Incorporation and release behavior of amitriptylene in core–shell–corona type triblock copolymer micelles

A Critical Sojourn of Polymeric Micelles: Technological Concepts, Recent Advances, and Future Prospects

Poorly soluble drug molecules/phytoconstituents are still a growing concern for biopharmaceutical delivery in the body. Polymeric micelles are the amphiphilic block copolymers and have been widely investigated as targeted nanocarriers for the treatment of various ailments. The versatility of nanocarriers is the self-assembling properties in the aqueous medium and forms a stable isotropic system in vivo. The hydrophobic core-hydrophilic shell configuration of the polymers used to the mixed micelles makes easy encapsulation of hydrophobic and hydrophilic drugs into the core. Polymeric micelles can also be combined with targeting ligands that increase their uptake by specific cells, decreasing off-target effects, and provide enhanced therapeutic effect. In the present review, we primarily focused on a critical appraisal of Polymeric micelles along with the method of preparation, mechanism of micelle formulation, and the ongoing formulations under clinical trials. In addition, the biological applications of this isotropic nanocarrier have been duly presented in each route of administration along with suitable case studies.

Effect of temperature and pH on the encapsulation and release of β-carotene from octenylsuccinated oat β-glucan micelles

Effect and working mechanism of temperature and pH on encapsulation and release of β-carotene from octenylsuccinated-oat-β-glucan-micelles (OSβG-Ms) were investigated. The stability and solubility of β-carotene, and changes in surface hydrophilicity, core hydrophobicity, and size of β-carotene-loaded-OSβG-Ms were determined. When exposed to temperature (25-45 °C) and pH (4.5-8.5), β-carotene solubilization changed in parabolic manners. Size and absolute zeta-potential of β-carotene-loaded-OSβG-Ms decreased with temperature, while they gave parabolic changing patterns with pH. Those results were ascribed to their hydrophilicity, hydrophobicity, and core/shell compactness via regulating molecule mobility, orientation, and interactions by temperature/pH. The higher temperature concluded with higher β-carotene release, while a U-shaped release profile was observed with pH. Besides its diffusion, erosion-induced shrinking and collapsing of OSβG-Ms favored β-carotene release at pH 1.2-4.5, which was replaced by swelling-induced structural-relaxation at pH 6.8-8.5. The results were favourable in controlling the behavior of β-carotene-loaded-OSβG-Ms by selectively applying environmental parameters.

Noncovalent Complexation of Amphotericin B with Poly(β-Amino Ester) Derivates for Treatment of C. Neoformans Infection

Our goal was to improve treatment outcomes for C. neoformans infection by designing nanocarriers that enhance drug-encapsulating capacity and stability. Thus, a noncovalent complex of methoxy poly(ethylene glycol)-poly(lactide)-poly(β-amino ester) (MPEG-PLA-PAE) and amphotericin B (AMB) was developed and characterized. The MPEG-PLA-PAE copolymer was synthesized by a Michael-type addition reaction; the copolymer was then used to prepare the AMB-loaded nanocomplex. AMB was in a highly aggregated state within complex cores. A high encapsulation efficiency (>90%) and stability of the AMB-loaded nanocomplex were obtained via electrostatic interaction between AMB and PAE blocks. This nanocomplex retained drug activity against C. neoformans in vitro. Compared with micellar AMB, the AMB nanocomplex was more efficient in terms of reducing C. neoformans burden in lungs, liver, and spleen, based on its improved biodistribution. The AMB/MPEG-PLA-PAE complex with enhanced drug-loading capacity and stability can serve as a platform for effective treatment of C. neoformans infection.

The design strategy of intelligent biomedical magnesium with controlled-release platform

Magnesium has a very promising adhibition in biomedical field for its excellent mechanical and biodegradable properties, however, the intelligent applications of biomedical magnesium developed difficultly due to its characteristic degradation. A intelligent biomedical magnesium was constructed on magnesium (Mg) surface by incorporating polydopamine (PD) and mechanized hollow mesoporous silica nanoparticles (HMSs) as smart delivery platform nanocontainers. The supramolecular nanovalves of mechanized HMSs consisted of alginate/chitosan multilayers by self-assembly, which are capable of entrapping rhodamine 6G in the mesopores and can release the cargo under the chemical environment of alkali or Mg iron stimuli that correspond to the degradation of biomedical Mg. The alkali/Mg²⁺ dual stimuli-responsive release property of the HMSs endows the biodegradable Mg with controlled release potential. The well-designed smart delivery nanocontainers were combined with polydopamine deposited on Mg for excellent adhesion properties and positively charged amino group of PD. Furthermore, when the biomedical Mg with these mechanized HMSs was degraded in the simulated body environment, the alkali/Mg²⁺-triggered release of cargos from this smart delivery platform could bring a more functional application.

Advancing the delivery of anticancer drugs: Conjugated polymer/triterpenoid composite

Exemplifying the synergy of anticancer properties of triterpenoids and ion retention qualities of conjugated polymers, we propose a conducting matrix to be a reservoir of anticancer compounds. In this study, poly(3,4-ethylenedioxythiophene), PEDOT, based matrix for electrically triggered and local delivery of the ionic form of anticancer drug, oleanolic acid (HOL), has been investigated. An initial, one-step fabrication procedure has been proposed, providing layers exhibiting good drug release properties and biological activity. Investigation of obtained systems and implementation of modifications revealed another route of fabrication. This procedure was found to yield layers possessing a significantly greater storage capacity of OL(-), as evidenced by the 52% increase in the drug concentrations attainable through electro-assisted release. Examination of the biological activity of immobilised and released OL(-) molecules proved that electrochemical treatment has negligible impact on the anticancer properties of OL(-), particularly when employing the three-step procedure, in which the range of applied potentials is limited. PEDOT/OL(-) composite has been demonstrated to be a robust and cost-effective material for controlled drug delivery.

Asymmetric block copolymers for supramolecular templating of inorganic nanospace materials

This review focuses on polymeric micelles consisting of asymmetric block copolymers as designed templates for several inorganic nanospace materials with a wide variety of compositions. The presence of chemically distinct domains of asymmetric triblock and diblock copolymers provide self-assemblies with more diverse morphological and functional features than those constructed by EOn POm EOn type symmetric triblock copolymers, thereby affording well-designed nanospace materials. This strategy can produce unprecedented nanospace materials, which are very difficult to prepare through other conventional organic templating approaches. Here, the recent development on the synthesis of inorganic nanospace materials are mainly focused on, such as hollow spheres, tubes, and porous oxides, using asymmetric triblock copolymers.

Rifampicin-loaded ‘flower-like’ polymeric micelles for enhanced oral bioavailability in an extemporaneous liquid fixed-dose combination with isoniazid

Background: Coadministration of rifampicin (RIF)/isoniazid (INH) is clinically recommended to improve the treatment of tuberculosis. Under gastric conditions, RIF undergoes fast hydrolysis (a pathway hastened by INH) and oral bioavailability loss. Aim: We aimed to assess the chemical stabilization and the oral pharmacokinetics of RIF nanoencapsulated within poly(ε-caprolactone)-b-PEG-b-poly(ε-caprolactone) ‘flower-like’ polymeric micelles. Materials & methods: The chemical stability of RIF was evaluated in vitro under acid conditions with and without INH, and the oral pharmacokinetics of RIF-loaded micelles in rats was compared with those of a suspension coded by the US Pharmacopeia. Results: Nanoencapsulation decreased the degradation rate of RIF with respect to the free drug. Moreover, in vivo data showed a statistically significant increase of RIF oral bioavailability (up to 3.3-times) with respect to the free drug in the presence of INH. Conclusion: Overall results highlight the potential of this nanotechnology platform to develop an extemporaneous liquid RIF/INH fixed-dose combination suitable for pediatric administration.

Original submitted 6 April 2013; Revised submitted 7 August 2013

pH-responsive polymeric micelles with core-shell-corona architectures as intracellular anti-cancer drug carriers

Polymeric micelles with core-shell-corona nanoarchitecture were designed for intracellular therapeutic anti-cancer drug carriers. Poly(styrene-b-acrylic acid-b-ethylene glycol) (PS-b-PAA-b-PEG) asymmetric triblock copolymer underwent self-assembly in aqueous solution to form spherical micelles with hydrophobic PS core, anionic PAA shell and hydrophilic PEG corona. The anti-cancer drug (doxorubicin, DOX) was successfully incorporated into the polymeric micelles. The in vitro release experiment confirmed that the release of DOX from the micelles was inhibited at pH 7.4. In contrast, an accelerated release of DOX was observed at mildly acidic conditions such as pH 4.5. The excellent biocompatibility of our PS-b-PAA-b-PEG-based micelles made the synthesized nano-carrier best suited for the delivery of anti-cancer drugs.

pH-sensitive micelles self-assembled from multi-arm star triblock co-polymers poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) for controlled anticancer drug delivery

A series of amphiphilic 4- and 6-armed star triblock co-polymers poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) (4/6AS-PCL-b-PDEAEMA-b-PPEGMA) were developed by a combination of ring opening polymerization and continuous activators regenerated by electron transfer atom transfer radical polymerization. The critical micelle concentration values of the star co-polymers in aqueous solution were extremely low (2.2-4.0mgl(-1)), depending on the architecture of the co-polymers. The self-assembled blank and doxorubicin (DOX)-loaded three layer micelles were spherical in shape with an average size of 60-220nm determined by scanning electron microscopy and dynamic light scattering. The in vitro release behavior of DOX from the three layer micelles exhibited pH-dependent properties. The DOX release rate was significantly accelerated by decreasing the pH from 7.4 to 5.0, due to swelling of the micelles at lower pH values caused by the protonation of tertiary amine groups in DEAEMA in the middle layer of the micelles. The in vitro cytotoxicity of DOX-loaded micelles to HepG2 cells suggested that the 4/6AS-PCL-b-PDEAEMA-b-PPEGMA micelles could provide equivalent or even enhanced anticancer activity and bioavailability of DOX and thus a lower dosage is sufficient for the same therapeutic efficacy. The results demonstrate that the pH-sensitive multilayer micelles could have great potential application in delivering hydrophobic anticancer drugs for improved cancer therapy.

β-Cyclodextrin hydrogels for the ocular release of antibacterial thiosemicarbazones

Two types of hydrophilic networks with conjugated beta-cyclodextrin (β-CD) were developed with the aim of engineering useful platforms for the localized release of an antimicrobial 5,6-dimethoxy-1-indanone N4-allyl thiosemicarbazone (TSC) in the eye and its potential application in ophthalmic diseases. Poly(2-hydroxyethyl methacrylate) soft contact lenses (SCLs) displaying β-CD, namely pHEMA-co-β-CD, and super-hydrophilic hydrogels (SHHs) of directly cross-linked hydroxypropyl-β-CD were synthesized and characterized regarding their structure (ATR/FT-IR), drug loading capacity, swelling and in vitro release in artificial lacrimal fluid. Incorporation of TSC to the networks was carried out both during polymerization (DP method) and after synthesis (PP method). The first method led to similar drug loads in all the hydrogels, with minor drug loss during the washing steps to remove unreacted monomers, while the second method evidenced the influence of structural parameters on the loading efficiency (proportion of CD units, mesh size, swelling degree). Both systems provided a controlled TSC release for at least two weeks, TSC concentrations (up to 4000μg/g dry hydrogel) being within an optimal therapeutic window for the antimicrobial ocular treatment. Microbiological tests against P. aeruginosa and S. aureus confirmed the ability of TSC-loaded pHEMA-co-β-CD network to inhibit bacterial growth.

Poly(ε-caprolactone), Eudragit® RS 100 and poly(ε-caprolactone)/Eudragit® RS 100 blend submicron particles for the sustained release of the antiretroviral efavirenz

The design of simple and scalable drug delivery systems to target the central nervous system (CNS) could represent a breakthrough in the addressment of the HIV-associated neuropathogenesis. The intranasal (i.n.) route represents a minimally invasive strategy to surpass the blood-brain barrier, though it demands the use of appropriate nanocarriers bearing high drug payloads and displaying sufficiently long residence time. The present work explored the development of submicron particles made of poly(ε-caprolactone) (PCL), Eudragit(®) RS 100 (RS a copolymer of ethylacrylate, methylmethacrylate and methacrylic acid esterified with quaternary ammonium groups) and their blends, loaded with the first-choice antiretroviral efavirenz (EFV) as an approach to fine tune the particle size and the release kinetics. Particles displaying hydrodynamic diameters between 90 and 530 nm were obtained by two methods: nanoprecipitation and emulsion/solvent diffusion/evaporation. In general, the former resulted in smaller particles and narrower size distributions. The encapsulation efficiency was greater than 94%, the drug weight content approximately 10% and the yield in the 72.5-90.0% range. The highly positive surface (>+30 mV) rendered the suspensions physically stable for more than one month. In vitro release assays indicated that the incorporation of the poly(methacrylate) into the composition reduced the burst effect and slowed the release rate down with respect to pure poly(ε-caprolactone) particles. The analysis of the release profile indicated that, in all cases, the kinetics adjusted well to the Higuchi model with R(adj)(2) values >0.9779. These findings suggested that the release was mainly controlled by diffusion. In addition, when data were analyzed by the Korsmeyer-Peppas model, n values were in the 0.520-0.587 range, indicating that the drug release was accomplished by the combination of two phenomena: diffusion and polymer chain relaxation. Based on ATR/FT-IR analysis that investigated drug/polymer matrix interactions, the potential role of the hydrophobic interactions of C-F groups of EFV with carbonyl groups in the backbone of PCL and poly(methacrylate) could be ruled out. The developed EFV-loaded particles appear as a useful platform to investigate the intranasal administration to increase the bioavailability in the CNS.