Polyelectrolyte microcapsules for sustained delivery of water-soluble drugs

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.

Polyelectrolyte Multilayered Capsules as Biomedical Tools

Polyelectrolyte multilayered capsules (PEMUCs) obtained using the Layer-by-Layer (LbL) method have become powerful tools for different biomedical applications, which include drug delivery, theranosis or biosensing. However, the exploitation of PEMUCs in the biomedical field requires a deep understanding of the most fundamental bases underlying their assembly processes, and the control of their properties to fabricate novel materials with optimized ability for specific targeting and therapeutic capacity. This review presents an updated perspective on the multiple avenues opened for the application of PEMUCs to the biomedical field, aiming to highlight some of the most important advantages offered by the LbL method for the fabrication of platforms for their use in the detection and treatment of different diseases.

Evaluating Release Kinetics from Alginate Beads Coated with Polyelectrolyte Layers for Sustained Drug Delivery

Current approaches in stem cell-based bone tissue engineering require a release of bioactive compounds over up to 2 weeks. This study presents a polyelectrolyte-layered system featuring sustained release of water-soluble drugs with decreased burst release. The bioactive compounds adenosine 5'-triphosphate (ATP), suramin, and A740003 (a less water-soluble purinergic receptor ligand) were incorporated into alginate hydrogel beads subsequently layered with different polyelectrolytes (chitosan, poly(allyl amine), alginate, or lignosulfonate). Drug release into aqueous medium was monitored over 14 days and evaluated using Korsmeyer-Peppas, Peppas-Sahlin, Weibull models, and a Langmuir-like "Two-Stage" model. Release kinetics strongly depended on both the drug and the polyelectrolyte system. For ATP, five alternating layers of poly(allyl amine) and alginate proved to be most effective in sustaining the release. Release of suramin could be prolonged best with lignosulfonate as polyanion. A740003 showed prolonged release even without layering. Applying polyelectrolyte layers significantly slowed down the burst release. Release curves could be best described with the Langmuir-like model.

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 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.

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.

Sol-Gel Synthesis of Ce4-x Sr1+x Fe5-x Zn x O14+δ [0 ≤ x ≤ 0.45] Superparamagnetic Oxide Systems and Its Magnetic, Dielectric, and Drug Delivery Properties

In this work, we have successfully synthesized superparamagnetic nanocomposites, Ce_4-x Sr_1+x Fe_5-x Zn _x O_14+δ (0 ≤ x ≤ 0.45) (CSFZ) (TA1-TA4: x = 0, 0.15, 0.30, and 0.45) via the Nitrate-citrate sol-gel method. X-ray diffraction studies show the formation of single-phase nanocomposites (NCs) and the average crystallite size is found to be 18 nm. Energy-dispersive X-ray spectroscopy analysis supports the formation of the desired product with the expected composition. The scanning electron microscopy image shows that the prepared samples are in spherical shape and highly porous in nature. Most of the particle sizes present in the image are in the range of 5-20 nm. The optical studies show an intense peak at 583 nm corresponding to the instantaneous existence of both Fe²⁺ and Fe³⁺ intervalence electronic charge transition bands. X-ray photoelectron spectra analysis confirms the presence of elements with their preferred oxidation state. The superparamagnetic nature of the prepared sample was confirmed by vibrating sample magnetometer analysis. Synthesized materials show a low saturate magnetic moment ranging from 0.3400 to 0.1075 emu/g. The coercivity and retentivity value of the synthesized NC is zero. The NCs show high encapsulation efficiency toward ciprofloxacin hydrochloride because of their unique structure and release the loaded drug molecules in a sustained manner up to 10 h at pH 7.4. Such NCs have high potential for use as multifunctional material in various fields such as optical properties, conductivity studies, dielectric, sensor, and drug delivery properties.

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.

Layer-by-layer Polyelectrolytes Coating of Alginate Microgels for Sustained Release of Sodium Benzoate and Zosteric Acid

The potential of sustaining release of very small (Mw < 250 g/mol) hydrophilic drugs up to several days from layer-by-layer (LbL) polyelectrolyte coated alginate microgels (Alg-Ms) was investigated. One purpose is to minimize post-surgical adhesions, which develop in 12 h to 3 days after surgery. The LbL polyelectrolyte layer would serve as a diffusion barrier for their release. The LbL polyelectrolyte bilayers were prepared using poly(allylamine) (PAH) and poly(styrene sulfonate) (PSS). Sodium benzoate (NaB, Mw = 144 g/mol) and zosteric acid (ZA, Mw = 244 g/mol), two anti-inflammatory and anti-microbial compounds, were used as model drugs. A higher number of PAH/PSS bilayer lead to a greater sustained release of both drugs, and with 4 bilayers, the release of NaB and ZA was prolonged from 24 h to 72 h and 120 h, respectively. Fitting the data to the Ritger-Peppas' equation showed that as the bilayer number increased, the release constant and/or exponent decreased, indicating the LbL PAH/PSS bilayer effectively reduced the permeability of these two very small hydrophilic drugs. The ability to prolong the release of such small hydrophilic molecules, which has rarely been investigated previously, would find broad applications in fields such as anti-adhesion treatment and antifouling coatings.

Polyelectrolyte microcapsules built on CaCO3 scaffolds for the integration, encapsulation, and controlled release of copigmented anthocyanins

The all-polysaccharide based polyelectrolyte microcapsules combining copigmentation for anthocyanin encapsulation and stabilization were fabricated. Copigmented complexes of chondroitin sulfate and anthocyanin were preloaded in CaCO₃ scaffold, and then microcapsules were created by coating the sacrificial CaCO₃ using layer-by-layer technique. It was observed that the preloading of copigmented complex affected the precipitation reaction of CaCO₃ and the subsequent entrapment of anthocyanin. With addition of anthocyanin from 0.125 to 0.75 mg, copigmentation can significantly increase the encapsulation efficiency of anthocyanin in CaCO₃, whereas such effect was not obvious at higher loadings. The leakage of anthocyanin during CaCO₃ core dissolution and storage was also inhibited by two polysaccharide layers coupled with copigmentation, which may be related to the formation of interconnecting networks. Additionally, a higher anthocyanin antioxidant activity was provided by carbohydrate matrix. These findings may allow for the encapsulation of large amounts of water-soluble components; particularly natural colorant by copigmented complex-polyelectrolyte structures.

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.

Layer-by-layer assembled biopolymer microcapsule with separate layer cavities generated by gas-liquid microfluidic approach

In this work, a layer-by-layer (LbL) assembled biopolymer microcapsule with separate layer cavities is generated by a novel and convenient gas-liquid microfluidic approach. This approach exhibits combined advantages of microfluidic approach and LbL assembly method, and it can straightforwardly build LbL-assembled capsules in mild aqueous environments at room temperature. In particular, using this approach we can build the polyelectrolyte multilayer capsule with favorable cavities in each layer, and without the need for organic solvent, emulsifying agent, or sacrificial template. Various components (e.g., drugs, proteins, fluorescent dyes, and nanoparticles) can be respectively encapsulated in the separate layer cavities of the LbL-assembled capsules. Moreover, the encapsulated capsules present the ability as colorimetric sensors, and they also exhibit the interesting release behavior. Therefore, the LbL-assembled biopolymer capsule is a promising candidate for biomedical applications in targeted delivery, controlled release, and bio-detection.

Regimes of electrostatic collapse of a highly charged polyelectrolyte in a poor solvent

We perform extensive molecular dynamics simulations of a highly charged, collapsed, flexible polyelectrolyte chain in a poor solvent for the case when the electrostatic interactions, characterized by the reduced Bjerrum length l_B, are strong. We find the existence of several sub-regimes in the dependence of the gyration radius of the chain R_g on l_B characterized by R_g ∼ l. In contrast to a good solvent, the exponent γ for a poor solvent crucially depends on the size and valency of the counterions. To explain the different sub-regimes, we generalize the existing counterion fluctuation theory by including a more complete account of all possible volume interactions in the free energy of the polyelectrolyte chain. We also show that the presence of condensed counterions modifies the effective attraction among the chain monomers and modulates the sign of the second virial coefficient under poor solvent conditions.

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.

Preparation of IL-loaded microreactors based on polyelectrolyte microcapsules

Encapsulation of ionic liquids (ILs) in crosslinked polyelectrolyte microcapsules, made via layer-by-layer assembly (LbL) was successfully conducted. Two different ILs were studied: 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim]BF4 and 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim]PF6. The polyelectrolyte microcapsules were successfully used as microcages for the synthesis of poly(methylmethacrylate) (PMMA), a non water-soluble polymer, in IL medium. Finally, the behaviour of the IL-loaded microreactors in polar and apolar solvents was evaluated. The strategies described in this study offer new routes for the preparation of microreactors incorporating IL which are of interest for many applications in the field of organic synthesis, catalysis and adsorption of active substances.

Polyelectrolyte Multilayers: A Versatile Tool for Preparing Antimicrobial Coatings

The prevention of pathogen colonization of medical implants represents a major medical and financial issue. The development of antimicrobial coatings aimed at protecting against such infections has thus become a major field of scientific and technological research. Three main strategies are developed to design such coatings: (i) the prevention of microorganisms adhesion and the killing of microorganisms (ii) by contact and (iii) by the release of active compounds in the vicinity of the implant. Polyelectrolyte multilayer (PEM) technology alone covers the entire widespread spectrum of functionalization possibilities. PEMs are obtained through the alternating deposition of polyanions and polycations on a substrate, and the great advantages of PEMs are that (i) they can be applied to almost any type of substrate whatever its shape and composition; (ii) various chemical, physicochemical, and mechanical properties of the coatings can be obtained; and (iii) active compounds can be embedded and released in a controlled manner. In this article we will give an overview of the field of PEMs applied to the design of antimicrobial coatings, illustrating the large versatility of the PEM technology.

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.

Controlled drug delivery through a novel PEG hydrogel encapsulated silica aerogel system

A novel composite material consisting of a silica aerogel core coated by a poly(ethylene) glycol (PEG) hydrogel was developed. The potential of this novel composite as a drug delivery system was tested with ketoprofen as a model drug due to its solubility in supercritical carbon dioxide. The results indicated that both drug loading capacity and drug release profiles could be tuned by changing hydrophobicity of aerogels, and that drug loading capacity increased with decreased hydrophobicity, while slower release rates were achieved with increased hydrophobicity. Furthermore, higher concentration of PEG diacrylate in the prepolymer solution of the hydrogel coating delayed the release of the drug which can be attributed to the lower permeability at higher PEG diacrylate concentrations. The novel composite developed in this study can be easily implemented to achieve the controlled delivery of various drugs and/or proteins for specific applications.

Introduction to nanocoatings produced by layer-by-layer (LbL) self-assembly

Studies on the adsorption of oppositely charged colloidal particles ultimately resulted in multilayered polyelectrolyte self-assembly. The inception of layer-by-layer constructed particles facilitated the production of multifunctional, stimuli-responsive carrier systems. An array of synthetic and natural polyelectrolytes, metal oxides and clay nanoparticles is available for the construction of multilayered nanocoats on a multitude of substrates or removable cores. Numerous substrates can be encapsulated utilizing this technique including dyes, enzymes, drugs and cells. Furthermore, the outer surface of the particles presents and ideal platform that can be functionalized with targeting molecules or catalysts. Some processing parameters determining the properties of these successive self-assembly constructs are the surface charge density, coating material concentration, rinsing and drying steps, temperature and ionic strength of the medium. Additionally, the simplicity of the layer-by-layer assembly technique and the availability of established characterization methods, render these constructs extremely versatile in applications of sensing, encapsulation and target- and trigger-responsive drug delivery.