Biomedical applications of polyelectrolytes

Nonelectrostatic Adsorption of Polyelectrolytes and Mediated Interactions between Solid Surfaces

Polymer-mediated interaction between two solid surfaces is directly connected to the properties of the adsorbed polymer layers. Nonelectrostatic interactions with a surface can significantly impact the adsorption of polyelectrolytes to charged surfaces. We use a classical density functional theory to study the effect of various polyelectrolyte solution properties on the adsorption and interaction between two like-charged surfaces. Our results show that nonelectrostatic interactions not only enhance polyelectrolyte adsorption but can also result in qualitatively different salt effects with respect to the adsorbed amount. In particular, we observe decreasing, increasing, and a previously unreported nonmonotonic behavior in the adsorbed amount of polymer with added salt under the conditions studied, although the nonmonotonic regime only occurs for a narrow range in the parameter space. With sufficient nonelectrostatic adsorption, the adsorbed polymer layers produce a long-range repulsive barrier that is strong enough to overcome dispersive interactions that cause surfaces to attract. Concurrently, a short-range bridging attraction is observed when the two polyelectrolyte layers span both the surfaces. Both the repulsive barrier and bridging attraction depend on the charge density of the polymer backbone and the bulk salt concentration but not on the chain length in the semidilute regime studied.

The Benefits of Smart Nanoparticles in Dental Applications

Dentistry, as a branch of medicine, has undergone continuous evolution over time. The scientific world has focused its attention on the development of new methods and materials with improved properties that meet the needs of patients. For this purpose, the replacement of so-called "passive" dental materials that do not interact with the oral environment with "smart/intelligent" materials that have the capability to change their shape, color, or size in response to an externally stimulus, such as the temperature, pH, light, moisture, stress, electric or magnetic fields, and chemical compounds, has received much attention in recent years. A strong trend in dental applications is to apply nanotechnology and smart nanomaterials such as nanoclays, nanofibers, nanocomposites, nanobubbles, nanocapsules, solid-lipid nanoparticles, nanospheres, metallic nanoparticles, nanotubes, and nanocrystals. Among the nanomaterials, the smart nanoparticles present several advantages compared to other materials, creating the possibility to use them in various dental applications, including preventive dentistry, endodontics, restoration, and periodontal diseases. This review is focused on the recent developments and dental applications (drug delivery systems and restoration materials) of smart nanoparticles.

Impact of the bulk aggregation on the adsorption of oppositely charged polyelectrolyte-surfactant mixtures onto solid surfaces

The understanding of the deposition of oppositely charged polyelectrolytes-surfactant mixtures onto solid surfaces presents a high interest in current days due to the recognized impact of the obtained layers on different industrial sectors and the performance of several consumer products (e.g. formulations of shampoos and hair conditioners). This results from the broad range of structures and properties that can present the mixed layers, which in most of the cases mirror the association process occurring between the polyelectrolyte chains and the oppositely charged surfactants in the bulk. Therefore, the understanding of the adsorption processes and characteristics of the adsorbed layers can be only attained from a careful examination of the self-assembly processes occurring in the solution. This review aims to contribute to the understanding of the interaction of polyelectrolyte-surfactant mixtures with solid surfaces, which is probably one of the most underexplored aspects of these type of systems. For this purpose, a comprehensive discussion on the correlations between the aggregates formed in the solutions and the deposition of the obtained complexes upon such association onto solid surfaces will be presented. This makes it necessary to take a closer look to the most important forces driving such processes.

Chitosan/alginate based multilayers to control drug release from ophthalmic lens

In this study we investigated the possibility of using layer-by-layer deposition, based in natural polymers (chitosan and alginate), to control the release of different ophthalmic drugs from three types of lens materials: a silicone-based hydrogel recently proposed by our group as drug releasing soft contact lens (SCL) material and two commercially available materials: CI26Y for intraocular lens (IOLs) and Definitive 50 for SCLs. The optimised coating, consisting in one double layer of (alginate - CaCl2)/(chitosan+glyoxal) topped with a final alginate-CaCl2 layer to avoid chitosan degradation by tear fluid proteins, proved to have excellent features to control the release of the anti-inflammatory, diclofenac, while keeping or improving the physical properties of the lenses. The coating leads to a controlled release of diclofenac from SCL and IOL materials for, at least, one week. Due to its high hydrophilicity (water contact angle≈0) and biocompatibility, it should avoid the use of further surface treatments to enhance the useŕs comfort. However, the barrier effect of this coating is specific for diclofenac, giving evidence to the need of optimizing the chemical composition of the layers in view of the desired drug.

Investigation of citric acid-glycerol based pH-sensitive biopolymeric hydrogels for dye removal applications: A green approach

Hydrogels are three dimensional polymeric structure with segments of hydrophilic groups. The special structure of hydrogels facilitates the diffusion of solutes into the interior network and possess numerous ionic and non-ionic functional groups, which can absorb or trap ionic dyes from waste water. The present investigation was devoted to the synthesis of a series of citric acid and glycerol based pH sensitive biopolymeric hydrogels using a solventless green approach via condensation polymerization in the presence of acidic medium. The formations of hydrogels were confirmed using various spectral investigations viz., FT-IR, (1)H and (13)C NMR. The thermal properties of various hydrogels have been studied using TGA, DTA and DSC analysis. The rationalized relationship was noticed with increasing of pH from 4.0 to 10.0. The surface morphologies of hydrogels were analyzed using SEM technique which was well supported from the results of swelling studies. Methylene blue has been selected as a cationic dye for its removal from various environmental sources using pH-sensitive biopolymeric hydrogels. The results of dye removal revealed that glycerol based biopolymeric hydrogels have shown an excellent dye removal capacity. Hence, the synthesized pH sensitive biopolymeric hydrogels have an adaptability with pH tuned properties might have greater potential opening in various environmental applications viz., metal ion removal, agrochemical release, purification of water, dye removal etc.

Polyelectrolyte-coated gold nanorods and their biomedical applications

Gold nanorods (GNRs) have been extensively used in biomedical applications, because of their favourable optical properties. Their longitudinal surface plasmon resonance can be tuned, providing a strong near-infrared (NIR) extinction coefficient peak within the tissue transparency window. However, the modification of the surface of GNRs is essential before they can be used for biomedical applications. The number of GNRs taken up by cells and their biodistribution depend on their surface modification. Here, we review the recent advances in modifying GNR surfaces with polyelectrolytes for biomedical applications. Major polyelectrolytes used to coat GNR surfaces over the past few years and the biocompatibility of polyelectrolyte-coated GNRs are discussed.

PEM anchorage on titanium using catechol grafting

BACKGROUND

This study deals with the anchorage of polyelectrolyte films onto titanium surfaces via a cathecol-based linker for biomedical applications.

METHODOLOGY

The following study uses a molecule functionalized with a catechol and a carboxylic acid: 3-(3,4-dihydroxyphenyl)propanoic acid. This molecule is anchored to the TiO(2) substrate via the catechol while the carboxylic acid reacts with polymers bearing amine groups. By providing a film anchorage of chemisorption type, it makes possible to deposit polyelectrolytes on the surface of titanium.

PRINCIPAL FINDINGS

Infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), contact angle and atomic force microscopy (AFM) measurements show that the different steps of grafting have been successfully performed.

CONCLUSIONS

This method based on catechol anchorage of polyelectrolytes open a window towards large possibilities of clinical applications.

Polypeptide nanocoatings for preventing dental and orthopaedic device-associated infection: pH-induced antibiotic capture, release, and antibiotic efficacy

Implant-associated infection is one of the most common and problematic complications for dental and orthopaedic patients. Modification of currently used implant surfaces aimed at bestowing them with antibacterial properties is a promising approach in the development of new biomaterials. In this study, a novel nanotechnology, that is, electrostatic self-assembly, was developed to construct biomimetic polypeptide nanocoatings on commonly used metal implants. A model antibacterial drug, cefazolin, was captured in the polypeptide nanocoating and its release was studied. We have shown that the capture and release of cefazolin was pH-induced and could be controlled, and the developed antibiotic-incorporated polypeptide multilayer nanocoatings could prevent Staphylococcus aureus colonization thus showing great potential for preventing implant-associated infection.

Self-cross-linking polyelectrolyte complexes for therapeutic cell encapsulation

Self-cross-linking polyelectrolytes are used to strengthen the surface of calcium alginate beads for cell encapsulation. Poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride), containing 30 mol % 2-aminoethyl methacrylate, and poly(sodium methacrylate), containing 30 mol % 2-(methacryloyloxy)ethyl acetoacetate, were prepared by radical polymerization. Sequential deposition of these polyelectrolytes on calcium alginate films or beads led to a shell consisting of a covalently cross-linked polyelectrolyte complex that resisted osmotic pressure changes as well as challenges with citrate and high ionic strength. Confocal laser fluorescence microscopy revealed that both polyelectrolytes were concentrated in the outer 7-25 microm of the calcium alginate beads. The thickness of this cross-linked shell increased with exposure time. GPC studies of solutions permeating through analogous flat model membranes showed molecular weight cut-offs between 150 and 200 kg/mol for poly(ethylene glycol), suitable for cell encapsulation. C 2C 12 mouse cells were shown to be viable within calcium alginate capsules coated with the new polyelectrolytes, even though some of the capsules showed fibroid overcoats when implanted in mice due to an immune response.

Chronobiology, drug delivery, and chronotherapeutics

Biological processes and functions are organized in space, as a physical anatomy, and time, as a biological time structure. The latter is expressed by short-, intermediate-, and long-period oscillations, i.e., biological rhythms. The circadian (24-h) time structure has been most studied and shows great importance to the practice of medicine and pharmacotherapy of patients. The phase and amplitude of key physiological and biochemical circadian rhythms contribute to the known predictable-in-time patterns in the occurrence of serious and life-threatening medical events, like myocardial infraction and stroke, and the manifestation and severity of symptoms of chronic diseases, like allergic rhinitis, asthma, and arthritis. Moreover, body rhythms can significantly affect responses of patients to diagnostic tests and, most important to the theme of this special issue, medications. Rhythmicity in the pathophysiology of disease is one basis for chronotherapeutics--purposeful variation in time of the concentration of medicines in synchrony with biological rhythm determinants of disease activity--to optimize treatment outcomes. A second basis is the control of undesired effects of medications, especially when the therapeutic range is narrow and the potential for adverse effects high, which is the case for cancer drugs. A third basis is to meet the biological requirements for frequency-modulated drug delivery, which is the case for certain neuroendocrine peptide analogues. Great progress has been realized with hydrogels, and they offer many advantages and opportunities in the design of chronotherapeutic systems for drug delivery via the oral, buccal, nasal, subcutaneous, transdermal, rectal, and vaginal routes. Nonetheless, innovative delivery systems will be necessary to ensure optimal application of chronotherapeutic interventions. Next generation drug-delivery systems must be configurable so they (i) require minimal volitional adherence, (ii) respond to sensitive biomarkers of disease activity that often vary in time as periodic (circadian rhythmic) and non-periodic (random) patterns to release medication to targeted tissue(s) on a real time as needed basis, and (iii) are cost-effective.

Preparation of a novel freeze thawed poly(vinyl alcohol) composite hydrogel for drug delivery applications

We describe a drug delivery system based on a physically cross-linked poly(vinyl alcohol) (PVA) hydrogel for the release of Theophylline (TH). A composite was created by freezing an aqueous solution of PVA/NaOH onto a PVA/poly(acrylic acid) substrate. This formed a strong interface and demonstrated greater physical strength than the hydrogel alone. Such systems have potential for a variety of localised controlled drug delivery applications, for example, as coatings for implantable devices. Importantly, the results suggest that a versatile synthetic platform is possible that may provide different functional materials or combination of such. The resultant samples were characterised using optical microscopy, modulated differential scanning calorimetry (MDSC) and dissolution testing. The microstructure of the gels was examined using micro-thermal analysis (microTA) which is a combination of atomic force microscopy and thermal analysis. TH was found to have an effect on the crystalline structure and dissolution showed a Fickian release, suggesting that swelling and crystallinity were the controlling mechanisms.

Investigation of a novel freeze-thaw process for the production of drug delivery hydrogels

Poly(vinyl alcohol) (PVA) is a water-soluble, biocompatible and biodegradable polymer, which has been widely applied in biomedical fields. In this paper, novel physically cross-linked hydrogels composed of PVA and comprising a blend of poly(vinyl alcohol) (PVA) with different concentrations of HCl, NaOH and NaCl are prepared by a freezing/thawing treatment of aqueous solutions. The structure and complexation of the electrolytes were studied by Fourier transform infrared (FTIR) spectroscopy. The mechanical properties were investigated using rheometery and the thermal transitions of the hydrogels were examined by modulated differential scanning calorimetry (MDSC). Freeze/thawed PVA gels containing NaOH showed overall enhanced swelling with increased mechanical strength over traditional gels prepared by chemical or irradiative crosslinking techniques. These novel physically cross-linked hydrogels show promise for a variety of biomedical and drug delivery applications.

Brownian dynamics simulations of polyelectrolyte adsorption in shear flow

Brownian dynamics simulations are used to study the adsorption of an isolated polyelectrolyte molecule onto an oppositely charged flat surface in the absence and the presence of an imposed shear flow. The polyelectrolyte is modeled as a freely jointed bead-rod chain where excluded volume interactions are incorporated by using a hard-sphere potential. The total charge along the backbone is distributed uniformly among all the beads, and the beads are allowed to interact with one another and the charged surface through screened Coulombic interactions. The simulations are performed by placing the molecule a fixed distance above the surface, and the adsorption behavior is then studied as a function of screening length. In the absence of an imposed flow, the chain is found to lie flat and extended on the adsorbing surface in the limit of weak screening, whereas in the limit of strong screening it desorbs from the surface and attains free-solution behavior. For intermediate screening, only a small portion of the chain adsorbs and it becomes highly extended in the direction normal to the surface. An imposed shear flow tends to orient the chain in the direction of flow and also leads to increased contact of the chain with the surface.

Electro-responsive drug delivery from hydrogels

Precise control over the release of drug from devices implanted in the body, such as quantity, timing, is highly desirable in order to optimise drug therapy. In this paper, the research on electrically-responsive drug delivery is reviewed. Electrically-controllable drug release from polyelectrolyte hydrogels has been demonstrated in vitro and in vivo (in rats). Pulsatile drug release profiles, in response to alternating application and removal of the electric field have been achieved. Responsive drug release from hydrogels results from the electro-induced changes in the gels, which may deswell, swell or erode in response to an electric field. The mechanisms of drug release include ejection of the drug from the gel as the fluid phase synereses out, drug diffusion along a concentration gradient, electrophoresis of charged drugs towards an oppositely charged electrode and liberation of the entrapped drug as the gel complex erodes. Electrically-responsive drug release is influenced by a number of factors such as the nature of the drug and of the gel, the experimental set-up, magnitude of the electric field etc. In this paper, electrically-responsive hydrogels, response of gels to an electric field and electrically-stimulated drug release are discussed.

Evaluation of the use of xanthan as vehicle for cationic antifungal peptides

Oral candidiasis frequently occurs in individuals with dry mouth syndrome (xerostomia), in immunocompromised patients and in denture wearers. The aim of this study was to develop a formulation which will prolong the retention time of antimicrobial agents at the site of application. The activity against Candida albicans of a synthetic cationic peptide dhvar 1, based on the human fungicidal salivary peptide histatin 5, was tested either in a mixture with the bioadhesive polymer xanthan, or after covalent coupling to this polymer. The presence of xanthan resulted in an increase of the LC50 value of the peptide from 2.6 (S.D.=0.6) to 5.8 (S.D.=4.0). Covalent coupling caused an additional increase of the LC50 value to 18.4 (S. D.=6.7). Coupling caused a reduction of the viscosity and elasticity of the xanthan solution related to the applied concentration of the coupling agent. Incubation of the peptide with clarified human whole saliva resulted in proteolytic degradation of the peptide. In the presence of xanthan the degradation occurred more slowly. It was concluded that xanthan is an appropriate vehicle for antimicrobial peptides in a retention increasing formulation.

Synthetic poly(beta-hydroxyalkanoates) with carboxylic acid or primary amine pendent groups and their complexes

Degradable polyelectrolyte complexes were made by mixing a degradable carboxyl-bearing polyacid, namely poly(beta-malic acid), with a degradable primary amine group-bearing polybase, namely poly(amino serinate), derived from serine. Both oppositely charged polyelectrolytes are functional polymers which belong to the family of poly(beta-hydroxy acid)-type aliphatic polyesters. Poly(amino serinate) polymers were synthesized by a new route starting from the N-carbobenzoxy derivative (N-Z) of DL- or L-serine. These derivatives were allowed to react with mesyl chloride to yield in one step corresponding N-protected derivatives of poly(N-Z-amino serinate) with molar masses in the 20000-40000 range after fractionation. Progressive deprotection of pendent primary amino groups was carried out using a HBr/acetic acid mixture and led to PAS with up to 95% deprotected amine repeat units for less than 15% decrease of the initial molar mass, as shown by N-reprotection with Z groups. Poly(beta-malic acid) and poly(amino serinate) were complexed by mixing aqueous solutions of the two polyelectrolytes: 1-1 neutral precipitates were formed regardless of the respective compositions, provided the molecular weights of both components were high enough. When allowed to age in aqueous media, the solid complexes went rapidly back into solution because of the hydrolytic degradation of at least one of the components. Whether the degradation of one component is affected by that of the other is still unknown.

In Vitro Cytotoxicity Testing of a Candidate Drug Delivery Material

Samples of a newly synthesised class of macromolecular compound, poly(N-allyl acrylamide)s, obtained by thermal condensation at 200°C of a polyelectrolyte complex, polyfallylammonium acrylate), were tested for both cytotoxicity and water absorption. The cytotoxicity tests (Level I), carried out on both an unmodified complex and a fully condensed polyamide, indicate that these materials exert no acute toxicity on 3T3 fibroblast cells. The water absorption tests, carried out on both partially condensed and fully condensed polyamides, at three different pH values, indicate that these materials are suitable to be used for the controlled delivery of drugs containing ionic or polar groups.