resistance against nonspecific adsorption of proteins such as lysozyme and albumin. Through the polymerization from the free surface of PSPB chain by ATRP, furthermore, N-methacryloyloxysuccinimide (MAOSu) residues were introduced, and the incubation of the telomer (PSPB-b-PMAOSu)-modified glass chip with a lectin (concanavalin A, Con A) gave a glass chip covered with the Con-A-modified PSPB brush. The Con A fixed to the zwitterionic telomer brush pursued specific binding of mannose residues accumulated on the surface of Au colloidal particles, resulting in the increase in absorbance at 550 nm ascribable to localized surface plasmon resonance, while the nonspecific adsorption of proteins to the surface of the glass chip was still largely suppressed. The present results indicate usefulness of the zwitterionic telomer surface with antibiofouling properties as a scaffold for specific sensing devices.

Polymeric phosphorylcholine-camptothecin conjugates prepared by controlled free radical polymerization and click chemistry

Novel polymer-drug conjugates, consisting of zwitterionic poly(methacryloyloxyethyl phosphorylcholine) (polyMPC) as the polymer component, and camptothecin (CPT) as the drug, were prepared by two methods. In one case, CPT was transformed by acylation into a functional initiator for copper catalyzed atom transfer radical polymerization (ATRP), and polyMPC was grown from this therapeutic initiator. In the other case, a one-pot ATRP-"click" conjugation strategy was employed to synthesize novel polyMPC structures containing multiple copies of the drug pendant to the zwitterionic polymer chain. The latter method allows polyMPC-graft-CPT conjugates to be prepared with a high weight percent drug loading (up to 14% CPT) with excellent solubility in pure water (>250 mg/mL). The linkage chemistry chosen between the polyMPC backbone and the pendant drugs proved critically important for assuring drug release within a time frame reasonable to consider these structures as a platform for injectable cancer therapeutics. Liberation of the drug from the polymer backbone was monitored by high-performance liquid chromatography, using size-exclusion and reverse-phase columns, and the toxicity of the polymer-drug conjugates was examined in cell culture against breast (MCF7), ovarian (OVCAR-3), and colorectal (COLO 205) cancer cell lines.

Photo-cross-linked hydrogels from thermoresponsive PEGMEMA-PPGMA-EGDMA copolymers containing multiple methacrylate groups: mechanical property, swelling, protein release, and cytotoxicity

Photo-cross-linked hydrogels from thermoresponsive polymers can be used as advanced injectable biomaterials via a combination of physical interaction (in situ thermal gelation) and covalent cross-links (in situ photopolymerization). This can lead to gels with significantly enhanced mechanical properties compared to non-photo-cross-linked thermoresponsive hydrogels. Moreover, the thermally phase-separated gels have attractive advantages over non-thermoresponsive gels because thermal gelation upon injection allows easy handling and holds the shape of the gels prior to photopolymerization. In this study, water-soluble thermoresponsive copolymers containing multiple methacrylate groups were synthesized via one-step deactivation enhanced atom transfer radical polymerization (ATRP) of poly(ethylene glycol) methyl ether methacrylate (PEGMEMA, M(n) = 475), poly(propylene glycol) methacrylate (PPGMA, M(n) = 375), and ethylene glycol dimethacrylate (EGDMA) and were used to form covalent cross-linked hydrogels by photopolymerization. The cross-linking density was found to have a significant influence on the mechanical and swelling properties of the photo-cross-linked gels. Release studies using lysozyme as a model protein demonstrated a sustained release profile that varied dependent on the copolymer composition, cross-linking density, and the temperature. Mouse C2C12 myoblast cells were cultured in the presence of the copolymers at concentrations up to 1 mg/mL. It was found that the majority of the cells remained viable, as assessed by Alamar Blue, lactate dehydrogenase (LDH), and Live/Dead cell viability/cytotoxicity assays. These studies demonstrate that thermoresponsive PEGMEMA-PPGMA-EGDMA copolymers offer potential as in situ photopolymerizable materials for tissue engineering and drug delivery applications through a combination of facile synthesis, enhanced mechanical properties, tunable cross-linking density, low cytotoxicity, and accessible functionality for further structure modifications.

Thermoresponsive and photocrosslinkable PEGMEMA-PPGMA-EGDMA copolymers from a one-step ATRP synthesis

Thermoresponsive and photocrosslinkable polymers can be used as injectable scaffolds in tissue engineering to yield gels in situ with enhanced mechanical properties and stability. They allow easy handling and hold their shapes prior to photopolymerization for clinical practice. Here we report a novel copolymer with both thermoresponsive and photocrosslinkable properties via a facile one-step deactivation enhanced atom transfer radical polymerization (ATRP) using poly(ethylene glycol) methyl ether methylacrylate (PEGMEMA, M(n) = 475) and poly(propylene glycol) methacrylate (PPGMA, M(n) = 375) as monofunctional vinyl monomers and up to 30% of ethylene glycol dimethacrylate (EGDMA) as multifunctional vinyl monomer. The resultant PEGMEMA-PPGMA-EGDMA copolymers have been characterized by gel permeation chromatography (GPC) and 1H NMR analysis, which demonstrate their multivinyl functionality and hyperbranched structures. These water-soluble copolymers show lower critical solution temperature (LCST) behavior at 32 degrees C, which is comparable to poly(N-isopropylacrylamide) (PNIPAM). The copolymers can also be cross-linked by photopolymerization through their multivinyl functional groups. Rheological studies clearly demonstrate that the photocrosslinked gels formed at a temperature above the LCST have higher storage moduli than those prepared at a temperature below the LCST. Moreover, the cross-linking density of the gels can be tuned to tailor their porous structures and mechanical properties by adjusting the composition and concentration of the copolymers. Hydrogels with a broad range of storage moduli from 10 to 400 kPa have been produced.

Perspectivas atuais para a obtenção controlada de polímeros e sua caracterização

O advento de técnicas de Polimerização Radicalar Controlada (CRP) permitiu a produção de (co)polímeros com baixo índice de polidispersidade assim como (co)polímeros com as mais diversas morfologias, usando-se para isso monômeros comuns para polimerização radicalar. Três tipos de CRP estão sendo extensamente aplicados para obtenção de polímeros sob medida: a Polimerização Radicalar por Transferência Atômica (ATRP), a Polimerização Mediada por Nitróxido (NMP) e a Transferência Reversível de Cadeia por Adição-Fragmentação (RAFT). Todas essas variantes são baseadas na diminuição das taxas de terminação da polimerização. A caracterização dos polímeros formados também é essencial para assegurar que se tenha realmente obtido os copolímeros que foi planejado. Uma visão geral atualizada de CRP e da caracterização de polímeros, e sua importância para a obtenção de (co)polímeros sob medida, é apresentada neste trabalho.

pH-Responsive polymers: synthesis, properties and applications

pH-Responsive polymers are systems whose solubility, volume, and chain conformation can be manipulated by changes in pH, co-solvent, and electrolytes. This review summarizes recent developments covering synthesis, physicochemical properties, and applications in various disciplines. A variety of synthetic methodologies comprising of emulsion polymerization and living radical polymerization techniques are described, and some of their salient features are highlighted. Several polymeric systems, such as homopolymers, block copolymers, microgels, hydrogels and polymer brushes at interfaces are reviewed, where important characteristics that govern their behavior in solutions are described. Potential applications of these systems in controlled drug delivery, personal and home care, industrial coatings, biological and membrane science, viscosity modifiers, colloid stabilization, and water remediation, are discussed.

In situ gelling stimuli-sensitive block copolymer hydrogels for drug delivery

Stimuli-sensitive block copolymer hydrogels, which are reversible polymer networks formed by physical interactions and exhibit a sol-gel phase-transition in response to external stimuli, have great potential in biomedical and pharmaceutical applications, especially in site-specific controlled drug-delivery systems. The drug may be mixed with a polymer solution in vitro and the drug-loaded hydrogel can form in situ after the in vivo administration, such as injection; therefore, stimuli-sensitive block copolymer hydrogels have many advantages, such as simple drug formulation and administration procedures, no organic solvent, site-specificity, a sustained drug release behavior, less systemic toxicity and ability to deliver both hydrophilic and hydrophobic drugs. Among the stimuli in the biomedical applications, temperature and pH are the most popular physical and chemical stimuli, respectively. The temperature- and/or pH-sensitive block copolymer hydrogels for biomedical applications have been extensively developed in the past decade. This review focuses on recent development of the preparation and application for drug delivery of the block copolymer hydrogels that respond to temperature, pH or both stimuli, including poly(N-substituted acrylamide)-based block copolymers, poloxamers and their derivatives, poly(ethylene glycol)-polyester block copolymers, polyelectrolyte-based block copolymers and the polyelectrolyte-modified thermo-sensitive block copolymers. In addition, the hydrogels based on other stimuli-sensitive block copolymers are discussed.