Stabilization of Pluronic P-105 Micelles with an Interpenetrating Network of N,N-Diethylacrylamide

Rationalizing the Design of Pluronics-Surfactant Mixed Micelles through Molecular Simulations and Experiments

Aqueous systems comprising polymers and surfactants are technologically important complex fluids with tunable features dependent on the chemical nature of each constituent, overall composition in mixed systems, and solution conditions. The phase behavior and self-assembly of amphiphilic polymers can be changed drastically in the presence of conventional ionic surfactants and need to be clearly understood. Here, the self-aggregation dynamics of a triblock copolymer (Pluronics L81, EO₃PO₄₃EO₃) in the presence of three cationic surfactants (with a 12C long alkyl chain but with different structural features), viz., dodecyltrimethylammonium bromide (DTAB), didodecyldimethylammonium bromide (DDAB), and ethanediyl-1,2-bis(dimethyldodecylammonium bromide) (12-2-12), were investigated in an aqueous solution environment. The nanoscale micellar size expressed as hydrodynamic diameter (D_h) of copolymer-surfactant mixed aggregates was evaluated using dynamic light scattering, while the presence of a varied micellar geometry of L81-cationic surfactant mixed micelles were probed using small-angle neutron scattering. The obtained findings were further validated from molecular dynamics (MD) simulations, employing a simple and transferable coarse-grained molecular model based on the MARTINI force field. L81 remained molecularly dissolved up to ∼20 °C but phase separated, forming turbid/translucent dispersion, close to its cloud point (CP) and existed as unstable vesicles. However, it exhibited interesting solution behavior expressed in terms of the blue point (BP) and the double CP in the presence of different surfactants, leading to mixed micellar systems with a triggered morphology transition from unstable vesicles to polymer-rich micelles and cationic surfactant-rich micelles. Such an amendment in the morphology of copolymer nanoaggregates in the presence of cationic surfactants has been well observed from scattering data. This is further rationalized employing the MD approach, which validated the effective interactions between Pluronics-cationic surfactant mixed micelles. Thus, our experimental results integrated with MD yield a deep insight into the nanoscale interactions controlling the micellar aggregation (Pluronics-rich micelles and surfactant-rich micelles) in the investigated mixed system.

Plant-inspired Pluronic-gallol micelles with low critical micelle concentration, high colloidal stability, and protein affinity

Polymeric micelles are the most common carriers used for hydrophobic drug delivery. However, they are vulnerable to physiological barriers, such as temperature changes and enzymatic degradation, and can be easily disassembled upon dilution below the critical micelle concentration (CMC) by body fluids after an intravenous injection. Here, we report that Pluronic® micelles with octyl gallate, which is a surfactant containing gallol moieties widely found in antioxidative plant polyphenols, have a low CMC, which improves their colloidal stability without the need for covalent crosslinking. Furthermore, the incorporated gallol moieties provide enzymatic degradation resistance to the micelles owing to their protein affinity, maintaining the hydrophobic cavity of unmodified Pluronic®. Thus, plant-inspired polymeric micelles with low CMC and bioavailability are promising multifunctional vehicles for drug delivery.

Rylene Dye-Loaded Polymeric Nanoparticles for Photothermal Eradication of Harmful Dinoflagellates, Akashiwo sanguinea and Alexandrium pacificum

In the era of climate changes, harmful dinoflagellate outbreaks that produce potent algal toxins, odor, and water discoloration in aquatic environments have been increasingly reported. Thus, various treatments have been attempted for the mitigation and management of harmful blooms. Here, we report engineered nanoparticles that consist of two different types of rylene derivatives encapsulated in polymeric micelles. In addition, to avoid dissociation of the aggregate, the core of micelle was stabilized via semi-interpenetrating network (sIPN) formation. On two types of the marine red-tide dinoflagellates, Akashiwo sanguinea and Alexandrium pacificum, the nanoparticle uptake followed by fluorescence labeling and photothermal effect was conducted. Firstly, fluorescence microscopy enabled imaging of the dinoflagellates with the ultraviolet chromophore, Lumogen Violet. Lastly, near-infrared (NIR) laser irradiation was exposed on the Lumogen IR788 nanoparticle-treated Ak. Sanguinea. The irradiation resulted in reduced cell survival due to the photothermal effect in microalgae. The results suggested that the nanoparticle, IR788-sIPN, can be applied for potential red-tide algal elimination.

Ultrasound-Mediated Cancer Therapeutics Delivery using Micelles and Liposomes: A Review

BACKGROUND

Existing cancer treatment methods have many undesirable side effects that greatly reduce the quality of life of cancer patients.

OBJECTIVE

This review will focus on the use of ultrasound-responsive liposomes and polymeric micelles in cancer therapy.

METHODS

This review presents a survey of the literature regarding ultrasound-triggered micelles and liposomes using articles recently published in various journals, as well as some new patents in this field.

RESULTS

Nanoparticles have proven promising as cancer theranostic tools. Nanoparticles are selective in nature, have reduced toxicity, and controllable drug release patterns making them ideal carriers for anticancer drugs. Numerous nanocarriers have been designed to combat malignancies, including liposomes, micelles, dendrimers, solid nanoparticles, quantum dots, gold nanoparticles, and, more recently, metal-organic frameworks. The temporal and spatial release of therapeutic agents from these nanostructures can be controlled using internal and external triggers, including pH, enzymes, redox, temperature, magnetic and electromagnetic waves, and ultrasound. Ultrasound is an attractive modality because it is non-invasive, can be focused on the diseased site, and has a synergistic effect with anticancer drugs.

CONCLUSION

The functionalization of micellar and liposomal surfaces with targeting moieties and the use of ultrasound as a triggering mechanism can help improve the selectivity and enable the spatiotemporal control of drug release from nanocarriers.

Polymeric Drug Delivery System Based on Pluronics for Cancer Treatment

Pluronic polymers (pluronics) are a unique class of synthetic triblock copolymers containing hydrophobic polypropylene oxide (PPO) and hydrophilic polyethylene oxide (PEO) arranged in the PEO-PPO-PEO manner. Due to their excellent biocompatibility and amphiphilic properties, pluronics are an ideal and promising biological material, which is widely used in drug delivery, disease diagnosis, and treatment, among other applications. Through self-assembly or in combination with other materials, pluronics can form nano carriers with different morphologies, representing a kind of multifunctional pharmaceutical excipients. In recent years, the utilization of pluronic-based multi-functional drug carriers in tumor treatment has become widespread, and various responsive drug carriers are designed according to the characteristics of the tumor microenvironment, resulting in major progress in tumor therapy. This review introduces the specific role of pluronic-based polymer drug delivery systems in tumor therapy, focusing on their physical and chemical properties as well as the design aspects of pluronic polymers. Finally, using newer literature reports, this review provides insights into the future potential and challenges posed by different pluronic-based polymer drug delivery systems in tumor therapy.

Dendrimer-based micelles with highly potent targeting to sites of active bone turnover for the treatment of bone metastasis

Bone-drug targeting therapies using nanoparticles based on targeting ligands remain challenging due to their uptake clearance at non-target sites such as the liver, kidney, and spleen. Furthermore, the distribution sites of nanoparticles in bones have not been fully investigated, thus halting the development of more effective bone metastasis treatment strategies. In this study, we developed nanoparticles self-assembled from cholesterol-terminated, polyethylene glycol-conjugated, aspartic acid (Asp)-modified polyamidoamine dendrimer (Asp-PAMAM-Micelles) with targeting to active bone turnover sites associated with bone metastasis pathogenesis. On analysis through whole-body single photon emission computed tomography/computed tomography (SPECT/CT) imaging, ¹¹¹In-Asp-PAMAM-Micelles showed high specificity to active bone turnover sites (especially the joints in the lower limbs, shoulder, and pelvis) after intravenous injection in mice. The lower limb bone uptake clearance for ¹¹¹In-Asp-PAMAM-Micelles encapsulating paclitaxel (PTX) was 3.5-fold higher than that for ¹¹¹In-unmodified PAMAM-Micelles (PTX). ³H-PTX encapsulated Asp-PAMAM-Micelles effectively accumulated in the lower limb bones in a similar manner as the ¹¹¹In-Asp-PAMAM-Micelles (PTX). In a bone metastatic tumor mouse model, the tumor growth in the lower limb bones was significantly inhibited by injection of Asp-PAMAM-Micelles (PTX) compared to unmodified PAMAM-Micelles (PTX). Our results demonstrate that Asp-PAMAM-Micelles are sophisticated drug delivery systems for highly potent targeting to active bone turnover sites.

Perspectives on: PEO-PPO-PEO Triblock Copolymers and their Biomedical Applications

Thermo-reversible polymeric gels represent an interesting class of materials that can be tailored for a wide range of applications. The triblock poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) based systems, PEO-PPO-PEO, show thermoreversible gelation around body temperature and, therefore, are particularly suitable for biomedical applications such as drug delivery, gene therapy and tissue engineering. The PEO-PPO-PEO tri-block copolymers have amphiphilic characteristics and self-assemble into micelles to form a variety of close packed structures. By varying the block composition (PEO/PPO ratio) and the molecular weight, it is possible to tailor the final properties of these systems to meet the specific application needs. In this report the thermodynamic basis of micellization of PEO-PPO-PEO systems is described. The factors influencing the micelles formation are discussed along with the methods used to investigate the micellization process and morphology as well as with the main applications of these systems in biomedical fields.

Complex Formation Between Lysozyme and Stabilized Micelles with a Mixed Poly(ethylene oxide)/Poly(acrylic acid) Shell

The electrostatic complexation between lysozyme and stabilized polymeric micelles (SPMs) with a poly(acrylic acid) (PAA) or a mixed poly(ethylene oxide)/poly(acrylic acid) (PEO/PAA) shell (SPMs with a mixed shell, SPMMS) and a temperature-responsive poly(propylene oxide) (PPO) core was investigated by means of dynamic, static, and electrophoretic light scattering. The SPMs and different types of SPMMS used resulted from the self-assembly of PAA-PPO-PAA triblock copolymer chains, or PAA-PPO-PAA and PEO-PPO-PEO triblock copolymer chain mixtures (with varying chain lengths and molar ratios) in aqueous solutions at pH 10 and the subsequent cross-linking of their PPO cores via loading and photo-cross-linking of pentaerythritol tetraacrylate (PETA). The solution behavior, structure and properties of the formed complexes at pH 7 and 0.01 M ionic strength, were studied as a function of the protein concentration in the solution (the concentration of the stabilized micelles was kept constant) or equivalently the ratio of the two components. The complexation process and properties of the complexes proved to be dependent on the protein concentration, while of particular interest was the effect of the structure of the shell of the SPMs on the stability/solubility of the complexes. Finally, the fluorescence and mid infrared spectroscopic investigation of the structure of the complexed protein showed that, although a small stretching of the protein molecules occurred in some cases, no protein denaturation takes place upon complexation.

Pluronic F127–chondroitin sulfate micelles prepared through a facile method for passive and active tumor targeting

Micelles based on Pluronic F127 and chondroitin sulfate with targeting properties were fabricated to specifically deliver DOX to tumors.

Self-Aggregation of Amphiphilic Dendrimer in Aqueous Solution: The Effect of Headgroup and Hydrocarbon Chain Length

The self-aggregation of amphiphilic dendrimers G1QPAMCm based on poly(amidoamine) PAMAM possessing the same hydrophilic group but differing in alkyl chain length in aqueous solution was investigated. Differences in the chemical structures lead to significant specificities in the aggregate building process. A variety of physicochemical parameters presented monotonous regularity with the increase in alkyl chain length in multibranched structure, as traditional amphiphilic molecules. A significant difference, however, existed in the morphology and the microenvironment of the microdomain of the aggregates, with G1QPAMCm with an alkyl chain length of 16 intending to form vesicles. To obtain supporting information about the aggregation mechanism, the thermodynamic parameters of micellization, the free Gibbs energy ΔGmic, and the entropy ΔSmic were derived subsequently, of which the relationship between the hydrophobic chain length and the thermodynamic properties indicated that the self-assembly process was jointly driven by enthalpy and entropy. Other than traditional surfactants, the contribution of enthalpy has not increased identically to the increase in hydrophobic interactions, which depends on the ratio of the alkyl chain length to the radius in the headgroup. Continuous increases in the hydrophobic chain length from 12 to 16 lead to the intracohesion of the alkyl chain involved in the process of self-assembly, weakening the hydrophobic interactions, and the increase in -ΔHmic, which offers an explanation of the formation of vesicular structures.

Ultrasonically triggered drug delivery: breaking the barrier

The adverse side-effects of chemotherapy can be minimized by delivering the therapeutics in time and space to only the desired target site. Ultrasound offers one fairly non-invasive method of accomplishing such precise delivery because its energy can disrupt nanosized containers that are designed to sequester the drug until the ultrasonic event. Such containers include micelles, liposomes and solid nanoparticles. Conventional micelles and liposomes are less acoustically sensitive to ultrasound because the strongest forces associated with ultrasound are generated by gas-liquid interfaces, which both of these conventional constructs lack. Acoustically activated carriers often incorporate a gas phase, either actively as preformed bubbles, or passively such as taking advantage of dissolved gasses that form bubbles upon insonation. Newer concepts include using liquids that form gas when insonated. This review focuses on the ultrasonically activated delivery of therapeutics from micelles, liposomes and solid particles. In vitro and in vivo results are summarized and discussed. Novel structural concepts from micelles and liposomes are presented. Mechanisms of ultrasonically activated release are discussed. The future of ultrasound in drug delivery is envisioned.

The use of ultrasound to release chemotherapeutic drugs from micelles and liposomes

Several drug delivery systems have been investigated to reduce the side effects of chemotherapy by encapsulating the therapeutic agent in a nanosized carrier until it reaches the tumor site. Many of these particles are designed to be responsive to the mechanical and thermal perturbations delivered by ultrasound. Once the nanoparticle reaches the desired location, ultrasound is applied to release the chemotherapy drug only in the vicinity of the targeted (cancer) site, thus avoiding any detrimental interaction with healthy cells in the body. Studies using liposomes and micelles have shown promising results in this area, as these nanoparticles with simple, yet effective structures, showed high efficiency as drug delivery vehicles both in vitro and in vivo. This article reviews the design and application of two novel nanosized chemotherapeutic carriers (i.e. micelles and liposomes) intended to be actuated by ultrasound.

Dual-frequency ultrasound activation of nanomicellar doxorubicin in targeted tumor chemotherapy

INTRODUCTION

This study investigated the therapeutic effect of dual-frequency sonication (3 MHz and 28 kHz) at low intensity levels in combination with micellar doxorubicin in the treatment of a tumor model of spontaneous breast adenocarcinoma in Balb/c mice.

METHODS

We used sonication frequencies 28 kHz and 3 MHz and their dual combinations in the progressive wave mode to enhance acoustic cavitation. Then, the antitumor effect of the simultaneous dual-frequency ultrasound (28 kHz and 3 MHz) at low intensity levels in combination with doxorubicin and micellar doxorubicin injection was investigated in a spontaneous model of breast adenocarcinoma in Balb/c mice. Sixty-three tumor-bearing mice were randomly divided into seven groups: control, sham, sonication with dual frequency, doxorubicin without sonication, doxorubicin with dual-frequency sonication, micellar doxorubicin without sonication, and micellar doxorubicin with dual-frequency sonication. The tumor volume change relative to the initial volume, tumor growth inhibition ratio, the required times for each tumor to reach two (T 2) and five (T 5) times its initial volume, and survival period were the tumor growth delay parameters which were calculated and recorded at various times after treatment.

RESULTS

The results of the combination of frequencies 28 kHz (0.04 W/cm(2)) and 3 MHz (2.00 W/cm(2)) showed remarkable enhancement of the cavitation activity compared with single-frequency sonication (P < 0.05). The micellar doxorubicin injection with sonication group showed a significant difference in the relative volume percent parameter compared with the other groups (P < 0.05). Additionally, the T 2 and T 5 times in the micellar doxorubicin with sonication group were significantly higher than in the other groups (P < 0.05). Also, the survival period of the mice in the micellar doxorubicin with sonication group was significantly longer than in the other groups (P < 0.05). These findings were verified histopathologically.

CONCLUSION

This study shows that simultaneous combined dual-frequency ultrasound sonication in continuous mode is effective in producing cavitation activity at low intensity. We conclude that dual-frequency sonication with micellar doxorubicin injection extends survival in a murine breast adenocarcinoma model.

Ultrasound-triggered Release from Micelles

Ultrasound is an ideal trigger for site-actuated drug delivery because it can be focused through the skin to internal targets without surgery. Thermal or mechanical energy can be delivered via tissue heating or bubble cavitation, respectively. Bubble cavitation, which concentrates energy that can trigger drug release from carriers, occurs more readily at low frequencies and at bubble resonant frequencies. Other mechanical and physical consequences of cavitation are reviewed. Micelles are nanosized molecular assemblies of amphiphilic molecules that spontaneously form in aqueous solution and possess a hydrophobic core capable of sequestering hydrophobic drugs. Micelles have traditionally been used to increase the solubility of hydrophobic therapeutics for oral and intravenous administration. For ultrasonic drug delivery, polymeric micelles containing polyethylene oxide blocks are preferred because they have longer circulation time in vivo. Passive delivery occurs when micelles accumulate in tumor tissues that have malformed capillaries with porous walls. In active delivery targeting ligands are attached to the micelles, which directs their binding to specific cells. Actuated delivery occurs when ultrasound causes drug release from micelles and is attributed to bubble cavitation since the amount released correlates with acoustic signatures of cavitation. The mechanisms of ultrasonic drug release are discussed, including the prevalent theory that gas bubble cavitation events create high shear stress and shock waves that transiently perturb the structure of the micelles and allow drug to escape from the hydrophobic core. Ultrasound also perturbs cell membranes, rendering them more permeable to drug uptake. Tumors in rats and mice have been successfully treated using low-frequency ultrasound and chemotherapeutics in polymeric micelles. Ultrasonically activated drug delivery has great clinical potential.

Temperature- and pH-sensitive Polymeric Micelles for Drug Encapsulation, Release and Targeting

More than 50% of the drugs in the market and 70% of the new candidates are poorly water soluble according to the Biopharmaceutic Classification System (BCS(. Poor aqueous solubility and physico-chemical stability of drugs in biological fluids remain key limitations in oral, parenteral and transdermal administration and contribute to an increase the drug attrition rate. Motivated by the outbreak of nanotechnology, different nanocarriers made of lipids and polymers have been designed and developed to address these limitations. Moreover, robust platforms were exploited to achieve the temporal and spatial release of drugs, thus constraining the systemic exposure to toxic agents and the appearance of severe adverse effects and improving the safety ratio. Owing to unique features such as (i( great chemical flexibility, (ii( capacity to host, solubilize and physico-chemically stabilize poorly water soluble drugs, (iii( ability to accumulate selectively in highly vascularized solid tumors and (iv( ability of single amphiphile molecules (unimers( to inhibit the activity of different pumps of the ATP-binding cassette superfamily (ABCs(, polymeric micelles have emerged as one of the most versatile nanotechnologies. Despite their diverse applications to improve the therapeutic outcomes, polymeric micelles remain clinically uncapitalized. The present chapter overviews the most recent applications of temperature- and pH-responsive polymeric micelles for the encapsulation, release and targeting of drugs and discusses the perspectives for these unique nanocarriers in the near future.

Polymeric micelles in anticancer therapy: targeting, imaging and triggered release

Micelles are colloidal particles with a size around 5-100 nm which are currently under investigation as carriers for hydrophobic drugs in anticancer therapy. Currently, five micellar formulations for anticancer therapy are under clinical evaluation, of which Genexol-PM has been FDA approved for use in patients with breast cancer. Micelle-based drug delivery, however, can be improved in different ways. Targeting ligands can be attached to the micelles which specifically recognize and bind to receptors overexpressed in tumor cells, and chelation or incorporation of imaging moieties enables tracking micelles in vivo for biodistribution studies. Moreover, pH-, thermo-, ultrasound-, or light-sensitive block copolymers allow for controlled micelle dissociation and triggered drug release. The combination of these approaches will further improve specificity and efficacy of micelle-based drug delivery and brings the development of a 'magic bullet' a major step forward.

Nanomedicinal strategies to treat multidrug-resistant tumors: current progress

Multidrug resistance (MDR) is a major impediment to the success of cancer chemotherapy. P-glycoprotein is an important and the best-known membrane transporter involved in MDR. Several strategies have been used to address MDR, especially P-glycoprotein-mediated drug resistance in tumors. However, clinical success has been limited, largely due to issues regarding lack of efficacy and/or safety. Nanoparticles have shown the ability to target tumors based on their unique physical and biological properties. To date, nanoparticles have been investigated primarily to address P-glycoprotein and the observed improved anticancer efficacy suggests that nanomedicinal strategies provide a new opportunity to overcome MDR. This article focuses on nanotechnology-based formulations and current nanomedicine approaches to address MDR in tumors and discusses the proposed mechanisms of action.

Distribution of doxorubicin in rats undergoing ultrasonic drug delivery

Ultrasound (US) increases efficacy of drugs delivered from micelles, but the pharmacokinetics have not been studied previously. In this study, US was used to deliver doxorubicin (Dox) sequestered in micelles in an in vivo rat model with bilateral leg tumors. One of two frequencies with identical mechanical index and intensity was delivered for 15 min to one tumor immediately after systemic injection of micellar Dox. Pharmacokinetics in myocardium, liver, skeletal muscle, and tumors were measured for 1 week. When applied in combination with micellar Dox, the ultrasoincated tumor had higher Dox concentrations at 30 min, compared to bilateral noninsonated controls. Initially, concentrations were highest in heart and liver, but within 24 h they decreased significantly. From 24 h to 7 days, concentrations remained highest in tumors, regardless of whether they received US or not. Comparison of insonated and noninsonated tumors showed 50% more Dox in the insonated tumor at 30 min posttreatment. Four weekly treatment produced additional Dox accumulation in the myocardium but not in liver, skeletal leg muscle, or tumors compared to single treatment. Controls showed that neither US nor the empty carrier impacted tumor growth. This study shows that US causes more release of drug at the targeted tumor.

Degradation kinetics of stabilized Pluronic micelles under the action of ultrasound

The majority of research in the area of acoustically-activated drug delivery from stabilized micelles has been focused on the rapid release of chemotherapy drugs from the core of such nano-carriers. Previous publications have shown that low-frequency ultrasound is able to release approximately 2% of Doxorubicin (Dox) from the core of Pluronic P105 micelles stabilized using a cross-linked network of N,N-diethylacrylamide (NanoDeliv) within 2 s of applying 70-kHz ultrasound. Here we use a custom-made ultrasound exposure chamber with fluorescence detection to measure the long-term fluorescence emissions of Dox from the NanoDeliv after 2 h of exposure to two ultrasound frequencies, 70 and 476 kHz, at a mechanical index of 0.9. Fluorescence measurements are then used to deduce the degradation kinetics of stabilized Pluronic micelles during 24 h following exposure to ultrasound. Results show that ultrasound does disrupt the covalent network of the stabilized micelles, but the time constant of network degradation is very long compared to the time constant pertaining to drug release from micelles. Experiments also show no significant difference in degradation rates when employing the two frequencies in question at the same mechanical index.

Ultrasonic-activated micellar drug delivery for cancer treatment

The use of nanoparticles and ultrasound in medicine continues to evolve. Great strides have been made in the areas of producing micelles, nanoemulsions, and solid nanoparticles that can be used in drug delivery. An effective nanocarrier allows for the delivery of a high concentration of potent medications to targeted tissue while minimizing the side effect of the agent to the rest of the body. Polymeric micelles have been shown to encapsulate therapeutic agents and maintain their structural integrity at lower concentrations. Ultrasound is currently being used in drug delivery as well as diagnostics, and has many advantages that elevate its importance in drug delivery. The technique is noninvasive, thus no surgery is needed; the ultrasonic waves can be easily controlled by advanced electronic technology so that they can be focused on the desired target volume. Additionally, the physics of ultrasound are widely used and well understood; thus ultrasonic application can be tailored towards a particular drug delivery system. In this article, we review the recent progress made in research that utilizes both polymeric micelles and ultrasonic power in drug delivery.

Role of frequency and mechanical index in ultrasonic-enhanced chemotherapy in rats

PURPOSE

The therapeutic effect of ultrasound and micellar-encapsulated doxorubicin was studied in vivo using a tumor-bearing rat model with emphasis on how tumor growth rate is affected by ultrasonic parameters such as frequency and intensity.

METHODS

This study employed ultrasound of two different frequencies (20, 476 kHz) and two pulse intensities, but identical mechanical indices and temporal average intensities. Ultrasound was applied weekly for 15 min to one of two bilateral leg tumors (DHD/K12/TRb colorectal epithelial cell line) in the rat model immediately after intravenous injection of micelle-encapsulated doxorubicin. This therapy was applied weekly for 6 weeks.

RESULTS

Results showed that tumors treated with drug and ultrasound displayed, on average, slower growth rates than non-insonated tumors (P = 0.0047). However, comparison between tumors that received 20 or 476-kHz ultrasound treatments showed no statistical difference (P = 0.9275) in tumor growth rate.

CONCLUSION

Application of ultrasound in combination with drug therapy was effective in reducing tumor growth rate, irrespective of which frequency was employed.

Template-assisted synthesis of nanogels from Pluronic-modified poly(acrylic acid)

A series of novel polymeric nanogels with core-shell morphology was developed. Block ionomer complexes of comb-graft poly(ethylene oxide)-b-poly(polypropylene oxide)-b-poly(ethylene oxide)-g-poly(acrylic acid) copolymers (Pluronic-PAA) and divalent metal cations were utilized as micellar templates for the synthesis of nanogels with sizes ranging from 100 to 200 nm in diameter. The Pluronic-PAA nanogels were confirmed to possess ionic cross-linked PAA cores and flexible hydrophilic shells from the Pluronic copolymer chains. The ionic character of the core provided for pH-dependent swelling/collapse behavior of the nanogels. These prepared nanogels are expected to be of utility as carriers for charged therapeutic or diagnostic agents.

Micelles and nanoparticles for ultrasonic drug and gene delivery

Drug delivery research employing micelles and nanoparticles has expanded in recent years. Of particular interest is the use of these nanovehicles that deliver high concentrations of cytotoxic drugs to diseased tissues selectively, thus reducing the agent's side effects on the rest of the body. Ultrasound, traditionally used in diagnostic medicine, is finding a place in drug delivery in connection with these nanoparticles. In addition to their non-invasive nature and the fact that they can be focused on targeted tissues, acoustic waves have been credited with releasing pharmacological agents from nanocarriers, as well as rendering cell membranes more permeable. In this article, we summarize new technologies that combine the use of nanoparticles with acoustic power both in drug and gene delivery. Ultrasonic drug delivery from micelles usually employs polyether block copolymers and has been found effective in vivo for treating tumors. Ultrasound releases drug from micelles, most probably via shear stress and shock waves from the collapse of cavitation bubbles. Liquid emulsions and solid nanoparticles are used with ultrasound to deliver genes in vitro and in vivo. The small packaging allows nanoparticles to extravasate into tumor tissues. Ultrasonic drug and gene delivery from nanocarriers has tremendous potential because of the wide variety of drugs and genes that could be delivered to targeted tissues by fairly non-invasive means.

Spectroscopic investigations into degradation of polymer membranes for fuel cells applications

The research was focused on synthesis of proton conductive, easily degradable polymer membranes, which can be used as a model system to verify the efficiency of transition metal ions (TMI) in prevention of polymer degradation. Two polymers composed of 2-hydroxyethyl methacrylate (HEMA), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), and styrenesulfonic acid (SS) were synthesized. The copolymers were characterized by gel permeation chromatography (GPC), elementary analysis, and FTIR and fluorescence spectroscopies. The results allowed determination of weight-average molecular weight and the copolymer composition. The protons of sulfonic groups were substituted by paramagnetic transition metal ions of various spin states (Cr(3+), S=3/2 and Mn(2+), S=5/2) with the loading varying from 0.5 up to 10 mol%. The effectiveness of spin catalysis was checked by EPR. The results obtained indicate enhancement of polymer stability in the presence of Mn(2+).

Polymeric micelles for drug targeting

Polymeric micelles are nano-delivery systems formed through self-assembly of amphiphilic block copolymers in an aqueous environment. The nanoscopic dimension, stealth properties induced by the hydrophilic polymeric brush on the micellar surface, capacity for stabilized encapsulation of hydrophobic drugs offered by the hydrophobic and rigid micellar core, and finally a possibility for the chemical manipulation of the core/shell structure have made polymeric micelles one of the most promising carriers for drug targeting. To date, three generations of polymeric micellar delivery systems, i.e. polymeric micelles for passive, active and multifunctional drug targeting, have arisen from research efforts, with each subsequent generation displaying greater specificity for the diseased tissue and/or targeting efficiency. The present manuscript aims to review the research efforts made for the development of each generation and provide an assessment on the overall success of polymeric micellar delivery system in drug targeting. The emphasis is placed on the design and development of ligand modified, stimuli responsive and multifunctional polymeric micelles for drug targeting.

Poly(ethylene oxide)-poly(propylene oxide) block copolymer micelles as drug delivery agents: improved hydrosolubility, stability and bioavailability of drugs

The low solubility in biological fluids displayed by about 50% of the drugs still remains the main limitation in oral, parenteral, and transdermal administration. Among the existing strategies to overcome these drawbacks, inclusion of hydrophobic drugs into polymeric micelles is one of the most attractive alternatives. Amphiphilic poly(ethylene oxide)-poly(propylene oxide) block copolymers are thermoresponsive materials that display unique aggregation properties in aqueous medium. Due to their ability to form stable micellar systems in water, these materials are broadly studied as hydrosolubilizers for poorly water-soluble drugs. The present review provides a concise description of the most important applications of PEO-PPO-based copolymers in the Pharmaceutical Technology field as means for attaining improved solubility, stability, release, and bioavailability of drugs.

Functionalized micellar systems for cancer targeted drug delivery

Polymer micelles are rapidly becoming a powerful nanomedicine platform for cancer therapeutic applications due to their small size (10-100 nm), in vivo stability, ability to solubilize water insoluble anticancer drugs, and prolonged blood circulation times. Recent data from clinical trials with three micelle formulations have highlighted these and other pharmacokinetic advantages with reduced systemic toxicity and patient morbidity compared to conventional drug formulation. While the initial anti-tumor efficacy of these systems seems promising, a strong research impetus has been placed on micelle functionalization in order to achieve tumor targeting and site-specific drug release, with the hope of reaching a more pronounced tumor response. Hence, the purpose of this review is to draw attention to the new developments of multi-functional polymer micelles for cancer therapy with special focus on tumor targeting and controlled drug release strategies.

Further investigation of the mechanism of Doxorubicin release from P105 micelles using kinetic models

The kinetics of the release of Doxorubicin from Pluronic P105 micelles during ultrasonication and its subsequent re-encapsulation upon cessation of insonation were investigated. Four mechanisms are proposed to explain the acoustically-triggered Doxorubicin (Dox) release and re-encapsulation from Pluronic P105 micelles. The four mechanisms are: micelle destruction; destruction of cavitating nuclei; reassembly of micelles, and the re-encapsulation of Dox. The first mechanism, the destruction of micelles during insonation, causes the release of Dox into solution. The micelles are destroyed because of cavitation events produced by collapsing nuclei, or bubbles in the insonated solution. The second mechanism, the slow destruction of cavitating nuclei, results in a slow partial recovery phase, when a small amount of Dox is re-encapsulated. The third and fourth mechanisms, the reassembly of micelles and the re-encapsulatin of Dox, are independent of ultrasound. These two mechanism are responsible for maintaining the drug release at a partial level, and for recovery after insonation ceases. A normal distribution was used to describe micellar size. Parameters for the model were determined based upon the best observed fit to experimental data. The resulting model provides a good approximation to experimental data for the release of Dox from Pluronic P105 micelles.

Shell-crosslinked Pluronic L121 micelles as a drug delivery vehicle

Pluronic block copolymers (PBCs) have been shown to reverse multidrug resistance (MDR) by inhibiting the P-glycoprotein (P-gp) pump in cancer cells. One of the problems encountered with the use of PBCs is that the micelles disassociate at low concentrations. The study focused on the stabilization of PBC L121 micelles by the formation of crosslinks within their outer shells. To form crosslinks, the two terminal alcohols on L121 were first chemically converted into aldehydes (L121-CHO) using the Dess-Martin periodinane. Diamine compounds were then used to bridge the converted aldehyde termini on L121-CHO via conjugated Schiff bases. After crosslinking, the morphology of the L121 micelles remained spherical in shape and the mean particle sizes of the micelles before and after crosslinking were comparable (100nm). After exposure of MDR KBv cells to free rhodamine-123 (R123), the accumulation of R123 in cells was limited due to the function of P-gp. In contrast, crosslinking of L121 micelles within their outer shells significantly reduced their critical micelle concentration and greatly enhanced their stability, while maintaining their ability to inhibit P-gp function in resistant cells. The results indicated that the L121 micelles with shell crosslinks may be useful as a drug delivery vehicle for cancer chemotherapy.

Polymer micelles with cross-linked ionic cores for delivery of anticancer drugs

This work reports the design of polymer micelles with cross-linked ionic cores that display high stability. Block ionomer complexes of poly(ethylene oxide)-b-poly(methacrylic acid) copolymer and divalent metal cations were utilized as micellar templates for the synthesis of the cross-linked micelles. Such micelles represent hydrophilic nanospheres of core-shell morphology. The core comprises a network of the cross-linked polyanions, which is surrounded by the shell of hydrophilic PEO chains. The ionic character of the core provided for pH-dependent swelling/collapse behavior of the nanogels. Cisplatin, a potent chemotherapeutic agent, was incorporated into the ionic core of the micelles with remarkably high efficiency (22% w/w). The drug-loaded micelles were stable in aqueous dispersions exhibiting no aggregation or precipitation for a prolonged period of time. Slow release of platinum complexes was observed in sustained manner from the cisplatin-loaded cross-linked micelles in physiological saline. In vitro studies using human A2780 ovarian carcinoma cells demonstrated that the cross-linked micelles rapidly internalized and delivered cisplatin into cells. These results indicated that polymer micelles with cross-linked ionic cores are promising for further fundamental material studies and practical applications as drug delivery carriers.

A polymeric micelle system with a hydrolysable segment for drug delivery

A potential anti-cancer drug-delivery polymeric micelle system with an in vitro degradation half-life of about 48 h that releases its drug upon application of ultrasound was synthesized. This vehicle was composed of an amphiphilic co-polymer, poly(ethylene oxide)-b-poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate-lactate(n)). The degree of polymerization of the lactate side group, n, was 0, 3 or 5. The molar ratio of NIPAAm to HEMA-lactate(n) to PEO in polymerization was optimized to produce an in vitro polymeric micelle half-life of about 48 h at 40 degrees C. 1,6-Diphenyl-1,3,5-hexatriene (DPH) was used as a fluorescent probe to study the hydrophobicity of the cores of the polymeric micelles. The results showed that the cores of the polymeric micelles were hydrophobic enough to sequester DPH and the anti-cancer drug doxorubicin (Dox). Dox was encapsulated into the polymeric micelles having a molar feed ratio of NIPAAm to HEMA-lactate3 to PEO equal to 20:5:1; this drug was released upon the application of low-frequency ultrasound. The Dox release was about 2% at room temperature and 4% at body temperature, and the drug returned to the polymeric micelles when insonation ceased.

Poly(ethylene oxide)-b-poly(N-isopropylacrylamide) nanoparticles with cross-linked cores as drug carriers

Micelle-like nanoparticles that could be used as drug-delivery carriers were developed. The unique feature of these nanoparticles was that the core of poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PEO-b-PNIPAAm) micelle was lightly cross-linked with a biodegradable cross-linker, N,N-bis(acryloyl)cystamine (BAC). The nanoparticles were characterized by dynamic light scattering and fluorescence measurements. When the BAC content ranged from 0.75 wt% to 0.2 wt% of the mass of NIPAAm, the diameters of the nanoparticles were less than 150 nm. The anti-cancer drug doxorubicin (Dox) and 1,6-diphenyl-1,3,5-hexatriene (DPH) were used as fluorescent probes to study the hydrophobicity of the cores of the nanoparticles; the results showed that the cores of the nanoparticles were hydrophobic enough to sequester Dox and DPH. The nanoparticles with 0.5 wt% BAC stored at room temperature were stable up to 2 weeks, even at dilute concentrations. The degradation of BAC by reducing agent beta-mercaptoethanol was investigated, and the nanoparticles were not detectable 14 days after adding beta-mercaptoethanol.

Ultrasonic drug delivery--a general review

Ultrasound has an ever-increasing role in the delivery of therapeutic agents, including genetic material, protein and chemotherapeutic agents. Cavitating gas bodies, such as microbubbles, are the mediators through which the energy of relatively non-interactive pressure waves is concentrated to produce forces that permeabilise cell membranes and disrupt the vesicles that carry drugs. Thus, the presence of microbubbles enormously enhances ultrasonic delivery of genetic material, proteins and smaller chemical agents. Numerous reports show that the most efficient delivery of genetic material occurs in the presence of cavitating microbubbles. Attaching the DNA directly to the microbubbles, or to gas-containing liposomes, enhances gene uptake even further. Ultrasonic-enhanced gene delivery has been studied in various tissues, including cardiac, vascular, skeletal muscle, tumour and even fetal tissue. Ultrasonic-assisted delivery of proteins has found most application in transdermal transport of insulin. Cavitation events reversibly disrupt the structure of the stratus corneum to allow transport of these large molecules. Other hormones and small proteins could also be delivered transdermally. Small chemotherapeutic molecules are delivered in research settings from micelles and liposomes exposed to ultrasound. Cavitation appears to play two roles: it disrupts the structure of the carrier vesicle and releases the drug; and makes cell membranes and capillaries more permeable to drugs. There remains a need to better understand the physics of cavitation of microbubbles and the impact that such cavitation has on cells and drug-carrying vesicles.