Cytotoxicity of polyethyleneimine (PEI), precursor base layer of polyelectrolyte multilayer films

Polyelectrolyte Multilayer Assemblies on Materials Surfaces: From Cell Adhesion to Tissue Engineering

Controlling the bulk and surface properties of materials is a real challenge for bioengineers working in the fields of biomaterials, tissue engineering and biophysics. The layer-by-layer (LbL) deposition method, introduced 20 years ago, consists in the alternate adsorption of polyelectrolytes that self-organize on the material's surface, leading to the formation of polyelectrolyte multilayer (PEM) films.1 Because of its simplicity and versatility, the procedure has led to considerable developments of biological applications within the past 5 years. In this review, we focus our attention on the design of PEM films as surface coatings for applications in the field of physical properties that have emerged as being key points in relation to biological processes. The numerous possibilities for adjusting the chemical, physical, and mechanical properties of PEM films have fostered studies on the influence of these parameters on cellular behaviors. Importantly, PEM have emerged as a powerful tool for the immobilization of biomolecules with preserved bioactivity.

Silica-iron oxide magnetic nanoparticles modified for gene delivery: a search for optimum and quantitative criteria

PURPOSE

To optimize silica-iron oxide magnetic nanoparticles with surface phosphonate groups decorated with 25-kD branched polyethylenimine (PEI) for gene delivery.

METHODS

Surface composition, charge, colloidal stabilities, associations with adenovirus, magneto-tranduction efficiencies, cell internalizations, in vitro toxicities and MRI relaxivities were tested for the particles decorated with varying amounts of PEI.

RESULTS

Moderate PEI-decoration of MNPs results in charge reversal and destabilization. Analysis of space and time resolved concentration changes during centrifugation clearly revealed that at >5% PEI loading flocculation gradually decreases and sufficient stabilization is achieved at >10%. The association with adenovirus occurred efficiently at levels over 5% PEI, resulting in the complexes stable in 50% FCS at a PEI-to-iron w/w ratio of ≥7%; the maximum magneto-transduction efficiency was achieved at 9-12% PEI. Primary silica iron oxide nanoparticles and those with 11.5% PEI demonstrated excellent r(2)* relaxivity values (>600 s(-1)(mM Fe)(-1)) for the free and cell-internalized particles.

CONCLUSIONS

Surface decoration of the silica-iron oxide nanoparticles with a PEI-to-iron w/w ratio of 10-12% yields stable aqueous suspensions, allows for efficient viral gene delivery and labeled cell detection by MRI.

Supercoiled Minivector DNA resists shear forces associated with gene therapy delivery

Supercoiled DNAs varying from 281 to 5302 bp were subjected to shear forces generated by aerosolization or sonication. DNA shearing strongly correlated with length. Typical sized plasmids (≥ 3000 bp) degraded rapidly. DNAs 2000-3000 bp persisted ~10 min. Even in the absence of condensing agents, supercoiled DNA <1200 bp survived nebulization, and increased forces of sonication were necessary to shear it. Circular vectors were considerably more resistant to shearing than linear vectors of the same length. DNA supercoiling afforded additional protection. These results show the potential of shear-resistant Minivector DNAs to overcome one of the major challenges associated with gene therapy delivery.

Inorganic material coatings and their effect on cytotoxicity

Inorganic materials have become an increasingly researched topic due to their applications in many areas especially health care. One major problem with them is the effect that their surface coatings have on cells. The same coatings that are meant to increase biocompatibility can actually invoke cytotoxicity. This tutorial review focuses on the various types of coatings and how their properties, such as electrostatic charge and hydrophobicity, affect the observed toxicity. The theorized mechanisms by which the coatings induce toxicity are also presented. Finally, the prospects for the future of this field are discussed.

Cytotoxicity of free versus multilayered polyelectrolytes

The cytotoxicity of polyelectrolytes commonly employed for layer-by-layer deposition of polyelectrolyte multilayers (PEMUs) was assessed using rat smooth muscle A7r5 and human osteosarcoma U-2 OS cells. Cell growth, viability, and metabolic assays were used to compare the responses of both cell lines to poly(acrylic acid), PAA, and poly(allylamine hydrochloride), PAH, in solution at concentrations up to 10 mM and to varying thicknesses of (PAA/PAH) PEMUs. Cytotoxicity correlated with increasing concentration of solution polyelectrolytes for both cell types and was greater for the positively charged PAH than for the negatively charged PAA. While metabolism and proliferation of both cell types was slower on PEMUs than on tissue culture plastic, little evidence for direct toxicity on cells was observed. In fact, evidence for more extensive adhesion and cytoskeletal organization was observed with PAH-terminated PEMUs. Differences in cell activity and viability on different thickness PEMU surfaces resulted primarily from differences in attachment for these adhesion-dependent cell lines.

Polyelectrolyte multilayers generated in a microfluidic device with pH gradients direct adhesion and movement of cells

In this study, multilayers from polyethylene imine, heparin and chitosan are prepared at three different pH values of 5, 7 and 9. Water contact angle and quartz microbalance measurements show that resulting multilayers differ in terms of wetting behaviour, layer mass and mechanical properties. The multilayer is then formed within a gradient generation microfluidic (μFL) device. Polyethylene imine or heparin solutions of pH 5 are introduced into one inlet and the same solutions but at pH 9 into another inlet of the μFL device. The pH gradient established during the multilayer formation can be visualized inside the microchamber by pH sensitive fluorophores and confocal laser scanning microscopy. From this setup it is expected that properties of multilayers displayed at distinct pH values can be realised in a gradient manner inside the μFL device. Behaviour of the osteoblast cell line MG-63 seeded and cultured on top of multilayers created inside the μFL device support this hypothesis. It is observed that more cells adhere and spread on multilayers build-up at the basic side of the μFL channel, while those cells on top of multilayers built at pH 5 are fewer and smaller. These results are consistent with the behaviour of MG-63 cells seeded on multilayers formed at discrete pH values. It is particularly interesting to see that cells start to migrate from multilayers built at pH 5 to those built at pH 9 during 6 h of culture. Overall, the presented multilayer formation setup applying pH gradients leads to surfaces that promote migration of cells.

Induction heating vs conventional heating for the hydrothermal treatment of nitinol and its subsequent 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate coating by surface-initiated atom transfer radical polymerization

Nitinol is an alloy of great interest in general and especially in the biomedical field where many researches are aimed to improve both its corrosion resistance and its biocompatibility. In this work, we report on the advantage of an induction heating treatment in pure water compared to a conventional hydrothermal procedure. Both treatments lead to a hydroxylation of the surface, a decrease of the nickel amount in the outer part of the oxide layer, and a drastically decreased corrosion current density. However, the amount of surface hydroxyl groups is higher in the case of the induction heating treatment, which in turn leads to a denser grafting of atom transfer radical polymerization initiators and ultimately to a thicker 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate (MPC) polymer layer than in the case of conventional heating treatments. X-ray photoelectron spectroscopy (XPS), static contact angle, and polarization curves measurements as well as scanning electron microscopy (SEM) have been used to characterize the obtained modified surfaces.

Cytocompatibility of medical biomaterials containing nickel by osteoblasts: a systematic literature review

The present review is based on a survey of 21 studies on the cytocompatibility of medical biomaterials containing nickel, as assessed by cell culture of human and animal osteoblasts or osteoblast-like cells. Among the biomaterials evaluated were stainless steel, NiTi alloys, pure Ni, Ti, and other pure metals. The materials were either commercially available, prepared by the authors, or implanted by various techniques to generate a protective layer of oxides, nitrides, acetylides. The observation that the layers significantly reduced the initial release of metal ions and increased cytocompatibility was confirmed in cell culture experiments. Physical and chemical characterization of the materials was performed. This included, e.g., surface characterization (roughness, wettability, corrosion behavior, quantity of released ions, microhardness, and characterization of passivation layer). Cytocompatibility tests of the materials were conducted in the cultures of human or animal osteoblasts and osteoblast-like cells. The following assays were carried out: cell proliferation and viability test, adhesion test, morphology (by fluorescent microscopy or SEM). Also phenotypic and genotypic markers were investigated. In the majority of works, it was found that the most cytocompatible materials were stainless steel and NiTi alloy. Pure Ni was rendered and less cytocompatible. All the papers confirmed that the consequence of the formation of protective layers was in significant increase of cytocompatibility of the materials. This indicates the possible further modifications of the manufacturing process (formation of the passivation layer).

Design of multifunctional non-viral gene vectors to overcome physiological barriers: dilemmas and strategies

Gene-based therapeutics hold great promise for medical advancement and have been used to treat various human diseases with mixed success. However, their therapeutic application in vivo is limited due largely to several physiological barriers. The design of non-viral gene vectors with the ability to overcome delivery obstacles is currently under extensive investigation. These efforts have placed an emphasis on the development of multifunctional vectors able to execute multiple tasks to simultaneously overcome both extracellular and intracellular obstacles. However, the assembly of these different functionalities into a single system to create multifunctional gene vectors faces many conflicts that largely limit the safe and efficient application of lipoplexes and polyplexes in a systemic delivery. In the review, we have described the dilemmas inherent in the design of a viable, non-viral gene vector equipped with multiple functionalities. The strategies directed towards individual delivery barriers are first summarized, followed by a focus on the design of so-called smart multifunctional vectors with the capability to overcome the delivery difficulties of gene medicines, including the so-called the "polycation dilemma", the "PEG dilemma" and the "package and release dilemma".

Truly nonionic polymer shells for the encapsulation of living cells

Engineering surfaces of living cells with natural or synthetic compounds can mediate intercellular communication and provide a protective barrier from hostile agents. We report on truly nonionic hydrogen-bonded LbL coatings for cell surface engineering. These ultrathin, highly permeable polymer membranes are constructed on living cells without the cationic component typically employed to increase the stability of LbL coatings. Without the cytotoxic cationic PEI pre-layer, the viability of encapsulated cells drastically increases to 94%, in contrast to 20% viability in electrostatically-bonded LbL shells. Moreover, the long-term growth of encapsulated cells is not affected, thus facilitating efficient function of protected cells in hostile environment.

Plasmid-encapsulated polyethylene glycol-grafted polyethylenimine nanoparticles for gene delivery into rat mesenchymal stem cells

Background:

Mesenchymal stem cell transplantation is a promising method in regenerative medicine. Gene-modified mesenchymal stem cells possess superior characteristics of specific tissue differentiation, resistance to apoptosis, and directional migration. Viral vectors have the disadvantages of potential immunogenicity, carcinogenicity, and complicated synthetic procedures. Polyethylene glycol-grafted polyethylenimine (PEG-PEI) holds promise in gene delivery because of easy preparation and potentially targeting modification.

Methods:

A PEG8k-PEI25k graft copolymer was synthesized. Agarose gel retardation assay and dynamic light scattering were used to determine the properties of the nanoparticles. MTT reduction, wound and healing, and differentiation assays were used to test the cytobiological characteristics of rat mesenchymal stem cells, fluorescence microscopy and flow cytometry were used to determine transfection efficiency, and atomic force microscopy was used to evaluate the interaction between PEG-PEI/plasmid nanoparticles and mesenchymal stem cells.

Results:

After incubation with the copolymer, the bionomics of mesenchymal stem cells showed no significant change. The mesenchymal stem cells still maintained high viability, resettled the wound area, and differentiated into adipocytes and osteoblasts. The PEG-PEI completely packed plasmid and condensed plasmid into stable nanoparticles of 100–150 nm diameter. After optimizing the N/P ratio, the PEG-PEI/plasmid microcapsules delivered plasmid into mesenchymal stem cells and obtained an optimum transfection efficiency of 15%–21%, which was higher than for cationic liposomes.

Conclusion:

These data indicate that PEG-PEI is a valid gene delivery agent and has better transfection efficiency than cationic liposomes in mesenchymal stem cells.

Polyelectrolyte multilayers in tissue engineering

The layer-by-layer assembly of sequentially adsorbed, alternating polyelectrolytes has become increasingly important over the past two decades. The ease and versatility in assembling polyelectrolyte multilayers (PEMs) has resulted in numerous wide ranging applications of these materials. More recently, PEMs are being used in biological applications ranging from biomaterials, tissue engineering, regenerative medicine, and drug delivery. The ability to manipulate the chemical, physical, surface, and topographical properties of these multilayer architectures by simply changing the pH, ionic strength, thickness, and postassembly modifications render them highly suitable to probe the effects of external stimuli on cellular responsiveness. In the field of regenerative medicine, the ability to sequester growth factors and to tether peptides to PEMs has been exploited to direct the lineage of progenitor cells and to subsequently maintain a desired phenotype. Additional novel applications include the use of PEMs in the assembly of three-dimensional layered architectures and as coatings for individual cells to deliver tunable payloads of drugs or bioactive molecules. This review focuses on literature related to the modulation of chemical and physical properties of PEMs for tissue engineering applications and recent research efforts in maintaining and directing cellular phenotype in stem cell differentiation.

Controlling Fibroblast Adhesion with Ph Modified Polyelectrolyte Multilayers

Tissue cells need to adhere to a biomaterial surface to promote their growth and differentiation and, thus, foster the integration of implants. As a result, surface features and their modification play an important role in biomedical applications. In this study, the layer-by-layer (LbL) technique was used to design self-assembled polyelectrolyte multilayer (PEM) coatings of polyethyleneimine (PEI) and heparin (HEP) on glass, which will control the adhesion of primary human dermal fibroblasts in a model system. The study showed that, among other surface features, the wettability of surfaces can be controlled by changing the conditions during multilayer self-assembly. Here, the pH value of the HEP solution was adjusted to acidic or alkaline values for terminal layers, which also led to a change in multilayer growth. Further, the study revealed that plain terminal layers were rather cytophobic. Upon pre-adsorption of fibronectin (FN), a clear effect on cell adhesion and morphology in dependence on the pH setup was evident. Proliferation studies clearly showed that terminal layers, which impaired cell adhesion, also inhibited growth of human fibroblasts under serum-conditions. On the other hand, on layers with pronounced cell adhesion an elevated cell growth was also observed. As a result, HEP terminated multilayers are interesting for applications requiring cell repellent properties, whereas PEI terminated multilayers could be used to promote cell adhesion and growth on implant surfaces.

Efficient intracellular gene delivery using the formulation composed of poly (L-glutamic acid) grafted polyethylenimine and histone

PURPOSE

Inefficient endosomal escape and poor nuclear import are thought to contribute to low gene transfer efficiency of polycations. To overcome these drawbacks, we prepared multiple gene delivery formulations including low cytotoxic polycation, histone containing NLSs and chloroquine as the endosomolytic agent.

METHODS

Comb-shaped poly (L-glutamic acid) grafted low-molecular-weight polyethylenimine (PLGE) copolymer was synthesized by aminolysis of poly-γ-benzyl-L-glutamate using low-molecular-weight polyethylenimine (800 Da). The formation of DNA/histone/PLGE terplex was observed by atomic force microscope and gel retardation assay. The particle size and zeta potential of DNA complexes with varying content of histone were also measured to confirm the terplex formation. Cytotoxicity of vectors was assayed by MTT. Multiple gene delivery formulations were optimized to their best transfection efficiency that was monitored by fluorescence microscope and flow cytometry. In vivo gene delivery of the optimal formulation was evaluated by the GFP-expression levels in drosophila melanogaster.

RESULTS

The DNA/histone/PLGE terplex was successfully formed. The PLGE and histone together condensed DNA into small, discrete particles (less than 200 nm in diameter) in isotonic solution. Cytotoxicity of PLGE and histone were much lower than that of PEI 25 K. Either histone or chloroquine contributed to enhancing the levels of transfection activity of PLGE polymer. However, chloroquine and histone did not show a synergistic effect on the improvement of transfection efficiency. The optimal formulation was the DNA/histone/PLGE terplex at the N/P ratio of 15 and histone/ DNA weight ratio of 0.8. Compared with Lipofectamine 2000 and PEI 25 K, the optimal formulation showed significantly increased levels of GFP-expression both in vitro and in vivo.

CONCLUSION

This formulation provided a versatile approach for preparing high efficiency of the polycation-based gene vectors. It also reinforced the finding of earlier studies that nuclear import and endosomal escape were rate-limiting steps for nonviral gene delivery.

Biophysical characterization of copolymer-protected gene vectors

A copolymer-protected gene vector (COPROG) is a three-component gene delivery system consisting of a preformed DNA and branched polyethylenimine (bPEI) complex subsequently modified by the addition of a copolymer (P6YE5C) incorporating both poly(ethylene glycol) (PEG) and anionic peptides. Using fluorescence correlation spectroscopy (FCS) and atomic force microscopy (AFM), we characterized and compared the self-assembly of bPEI/DNA particles and COPROG complexes. In low salt buffer, both bPEI/DNA and COPROG formulations form stable nanoparticles with hydrodynamic radii between 60-120 nm. COPROG particles, as compared to bPEI/DNA, show greatly improved particle stability to both physiological salt as well as low pH conditions. Binding stoichiometry of the three-component COPROG system was investigated by dual-color fluorescence cross-correlation spectroscopy (FCCS). It was found that a significant fraction of P6YE5C copolymer aggregates with excess bPEI forming bPEI/P6YE5C "ghost complexes" with no DNA inside. The ratio of ghost particles to COPROG complexes is about 4:1. In addition, we find a large fraction of excess P6YE5C copolymer, which remains unbound in solution. We observe a 2-4-fold enhanced reporter gene expression with COPROG formulations at various equivalents as compared to bPEI-DNA alone. We believe that both complex stabilization as well as the capture of excess bPEI into ghost particles induced by the copolymer is responsible for the improvement in gene expression.

Multiple functionalities of polyelectrolyte multilayer films: new biomedical applications

The design of advanced functional materials with nanometer- and micrometer-scale control over their properties is of considerable interest for both fundamental and applied studies because of the many potential applications for these materials in the fields of biomedical materials, tissue engineering, and regenerative medicine. The layer-by-layer deposition technique introduced in the early 1990s by Decher, Moehwald, and Lvov is a versatile technique, which has attracted an increasing number of researchers in recent years due to its wide range of advantages for biomedical applications: ease of preparation under "mild" conditions compatible with physiological media, capability of incorporating bioactive molecules, extra-cellular matrix components and biopolymers in the films, tunable mechanical properties, and spatio-temporal control over film organization. The last few years have seen a significant increase in reports exploring the possibilities offered by diffusing molecules into films to control their internal structures or design "reservoirs," as well as control their mechanical properties. Such properties, associated with the chemical properties of films, are particularly important for designing biomedical devices that contain bioactive molecules. In this review, we highlight recent work on designing and controlling film properties at the nanometer and micrometer scales with a view to developing new biomaterial coatings, tissue engineered constructs that could mimic in vivo cellular microenvironments, and stem cell "niches."

Characteristics of model polyelectrolyte multilayer films containing laponite clay nanoparticles

Polyelectrolyte films structure formed by the "layer-by-layer" (LbL) technique can be enriched by addition of charged nanoparticles like carbon nanotubes and silver or hydroxyapatite nanoparticles, which can improve properties of the polyelectrolyte films or modify their functionality. In our paper we examined the formation and properties of model polyelectrolyte multilayers containing a synthetic layered silicate, Laponite. The Laponite nanoparticles were incorporated into multilayer films, which were formed from weak, branched polycation PEI and strong polyanion PSS. Since charge of PEI is pH-dependent, we build up multilayer films in two deposition conditions: pH = 6 when PEI was strongly charged and pH = 10.5 when charge density of PEI was low. Thicknesses of the films constructed with various numbers of Laponite layers were measured by single wavelength ellipsometry. We also determined the differences in permeability for selected electroactive molecules using cyclic voltamperometry. Properties of the films containing clay nanoparticles were compared with model polyelectrolyte multilayer films PEI/PSS formed at the same conditions. We found that Laponite nanoparticles strongly influenced PEI/PSS multilayer film properties. Replacement of PSS by Laponite eliminated the oscillations of the film thickness in the case when PEI was weakly charged. PSS layer adsorbed on top of PEI/Laponite bilayers increased the thickness of multilayer films and improved their barrier properties so synergistic effects between these properties for polyelectrolytes and Laponite nanoparticles could be observed.

Immobilization of poly (ethylene imine) on poly (L-lactide) promotes MG63 cell proliferation and function

Poly (ethylene imine) (PEI) is a polycation widely used for DNA transfection to cells but also applied as primary polycation for layer-by-layer (LBL) assembly of polyelectrolytes. The aim of the present study was to investigate the effect of modification with PEI on the biocompatibility of poly (L-lactide) (PLLA) films. PEI with different molecular weight was immobilized on PLLA by either adsorption or covalent binding. Cell morphologies, immuno-fluorescence staining, cell proliferation by lactate dehydrogenase assay and cell differentiation by alkaline phosphatase assay were utilized to assess the biocompatibility of the modified PLLA using osteoblast cell line MG63. Results revealed that PEI modification remarkably improved cell adhesion, viability, proliferation and function compared with plain PLLA. Hence, PEI-modified PLLA is acceptable as transfection vehicle for engineering of bone and other tissues, or as primary layer to allow LBL assembly to generate biomimetic surface coatings.

pH-dependent modulation of fibroblast adhesion on multilayers composed of poly(ethylene imine) and heparin

Adhesion of tissue cells is a prerequisite for their growth and differentiation but prevents also apoptosis. Here the layer-by-layer technique (LbL) was used to design multilayer structures of poly(ethylene imine) (PEI) and heparin (HEP) on glass as model biomaterial to control the adhesion of primary human dermal fibroblasts. Distinct surface features like wettability, charge and lateral structures were controlled by changing the pH value of the HEP solution during multilayer assembly to acidic, neutral or alkaline values. While plain terminal layers were rather cytophobic, the pre-adsorption of serum or fibronectin (FN) caused a distinct change in cell morphology in dependence on the pH setup. The effect of serum was more prominent on PEI layers probably due to their positive surface charge, whereas the effect of FN was more pronounced on HEP terminated multilayers possibly due to its ability to bind FN specifically. Those layers which hampered cell adhesion also inhibited growth of human fibroblasts under serum conditions. Conversely, on layers where cell adhesion was increased also an elevated growth and, thus, metabolic activity was observed.

Influence of pH on the structure of multilayer films composed of strong and weak polyelectrolytes

The sequential adsorption of oppositely charged polyelectrolytes called the "layer by layer" technique is a method for formation of ultrathin films with controlled thickness and interfacial properties. Composition of polyelectrolyte solutions, pH, and electrolyte concentration are important parameters governing formation of multilayer films. Since pH is the factor controlling charge of weak polyelectrolytes, the structure of multilayers should be sensitive to its value. In this paper we focused on formation of PE multilayer films composed from weak and strong polyelectrolytes. We used weak, branched polycation polyethyleneimine (PEI, 70 kDa) and strong polyanion poly-4-styrenesulfonate (PSS, 70 kDa) to form films by the layer-by-layer technique on the surface of silicon wafers under two deposition conditions: pH = 6 when PEI was strongly charged and pH = 10.5 when the charge density of PEI was low. Thicknesses of films were measured by single wavelength ellipsometry, and the results were confronted with ones concerning mass of the adsorbed films obtained by quartz crystal microbalance. We found that, depending on pH of the solutions, combination of weakly and strongly charged polyelectrolytes gave either linear or nonmonotonic increase of film thickness with a number of deposited PE layers. We observed a good correlation between multilayer film thickness and adsorbed mass. The atomic force microscopy images of surface topography of PEI/PSS films demonstrated large differences between films deposited at pH = 6 and 10.5. Additionally the cyclic voltamperometry was used to determine the differences in permeability of films formed at various pH conditions.

Surface immobilization of poly(ethyleneimine) and plasmid DNA on electrospun poly(L-lactic acid) fibrous mats using a layer-by-layer approach for gene delivery

The method of coating electrospun ultrafine poly(L-lactic acid) fibers with DNA, by building up polyelectrolyte layer(s) of poly(ethyleneimine) (PEI) and plasmid DNA using an electrostatic layer-by-layer deposition method, for gene delivery is presented. The pGL3 encoding luciferase was applied as plasmid DNA. The quantity of pGL3 immobilized on individual fibers increased with increasing pGL3 concentration in the immersion solution (0.017-0.870 mg/mL) and increasing bilayer number of PEI/pGL3 (single-triple). With the exception of one specimen prepared under the condition 0.870 mg/mL pGL3 solution and double PEI/pGL3 layers, the transfection efficiency of COS-7 cells, defined by the ratio of fluorescence intensity (resulting from the presence of luciferase) with respect to the quantity of cellular protein on the fibrous mat increased with increasing quantity of pGL3 on the fibers. In addition to the ease of controlling the quality of polyelectrolyte bilayer(s) by simply changing the concentrations of substances and number of immersing cycles, the features of the electrospun fibrous mat such as a very large surface-to-volume ratio and flexibility, could potentially be employed as a strategy for gene therapy combined with tissue engineering technology.

Structural stability and bioapplicability assessment of hyaluronic acid-chitosan polyelectrolyte multilayers on titanium substrates

Since bacterial infections associated with implants remain a major cause of their failure, this study investigated the use of polyelectrolyte multilayers (PEMs) comprising hyaluronic acid (HA) and chitosan (CH) to confer antibacterial properties on titanium (Ti). HA and CH were deposited on Ti using the layer-by-layer deposition method. The antibacterial efficacy of the functionalized Ti substrates was assessed using Escherichia coli and Staphylococcus aureus. The number of adherent bacteria on Ti functionalized with HA and CH PEMs was up to an order of magnitude lower than that on the pristine Ti. The effects of chemical crosslinking of the PEMs on the structural stability and antibacterial efficacy were investigated. The chemical crosslinking of the PEMs imparts greater structural stability and preserves the antibacterial properties even after the prolonged immersion in phosphate-buffered saline. The cytotoxicity of the PEMs to osteoblasts was evaluated using the MTT assay. The results showed that the biocompatible and long-lasting antibacterial nature of the functionalized Ti substrates offers great potential for reducing implant-associated infections.

Biological evaluation of N-octyl-O-sulfate chitosan as a new nano-carrier of intravenous drugs

An amphiphilic chitosan derivate, N-octyl-O-sulfate chitosan (NOSC) was prepared by octylation of amino group at C-2 position and sulfonylation at C-6 position. Micelle formed by NOSC has great capability in solubilization of water-insoluble drug paclitaxel. Enormous attention was attracted by the potential application of NOSC as a new drug delivery system. Tritium labeled NOSC ((3)H NOSC) was injected by tail vein at dose of 13.44 mg/kg in mice; kidney retained the maximum amount of NOSC all the time even after 24h following the injection. Pharmacokinetic parameters (the area under the plasma concentration-time curve, maximum plasma concentration, apparent plasma half-life of distribution phase and elimination phase, mean residence time, apparent volume of distribution, total body clearance) were obtained by fluorometric method in rats. The results showed a linear pharmacokinetics proceeding of FITC-NOSC in vivo. 75.4+/-11.6% (3)H NOSC of dose was excreted in urine over a 7-day period, urinary excretion was the predominant way of excretion of NOSC compared with bilary or fecal pathway. A series of safety studies consisted of acute toxicity study, intravenous stimulation study, injection anaphylaxis study, hemolysis study and cell viability assay were performed to warrant the biocompatibility of the NOSC as intravenous materials. The LD(50) value of NOSC administrated by i.v. and i.p. were calculated as 102.59 and 130.53 mg/kg, respectively. No intravenous stimulation, injection anaphylaxis, hemolysis and cytotoxicity were observed in the safety studies. The tissue distribution, pharmacokinetics, excretion and safety study were persuasive for the potential application of NOSC as a new drug carrier.

Response of fibroblast activity and polyelectrolyte multilayer films coating titanium

OBJECTIVES

The study of surface properties is a recent and crucial issue in the biomaterial fields applied to Odontology. The reference biomaterial in dental implantology is titanium. The principal objective is a perfect bio-integration in the oral ecosystem, both in terms of mucosal and bone tissues. The aim of this work was to optimize the tissue-titanium interface by applying polyelectrolyte multilayer films on the surface of titanium.

METHODS

The experimental study was undertaken on pure titanium samples. Two types of film ending with polycations or polyanions were selected. Both film types were built with a first poly(ethyleneimine) (PEI) base layer and composed either of poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) or of hyaluronic acid (HA) and poly(l-lysine) (PLL) layers. Final architectures were as follows: PEI-(PSS/PAH)(10), or PEI-(PSS/PAH)(10)-PSS, or chemically cross-linked PEI-(HA/PLL)(10) or PEI-(HA/PLL)(10)-HA. An analysis of the physicochemical characteristics of the surfaces was carried out by tensiometry measurements (dynamic contact angle, wettability, contact angle hysteresis) and atomic force microscopy. A biological study with human fibroblasts was followed over a 7-day culture period at days 0, 2, 4 and 7 to observe the cellular response in terms of morphology (scanning electron microscopy) and viability (Mosmann's test).

RESULTS

The results showed that polyelectrolyte multilayer films could be successfully deposited onto titanium as previously described for glass or composite. Fibroblast adhesion and proliferation was strongly dependent on film type. SEM observations of cells on the different films agreed with the viability cell test. Furthermore, films containing PSS/PAH generated a better cellular response than films containing cross-linked HA/PLL.

CONCLUSION

PSS/PAH polyelectrolyte films coating titanium could represent a new approach for oral bio-integration with great potential for clinical application in the fields of dental implantology. More particularly, the specific biofunctionalization of PSS/PAH films coating titanium could be envisioned by introducing layers of molecules that encourage the bio-integration process between the films.