Polymeric micelles for the delivery of poorly soluble drugs: From nanoformulation to clinical approval

Over the last three decades, polymeric micelles have emerged as a highly promising drug delivery platform for therapeutic compounds. Particularly, poorly soluble small molecules with high potency and significant toxicity were encapsulated in polymeric micelles. Polymeric micelles have shown improved pharmacokinetic profiles in preclinical animal models and enhanced efficacy with a superior safety profile for therapeutic drugs. Several polymeric micelle formulations have reached the clinical stage and are either in clinical trials or are approved for human use. This furthers interest in this field and underscores the need for additional learning of how to best design and apply these micellar carriers to improve the clinical outcomes of many drugs. In this review, we provide detailed information on polymeric micelles for the solubilization of poorly soluble small molecules in topics such as the design of block copolymers, experimental and theoretical analysis of drug encapsulation in polymeric micelles, pharmacokinetics of drugs in polymeric micelles, regulatory approval pathways of nanomedicines, and current outcomes from micelle formulations in clinical trials. We aim to describe the latest information on advanced analytical approaches for elucidating molecular interactions within the core of polymeric micelles for effective solubilization as well as for analyzing nanomedicine's pharmacokinetic profiles. Taking into account the considerations described within, academic and industrial researchers can continue to elucidate novel interactions in polymeric micelles and capitalize on their potential as drug delivery vehicles to help improve therapeutic outcomes in systemic delivery.

Role of integrated cancer nanomedicine in overcoming drug resistance

Cancer remains a major killer of mankind. Failure of conventional chemotherapy has resulted in recurrence and development of virulent multi drug resistant (MDR) phenotypes adding to the complexity and diversity of this deadly disease. Apart from displaying classical physiological abnormalities and aberrant blood flow behavior, MDR cancers exhibit several distinctive features such as higher apoptotic threshold, aerobic glycolysis, regions of hypoxia, and elevated activity of drug-efflux transporters. MDR transporters play a pivotal role in protecting the cancer stem cells (CSCs) from chemotherapy. It is speculated that CSCs are instrumental in reviving tumors after the chemo and radiotherapy. In this regard, multifunctional nanoparticles that can integrate various key components such as drugs, genes, imaging agents and targeting ligands using unique delivery platforms would be more efficient in treating MDR cancers. This review presents some of the important principles involved in development of MDR and novel methods of treating cancers using multifunctional-targeted nanoparticles. Illustrative examples of nanoparticles engineered for drug/gene combination delivery and stimuli responsive nanoparticle systems for cancer therapy are also discussed.

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.

PEG-b-PLA micelles and PLGA-b-PEG-b-PLGA sol-gels for drug delivery

Poly(ethylene glycol)-block-poly(D,L-lactic acid) (PEG-b-PLA) micelles and poly(D,L-lactic-co-glycolic acid)-block-polyethylene glycol)-block-poly(D,L-lactic-co-glycolic acid) (PLGA-b-PEG-b-PLGA) sol-gels have been extensively researched for systemic and localized drug delivery applications, respectively, and they have both progressed into humans for paclitaxel, an important yet poorly water-soluble chemotherapeutic agent. In this review article, preclinical and clinical research on PEG-b-PLA micelles and PLGA-b-PEG-b-PLGA sol-gels that has focused on paclitaxel will be updated, and recent research on other poorly water-soluble anticancer agents and delivery of drug combinations (i.e. multi-drug delivery) that seeks synergistic anticancer efficacy will be summarized. PEG-b-PLA micelles are a first-generation platform for the systemic multi-delivery of poorly water soluble anticancer agents. PLGA-b-PEG-b-PLGA sol-gels are a first-generation platform for the localized multi-drug delivery of water-soluble and/or poorly water-soluble anticancer agents. In summary, PEG-b-PLA micelles and PLGA-b-PEG-b-PLGA sol-gels may safely enable pre-clinical evaluation and clinical translation of poorly water-soluble anticancer agents, especially for promising, rapidly emerging anticancer combinations.

Injectable thermosensitive hydrogel systems based on functional PEG/PCL block polymer for local drug delivery

Injectable in situ thermosensitive hydrogels have potential applications in tissue engineering and drug delivery. The hydrogel formulations exist as aqueous solutions at room temperature but rapidly solidify into gels at 37 °C in situ, making them highly suitable for administering drugs in a minimally invasive manner to the target organ(s). The hydrogel formed with nanoparticles assembled with amphiphilic polymer blocks of polyethyleneglycol (PEG) and biodegradable polycaprolactone (PCL) have been tested as platforms for targeted and sustained drug delivery, and have shown encouraging results. In this review, we summarize the influence of the molecular weight, PEG/PCL ratio and functional structure of hydrophobic PCL blocks on the critical gelation temperature, gelling behavior and drug release kinetics of the hydrogels. The current studies on the biomedical applications of thermosensitive PEG/PCL hydrogels have also been discussed.

Topographically-designed triboelectric nanogenerator via block copolymer self-assembly

Herein, we report a facile and robust route to nanoscale tunable triboelectric energy harvesters realized by the formation of highly functional and controllable nanostructures via block copolymer (BCP) self-assembly. Our strategy is based on the incorporation of various silica nanostructures derived from the self-assembly of BCPs to enhance the characteristics of triboelectric nanogenerators (TENGs) by modulating the contact-surface area and the frictional force. Our simulation data also confirm that the nanoarchitectured morphologies are effective for triboelectric generation.

Biodegradable nanofibrous temperature-responsive gelling microspheres for heart regeneration

Myocardial infarction (heart attack) is the number one killer of heart patients. Existing treatments for heart attack do not address the underlying problem of cardiomyocyte (CM) loss and cannot regenerate the myocardium. Introducing exogenous cardiac cells is required for heart regeneration due to the lack of resident progenitor cells and very limited proliferative potential of adult CMs. Poor retention of transplanted cells is the critical bottleneck of heart regeneration. Here, we report the invention of a poly(l-lactic acid)-b-poly(ethylene glycol)-b-poly(N-Isopropylacrylamide) copolymer and its self-assembly into nanofibrous gelling microspheres (NF-GMS). The NF-GMS undergo thermally responsive transition to form not only a 3D hydrogel after injection in vivo, but also exhibit architectural and structural characteristics mimicking the native extracellular matrix (ECM) of nanofibrous proteins and gelling proteoglycans or polysaccharides. By integrating the ECM-mimicking features, injectable form, and the capability of maintaining 3D geometry after injection, the transplantation of hESC-derived CMs carried by NF-GMS led to a striking 10-fold graft size increase over direct CM injection in an infarcted rat model, which is the highest reported engraftment to date. Furthermore, NF-GMS carried CM transplantation dramatically reduced infarct size, enhanced integration of transplanted CMs, stimulated vascularization in the infarct zone, and led to a substantial recovery of cardiac function. The NF-GMS may also serve as advanced injectable and integrative biomaterials for cell/biomolecule delivery in a variety of biomedical applications.

Hydrothermally synthesized PEGylated calcium phosphate nanoparticles incorporating Gd-DTPA for contrast enhanced MRI diagnosis of solid tumors

Organic-inorganic hybrid nanoparticles with calcium phosphate (CaP) core and PEGylated shell were developed to incorporate magnetic resonance imaging (MRI) contrast agent diethylenetriaminepentaacetic acid gadolinium (III) (Gd-DTPA) for noninvasive diagnosis of solid tumors. A two-step preparation method was applied to elaborate hybrid nanoparticles with a z-average hydrodynamic diameter about 80nm, neutral surface ξ-potential and high colloidal stability in physiological environments by self-assembly of poly(ethylene glycol)-b-poly(aspartic acid) block copolymer, Gd-DTPA, and CaP in aqueous solution, followed with hydrothermal treatment. Incorporation into the hybrid nanoparticles allowed Gd-DTPA to show significant enhanced retention ratio in blood circulation, leading to high accumulation in tumor positions due to enhanced permeability and retention (EPR) effect. Moreover, Gd-DTPA revealed above 6 times increase of relaxivity in the nanoparticle system compared to free form, and eventually, selective and elevated contrast enhancements in the tumor positions were observed. These results indicate the high potential of Gd-DTPA-loaded PEGylated CaP nanoparticles as a novel contrast agent for noninvasive cancer diagnosis.

Nanoscale simultaneous chemical and mechanical imaging via peak force infrared microscopy

Nondestructive chemical and mechanical measurements of materials with ~10-nm spatial resolution together with topography provide rich information on the compositions and organizations of heterogeneous materials and nanoscale objects. However, multimodal nanoscale correlations are difficult to achieve because of the limitation on spatial resolution of optical microscopy and constraints from instrumental complexities. We report a novel noninvasive spectroscopic scanning probe microscopy method-peak force infrared (PFIR) microscopy-that allows chemical imaging, collection of broadband infrared spectra, and mechanical mapping at a spatial resolution of 10 nm. In our technique, chemical absorption information is directly encoded in the withdraw curve of the peak force tapping cycle after illumination with synchronized infrared laser pulses in a simple apparatus. Nanoscale phase separation in block copolymers and inhomogeneity in CH₃NH₃PbBr₃ perovskite crystals are studied with correlative infrared/mechanical nanoimaging. Furthermore, we show that the PFIR method is sensitive to the presence of surface phonon polaritons in boron nitride nanotubes. PFIR microscopy will provide a powerful analytical tool for explorations at the nanoscale across wide disciplines.

Poly(ethylene glycol)-b-poly(lysine) copolymer bearing nitroaromatics for hypoxia-sensitive drug delivery

Hypoxia occurs in a variety of pathological conditions including stroke, rheumatoid arthritis, atherosclerosis, and tumors. In this study, an amphiphilic block copolymer, composed of poly(ethylene glycol) as the hydrophilic block and poly(ε-(4-nitro)benzyloxycarbonyl-L-lysine) as the hydrophobic block, was prepared for hypoxia-sensitive drug delivery. Owing to its amphiphilic nature, the block copolymer formed micelles and encapsulated doxorubicin (DOX) in an aqueous condition. The DOX-loaded micelles exhibited rapid intracellular release of DOX under the hypoxic condition, implying high potential as a drug carrier for cancer therapy.

STATEMENT OF SIGNIFICANCE

Hypoxia occurs in a variety of pathological conditions including stroke, rheumatoid arthritis, atherosclerosis, and tumors. In this study, we developed a novel type of hypoxia-sensitive polymeric micelles (HS-PMs) that can specifically release the drug under the hypoxic conditions. HS-PMs were prepared using poly(ethylene glycol) as the hydrophilic block and poly(ε-(4-nitro)benzyloxycarbonyl-L-lysine) as the hydrophobic block. Owing to its amphiphilic nature, the block copolymer formed micelles and encapsulated doxorubicin (DOX) in an aqueous condition. The DOX-loaded micelles exhibited rapid intracellular release of DOX under the hypoxic condition. Overall, it is evident that the HS-PMs prepared in this study have the potential to effectively deliver hydrophobic drugs into the hypoxic cells involved in various intractable diseases.

Facile assembly and loading of theranostic polymersomes via multi-impingement flash nanoprecipitation

Flash nanoprecipitation (FNP) has proven to be a powerful tool for the rapid and scalable assembly of solid-core nanoparticles from block copolymers. The process can be performed using a simple confined impingement jets mixer and provides an efficient and reproducible method of loading micelles with hydrophobic drugs. To date, FNP has not been applied for the fabrication of complex or vesicular nanoarchitectures capable of encapsulating hydrophilic molecules or bioactive protein therapeutics. Here, we present FNP as a single customizable method for the assembly of bicontinuous nanospheres, filomicelles and vesicular, multilamellar and tubular polymersomes from poly(ethylene glycol)-bl-poly(propylene sulfide) block copolymers. Multiple impingements of polymersomes assembled via FNP were shown to decrease vesicle diameter and polydispersity, allowing gram-scale fabrication of monodisperse polymersomes within minutes. Furthermore, we demonstrate that FNP supports the simultaneous loading of both hydrophobic and hydrophilic molecules respectively into the polymersome membrane and aqueous lumen, and encapsulated enzymes were found to be released and remain active following vesicle lysis. As an example application, theranostic polymersomes were generated via FNP that were dual loaded with the immunosuppressant rapamycin and a fluorescent dye to link targeted immune cells with the elicited immunomodulation of T cells. By expanding the capabilities of FNP, we present a rapid, scalable and reproducible method of nanofabrication for a wide range of nanoarchitectures that are typically challenging to assemble and load with therapeutics for controlled delivery and theranostic strategies.

Redox-responsive micelles self-assembled from dynamic covalent block copolymers for intracellular drug delivery

Redox-responsive micelles self-assembled from dynamic covalent block copolymers with double disulfide linkage in the backbone have been developed successfully. The amphiphilic block copolymers PEG-PLA associated with complementary H-bonding sequences can self-assemble into spherical micelles in aqueous media with sizes from 34 nm to 107 nm with different molar mass of PEG and PLA. Moreover, in vitro drug release analyses indicate that reductive environment can result in triggered drug release profiles. The glutathione (GSH) mediated intracellular drug delivery was investigated against HeLa human cervical carcinoma cell line. Flow cytometry and fluorescence microscopy measurements demonstrated that the micelles exhibited faster drug release in glutathione monoester (GSH-OEt) pretreated HeLa cells than that in the nonpretreated cells. Cytotoxicity assay of DOX-loaded micelles indicated the higher cellular proliferation inhibition against 10 mM of GSH-OEt pretreated HeLa cells than that of the nonpretreated ones. These reduction-responsive, biodegradable and biocompatibility micelles could provide a favorable platform to construct excellent drug delivery systems for cancer therapy.

Block copolymers at interfaces: interactions with physiological media

Triblock copolymers (also known as Pluronics or poloxamers) are biocompatible molecules composed of hydrophobic and hydrophilic blocks with different lengths. They have received much attention recently owing to their applicability for targeted delivery of hydrophobic compounds. Their unique molecular structure facilitates the formation of dynamic aggregates which are able to transport lipid soluble compounds. However, these structures can be unstable and tend to solubilize within the blood stream. The use of nanoemulsions as carriers for the lipid soluble compounds appears as a new alternative with improved protection against physiological media. The interfacial behavior of block copolymers is directly related to their peculiar molecular structure and further knowledge could provide a rational use in the design of poloxamer-stabilized nanoemulsions. This review aims to combine the new insights gained recently into the interfacial properties of block copolymers and their performance in nanoemulsions. Direct studies dealing with the interactions with physiological media are also reviewed in order to address issues relating metabolism degradation profiles. A better understanding of the physico-chemical and interfacial properties of block copolymers will allow their manipulation to modulate lipolysis, hence allowing the rational design of nanocarriers with efficient controlled release.

Hypoxia-responsive block copolymer radiosensitizers as anticancer drug nanocarriers for enhanced chemoradiotherapy of bulky solid tumors

Radiosensitizers play an important role in the clinical radiotherapy of hypoxic solid tumors to improve therapeutic efficacy. However, the in vivo performance of clinically used small-molecule radiosensitizers is commonly compromised by low bioavailability in hypoxic tumor regions. Herein, amphiphilic block copolymer radiosensitizers are prepared from clinically approved poly(ethylene glycol)-block-poly(l-glutamic acid) (PEG-b-PLG) and metronidazole (MN) to obtain MN-grafted PEG-b-PLG (PEG-b-P(LG-g-MN)) via condensation reaction, which can self-assemble into core-shell micelles as nanoparticle-formulated radiosensitizers in aqueous solution. The radiosensitizers are demonstrated to possess significantly higher sensitization enhancement ratio (SER) of 2.18 and potent in vivo tumor ablation capability upon exposure to electron beam irradiation compared with clinically used sodium glycididazole (GS) with SER of 1.32. Moreover, after optimizing the ratios of carboxyl and MN groups, PEG-b-P(LG-g-MN) micelles can be used to encapsulate doxorubicin (DOX@HMs) efficiently. Hypoxia-responsive structural transformation of MN into hydrophilic aminoimidazole triggers fast DOX release from DOX@HMs. After intravenous injection of DOX@HMs, potent ablation capability against bulky solid tumors (∼500 mm³) is realized at a low radiation dose (4 Gy) via enhanced chemoradiotherapy. Therefore, the developed novel amphiphilic block copolymer radiosensitizers can be concurrently used as high-efficiency radiosensitizers and hypoxia-responsive DOX nanocarriers for enhanced chemoradiotherapy.

Harnessing amphiphilic polymeric micelles for diagnostic and therapeutic applications: Breakthroughs and bottlenecks

Amphiphilic block copolymers are widely utilized in the design of formulations owing to their unique physicochemical properties, flexible structures and functional chemistry. Amphiphilic polymeric micelles (APMs) formed from such copolymers have gained attention of the drug delivery scientists in past few decades for enhancing the bioavailability of lipophilic drugs, molecular targeting, sustained release, stimuli-responsive properties, enhanced therapeutic efficacy and reducing drug associated toxicity. Their properties including ease of surface modification, high surface area, small size, and enhanced permeation as well as retention (EPR) effect are mainly responsible for their utilization in the diagnosis and therapy of various diseases. However, some of the challenges associated with their use are premature drug release, low drug loading capacity, scale-up issues and their poor stability that need to be addressed for their wider clinical utility and commercialization. This review describes comprehensively their physicochemical properties, various methods of preparation, limitations followed by approaches employed for the development of optimized APMs, the impact of each preparation technique on the physicochemical properties of the resulting APMs as well as various biomedical applications of APMs. Based on the current scenario of their use in treatment and diagnosis of diseases, the directions in which future studies need to be carried out to explore their full potential are also discussed.

Orientation Control in Thin Films of a High-χ Block Copolymer with a Surface Active Embedded Neutral Layer

Directed self-assembly (DSA) of block copolymers (BCPs) is an attractive advanced patterning technology being considered for future integrated circuit manufacturing. By controlling interfacial interactions, self-assembled microdomains in thin films of polystyrene-block-poly(methyl methacrylate), PS-b-PMMA, can be oriented perpendicular to surfaces to form line/space or hole patterns. However, its relatively weak Flory interaction parameter, χ, limits its capability to pattern sub-10 nm features. Many BCPs with higher interaction parameters are capable of forming smaller features, but these "high-χ" BCPs typically have an imbalance in surface energy between the respective blocks that make it difficult to achieve the required perpendicular orientation. To address this challenge, we devised a polymeric surface active additive mixed into the BCP solution, referred to as an embedded neutral layer (ENL), which segregates to the top of the BCP film during casting and annealing and balances the surface tensions at the top of the thin film. The additive comprises a second BCP with a "neutral block" designed to provide matched surface tensions with the respective polymers of the main BCP and a "surface anchoring block" with very low surface energy that drives the material to the air interface during spin-casting and annealing. The surface anchoring block allows the film to be annealed above the glass transition temperature of the two materials without intermixing of the two components. DSA was also demonstrated with this embedded neutral top layer formulation on a chemical patterned template using a single step coat and simple thermal annealing. This ENL technology holds promise to enable the use of high-χ BCPs in advanced patterning applications.

Pseudomonas putida KT2442 as a platform for the biosynthesis of polyhydroxyalkanoates with adjustable monomer contents and compositions

The β-oxidation weakened Pseudomonas putida were established as a platform for the production of polyhydroxyalkanoates (PHA) with adjustable monomer compositions and micro-structures. When mutant P. putida KTOYO6ΔC (phaPCJA.c) was cultivated on mixtures of sodium butyrate and sodium hexanoate (C4:C6), random copolymers of P(3HB-co-3HHx) consisting of 3-hydroxybutyrate (3HB), 3-hydroxyhexanoate (3HHx), were accumulated with 3HHx content ranged from 19 mol% to 75 mol%. While recombinant P. putida KTQQ20 grown on mixtures of sodium hexanoate and decanoic acid (C6:C10), produced random copolymers of P(3HHx-co-3HD) consisting of 3-hydroxyhexanoate (3HHx) and 3-hydroxydecanoate (3HD), the monomer fraction of 3HHx ranged from 16 mol% to 63 mol%. The comonomer compositions were easily regulated by varying the fatty acid concentrations. P. putida KTQQ20 produced a novel diblock copolymer P3HHx-b-P(3HD-co-3HDD) consisting of 49 mol% P3HHx and 51 mol% P(3HD-co-3HDD) [35.25 mol% 3HDD (3-hydroxydodecanoate)], which was characterized by (13)C NMR, HMBC NMR, DSC, GPC and universal testing machine.

Direct synthesis of nitrogen-doped mesoporous carbons from triazine-functionalized resol for CO2 uptake and highly efficient removal of dyes

In this study we synthesized a triazine-formaldehyde phenolic resin as a nitrogen-containing resol (N-resol) through the condensation of 2,4,6-tris(4-hydroxyphenyl)triazine and formaldehyde. We then used this N-resol as a carbon and nitrogen atom source, mixing it with a diblock copolymer of PEO-b-PCL as the soft template, for the direct synthesis of N-doped mesoporous carbons. Interestingly, the self-assembled N-resol/PEO-b-PCL blends underwent a mesophase transition from cylinder to gyroid and back again to cylinder structures upon increasing the N-resol concentration (i.e., cylinder at 50/50; gyroid at 60/40; cylinder at 70/30). After removing the soft template at 700 °C, the resultant N-doped mesoporous carbons possessed high N atom contents (up to 13 wt%) and displayed gyroid and cylinder nanostructures. The synthesized N-doped mesoporous carbons exhibited excellent CO₂ uptake capacities (up to 72 and 150 mg g^-1 at 298 and 273 K, respectively). Furthermore, the N-doped mesoporous gyroid carbon structure displayed high adsorption capacities toward organic dyes in water. The maximum adsorption capacities of rhodamine B and methylene blue in water reached as high as 204.08 and 308.64 mg g^-1, respectively; furthermore, these N-doped mesoporous carbons also maintained up to 98 % of their maximum adsorption capacities within 45 min.

Adsorption of poly(ethylene oxide)-containing amphiphilic polymers on solid-liquid interfaces: Fundamentals and applications

The adsorption of amphiphilic molecules of varying size on solid-liquid interfaces modulates the properties of colloidal systems. Nonionic, poly(ethylene oxide) (PEO)-based amphiphilic molecules are particularly useful because of their graded hydrophobic-hydrophilic nature, which allows for adsorption on a wide array of solid surfaces. Their adsorption also results in other useful properties, such as responsiveness to external stimuli and solubilization of hydrophobic compounds. This review focuses on the adsorption properties of PEO-based amphiphiles, beginning with a discussion of fundamental concepts pertaining to the adsorption of macromolecules on solid-liquid interfaces, and more specifically the adsorption of PEO homopolymers. The main portion of the review highlights studies on factors affecting the adsorption and surface self-assembly of PEO-PPO-PEO block copolymers, where PPO is poly(propylene oxide). Block copolymers of this type are commercially available and of interest in several fields, due to their low toxicity and compatibility in aqueous systems. Examples of applications relevant to the interfacial behavior of PEO-PPO-PEO block copolymers are paints and coatings, detergents, filtration, and drug delivery. The methods discussed herein for manipulating the adsorption properties of PEO-PPO-PEO are emphasized for their ability to shed light on molecular interactions at interfaces. Knowledge of these interactions guides the formulation of novel materials with useful mesoscale organization and micro- and macrophase properties.

Templated Self-Assembly of a PS- Branch-PDMS Bottlebrush Copolymer

The self-assembly of block copolymers (BCPs) with novel architectures offers tremendous opportunities in nanoscale patterning and fabrication. Here, the thin film morphology, annealing kinetics, and topographical templating of an unconventional Janus-type "PS- branch-PDMS" bottlebrush copolymer (BBCP) are described. In the Janus-type BBCP, each segment of the bottlebrush backbone connects two immiscible side chain blocks. Thin films of a Janus-type BBCP with M_n = 609 kg/mol exhibited 22 nm period cylindrical microdomains with long-range order under solvent vapor annealing, and the effects of as-cast film thickness, solvent vapor pressure, and composition of the binary mixture of solvent vapors are described. The dynamic self-assembly process was characterized using in situ grazing-incidence X-ray scattering. Templated self-assembly of the BBCP within lithographically patterned substrates was demonstrated, showing distinct pattern orientation and dimensions that differ from conventional BCPs. Self-consistent field theory is used to elucidate details of the templated self-assembly behavior within confinement.

Polymer grafted magnetic nanoparticles for delivery of anticancer drug at lower pH and elevated temperature

Efficient and controlled delivery of therapeutics to tumor cells is one of the important issues in cancer therapy. In the present work, a series of pH- and temperature-responsive polymer grafted iron oxide nanoparticles were prepared by simple coupling of aminated iron oxide nanoparticle with poly(N-isopropylacrylamide-ran-poly(ethylene glycol) methyl ether acrylate)-block-poly(acrylic acid) (P(NIPA-r-PEGMEA)-b-PAA). For this, three water soluble block polymers were prepared via reversible addition fragmentation transfer (RAFT) polymerization technique. At first, three different block copolymers were prepared by polymerizing mixture of NIPA and PEGMEA (with varying mole ratio) in presence of poly(tert-butyl acrylate) (PtBA) macro chain transfer agent. Subsequently, P(NIPA-r-PEGMEA)-b-PAA copolymers were synthesized by hydrolyzing tert-butyl acrylate groups of the P(NIPA-r-PEGMEA)-b-PtBA copolymers. The resulting polymers were then grafted to iron oxide nanoparticles, and these functionalized nanoparticles were thoroughly characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), zeta potential measurements, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). Doxorubicin (DOX), an anti-cancer drug, was loaded into the polymer coated nanoparticles and its release behavior was subsequently studied at different pH and temperatures. The drug release pattern revealed a sustained release of DOX preferentially at the desired lysosomal pH of cancer cells (pH 5.0) and slightly above the physiological temperature depending upon the composition of the copolymers. The potential anticancer activity of the polymer grafted DOX loaded nanoparticles were established by MTT assay and apoptosis study of cervical cancer ME 180cells in presence of the nanoparticles. Thus, these particles can be utilized for controlled delivery of anticancer drugs at the desired lysosomal pH and/or by slightly heating the cells using magnetic hyperthermia.

Heat Capacity of Spider Silk-like Block Copolymers

We synthesized and characterized a new family of di-block copolymers based on the amino acid sequences of Nephila clavipes major ampulate dragline spider silk, having the form HAB_n and HBA_n (n=1-3), comprising an alanine-rich hydrophobic block, A, a glycine-rich hydrophilic block, B, and a histidine tag, H. The reversing heat capacities, C_p(T), for temperatures below and above the glass transition, T_g, were measured by temperature modulated differential scanning calorimetry. For the solid state, we then calculated the heat capacities of our novel block copolymers based on the vibrational motions of the constituent poly(amino acid)s, whose heat capacities are known or can be estimated from the ATHAS Data Bank. For the liquid state, the heat capacity was estimated by using the rotational and translational motions in the polymer chain. Excellent agreement was found between the measured and calculated values of the heat capacity, showing that this method can serve as a standard by which to assess the C_p for other biologically inspired block copolymers. The fraction of beta sheet crystallinity of spider silk block copolymers was also determined by using the predicted C_p, and was verified by wide angle X-ray diffraction and Fourier transform infrared spectroscopy. The glass transition temperatures of spider silk block copolymer were fitted by Kwei's equation and the results indicate that attractive interaction exists between the A-block and B-block.

Synthesis of block copolymers used in polymersome fabrication: Application in drug delivery

Amphiphilic block copolymers are common materials used for the fabrication of various nanostructures with biomedical applications including nanocapsules, nanospheres, micelles and polymeric vesicles. According to the literature, polymersomes have several advantages compared to other nanostructures used as drug delivery systems comprising better stability, facile synthesis, prolonged circulation time, and passive/active targeting capability. Various types of nanoparticles are formed by varying the ratio of the hydrophobic/hydrophilic blocks. Changing hydrophobic/hydrophilic ratio of amphiphilic block copolymers has an impact on the structural characteristics of polymers such as changing molecular weight and surface functionalization of the block copolymer. Thus, polymerization strategies are an important factor that influences polymersomes quality. In this review, different polymerization strategies for the synthesis of block copolymers applied in polymersomes formation, are described.

Ultrasound responsive block copolymer micelle of poly(ethylene glycol)-poly(propylene glycol) obtained through click reaction

The well-defined amphiphilic poly(ethylene glycol)-block-poly(propylene glycol) copolymer containing 1, 2, 3-triazole moiety and multiple ester bonds (PEG-click-PPG) was prepared by click reaction strategy. The PEG-click-PPG copolymer can self-assemble into spherical micelles in aqueous solution. It is found that high intensity focused ultrasound (HIFU) can open the copolymer PEG-click-PPG micelles and trigger the release of the payload in the micelle. The multiple ester bonds introduced in the junction point of the copolymer chain through click reactions were cleaved under HIFU, and leads to the disruption of the copolymer micelle and fast release of loaded cargo. The click reaction provides a convenient way to construct ultrasound responsive copolymer micelles with weak bonds.

A slow-release system of bacterial cellulose gel and nanoparticles for hydrophobic active ingredients

A combination of bacterial cellulose (BC) gel and amphiphilic block copolymer nanoparticles was investigated as a drug delivery system (DDS) for hydrophobic active ingredients. Poly(ethylene oxide)-b-poly(caprolactone) (PEO-b-PCL) and retinol were used as the block copolymer and hydrophobic active ingredient, respectively. The BC gel was capable of incorporating copolymer nanoparticles and releasing them in an acetic acid-sodium acetate buffer solution (pH 5.2) at 37 °C. The percentage of released copolymer reached a maximum value of approximately 60% after 6h and remained constant after 24h. The percentage of retinol released from the copolymer-containing BC gel reached a maximum value at 4h. These results show that the combination of BC gel and nanoparticles is a slow-release system that may be useful in the cosmetic and biomedical fields for skin treatment and preparation.