Self-assembled thermo- and pH responsive micelles of poly(10-undecenoic acid-b-N-isopropylacrylamide) for drug delivery

Poly(N-allyl acrylamide) as a Reactive Platform toward Functional Hydrogels

The synthesis of poly(N-allyl acrylamide) (PNAllAm) as a platform for the preparation of functional hydrogels is described. The PNAllAm was synthesized via organocatalyzed amidation of poly(methyl acrylate) (PMA) with allylamine and characterized by ¹H NMR spectroscopy, size exclusion chromatography (SEC), and turbidimetry, which allowed an estimation of the lower critical solution temperature of ∼26 °C in water. The PNAllAm was then used to make functional hydrogels via photoinitiated thiol-ene chemistry, where dithiothreitol (DTT) was used to cross-link the polymer chains. In addition, mercaptoethanol (ME) was added as a functional thiol to modulate the hydrogel properties. A decrease of the volume-phase transition temperature of the resulting hydrogels was observed with increasing ME content. Altogether this work introduces a straightforward way for the preparation of PNAllAm from PMA and demonstrates its value as a reactive polymer platform for the generation of functional hydrogels.

Thermo- and pH-sensitive nanoparticles of poly (N-isopropylacrylamide-decenoic acid-1-vinylimidazole) for ultrasound switchable fluorescence imaging

We herein report the synthesis of poly (9-decenoic acid-1-vinylimidazole-N-isopropylacrylamide) nanoparticles containing indocyanine green (ICG) in one pot and in water phase throughout the reaction. We have shown that copolymers of 9-decenoic acid and 1-vinylimidazole, or 9-decenoic acid alone, have an enhanced sensitivity to pH values between 7.4 and 6.8 and are superior to the widely used acrylic acid. We have also shown that incorporation of acidic comonomers leads to the favorable outcome of a higher fluorescence signal intensity in lower pH values, whereas the opposite is true of basic comonomers, where the fluorescence signal intensity is lower at low pH values. It was shown that to keep the pH response favorable the molar ratio of basic comonomers to acidic comonomers should roughly equal 1:4. We controlled the lower critical solution temperature (LCST) of the nanoparticles from around 30 to 38°C for different applications by adding acrylamide comonomers. Finally, the nanoparticles at varying pH values, when imaged by an ultrasound switchable fluorescence (USF) imaging system, showed pH sensitivity and thermosensitivity at physiological and tumor pH.

Next Generation Strategy for Tuning the Thermoresponsive Properties of Micellar and Hydrogel Drug Delivery Vehicles Using Ionic Liquids

Amongst the greatest challenges in developing injectable controlled thermoresponsive micellar and hydrogel drug delivery vehicles include tuning the cloud point (CP) and reducing the gelation temperature (Tgel), below 37 °C,...

Understanding functional group and assembly dynamics in temperature responsive systems leads to design principles for enzyme responsive assemblies

Understanding the molecular rules behind the dynamics of supramolecular assemblies is fundamentally important for the rational design of responsive assemblies with tunable properties. Herein, we report that the dynamics of temperature-sensitive supramolecular assemblies is not only affected by the dehydration of oligoethylene glycol (OEG) motifs, but also by the thermally-promoted molecular motions. These counteracting features set up a dynamics transition point (DTP) that can be modulated with subtle variations in a small hydrophobic patch on the hydrophilic face of the amphiphilic assembly. Understanding the structural factors that control the dynamics of the assemblies leads to rational design of enzyme-responsive assemblies with tunable temperature responsive profiles.

100th Anniversary of Macromolecular Science Viewpoint: Poly(N-isopropylacrylamide)-Based Thermally Responsive Micelles

Poly(N-isopropylacrylamide) (PNIPAAm)-based thermally responsive micelles are of great importance as smart materials for a number of applications such as drug delivery and biosensing, owing to their tunable lower critical solution temperature (LCST). Their design and synthesis in the nanoscale size range have been widely studied, and research interest in their structural and physic-chemical properties is continually growing. In this Viewpoint, representative research on the construction of PNIPAAm-based thermally responsive micelles as well as their applications are highlighted and discussed, which would serve as a good start for newcomers in this field and a positive guide for future research.

Dual responsive PMEEECL–PAE block copolymers: a computational self-assembly and doxorubicin uptake study

The self-assembly behaviour of dual-responsive block copolymers and their ability to solubilize the anticancer drug doxorubicin (DOX) has been investigated using all-atom molecular dynamics (MD) simulations, MARTINI coarse-grained (CG) force field simulation and Scheutjens–Fleer self-consistent field (SCF) computations. These diblock copolymers, composed of poly{γ-2-[2-(2-methoxyethoxy)ethoxy]ethoxy-ε-caprolactone} (PMEEECL) and poly(β-amino ester) (PAE) are dual-responsive: the PMEEECL block is thermoresponsive (becomes insoluble above a certain temperature), while the PAE block is pH-responsive (becomes soluble below a certain pH). Three MEEECL₂₀–AE_M compositions with M = 5, 10, and 15, have been studied. All-atom MD simulations have been performed to calculate the coil-to-globule transition temperature (T_cg) of these copolymers and finding appropriate CG mapping for both PMEEECL–PAE and DOX. The output of the MARTINI CG simulations is in agreement with SCF predictions. The results show that DOX is solubilized with high efficiency (75–80%) at different concentrations inside the PMEEECL–PAE micelles, although, interestingly, the loading efficiency is reduced by increasing the drug concentration. The non-bonded interaction energy and the RDF between DOX and water beads confirm this result. Finally, MD simulations and SCF computations reveal that the responsive behaviour of PMEEECL–PAE self-assembled structures take place at temperature and pH ranges appropriate for drug delivery.

The self-assembly behaviour of dual-responsive block copolymers and their ability to solubilize the drug doxorubicin is demonstrated using molecular dynamics simulations, coarse-grained force field simulations and self-consistent field theory.

Synthesis of Thermosensitive Conjugated Triblock Copolymers by Sequential Click Couplings for Drug Delivery and Cell Imaging

The elegant integration of an excellent light-emitting segment and a biorelevant signal-responsive moiety could generate advanced polymeric delivery systems with simultaneously favorable diagnostic and therapeutic functions with respect to cancer theranostics. Although polymeric delivery systems based on fluorescent polyfluorene (PF) or thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) have been extensively developed, the preparation of a ternary polymer formulation composed of a PF block, a PNIPAAm sequence, and a hydrophilic moiety remains rarely explored likely because of the difficulty in integrating different synthesis strategies for polymer synthesis. To this end, herein we reported the design and controlled synthesis of a PF- and PNIPAAm-based amphiphilic triblock copolymer, PF₁₁-b-PNIPAAm₁₂₀-b-poly(oligo(ethylene glycol) monomethyl ether methacrylate)₁₇ (PF₁₁-b-PNIPAAm₁₂₀-b-POEGMA₁₇), with a well-defined structure by a strategy of sequential click couplings between Suzuki-coupling-generated PF and atom-transfer radical polymerization (ATRP)-produced PNIPAAm and POEGMA. The as-prepared triblock copolymers can self-assemble into micelles with a core-shell-corona (CSC) structure that is composed of an inner hydrophobic core of the PF moiety for fluorescent tracking and drug encapsulation, a thermosensitive middle shell of PNIPAAm block for thermomodulated drug loading and release, and a hydrophilic outer corona of the POEGMA segment for micelle stabilization. Interestingly, the doxorubicin (DOX)-loaded micelles prepared at 25 °C had a greater drug loading capacity than the analogues fabricated at 37 °C due to the better stability of the former formulation, leading to its higher in vitro cytotoxicity in HeLa cells. Together with the integration of a localized hyperthermia-triggered drug release profile and efficiently intracellular trafficking of the nanocarriers by monitoring the fluorescence of the PF moiety, this formulation demonstrates a great potential for cancer theranostics.

Polymeric micelles: Basic research to clinical practice

Rapidly developing polymeric micelles as potential targeting carriers has intensified the need for better understanding of the underlying principles related to the selection of suitable delivery materials for designing, characterizing, drug loading, improving stability, targetability, biosafety and efficacy. The emergence of advanced analytical tools such as fluorescence resonance energy transfer and dissipative particle dynamics has identified new dimensions of these nanostructures and their behavior in much greater details. This review summarizes recent efforts in the development of polymeric micelles with respect to their architecture, formulation strategy and targeting possibilities along with their preclinical and clinical aspects. Literature of the past decade is discussed critically with special reference to the chemistry involved in the formation and clinical applications of these versatile materials. Thus, our main objective is to provide a timely update on the current status of polymeric micelles highlighting their applications and the important parameters that have led to successful delivery of drugs to the site of action.

N-Acetyl-D-glucosamine decorated polymeric nanoparticles for targeted delivery of doxorubicin: Synthesis, characterization and in vitro evaluation

A novel targeting drug delivery system containing poly(styrene-alt-maleic anhydride)58-b-polystyrene130 (P(St-alt-MA)58-b-PSt130) as a copolymer backbone, N-acetyl glucosamine (NAG) as a targeting moiety was designed and synthesized. The NAG grafted copolymer (NAG-P(St-alt-MA)58-b-PSt130) was characterized by FTIR and (1)H NMR. The NAG-P(St-alt-MA)58-b-PSt130 nanoparticles exhibited spherical shapes with an average diameter about 56.27±0.43 nm, low critical micelle concentration of 0.028 mg/mL, negative zeta potential -41.46±0.99 mV, high drug loading 25.83±1.09% and encapsulation efficiency 69.69±3.98%. In vitro cell cytotoxicity was conducted to confirm the safety of the NAG-P(St-alt-MA)58-b-PSt130 nanoparticles. Confocal laser scanning microscopy (CLSM) and flow cytometry (FCM) results showed that the NAG targeting moiety enhanced the internalization and targeting ability of NAG-P(St-alt-MA)58-b-PSt130 nanoparticles. Anticancer activity toward MCF-7 cells and HT29 cells showed that DOX-loaded NAG-P(St-alt-MA)58-b-PSt130 nanoparticles exhibited a higher antitumor activity compared to DOX-loaded P(St-alt-MA)58-b-PSt130 nanoparticles, which could attribute to NAG receptor-mediated endocytosis. These results suggest that the biocompatible and non-toxic NAG-P(St-alt-MA)58-b-PSt130 nanoparticles may be used as an effective targeting drug delivery system for cancer therapy.

Temperature- and redox-responsive magnetic complex micelles for controlled drug release

PCL-SS-PDMAEMA/Fe₃O₄ magnetic complex micelles can present dual temperature- and redox-responses, magnetism and magnetothermal properties.

Thermoresponsive block copolymer micelles with tunable pyrrolidone-based polymer cores: structure/property correlations and application as drug carriers

Residue structure affects the physicochemical properties, drug loading efficiency, and thermoresponsive drug release profiles of block copolymer micelles with pyrrolidone-based polymer cores.

Thermo- and pH-responsive copolymers based on PLGA-PEG-PLGA and poly(L-histidine): synthesis and in vitro characterization of copolymer micelles

A series of novel thermo- and pH-responsive block copolymers of PHis-PLGA-PEG-PLGA-PHis composed of poly(ethylene glycol) (PEG), poly(D,L-lactide-co-glycolide) (PLGA) and poly(L-histidine) (PHis) were synthesized and used for the construction of stimuli-responsive copolymer micelles. The starting polymers of PLGA-PEG-PLGA and PHis were synthesized by ring-opening polymerization of dl-lactide and glycolide with PEG as an initiator and L-histidine N-carboxylanhydride with isopropylamine as an initiator, respectively. The final copolymer was obtained by the coupling reaction of PHis with PLGA-PEG-PLGA. The copolymer micelles were constructed to have an inner core consisting of two hydrophobic blocks (PLGA and deprotonated PHis) and an outer hydrophilic PEG shell. The temperature- and pH-induced structure changes of the micelles were characterized by an alteration in particle size, a decrease in pyrene fluorescence intensity, and a variation of (1)H NMR spectra in D2O. It was speculated that the hydrophobic-hydrophilic transitions of PEG and PHis in response to temperature and pH variations accounted for the destabilization of micelles. In vitro release profiles, cell cytotoxicity and intracellular location studies further confirmed the temperature- and pH-responsive properties of the copolymer micelles. These results demonstrate the potential of the developed copolymers to be stimuli-responsive carriers for targeted delivery of anti-cancer drugs.

Multi-stimuli responsive polymers – the all-in-one talents

The integration of several responsive moieties within one polymer yields smart polymers exhibiting a multifaceted responsive behaviour.

Supramolecular hydrogels from inclusion complexation of α-cyclodextrin with densely grafted chains in micelles for controlled drug and protein release

An amphiphilic Py-PCL-b-POEGMA copolymer was prepared by the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). Based on the host-guest inclusion complexation of α-CD with densely grafted chains of the POEGMA shell in Py-PCL-b-POEGMA micelles, supramolecular micellar hydrogels were obtained by adding α-CD into Py-PCL-b-POEGMA micellar solutions. Resulting from the dissociation of α-CD from the ICs upon heating, the Py-PCL-b-POEGMA IC-based supramolecular hydrogels presented thermo-responsive properties. As they were heated, the IC-based hydrogels underwent gel-sol transformation because of the breakage of the physical cross-links. Benefiting from the fluorescent pyrene group in the Py-PCL-b-POEGMA copolymer, the system showed fluorescent properties. And the fluorescent intensity decreased obviously and regularly during the sol-gel transformation process, which makes it possible to detect the sol-gel transformation through sensing the fluorescent intensity of the system. Due to the biodegradable and biocompatible properties, the IC-based hydrogels were used as carriers for delivery systems. The hydrogels showed good properties for controlled release, and the release rate and level can be controlled by temperature.

Cyclodextrin-Responsive Micelles Based on Poly(ethylene glycol)-Polypeptide Hybrid Copolymers as Drug Carriers

Novel drug carriers based on poly(ethylene glycol) (PEG)-polypeptide copolymers, four-armed poly(ε-adamantane-l-lysine)₂-block-poly(ethylene glycol)-block-poly(ε-adamantane-l-lysine)₂ (PLys(Ad)₂-b-PEG-b-PLys(Ad)₂), have been prepared. The copolymers were synthesized via the ring-opening polymerization of amino acid N-carboxyanhydrides. The copolymers could spontaneously form core-shell micelles in aqueous solutions. It has been found that these micelles undergo triggered disassembly in response to an additional β-cyclodextrin (β-CD). The in vitro drug release in response to β-CD has been studied, and the result shows that the release of the entrapped drug doxorubicin (DOX) from the micelles could be accelerated by the addition of β-CD. Their cytotoxicity and cell internalization behavior were also investigated in detail. These micelles are expected to have great potential in controlled drug release applications.

Stimulus-sensitive polymeric nanoparticles and their applications as drug and gene carriers

Polymeric nanoparticles are promising candidates as drug and gene carriers. Among polymeric nanoparticles, those that are responsive to internal or external stimuli are of greater interest because they allow more efficient delivery of therapeutics to pathological regions. Stimulus-sensitive polymeric nanoparticles have been fabricated based on numerous nanostructures, including micelles, vesicles, crosslinked nanoparticles, and hybrid nanoparticles. The changes in chemical or physical properties of polymeric nanoparticles that occur in response to single, dual, or multiple stimuli endow these nanoparticles with the ability to retain cargoes during circulation, target the pathological region, and release their cargoes after cell internalization. This Review focuses on the most recent developments in the preparation of stimulus-sensitive polymeric nanoparticles and their applications in drug and gene delivery.

pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates

Titratable polyanions, and more particularly polymers bearing carboxylate groups, have been used in recent years to produce a variety of pH-sensitive colloids. These polymers undergo a coil-to-globule conformational change upon a variation in pH of the surrounding environment. This conformational change can be exploited to trigger the release of a drug from a drug delivery system in a pH-dependent fashion. This review describes the current status of pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates and their performance as nano-scale drug delivery systems, with emphasis on our recent contribution to this field.