Reversible polyelectrolyte capsules as carriers for protein delivery

Incorporation of CuS nanorods in polyelectrolyte multilayer microcapsules improved cancer cell cytotoxicity and signal intensity in ultrasound imaging

The fabrications of hollow microcapsules (MCs) with new architecture and ability to incorporate different nanomaterials have received great interest for targeted cancer therapy. Recently, CuS based nanomaterials have been demonstrated to possess the ability to mimic Fenton-like activity in tumor environment and inducing cancer cell apoptosis by generating highly reactive oxygen species (ROS). In this study, we have developed poly(allylamine) hydrochloride (PAH)/dextran sulfate (DS) polyelectrolyte MCs capable of carrying doxorubicin (DOX) for targeted cancer therapy and ultrasound imaging. The electron microscopy investigations showed the formation of polymeric MCs of 3 µm in size with incorporated CuS NRs in their interior structure. The surface modification of MCs with folic acid (FA), and encapsulation of model hydrophilic molecules in MCs was studied by UV-Visible (UV-Vis) spectroscopy, Fourier transform infra-red (FTIR) spectroscopy and confocal laser scanning microscopy. The encapsulation efficiency of DOX was found to be 56 % and the release was found to be linear at pH 5.5 and 7.4 in the absence of ultrasound exposure. The ultrasound exposure resulted in sudden rupture of MCs at 1 MHz and 1 W/cm2 and caused burst release of DOX at both pH conditions. The FA decorated PAH/DS/CuS NR MCs exhibited improved anti-cancer activity against MDA-MB-231 cells the synergistic effects of ultrasound mediated burst release of chemotherapeutic drug DOX, GSH-stimulated Reactive oxygen species (ROS) and targeted folate activity. Further, the capsules showed better echogenicity than that of control PAH/DS MCs when imaged under medical ultrasound-scanning system. Hence, the MCs demonstrated in this study have huge potential for targeted cancer theranostics by offering an option to image the cancer cells during the treatment period.

Co-encapsulation and release of apigenin and ascorbic acid in polyelectrolyte multilayer capsules for targeted polycystic ovary syndrome

Polycystic ovary syndrome (PCOS), a prevalent endocrine disorder in women of reproductive age, is linked to hormonal imbalances and oxidative stress. Our study investigates the regenerative potential of apigenin (AP, hydrophobic) and ascorbic acid (AC, hydrophilic) encapsulated within poly (allylamine hydrochloride) and dextran sulfate (PAH/DS) hollow microcapsules for PCOS. These microcapsules, constructed using a layer-by-layer (LbL) assembly, are found to be 4 ± 0.5 μm in size. Our research successfully demonstrates the co-encapsulation of AP and AC in a single PAH/DS system with high encapsulation efficiency followed by successful release at physiological conditions by CLSM investigations. In vitro tests with testosterone-treated CHO cells reveal that the dual-drug-loaded PAH/DS capsules effectively reduce intracellular ROS levels and apoptosis and offering protection. In an in-vivo zebrafish model, these capsules demonstrate active biodistribution to targeted ovaries and reduce testosterone levels through radical scavenging. Histopathological examinations show that the injected dual-drug-loaded PAH/DS microcapsules assist in the development of ovarian follicles in testosterone-treated zebrafish. Hence, this dual-drug-loaded system, capable of co-encapsulating two natural compounds, effectively interacts with ovarian cells, reducing cellular damage and normalizing PCOS conditions.

Layer-By-Layer Synthesis of the pH-Responsive Hollow Microcapsule and Investigation of Its Drug Delivery and Anticancer Properties

Multilayered pH-responsive hollow microcapsules with non-toxicity and biological specificity advantages were prepared from two kinds of polymers i.e., chitosan (CH) and poly (ethylene glycol dimethacrylate-co-methacrylic acid) (PE) via layer-by-layer (LbL) method, which is followed by subsequent removal of silica core. The hollow nature of obtained spherical microcapsules was found by transmission electron microscopy (TEM). The microcapsules were prepared as gemcitabine (GM) and curcumin (CR) carriers. The drugs have been loaded within the microcapsules during or after the synthetic procedure. Although acceptable loading efficiencies (LE) were obtained in both methods, the amount of drug loaded during the synthesis method is relatively higher. Values above 78% and 87%, for releasing efficiency (RE%) and encapsulation efficiency (EE%), respectively, demonstrate the high potential of the prepared microcapsules for drug delivery. In addition, the difference between the amount of drug released in acidic and neutral pH indicates the pH-responsivity of the prepared microcapsules. Moreover, the dose-dependent high cytotoxicity effect of the prepared microcapsules was observed on the HCT116 colorectal carcinoma cells.

Controlling the Interaction between Starchy Polyelectrolyte Layers for Adjusting Protein Release from Nanocapsules in a Simulated Gastrointestinal Tract

Orally delivered bioactive proteins face great challenges in the harsh environment of the upper gastrointestinal tract (GIT) in the field of functional foods based on bioactive proteins. Therefore, it is necessary to design carriers and delivery systems that have the potential to overcome the problem of lower bioaccessibility for protein cargoes. In this work, we present a starchy oral colon-targeting delivery system, capable of improving the release profile of the protein cargoes. The starchy oral colon-targeting delivery system was fabricated using layer-by-layer assembly of starchy polyelectrolytes (carboxymethyl anionic starch and spermine cationic starch) onto the surface of protein nanoparticles via electrostatic interaction. The dynamic change in the interaction between the starchy polyelectrolytes affected the shell aggregation structure and determined the release kinetics of nanocapsules in the GIT. Specifically, the stronger interactions between the starchy layers and the thicker and more compact shell layer kept the nanocapsule intact in the simulated gastric and intestinal fluids, better-protecting the protein from degradation by digestive fluids, thus avoiding the burst release effect in the SGF and SIF. However, the nanocapsule could quickly swell with the decreasing molecular interactions between starchy polyelectrolytes, increasing protein release (63.61%) in the simulated colonic fluid. Therefore, release behaviors of protein cargoes could be appropriately controlled by adjusting the number of deposited layers of pH-sensitive starchy polyelectrolytes on the nanocapsule. This could improve the bioaccessibility of oral targeted delivery of bioactive proteins to the colon.

LbL Nano-Assemblies: A Versatile Tool for Biomedical and Healthcare Applications

Polyelectrolytes (PEs) have been the aim of many research studies over the past years. PE films are prepared by the simple and versatile layer-by-layer (LbL) approach using alternating assemblies of polymer pairs involving a polyanion and a polycation. The adsorption of the alternating PE multiple layers is driven by different forces (i.e., electrostatic interactions, H-bonding, charge transfer interactions, hydrophobic forces, etc.), which enable an accurate control over the physical properties of the film (i.e., thickness at the nanoscale and morphology). These PE nano-assemblies have a wide range of biomedical and healthcare applications, including drug delivery, protein delivery, tissue engineering, wound healing, and so forth. This review provides a concise overview of the most outstanding research on the design and fabrication of PE nanofilms. Their nanostructures, molecular interactions with biomolecules, and applications in the biomedical field are briefly discussed. Finally, the perspectives of further research directions in the development of LbL nano-assemblies for healthcare and medical applications are highlighted.

Recent Advances in Surface Nanoengineering for Biofilm Prevention and Control. Part II: Active, Combined Active and Passive, and Smart Bacteria-Responsive Antibiofilm Nanocoatings

The second part of our review describing new achievements in the field of biofilm prevention and control, begins with a discussion of the active antibiofilm nanocoatings. We present the antibiofilm strategies based on antimicrobial agents that kill pathogens, inhibit their growth, or disrupt the molecular mechanisms of biofilm-associated increase in resistance and tolerance. These agents of various chemical structures act through a plethora of mechanisms targeting vital bacterial metabolic pathways or cellular structures like cell walls and cell membranes or interfering with the processes that underlie different stages of the biofilm life cycle. We illustrate the latter action mechanisms through inhibitors of the quorum sensing signaling pathway, inhibitors of cyclic-di-GMP signaling system, inhibitors of (p)ppGpp regulated stringent response, and disruptors of the biofilm extracellular polymeric substances matrix (EPS). Both main types of active antibiofilm surfaces, namely non-leaching or contact killing systems, which rely on the covalent immobilization of the antimicrobial agent on the surface of the coatings and drug-releasing systems in which the antimicrobial agent is physically entrapped in the bulk of the coatings, are presented, highlighting the advantages of each coating type in terms of antibacterial efficacy, biocompatibility, selective toxicity, as well as drawbacks and limitations. Developments regarding combined strategies that join in a unique platform, both passive and active elements are not omitted. In such platforms with dual functionality, passive and active strategies can be applied either simultaneously or sequentially. We especially emphasize those systems that can be reversely and repeatedly switched between the non-fouling status and the bacterial killing status, thereby allowing several bacteria-killing/surface regeneration cycles to be performed without significant loss of the initial bactericidal activity. Eventually, smart antibiofilm coatings that release their antimicrobial payload on demand, being activated by various triggers such as changes in local pH, temperature, or enzymatic triggers, are presented. Special emphasis is given to the most recent trend in the field of anti-infective surfaces, specifically smart self-defensive surfaces for which activation and switch to the bactericidal status are triggered by the pathogens themselves.

Multilayer capsules encapsulating nimbin and doxorubicin for cancer chemo-photothermal therapy

Layer-by-layer (LbL) assembled poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) microcapsules were designed to incorporate gold nanorods (NRs) and co-encapsulate and release two drugs for cancer therapy. Calcium carbonate (CaCO₃) microparticles modified with preformed NRs were used as sacrificial templates for the fabrication of hollow PAH/PMA/NR capsules incorporated with NRs. The hollow capsules were found to be 4.5 ± 0.5 µm in size and appeared with uniformly distributed NRs in the interior of the capsules. The morphology of the capsules transformed from pore free continuous structure to porous structure under laser light irradiation at 808 nm and 0.5 W cm^-2. The encapsulation experiments showed that the hydrophilic drug (doxorubicin hydrochloride, Dox) was encapsulated in the interior of the capsules while the hydrophobic drug (nimbin, NB) was entrapped in the porous polymeric network of the layer components. The encapsulation efficiency was found to be 30% for both Dox and NB. The release experiments showed an initial burst release followed by sustained release up to 3 h. Notably, the release was completed within 30 min under NIR irradiation at 808 nm. The estimated IC₅₀ values against THP-1 cells were 75 and 1.8 µM for NB and Dox, respectively. The dual drug loaded capsules showed excellent anticancer activity against THP-1 cells under NIR light exposure in in-vitro experiments. Thus, such remotely addressable dual-drug loaded capsules with the provision for encapsulation of natural drugs demonstrate high potential for use as theranostics in cancer therapy.

Multilayer capsules made of weak polyelectrolytes: a review on the preparation, functionalization and applications in drug delivery

Multilayer capsules have been of great interest for scientists and medical communities in multidisciplinary fields of research, such as drug delivery, sensing, biomedicine, theranostics and gene therapy. The most essential attributes of a drug delivery system are considered to be multi-functionality and stimuli responsiveness against a range of external and internal stimuli. Apart from the highly explored strong polyelectrolytes, weak polyelectrolytes offer great versatility with a highly controllable architecture, unique stimuli responsiveness and easy tuning of the properties for intracellular delivery of cargo. This review describes the progress in the preparation, functionalization and applications of capsules made of weak polyelectrolytes or their combination with biopolymers. The selection of a sacrificial template for capsule formation, the driving forces involved, the encapsulation of a variety of cargo and release based on different internal and external stimuli have also been addressed. We describe recent perspectives and obstacles of weak polyelectrolyte/biopolymer systems in applications such as therapeutics, biosensing, bioimaging, bioreactors, vaccination, tissue engineering and gene delivery. This review gives an emerging outlook on the advantages and unique responsiveness of weak polyelectrolyte based systems that can enable their widespread use in potential applications.

Analysis of the structure-function relationship of alpha amylase complexed with polyacrylic acid

Alpha-amylase is frequently used in technologies that require its immobilization, stabilization or encapsulation. Polyacrylic acid is a very suitable polymer for these purposes because it can bind to enzymes and then be released under certain conditions without altering the functional capacity of enzymes. The consequences produced by polyacrylic acid on alpha-amylase structure and function have been investigated through various techniques. Calorimetric measurements allowed examining the nature of the binding reaction, stoichiometry and affinity, while spectroscopic techniques provided additional information about functional and structural perturbations of the enzyme. Isothermal titration calorimetry (ITC) revealed a mixed interaction and a binding model with a large number of molecules of protein per molecule of polyacrylic acid. One the one hand circular dichroism (CD) spectroscopy showed that alpha-amylase loses its secondary structure in the presence of increasing concentrations of polyacrylic acid, while it is stabilized by the polyelectrolyte at low pH. On the other hand, fluorescence spectra revealed that the three-dimensional enzyme structure was not affected in the microenvironment of tryptophan residues. Differential scanning calorimetry (DSC) thermograms showed that only one domain of alpha-amylase is affected in its conformational stability by the polymer. The unfolding process proved to be partially reversible. Finally, the enzyme retained more than 90 % of its catalytic activity even in excess of the polymer.

Hydrogen-Bonded Multilayer Thin Films and Capsules Based on Poly(2-n-propyl-2-oxazoline) and Tannic Acid: Investigation on Intermolecular Forces, Stability, and Permeability

In recent years, hydrogen-bonded multilayer thin films and capsules based on neutral and nontoxic building blocks have been receiving interest for the design of stimuli-responsive drug delivery systems and for the preparation of thin-film coatings. Capsule systems made of tannic acid (TA), a natural polyphenol, as a hydrogen bonding donor and poly(2-n-propyl-2-oxazoline) (PnPropOx), a polymer with lower critical solution temperature around 25 °C, as a hydrogen bonding acceptor are advantageous over other conventional hydrogen-bonded systems because of their high stability in physiological pH range, biocompatibility, good renal clearance, stealth behavior, and stimuli responsiveness for temperature and pH. In this work, investigations on the interactive forces in TA/PnPropOx capsule formation, film thickness, stability, and permeability are reported. The multilayer thin films were assembled on quartz substrates, and the layer-by-layer film growth was investigated by UV-vis spectroscopy, atomic force microscopy, and profilometry. Hollow capsules were fabricated by sequential coating of TA and PnPropOx onto CaCO₃ colloidal particles, followed by template dissolution with a 0.2 M ethylenediaminetetraacetic acid solution. The obtained capsules and multilayer thin films were found to be stable over a wide pH range of 2-9. It is found that both hydrogen bonding and hydrophobic interactions are responsible for the enhanced stability of the capsules at higher pH range. Swelling followed by dissolution of the capsules was observed at a pH value lower than 2, while the capsules undergo shrinking at a pH value higher than 8 and finally transform into a particle-like morphology before dissolution. The TA/PnPropOx capsules reported here could be used as a temperature-responsive drug delivery system in controlled drug delivery applications.

Reusable Hollow Polymer Microreactors Incorporated with Anisotropic Nanoparticles for Catalysis Application

We report a methodology to encapsulate gold nanorods (AuNRs) and gold bipyramids (AuBPs) into polyelectrolyte capsules for catalytic application. Microreactors (capsules with encapsulated NRs or BPs) were fabricated by sequential deposition of poly(allylamine hydrochloride) and dextran sulfate on modified sacrificial template, followed by core dissolution. AuNRs and AuBPs of size 25-30 nm were successfully encapsulated in the fabricated polyelectrolyte capsules and were stable and distributed uniformly in the interior. Fabricated microreactors were investigated as catalysts for the reduction of p-nitrophenol to p-aminophenol in the presence of sodium borohydride in aqueous phase. Reaction parameters such as order, conversion, and rate constants were estimated for microreactors and compared to free anisotropic nanoparticles in suspension. The reaction rate was higher for NRs in both free and capsule forms compared to BPs. Microreactors demonstrated excellent catalytic activity even after three times of use. Such capsules have high potential for use as microreactors in applications such as catalysis, drug delivery, imaging, and cancer chemo-photothermal therapy.

Internal Structure of Matrix-Type Multilayer Capsules Templated on Porous Vaterite CaCO₃ Crystals as Probed by Staining with a Fluorescence Dye

Multilayer capsules templated on decomposable vaterite CaCO₃ crystals are widely used as vehicles for drug delivery. The capsule represents typically not a hollow but matrix-like structure due to polymer diffusion into the porous crystals during multilayer deposition. The capsule formation mechanism is not well-studied but its understanding is crucial to tune capsule structure for a proper drug release performance. This study proposes new approach to noninvasively probe and adjust internal capsule structure. Polymer capsules made of poly(styrene-sulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDAD) have been stained with fluorescence dye rhodamine 6G. Physical-chemical aspects of intermolecular interactions required to validate the approach and adjust capsule structure are addressed. The capsules consist of a defined shell (typically 0.5⁻2 µm) and an internal matrix of PSS-PDAD complex (typically 10⁻40% of a total capsule volume). An increase of ionic strength and polymer deposition time leads to the thickening of the capsule shell and formation of a denser internal matrix, respectively. This is explained by effects of a polymer conformation and limitations in polymer diffusion through the crystal pores. We believe that the design of the capsules with desired internal structure will allow achieving effective encapsulation and controlled/programmed release of bioactives for advanced drug delivery applications.

Chitosan-alginate BSA-gel-capsules for local chemotherapy against drug-resistant breast cancer

BACKGROUND AND OBJECT

Polyelectrolyte microcapsule is a promising candidate for multifunctional drug delivery system. However, the lack of reports about animal experiments have greatly slowed down their development for drug delivery. We engineered biodegradable chitosan-alginate polyelectrolyte multilayer capsule filled with bovine serum albumin gel (BSA-gel-capsule). Herein, we demonstrated their applicability for local chemotherapy, a means of treating local or regional malignancies by direct administration of anti-tumor agents to tumor sites.

METHOD

Doxorubicin (DOX) was loaded in BSA-gel-capsules and DOX-resistant cell line (MCF-7/ADR cells) was employed for antitumor studies in vitro. The cytotoxicity, cellular uptake and distribution of DOX from BSA-gel-capsules were studied. Afterwards, MCF-7/ADR xenografts tumor model was established in nude mice. The in vivo antitumor efficacy of DOX-loaded BSA-gel-capsules by intratumor injection was then evaluated.

RESULT

Compared with free DOX, more effective cytotoxicity against MCF-7/ADR cells after treatment with DOX-loaded BSA-gel-capsules was revealed, demonstrating the positive reversal effect on drug-resistance. Thereafter, the more cellular uptake and nucleus distribution of DOX from BSA-gel-capsules in MCF-7/ADR cells provided convincing explanation for the reversal effect. DOX-loaded BSA-gel-capsules displayed remarkably more antitumor efficacy than free DOX in MCF-7/ADR cell-xenografted mice. Finally, the high DOX accumulation and prolonged retention in tumor site after local administration of DOX-loaded BSA-gel-capsules was demonstrated, displaying the unique advantages of BSA-gel-capsules for local chemotherapy.

CONCLUSION

These findings indicate that DOX-loaded BSA-gel-capsules should be considered a potential candidate for the treatment of drug-resistant breast cancer. This paper provides a feasibility for the local chemotherapy of polyelectrolyte microcapsules, which will be a big step towards their application as drug delivery vehicles.

Polyelectrolyte capsules preloaded with interconnected alginate matrix: An effective capsule system for encapsulation and release of macromolecules

In recent years, the design of stimuli-responsive hollow polymeric capsules is of tremendous interest for the scientific community because of the broad application of these capsules in the biomedical field. The use of weak polyelectrolytes as layer components for capsule fabrication is especially interesting as it results in hollow capsules that show unique release characteristics under physiological conditions. In this work, a methodology to prepare sub-micron sized alginate doped calcium carbonate (CaCO₃) particles through controlled precipitation in the presence of alginate is reported. Hollow capsules obtained by Layer-by-Layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) are showing an interconnected alginate matrix in the interior of the capsules. Investigations showed that the presence of alginate matrix enhances the encapsulation of cationic molecules (e.g. doxorubicin hydrochloride) manifold by charge controlled attraction mechanism. Capsule permeability investigated by confocal laser scanning microscopy revealed that the transformation from an open state to closed state is accompanied by an intermediate state where capsules are neither open nor closed. Furthermore, time dependent study indicated that the encapsulation process is linear as a function of time. The cell viability experiments demonstrated excellent biocompatibility of hollow capsules with mouse embryonic fibroblast cells. Anticancer investigations showed that DOX loaded capsules have significant anti-proliferative characteristics against HeLa cells. Such capsules have high potential for use as drug carrier for cationic drugs in cancer therapy.

Interfacial rheological properties of self-assembling biopolymer microcapsules

Tuning the mechanical properties of microcapsules through a cost-efficient route of fabrication is still a challenge. The traditional method of layer-by-layer assembly of microcapsules allows building a tailored composite multi-layer membrane but is technically complex as it requires numerous steps. The objective of this article is to characterize the interfacial rheological properties of self-assembling biopolymer microcapsules that were obtained in one single facile step. This thorough study provides new insights into the mechanics of these weakly cohesive membranes. Firstly, suspensions of water-in-oil microcapsules were formed in microfluidic junctions by self-assembly of two oppositely charged polyelectrolytes, namely chitosan (water soluble) and phosphatidic fatty acid (oil soluble). In this way, composite membranes of tunable thickness (between 40 and 900 nm measured by AFM) were formed at water/oil interfaces in a single step by changing the composition. Secondly, microcapsules were mechanically characterized by stretching them up to break-up in an extensional flow chamber which extends the relevance and convenience of the hydrodynamic method to weakly cohesive membranes. Finally, we show that the design of microcapsules can be 'engineered' in an extensive way since they present a wealth of interfacial rheological properties in terms of elasticity, plasticity and yield stress whose magnitudes can be controlled by the composition. These behaviors are explained by the variation of the membrane thickness with the physico-chemical parameters of the process.

Anisotropic noble metal nanoparticles: Synthesis, surface functionalization and applications in biosensing, bioimaging, drug delivery and theranostics

Anisotropic nanoparticles have fascinated scientists and engineering communities for over a century because of their unique physical and chemical properties. In recent years, continuous advances in design and fabrication of anisotropic nanoparticles have opened new avenues for application in various areas of biology, chemistry and physics. Anisotropic nanoparticles have the plasmon absorption in the visible as well as near-infrared (NIR) region, which enables them to be used for crucial applications such as biological imaging, medical diagnostics and therapy ("theranostics"). Here, we describe the progress in anisotropic nanoparticles achieved since the millennium in the area of preparation including various shapes and modification of the particle surface, and in areas of application by providing examples of applications in biosensing, bio-imaging, drug delivery and theranostics. Furthermore, we also explain various mechanisms involved in cellular uptake of anisotropic nanoparticles, and conclude with our opinion on various obstacles that limit their applications in biomedical field.

STATEMENT OF SIGNIFICANCE

Anisotropy at the molecular level has always fascinated scientists and engineering communities for over a century, however, the research on novel methods through which shape and size of nanoparticles can be precisely controlled has opened new avenues for anisotropic nanoparticles in various areas of biology, chemistry and physics. In this manuscript, we describe progress achieved since the millennium in the areas of preparation of various shapes of anisotropic nanoparticles, investigate various methods involved in modifying the surface of these NPs, and provide examples of applications in biosensing and bio-imaging, drug delivery and theranostics. We also present mechanisms involved in cellular uptake of nanoparticles, describe different methods of preparation of anisotropic nanoparticles including biomimetic and photochemical synthesis, and conclude with our opinion on various obstacles that limit their applications in biomedical field.

Hydrogen bonded capsules by layer-by-layer assembly of tannic acid and poly(2-n-propyl-2-oxazoline) for encapsulation and release of macromolecules

We report hydrogen bonded capsules with the built-in ability to release loaded bioactive molecules at a physiological temperature of 37 °C.

Layer-by-layer assembly for biomedical applications in the last decade

In the past two decades, the design and manufacture of nanostructured materials has been of tremendous interest to the scientific community for their application in the biomedical field. Among the available techniques, layer-by-layer (LBL) assembly has attracted considerable attention as a convenient method to fabricate functional coatings. Nowadays, more than 1000 scientific papers are published every year, tens of patents have been deposited and some commercial products based on LBL technology have become commercially available. LBL presents several advantages, such as (1): a precise control of the coating properties; (2) environmentally friendly, mild conditions and low-cost manufacturing; (3) versatility for coating all available surfaces; (4) obtainment of homogeneous film with controlled thickness; and (5) incorporation and controlled release of biomolecules/drugs. This paper critically reviews the scientific challenge of the last 10 years--functionalizing biomaterials by LBL to obtain appropriate properties for biomedical applications, in particular in tissue engineering (TE). The analysis of the state-of-the-art highlights the current techniques and the innovative materials for scaffold and medical device preparation that are opening the way for the preparation of LBL-functionalized substrates capable of modifying their surface properties for modulating cell interaction to improve substitution, repair or enhancement of tissue function.

Bioresorbable polyelectrolytes for smuggling drugs into cells

There is ample evidence that biodegradable polyelectrolyte nanocapsules are multifunctional vehicles which can smuggle drugs into cells, and release them upon endogenous activation. A large number of endogenous stimuli have already been tested in vitro, and in vivo research is escalating. Thus, the interest in the design of intelligent polyelectrolyte multilayer (PEM) drug delivery systems is clear. The need of the hour is a systematic translation of PEM-based drug delivery systems from the lab to clinical studies. Reviews on multifarious stimuli that can trigger the release of drugs from such systems already exist. This review summarizes the available literature, with emphasis on the recent progress in PEM-based drug delivery systems that are receptive in the presence of endogenous stimuli, including enzymes, glucose, glutathione, pH, and temperature, and addresses different active and passive drug targeting strategies. Insights into the current knowledge on the diversified endogenous approaches and methodological challenges may bring inspiration to resolve issues that currently bottleneck the successful implementation of polyelectrolytes into the catalog of third-generation drug delivery systems.

Multilayered polyelectrolyte microcapsules: interaction with the enzyme cytochrome C oxidase

Cell-sized polyelectrolyte capsules functionalized with a redox-driven proton pump protein were assembled for the first time. The interaction of polyelectrolyte microcapsules, fabricated by electrostatic layer-by-layer assembly, with cytochrome c oxidase molecules was investigated. We found that the cytochrome c oxidase retained its functionality, that the functionalized microcapsules interacting with cytochrome c oxidase were permeable and that the permeability characteristics of the microcapsule shell depend on the shell components. This work provides a significant input towards the fabrication of an integrated device made of biological components and based on specific biomolecular functions and properties.

Encapsulation of albumin in self-assembled layer-by-layer microcapsules: comparison of co-precipitation and adsorption techniques

OBJECTIVE

The objective of this study is to prepare and characterize polymeric self-assembled layer-by-layer microcapsules (LbL-MC) to deliver a model protein, bovine serum albumin (BSA). The aim is to compare the BSA encapsulation in LbL-MC using co-precipitation and adsorption methods.

MATERIALS AND METHODS

In co-precipitation method, BSA was co-precipitated with growing calcium carbonate particles to form a core template. Later, poly(styrene sulfonate) and poly(allylamine hydrochloride) were sequentially adsorbed onto the CaCO3 templates. In adsorption method, preformed LbL-MC were incubated with BSA and encapsulation efficiency is optimized for pH and salt concentration. Free and BSA-encapsulated LbL-MC were characterized using Zetasizer, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy and differential scanning calorimeter. Later, in vitro release studies were performed using dialysis membrane method at pH 4, 7.4 and 9.

RESULTS AND DISCUSSION

Results from Zetasizer and SEM showed free LbL-MC with an average size and zeta-potential of 2.0 ± 0.6 μm and 8.1 ± 1.9 mV, respectively. Zeta-potential of BSA-loaded LbL-MC was (-)7.4 ± 0.7 mV and (-)5.7 ± 1.0 mV for co-precipitation and adsorption methods, respectively. In adsorption method, BSA encapsulation in LbL-MC was found to be greater at pH 6.0 and 0.2 M NaCl. Co-precipitation method provided four-fold greater encapsulation efficiency (%) of BSA in LbL-MC compared with adsorption method. At pH 4, the BSA release from LbL-MC was extended up to 120 h. Polyacrylamide gel electrophoresis showed that BSA encapsulated in LBL-MC through co-precipitation is stable toward trypsin treatment.

CONCLUSION

In conclusion, co-precipitation method provided greater encapsulation of BSA in LbL-MC. Furthermore, LbL-MC can be developed as carriers for pH-controlled protein delivery.

Release retardation of model protein on polyelectrolyte-coated PLGA nano- and microparticles

PEM capsules have been proposed for vehicles of drug microencapsulation, with the release triggered by pH, salt, magnetic field, or light. When built on another carrier encapsulating drugs, such as nanoparticles, it could provide additional release barrier to the releasing drug, providing further control to drug release. Although liposomes have received considerable attention with PEM coating for sustained drug release, similar results employing PEM built on poly(lactic-co-lycolic acid) (PLGA) particles is scant. In this work, we demonstrate that the build-up pH and polyelectrolyte pairs of PEM affect the release retardation of BSA from PLGA particles. PAH/PSS pair, the most commonly used polyelectrolyte pair, was used in comparison with PLL/DES. In addition, we also demonstrate that the release retardation effect of PEM-coated PLGA particles diminishes as the particle size increases. We attribute this to the diminishing relative thickness of the PEM coating with respect to the size of the particle as the particle size increases, reducing the diffusional resistance of the PEM.

Tailor-made hollow silver nanoparticle cages assembled with silver nanoparticles: an efficient catalyst for epoxidation

A novel approach toward the synthesis of hollow silver nanoparticle (NP) cages built with building blocks of silver NPs by layer-by-layer (LbL) assembly is demonstrated. The size of the NP cage depends on the size of template used for the LbL assembly. The microcages showed a uniform distribution of spherical silver nanoparticles with an average diameter of 20 ± 5 nm, which increased to 40 ± 5 nm when the AgNO3 concentration was increased from 25 to 50 mM. Heat treatment of the polyelectrolyte capsules at 80 °C near their pKa values yielded intact nano/micro cages. These cages produced a higher conversion for the epoxidation of olefins and maintained their catalytic activity even after four successive uses. The nanocages exhibited unique and attractive characteristics for metal catalytic systems, thus offering the scope for further development as heterogeneous catalysts.

Polyelectrolyte/silver nanocomposite multilayer films as multifunctional thin film platforms for remote activated protein and drug delivery

We demonstrate a nanoparticle loading protocol to develop a transparent, multifunctional polyelectrolyte multilayer film for externally activated drug and protein delivery. The composite film was designed by alternate adsorption of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on a glass substrate followed by nanoparticle synthesis through a polyol reduction method. The films showed a uniform distribution of spherical silver nanoparticles with an average diameter of 50±20 nm, which increased to 80±20 nm when the AgNO3 concentration was increased from 25 to 50 mM. The porous and supramolecular structure of the polyelectrolyte multilayer film was used to immobilize ciprofloxacin hydrochloride (CH) and bovine serum albumin (BSA) within the polymeric network of the film. When exposed to external triggers such as ultrasonication and laser light the loaded films were ruptured and released the loaded BSA and CH. The release of CH is faster than that of BSA due to a higher diffusion rate. Circular dichroism measurements confirmed that there was no significant change in the conformation of released BSA in comparison with native BSA. The fabricated films showed significant antibacterial activity against the bacterial pathogen Staphylococcus aureus. Applications envisioned for such drug-loaded films include drug and vaccine delivery through the transdermal route, antimicrobial or anti-inflammatory coatings on implants and drug-releasing coatings for stents.

Target-molecule-triggered rupture of aptamer-encapsulated polyelectrolyte microcapsules

Polyelectrolyte microcapsules have great potential for serving as carriers for the delivery of their contents when triggered by an external stimulus. Aptamers are synthetic ssDNA or RNA that can bind to specific targets with high affinity and selectivity. Aptamers may retain these superior molecular recognition properties after encapsulation within polymer microcapsules. In this work, stable polyelectrolyte microcapsules with encapsulated aptamers were obtained by the layer-by-layer (LbL) method. Polyelectrolyte films were deposited onto a CaCO3 template that had been predoped with polystyrene sulfonate (PSS) and aptamer sequences (SA) that have an affinity for the dye sulforhodamine B (SRB). The PSS and aptamers are thought to serve as an internal scaffold supporting the microcapsule walls. These microcapsules would present target-molecule-triggered rupture properties. Microcapsule collapse was triggered by the binding of SRB to the encapsulated aptamer. The specificity of microcapsule collapse was investigated using a similar dye, tetramethylrosamine (TMR), which does not have affinity for SA. A high concentration of TMR did not lead to the collapse of the microcapsules. The effect of target binding on the microcapsules was confirmed by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). These microcapsules may have potential applications in targeted delivery systems for the controlled release of drugs, pesticides, or other payloads.

Linseed oil based nanocapsules as delivery system for hydrophobic quantum dots

In the present work, the CdSe/ZnS hydrophobic quantum dots were embedded within the polyelectrolyte nanocapsules. The core of the capsules, which consists of a mixture of the linseed oil with chloroform, was prepared using the spontaneous emulsification technique. The obtained emulsions were stabilized with lecithin and encapsulated using the layer-by-layer (LbL) adsorption of polyelectrolytes. The pair of biocompatible polyelectrolytes was used: the cationic poly-l-lysine hydrobromide (PLL) together with the anionic poly-d-glutamic acid sodium salt. The saturation LbL method, which is based on the stepwise formation of consecutive layers on the initial emulsion without the intermediate rinsing step, was applied to form the capsule shells. Their growth was evidenced by the capsule size and electrophoretic mobility measurements. The emulsion and the capsules were deposited on a mica surface and the deposit topology was examined by the means of atomic force microscopy (AFM). The presence of quantum dots within the oil cores was confirmed by recording the fluorescent spectra of the samples containing CdSe/ZnS. In order to evaluate cytotoxicity of the capsules, their influence on the viability of mouse embryonic fibroblasts was examined using the MTT test, followed by optical-microscope observation of morphology of the cells after hematoxylin-eosin staining.

Polyelectrolyte capsules packaging BSA gels for pH-controlled drug loading and release and their antitumor activity

Polyelectrolyte multilayer capsules, promising candidates for multifunctional drug delivery systems, have recently received increased interest. However, the low encapsulation efficiency of drugs and the lack of reports about animal experiments have greatly slowed down their development for drug delivery. Here, a polyelectrolyte multilayer capsule filled with bovine serum albumin gel (BSA-gel-capsule) was constructed by a layer-by-layer assembly technique and thermally induced gelation of BSA. Owing to the charge variability of BSA with change in pH, BSA-gel-capsules not only showed a pronounced accumulation effect of drugs into capsules, but also displayed excellent pH-controlled loading and release properties. Moreover, a remarkable targeting action to the lung was discovered after intravenous injection of fluorescein isothiocyanate (FITC)-labeled BSA-gel-capsules into mice. After treatment with doxorubicin-loaded BSA-gel-capsules, effective cytotoxicity against B16-F10 cells and inhibition of the pulmonary melanoma growth were revealed. This paper introduces a new type of smart microstructure with notable pH-responsive ability. This material renders feasible the intravenous administration of polyelectrolyte microcapsules, which will be a big step towards their application as drug delivery vehicles.

A cell penetrating peptide-integrated and enediyne-energized fusion protein shows potent antitumor activity

Arginine-rich peptides belong to a subclass of cell penetrating peptides that are taken up by living cells and can be detected freely diffusing inside the cytoplasm and nucleoplasm. This phenomenon has been attributed to either an endocytotic mode of uptake and a subsequent release from vesicles or a direct membrane penetration. Lidamycin is an antitumor antibiotic, which consists of an active enediyne chromophore (AE) and a noncovalently bound apoprotein (LDP). In the present study, a fusion protein (Arg)(9)-LDP composed of cell penetrating peptide (Arg)(9) and LDP was prepared by DNA recombination, and the enediyne-energized fusion protein (Arg)(9)-LDP-AE was prepared by molecular reconstitution. The data in fixed cells demonstrated that (Arg)(9)-LDP could rapidly enter cells, and the results based on fluorescence activated cell sorting indicated that the major route for (Arg)(9)-mediated cellular uptake of protein molecules was endocytosis. (Arg)(9)-LDP-AE demonstrated more potent cytotoxicity against different carcinoma cell lines than lidamycin in vitro. In the mouse hepatoma 22 model, (Arg)(9)-LDP-AE (0.3mg/kg) suppressed the tumor growth by 89.2%, whereas lidamycin (0.05 mg/kg) by 74.6%. Furthermore, in the glioma U87 xenograft model in nude mice, (Arg)(9)-LDP-AE at 0.2mg/kg suppressed tumor growth by 88.8%, compared with that of lidamycin by 62.9% at 0.05 mg/kg. No obvious toxic effects were observed in all groups during treatments. The results showed that energized fusion protein (Arg)(9)-LDP-AE was more effective than lidamycin and would be a promising candidate for glioma therapy. In addition, this approach to manufacturing fusion proteins might serve as a technology platform for the development of new cell penetrating peptides-based drugs.

Graphene oxide based multilayer capsules with unique permeability properties: facile encapsulation of multiple drugs

Novel composite graphene oxide (GO)/poly(allylamine hydrochloride) (PAH) multilayer capsules have been fabricated by layer-by-layer (LbL) assembly. They were found to possess unique permeability properties compared to traditional LbL capsules. These hybrid capsules showed special "core-shell" loading property for encapsulation of dual drugs simultaneously into the core and shell of the capsules respectively.

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.

Shape deformation and recovery of multilayer microcapsules after being squeezed through a microchannel

The deformation and recovery behaviors of multilayer microcapsules were investigated after being forced to flow through a microchannel. The microchannel device with a constriction (5.7 μm in depth) in the middle was designed, and the multilayer microcapsules with different size and layer thickness (and thereby different mechanical strength) were used. Deformation in the microchannel was observed for all the capsules with a size larger than the constriction height, and its extent was mainly governed by the difference between capsule size and constriction height. The squeezed microcapsules could recover their original spherical shape when the deformation extent was smaller than 16%, whereas permanent physical deformation took place when the deformation extent was larger than 34%. The capsules filled with polyelectrolytes could greatly enhance their shape recovery ability due to the higher osmotic pressure in the capsule interior and could well maintain the preloaded low-molecular-weight dyes regardless of the squeezing.