Stimuli-responsive LbL capsules and nanoshells for drug delivery

Controlled enzyme-catalyzed degradation of polymeric capsules templated on CaCO₃: influence of the number of LbL layers, conditions of degradation, and disassembly of multicompartments

Enzyme-catalyzed degradation of CaCO₃-templated capsules is presented. We investigate a) biodegradable, b) mixed biodegradable/synthetic, and c) multicompartment polyelectrolyte multilayer capsules with different numbers of polymer layers. Using confocal laser scanning microscopy we observed the kinetics of the non-specific protease Pronase-induced degradation of capsules is slowed down on the order of hours by either increasing the number of layers in the wall of biodegradable capsules, or by inserting synthetic polyelectrolyte multilayers into the shell comprised of biodegradable polymers. The degradation rate increases with the concentration of Pronase. Controlled detachment of subcompartments of multicompartment capsules, with potential for intracellular delivery or in-vivo applications, is also shown.

Layer-by-layer assembled multilayers of polyethylenimine-stabilized platinum nanoparticles and PEDOT:PSS as anodes for the methanol oxidation reaction

Polyethylenimine-capped platinum nanoparticles (PEI-capped Pt NPs) are synthesized by photoreduction and qualified as a component for electrostatic layer-by-layer assembly and subsequent electrocatalysis. The PEI-capped Pt NPs are characterized for size and charge using scanning force microscopy, transmission electron microscopy, dynamic light scattering and zetapotential. Well-defined multilayers are produced via thin film electrostatic assembly of PEI-capped Pt NPs with the conducting polymer: poly(3,4-ethylenedioxythiophene):poly(p-styrenesulfonate) [(PEDOT:PSS)(-)Na(+)]. The composite thin films are subsequently characterized by ultraviolet-visible spectroscopy, scanning force microscopy, inductively coupled plasma mass spectroscopy and thermogravimetric analysis. The layer-by-layer deposition process was found to proceed in a controlled manner which permits the fabrication of stable and uniform multilayer thin films. [PEI-capped Pt NPs/(PEDOT:PSS)] multilayers were found to be an active catalyst coating for the oxidation of methanol and a 20 bilayer film proceeds with a stable level of catalyst activity for over 1000 oxidation cycles.

Double-walled hollow polymeric microspheres with independent pH and temperature dual-responsive and magnetic-targeting function from onion-shaped core-shell structures

The magnetic-targeting stimuli-responsive hollow polymeric microspheres show unique performance as the intelligent carriers for the site specific controlled delivery of drugs or genes. In the work, the well-defied dual-responsive double-walled hollow microspheres with movable magnetic cores were prepared from the penta-layer onion-shaped core-shell microspheres. Their double-walled shells were independent, with the pH-responsive crosslinked poly(methacrylic acid) (PMAA) layer as the inner shell and the temperature responsive crosslinked poly(N-isopropylacrylamide) (PNIPAM) layer as the outer shell. The combination of the pH and temperature dual-responsive and the magnetic-targeting function make the hollow microspheres to be the most promising intelligent carriers in the biomedical fields.

Biomimetic delivery with micro- and nanoparticles

The nascent field of biomimetic delivery with micro- and nanoparticles (MNP) has advanced considerably in recent years. Drawing inspiration from the ways that cells communicate in the body, several different modes of "delivery" (i.e., temporospatial presentation of biological signals) have been investigated in a number of therapeutic contexts. In particular, this review focuses on (1) controlled release formulations that deliver natural soluble factors with physiologically relevant temporal context, (2) presentation of surface-bound ligands to cells, with spatial organization of ligands ranging from isotropic to dynamically anisotropic, and (3) physical properties of particles, including size, shape and mechanical stiffness, which mimic those of natural cells. Importantly, the context provided by multimodal, or multifactor delivery represents a key element of most biomimetic MNP systems, a concept illustrated by an analogy to human interpersonal communication. Regulatory implications of increasingly sophisticated and "cell-like" biomimetic MNP systems are also discussed.

UV-cross-linkable multilayer microcapsules made of weak polyelectrolytes

Microcapsules composed of weak polyelectrolytes modified with UV-responsive benzophenone (BP) groups were fabricated by the layer-by-layer (LbL) technique. Being exposed to UV lights, capsules shrunk in the time course of minutes at irradiation intensity of 5 mW/cm(2). The shrinkage adjusted the capsule permeability, providing a novel way to encapsulate fluorescence-labeled dextran molecules without heating. Cross-linking within the capsule shells based on hydrogen abstraction via excited benzophenone units by UV showed a reliable and swift approach to tighten and stabilize the capsule shell without losing the pH-responsive properties of the weak polyelectrolyte multilayers.

Revolutionizing drug delivery through biodegradable multilayered particles

Modern drug discovery technologies are discovering more and more potent therapeutic agents with narrow therapeutic windows, thus necessitating the improvement of current particulate drug delivery systems. Conventional single-layered polymeric particles have limited control over drug release profiles, including burst release, the inability to provide zero-order, pulsatile, time-delayed release and controlled release of multiple drugs. In an attempt to better control drug release kinetics, the development of multilayered microparticles has been introduced. In this review, we give an overview of the fabrication and characterization techniques of multilayered polymeric microparticles. We also focus on the one-step solvent evaporation technique, and the key process parameters in this technique that affect the formation of microparticle configurations. In addition, the benefits and challenges of multilayered microparticulate system for drug delivery were discussed. This review intends to portray how distinctive structural attributes and degradation behaviors of multilayered microparticles can be exploited to fine-tune drug release profiles and kinetics.

Numerical deflation of beach balls with various Poisson's ratios: from sphere to bowl's shape

We present a numerical study of the shape taken by a spherical elastic surface when the volume it encloses is decreased. For the range of 2D parameters where such a surface may model a thin shell of an isotropic elastic material, the mode of deformation that develops a single depression is investigated in detail. It occurs via buckling from sphere toward an axisymmetric dimple, followed by a second buckling where the depression loses its axisymmetry through folding along portions of meridians. For the thinnest shells, a direct transition from the spherical conformation to the folded one can be observed. We could exhibit unifying master curves for the relative volume variation at which first and second buckling occur, and clarify the role of Poisson's ratio. In the folded conformation, the number of folds and inner pressure are investigated, allowing us to infer shell features from mere observation and/or knowledge of external constraints.

Nanoplasmonics for dual-molecule release through nanopores in the membrane of red blood cells

A nanoplasmonics-based opto-nanoporation method of creating nanopores upon laser illumination is applied for inducing diffusion and triggered release of small and large molecules from red blood cells (RBCs). The method is implemented using absorbing gold nanoparticle (Au-NP) aggregates on the membrane of loaded RBCs, which, upon near-IR laser light absorption, induce release of encapsulated molecules from selected cells. The binding of Au-NPs to RBCs is characterized by Raman spectroscopy. The process of release is driven by heating localized at nanoparticles, which impacts the permeability of the membrane by affecting the lipid bilayer and/or trans-membrane proteins. Localized heating and temperature rise around Au-NP aggregates is simulated and discussed. Research reported in this work is relevant for generating nanopores for biomolecule trafficking through polymeric and lipid membranes as well as cell membranes, while dual- and multi-molecule release is relevant for theragnostics and a wide range of therapies.

Polyelectrolyte based molecular carriers: The role of self-assembled proteins in permeability properties

Polyelectrolyte capsules are seen as promising nanotechnology based drug delivery systems. In previous works, we have demonstrated the possibility to fabricate bio-activated surface layer containing capsules with improved features in terms of biocompatibility. In this study, we have characterized the permeability properties of such capsules towards low and high molecular weight molecules, including proteins. The results indicated that the presence of the surface layer strongly affects the permeability properties of the capsules in terms of loading capacity which was found to be higher compared to that of plain capsules. These properties make such systems interesting candidates as drug delivery platforms.

Up-conversion cell imaging and pH-induced thermally controlled drug release from NaYF4/Yb3+/Er3+@hydrogel core-shell hybrid microspheres

In this study, we report a new controlled release system based on up-conversion luminescent microspheres of NaYF(4):Yb(3+)/Er(3+) coated with the smart hydrogel poly[(N-isopropylacrylamide)-co-(methacrylic acid)] (P(NIPAM-co-MAA)) (prepared using 5 mol % of MAA) shell. The hybrid microspheres show bright up-conversion fluorescence under 980 nm laser excitation, and turbidity measurements show that the low critical solution temperature of the polymer shell is thermo- and pH-dependent. We have exploited the hybrid microspheres as carriers for Doxorubicin hydrochloride (DOX) due to its stimuli-responsive property as well as good biocompatibility via MTT assay. It is found that the drug release behavior is pH-triggered thermally sensitive. Changing the pH to mildly acidic condition at physiological temperature deforms the structure of the shell, causing the release of a large number of DOX from the microspheres. The drug-loaded microspheres exhibit an obvious cytotoxic effect on SKOV3 ovarian cancer cells. The endocytosis process of drug-loaded microspheres is observed using confocal laser scanning microscopy and up-conversion luminescence microscopy. Meanwhile, the as-prepared NaYF(4):Yb(3+)/Er(3+)@SiO(2)@P(NIPAM-co-MAA) microspheres can be used as a luminescent probe for cell imaging. In addition, the extent of drug release can be monitored by the change of up-conversion emission intensity. These pH-induced thermally controlled drug release systems have potential to be used for in vivo bioimaging and cancer therapy by the pH of the microenvironment changing from 7.4 (normal physiological environment) to acidic microenvironments (such as endosome and lysosome compartments) owing to endocytosis.

Targeted polymeric therapeutic nanoparticles: design, development and clinical translation

Polymeric materials have been used in a range of pharmaceutical and biotechnology products for more than 40 years. These materials have evolved from their earlier use as biodegradable products such as resorbable sutures, orthopaedic implants, macroscale and microscale drug delivery systems such as microparticles and wafers used as controlled drug release depots, to multifunctional nanoparticles (NPs) capable of targeting, and controlled release of therapeutic and diagnostic agents. These newer generations of targeted and controlled release polymeric NPs are now engineered to navigate the complex in vivo environment, and incorporate functionalities for achieving target specificity, control of drug concentration and exposure kinetics at the tissue, cell, and subcellular levels. Indeed this optimization of drug pharmacology as aided by careful design of multifunctional NPs can lead to improved drug safety and efficacy, and may be complimentary to drug enhancements that are traditionally achieved by medicinal chemistry. In this regard, polymeric NPs have the potential to result in a highly differentiated new class of therapeutics, distinct from the original active drugs used in their composition, and distinct from first generation NPs that largely facilitated drug formulation. A greater flexibility in the design of drug molecules themselves may also be facilitated following their incorporation into NPs, as drug properties (solubility, metabolism, plasma binding, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, but also become in-part the function of the physicochemical properties of the NP. The combination of optimally designed drugs with optimally engineered polymeric NPs opens up the possibility of improved clinical outcomes that may not be achievable with the administration of drugs in their conventional form. In this critical review, we aim to provide insights into the design and development of targeted polymeric NPs and to highlight the challenges associated with the engineering of this novel class of therapeutics, including considerations of NP design optimization, development and biophysicochemical properties. Additionally, we highlight some recent examples from the literature, which demonstrate current trends and novel concepts in both the design and utility of targeted polymeric NPs (444 references).

Tumor-targeting hyaluronic acid nanoparticles for photodynamic imaging and therapy

Tumor-targeted imaging and therapy have been the challenging issue in the clinical field. Herein, we report tumor-targeting hyaluronic acid nanoparticles (HANPs) as the carrier of the hydrophobic photosensitizer, chlorin e6 (Ce6) for simultaneous photodynamic imaging and therapy. First, self-assembled HANPs were synthesized by chemical conjugation of aminated 5β-cholanic acid, polyethylene glycol (PEG), and black hole quencher3 (BHQ3) to the HA polymers. Second, Ce6 was readily loaded into the HANPs by a simple dialysis method resulting in Ce6-loaded hyaluronic acid nanoparticles (Ce6-HANPs), wherein in the loading efficiency of Ce6 was higher than 80%. The resulting Ce6-HANPs showed stable nano-structure in aqueous condition and rapid uptake into tumor cells. In particular Ce6-HANPs were rapidly degraded by hyaluronidases abundant in cytosol of tumor cells, which may enable intracellular release of Ce6 at the tumor tissue. After an intravenous injection into the tumor-bearing mice, Ce6-HANPs could efficiently reach the tumor tissue via the passive targeting mechanism and specifically enter tumor cells through the receptor-mediated endocytosis based on the interactions between HA of nanoparticles and CD44, the HA receptor on the surface of tumor cells. Upon laser irradiation, Ce6 which was released from the nanoparticles could generate fluorescence and singlet oxygen inside tumor cells, resulting in effective suppression of tumor growth. Overall, it was demonstrated that Ce6-HANPs could be successfully applied to in vivo photodynamic tumor imaging and therapy simultaneously.

Stimuli-responsive polymers and their applications in nanomedicine

This review focuses on smart nano-materials built of stimuli-responsive (SR) polymers and will discuss their numerous applications in the biomedical field. The authors will first provide an overview of different stimuli and their corresponding, responsive polymers. By introducing myriad functionalities, SR polymers present a wide range of possibilities in the design of stimuli-responsive devices, making use of virtually all types of polymer constructs, from self-assembled structures (micelles, vesicles) to surfaces (polymer brushes, films) as described in the second section of the review. In the last section of this review the authors report on some of the most promising applications of stimuli-responsive polymers in nanomedicine. In particular, we will discuss applications pertaining to diagnosis, where SR polymers are used to construct sensors capable of selective recognition and quantification of analytes and physical variables, as well as imaging devices. We will also highlight some examples of responsive systems used for therapeutic applications, including smart drug delivery systems (micelles, vesicles, dendrimers...) and surfaces for regenerative medicine.

Controlled release of nanoparticles and macromolecules from responsive microgel capsules

Using a mesoscale computational model, we probe the release of nanoparticles and linear macromolecules from hollow microgel capsules that swell and deswell in response to external stimuli. Our simulations reveal that responsive microcapsules can be effectively utilized for steady and pulsatile release of encapsulated solutes. Swollen gel capsules allow steady, diffusive release of nanoparticles and polymer chains, whereas gel deswelling causes burst-like discharge of solutes driven by an outward flow of the solvent enclosed within a shrinking capsule. We demonstrate that this hydrodynamic release can be regulated by introducing rigid microscopic rods in the capsule interior. Thus, our findings disclose an efficient approach for controlled release from stimuli-responsive microcarriers that could be useful for designing advanced drug delivery systems.

Electrochemically controlled drug-mimicking protein release from iron-alginate thin-films associated with an electrode

Novel biocompatible hybrid-material composed of iron-ion-cross-linked alginate with embedded protein molecules has been designed for the signal-triggered drug release. Electrochemically controlled oxidation of Fe(2+) ions in the presence of soluble natural alginate polymer and drug-mimicking protein (bovine serum albumin, BSA) results in the formation of an alginate-based thin-film cross-linked by Fe(3+) ions at the electrode interface with the entrapped protein. The electrochemically generated composite thin-film was characterized by electrochemistry and atomic force microscopy (AFM). Preliminary experiments demonstrated that the electrochemically controlled deposition of the protein-containing thin-film can be performed at microscale using scanning electrochemical microscopy (SECM) as the deposition tool producing polymer-patterned spots potentially containing various entrapped drugs. Application of reductive potentials on the modified electrode produced Fe(2+) cations which do not keep complexation with alginate, thus resulting in the electrochemically triggered thin-film dissolution and the protein release. Different experimental parameters, such as the film-deposition time, concentrations of compounds and applied potentials, were varied in order to demonstrate that the electrodepositon and electrodissolution of the alginate composite film can be tuned to the optimum performance. A statistical modeling technique was applied to find optimal conditions for the formation of the composite thin-film for the maximal encapsulation and release of the drug-mimicking protein at the lowest possible potential.

Degradable Cross-Linked Nanoassemblies as Drug Carriers for Heat Shock Protein 90 Inhibitor 17-N-Allylamino-17-demethoxy-geldanamycin

Cross-linked nanoassemblies (CNAs) with a degradable core were prepared for sustained release of 17-N-allylamino-17-demethoxygeldanamycin (17-AAG), a potent inhibitor of heat shock protein 90 (HSP90). The particle size of CNAs ranged between 100 and 250 nm, which changed depending on the cross-linking yields and drug entrapment method. CNAs with a 1% cross-linking yield entrapped 17-AAG in aqueous solutions, yet degraded in 3 hrs. CNAs entrapped 5.2 weight% of 17-AAG as the cross-linking yield increased to 10%, retaining more than 80% of particles for 24 hrs. CNAs with drugs entrapped after the cross-linking reactions were 100 nm and remained stable in both pH 7.4 and 5.0, corresponding to the physiological, tumoral, and intracellular environments. Drug was completely released from CNAs in 48 hrs, which would potentially maximize drug delivery and release efficiency within tumor tissues. Drug release patterns were not negatively affected by changing the cross-linking yields of CNAs. CNAs entrapping 17-AAG suppressed the growth of human non-small cell lung cancer A549 cells as equally effective as free drugs. The results demonstrated that CNAs would be a promising formulation that can be used in aqueous solutions for controlled delivery and release of 17-AAG.