Effect of functionalization of multilayered polyelectrolyte films on motoneuron growth

Biocompatible Macroion/Growth Factor Assemblies for Medical Applications

Growth factors are a class of proteins that play a role in the proliferation (the increase in the number of cells resulting from cell division) and differentiation (when a cell undergoes changes in gene expression becoming a more specific type of cell) of cells. They can have both positive (accelerating the normal healing process) and negative effects (causing cancer) on disease progression and have potential applications in gene therapy and wound healing. However, their short half-life, low stability, and susceptibility to degradation by enzymes at body temperature make them easily degradable in vivo. To improve their effectiveness and stability, growth factors require carriers for delivery that protect them from heat, pH changes, and proteolysis. These carriers should also be able to deliver the growth factors to their intended destination. This review focuses on the current scientific literature concerning the physicochemical properties (such as biocompatibility, high affinity for binding growth factors, improved bioactivity and stability of the growth factors, protection from heat, pH changes or appropriate electric charge for growth factor attachment via electrostatic interactions) of macroions, growth factors, and macroion-growth factor assemblies, as well as their potential uses in medicine (e.g., diabetic wound healing, tissue regeneration, and cancer therapy). Specific attention is given to three types of growth factors: vascular endothelial growth factors, human fibroblast growth factors, and neurotrophins, as well as selected biocompatible synthetic macroions (obtained through standard polymerization techniques) and polysaccharides (natural macroions composed of repeating monomeric units of monosaccharides). Understanding the mechanisms by which growth factors bind to potential carriers could lead to more effective delivery methods for these proteins, which are of significant interest in the diagnosis and treatment of neurodegenerative and civilization diseases, as well as in the healing of chronic wounds.

A self-assembled layer-by-layer surface modification to fabricate the neuron-rich model from neural stem/precursor cells

BACKGROUND/PURPOSE

In vitro neural cell-based models have been widely used to mimic the in vivo neural tissue environments and quantitatively understand the effects of pharmaceutical molecules on neural diseases. Recently, several biomimetic neural tissue models have been widely developed by using biomaterials or surface modification. However, the complex protocols of material synthesis or surface modification lack an easy execution to fabricate the neuron favorite environment.

METHODS

In this study, we utilized a layer-by-layer technique as a surface modification method for regulating the behaviors of neural stem/precursor cells (NSPCs) on material surfaces. Polyelectrolyte multilayers (PEMs) via alternate deposition of poly (allylamine hydrochloride) (PAH) and poly (sodium-4-styrenesulfonate) (PSS) were used to culture NSPCs. After incubation for 7 days, the neuronal differentiation of NSPCs and synapse function of differentiated neurons were identified by immunocytochemistry for lineage specific markers.

RESULTS

Compared with the only PAH film, the PSS-ending film (neuron-rich model) was shown to significantly promote differentiation of NSPCs into neurons (more than 50%), form a neuronal network structure; and differentiated neurons exhibiting functional synaptic activity.

CONCLUSION

This study shows that the PEMs provided an easily alternative approach to modify the surface properties; and might be a method to obtain a neuron-rich model for the biological/pharmaceutical applications.

Polyelectrolyte membrane scaffold sustains growth of neuronal cells

Cell immobilization within nano‐thin polymeric shells can provide an optimal concentration of biological material in a defined space and facilitate its directional growth. Herein, polyelectrolyte membrane scaffolds were constructed using a layer‐by‐layer approach to determine the possibility of promoting improved growth of rat cortical neuronal cells. Membrane presence was confirmed by Fourier transform infrared spectroscopy, Zeta potential, and atomic force and scanning electron microscopy. Scaffold performance toward neuronal cell growth was assessed in vitro during a 14‐day culture. Cell conditions were analyzed immunocytochemically. Furthermore, western blot and real‐time PCR analyses were used to validate the presence of neuronal and glial cells on the scaffolds. We observed that alginate/chitosan, alginate/polylysine, and polyethyleneimine/chitosan scaffolds promote neuronal growth similarly to the control, poly‐d‐lysine/laminin. We conclude that membranes maintaining cell viability, integrity and immobilization in systems supporting neuronal regeneration can be applied in neurological disease or wound healing treatment. © 2018 The Authors. Journal of Biomedical Materials Research Part A published by Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 839–850, 2019.

Layers and Multilayers of Self-Assembled Polymers: Tunable Engineered Extracellular Matrix Coatings for Neural Cell Growth

Growing primary cells and tissue in long-term cultures, such as primary neural cell culture, presents many challenges. A critical component of any environment that supports neural cell growth in vivo is an appropriate 2-D surface or 3-D scaffold, typically in the form of a thin polymer layer that coats an underlying plastic or glass substrate and aims to mimic critical aspects of the extracellular matrix. A fundamental challenge to mimicking a hydrophilic, soft natural cell environment is that materials with these properties are typically fragile and are difficult to adhere to and stabilize on an underlying plastic or glass cell culture substrate. In this review, we highlight the current state of the art and overview recent developments of new artificial extracellular matrix (ECM) surfaces for in vitro neural cell culture. Notably, these materials aim to strike a balance between being hydrophilic and soft while also being thick, stable, robust, and bound well to the underlying surface to provide an effective surface to support long-term cell growth. We focus on improved surface and scaffold coating systems that can mimic the natural physicochemical properties that enhance neuronal survival and growth, applied as soft hydrophilic polymer coatings for both in vitro cell culture and for implantable neural probes and 3-D matrixes that aim to enhance stability and longevity to promote neural biocompatibility in vivo. With respect to future developments, we outline four emerging principles that serve to guide the development of polymer assemblies that function well as artificial ECMs: (a) design inspired by biological systems and (b) the employment of principles of aqueous soft bonding and self-assembly to achieve (c) a high-water-content gel-like coating that is stable over time in a biological environment and possesses (d) a low modulus to more closely mimic soft, compliant real biological tissue. We then highlight two emerging classes of thick material coatings that have successfully captured these guiding principles: layer-by-layer deposited water-soluble polymers (LbL) and silk fibroin (SF) materials. Both materials can be deposited from aqueous solution yet transition to a water-insoluble coating for long-term stability while retaining a softness and water content similar to those of biological materials. These materials hold great promise as next-generation biocompatible coatings for tissue engineers and for chemists and biologists within the biomedical field.

Association between biomechanical alterations and migratory ability of semaphorin-3A-treated thymocytes

BACKGROUND

Class 3 semaphorins are soluble proteins involved in cell adhesion and migration. Semaphorin-3A (Sema3A) was initially shown to be involved in neuronal guidance, and it has also been reported to be associated with immune disorders. Both Sema3A and its receptors are expressed by most immune cells, including monocytes, macrophages, and lymphocytes, and these proteins regulate cell function. Here, we studied the correlation between Sema3A-induced changes in biophysical parameters of thymocytes, and the subsequent repercussions on cell function.

METHODS

Thymocytes from mice were treated in vitro with Sema3A for 30min. Scanning electron microscopy was performed to assess cell morphology. Atomic force microscopy was performed to further evaluate cell morphology, membrane roughness, and elasticity. Flow cytometry and/or fluorescence microscopy were performed to assess the F-actin cytoskeleton and ROCK2. Cell adhesion to a bovine serum albumin substrate and transwell migration assays were used to assess cell migration.

RESULTS

Sema3A induced filopodia formation in thymocytes, increased membrane stiffness and roughness, and caused a cortical distribution of the cytoskeleton without changes in F-actin levels. Sema3A-treated thymocytes showed reduced substrate adhesion and migratory ability, without changes in cell viability. In addition, Sema3A was able to down-regulate ROCK2.

CONCLUSIONS

Sema3A promotes cytoskeletal rearrangement, leading to membrane modifications, including increased stiffness and roughness. This effect in turn affects the adhesion and migration of thymocytes, possibly due to a reduction in ROCK2 expression.

GENERAL SIGNIFICANCE

Sema3A treatment impairs thymocyte migration due to biomechanical alterations in cell membranes.

Rat Nerve Regeneration with the Use of a Polymeric Membrane Loaded with NGF

Exogenous neurotrophic factors, delivered by various systems, are used to improve nerve regeneration. This study tested the effectiveness of a polymeric membrane loaded with Nerve Growth Factor (NGF) on mental nerve regeneration after a crush injury in rats. We tested NGF application, known to play a role in afferent fiber repair in dental neurobiology, to see if it could improve the regeneration. Afferent neurogram recordings and histological analyses of the trigeminal ganglion neurons were performed. One month after the crush injury, early regeneration was observed independently of exogenous NGF. However, as compared with the activity level recorded before the injury, the afferent activity was reduced by 28.5% without NGF, and the mean number of labeled neurons decreased. With NGF, activity was increased by 30.8%, with no significant histological difference compared with animals without lesions. NGF application through a polymeric membrane can influence degenerative and/or regenerative processes after a crush injury.

Biomimetic Extracellular Environment Based on Natural Origin Polyelectrolyte Multilayers

Surface modification of biomaterials is a well-known approach to enable an adequate biointerface between the implant and the surrounding tissue, dictating the initial acceptance or rejection of the implantable device. Since its discovery in early 1990s layer-by-layer (LbL) approaches have become a popular and attractive technique to functionalize the biomaterials surface and also engineering various types of objects such as capsules, hollow tubes, and freestanding membranes in a controllable and versatile manner. Such versatility enables the incorporation of different nanostructured building blocks, including natural biopolymers, which appear as promising biomimetic multilayered systems due to their similarity to human tissues. In this review, the potential of natural origin polymer-based multilayers is highlighted in hopes of a better understanding of the mechanisms behind its use as building blocks of LbL assembly. A deep overview on the recent progresses achieved in the design, fabrication, and applications of natural origin multilayered films is provided. Such films may lead to novel biomimetic approaches for various biomedical applications, such as tissue engineering, regenerative medicine, implantable devices, cell-based biosensors, diagnostic systems, and basic cell biology.

Breast Cancer/Stromal Cells Coculture on Polyelectrolyte Films Emulates Tumor Stages and miRNA Profiles of Clinical Samples

In this study, we demonstrate a method for controlling breast cancer cells adhesion on polyelectrolyte multilayer (PEM) films without the aid of adhesive proteins/ligands to study the role of tumor and stromal cell interaction on cancer biology. Numerous studies have explored engineering coculture of tumor and stromal cells predominantly using transwell coculture of stromal cells cultured onto coverslips that were subsequently added to tumor cell cultures. However, these systems imposed an artificial boundary that precluded cell-cell interactions. To our knowledge, this is the first demonstration of patterned coculture of tumor cells and stromal cells that captures the temporal changes in the miRNA signature as the breast tumor develops through various stages. In our study we used synthetic polymers, namely poly(diallyldimethylammonium chloride) (PDAC) and sulfonated poly(styrene) (SPS), as the polycation and polyanion, respectively, to build PEMs. Breast cancer cells attached and spread preferentially on SPS surfaces while stromal cells attached to both SPS and PDAC surfaces. SPS patterns were formed on PEM surfaces, by either capillary force lithography (CFL) of SPS onto PDAC surfaces or vice versa, to obtain patterns of breast cancer cells and patterned cocultures of breast cancer and stromal cells. In this study, we utilized cancer cells derived from two different tumor stages and two different stromal cells to effectively model a heterogeneous tumor microenvironment and emulate various tumor stages. The coculture model mimics the proliferative index (Ki67 expression) and tumor aggressiveness (HER-2 expression) akin to those observed in clinical tumor samples. We also demonstrated that our patterned coculture model captures the temporal changes in the miRNA-21 and miRNA-34 signature as the breast tumor develops through various stages. The engineered coculture platform lays groundwork toward precision medicine wherein patient-derived tumor cells can be incorporated within our in vitro models to identify potential pathways and drug treatment regimens for individual patients.

Functionalised nanoscale coatings using layer-by-layer assembly for imparting antibacterial properties to polylactide-co-glycolide surfaces

In order to achieve high local biological activity and reduce the risk of side effects of antibiotics in the treatment of periodontal and bone infections, a localised and temporally controlled delivery system is desirable. The aim of this research was to develop a functionalised and resorbable surface to contact soft tissues to improve the antibacterial behaviour during the first week after its implantation in the treatment of periodontal and bone infections. Solvent-cast poly(d,l-lactide-co-glycolide acid) (PLGA) films were aminolysed and then modified by Layer-by-Layer technique to obtain a nano-layered coating using poly(sodium4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) as polyelectrolytes. The water-soluble antibiotic, metronidazole (MET), was incorporated from the ninth layer. Infrared spectroscopy showed that the PSS and PAH absorption bands increased with the layer number. The contact angle values had a regular alternate behaviour from the ninth layer. X-ray Photoelectron Spectroscopy evidenced two distinct peaks, N1s and S2p, indicating PAH and PSS had been introduced. Atomic Force Microscopy showed the presence of polyelectrolytes on the surface with a measured roughness about 10nm after 20 layers' deposition. The drug release was monitored by Ultraviolet-visible spectroscopy showing 80% loaded-drug delivery in 14 days. Finally, the biocompatibility was evaluated in vitro with L929 mouse fibroblasts and the antibacterial properties were demonstrated successfully against the keystone periodontal bacteria Porphyromonas gingivalis, which has an influence on implant failure, without compromising in vitro biocompatibility. In this study, PLGA was successfully modified to obtain a localised and temporally controlled drug delivery system, demonstrating the potential value of LbL as a coating technology for the manufacture of medical devices with advanced functional properties.

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.

Brain derived neurotrophic factor release from layer-by-layer coated agarose nerve guidance scaffolds

Agarose nerve guidance scaffolds (NGS) seeded with cells expressing brain derived neurotrophic factor (BDNF) have demonstrated robust nerve regeneration in the rat central nervous system. The purpose of this work was to explore whether agarose NGS coated with hydrogen-bonded layer-by-layer (HLbL) could provide an acellular method of delivering prolonged and consistent dosages of active BDNF. Our results show that HLbL-coated agarose NGS could release BDNF over 10days in consistent dosages averaging 80.5±12.5(SD)ng/mL. Moreover, the BDNF released from HLbL was confirmed active by in vitro cell proliferation assays. To our knowledge, this is the first report demonstrating that HLbL assembled onto a hydrogel can provide consistent, prolonged release of active BDNF in clinically relevant dosages.

Rational design of a degradable polyanion for layer-by-layer assembly for encapsulation and release of cationic functional biomolecules

We designed and synthesized a novel degradable polyanion, poly(phthalic ethylene glycol ester), that assembles with various polycationic biomolecules to form layer-by-layer films to encapsulate and release physiologically active biomolecules.

Accelerated neuronal differentiation toward motor neuron lineage from human embryonic stem cell line (H9)

Motor neurons loss plays a pivotal role in the pathoetiology of various debilitating diseases such as, but not limited to, amyotrophic lateral sclerosis, primary lateral sclerosis, progressive muscular atrophy, progressive bulbar palsy, pseudobulbar palsy, and spinal muscular atrophy. However, advancement in motor neuron replacement therapy has been significantly constrained by the difficulties in large-scale production at a cost-effective manner. Current methods to derive motor neuron heavily rely on biochemical stimulation, chemical biological screening, and complex physical cues. These existing methods are seriously challenged by extensive time requirements and poor yields. An innovative approach that overcomes prior hurdles and enhances the rate of successful motor neuron transplantation in patients is of critical demand. Iron, a trace element, is indispensable for the normal development and function of the central nervous system. Whether ferric ions promote neuronal differentiation and subsequently promote motor neuron lineage has never been considered. Here, we demonstrate that elevated iron concentration can drastically accelerate the differentiation of human embryonic stem cells (hESCs) toward motor neuron lineage potentially via a transferrin mediated pathway. HB9 expression in 500 nM iron-treated hESCs is approximately twofold higher than the control. Moreover, iron treatment generated more matured and functional motor neuron-like cells that are ∼1.5 times more sensitive to depolarization when compared to the control. Our methodology renders an expedited approach to harvest motor neuron-like cells for disease, traumatic injury regeneration, and drug screening.

Ordered and kinetically discrete sequential protein release from biodegradable thin films

Multidrug regimens can sometimes treat recalcitrant diseases when single-drug therapies fail. Recapitulating complex multidrug administration from controlled release films for localized delivery remains challenging because their release kinetics are frequently intertwined, and an initial burst release of each drug is usually uncontrollable. Kinetic control over protein release is demonstrated by cross-linking layer-by-layer films during the assembly process. We used biodegradable and naturally derived components and relied on copper-free click chemistry for bioorthogonal covalent cross-links throughout the film that entrap but do not modify the embedded protein. We found that this strategy restricted the interdiffusion of protein while maintaining its activity. By depositing a barrier layer and a second protein-containing layer atop this construct, we generated well-defined sequential protein release with minimal overlap that follows their spatial distribution within the film.

Spatial patterning of BMP-2 and BMP-7 on biopolymeric films and the guidance of muscle cell fate

In the cellular microenvironment, growth factor gradients are crucial in dictating cell fate. Towards developing materials that capture the native microenvironment we engineered biomimetic films that present gradients of matrix-bound bone morphogenetic proteins (BMP-2 and BMP-7). To this end layer-by-layer films composed of poly(L-lysine) and hyaluronan were combined in a simple microfluidic device enabling spatially controlled growth factor diffusion along the film. Linear long-range gradients of both BMPs induced the trans-differentiation of C2C12 myoblasts towards the osteogenic lineage in a dose dependent manner with a different signature for each BMP. The osteogenic marker alkaline phosphatase (ALP) increased in a linear manner for BMP-7 and non-linearly for BMP-2. Moreover, an increased expression of the myogenic marker troponin T was observed with decreasing matrix-bound BMP concentration, providing a substrate that it is both osteo- and myo-inductive. Lastly, dual parallel matrix-bound gradients of BMP-2 and -7 revealed a complete saturation of the ALP signal. This suggested an additive or synergistic effect of the two BMPs. This simple technology allows for determining quickly and efficiently the optimal concentration of matrix-bound growth factors, as well as for investigating the presentation of multiple growth factors in their solid-phase and in a spatially controlled manner.

In vitro evaluation of chondrosarcoma cells and canine chondrocytes on layer-by-layer (LbL) self-assembled multilayer nanofilms

Short-term cell-substrate interactions of two secondary chondrocyte cell lines (human chondrosarcoma cells, canine chondrocytes) with layer-by-layer self-assembled multilayer nanofilms were investigated for a better understanding of cellular-behaviour dependence on a number of nanofilm layers. Cell-substrate interactions were studied on polyelectrolyte multilayer nanofilms (PMNs) of eleven different biomaterials. Surface characterization of PMNs performed using AFM showed increasing surface roughness with increasing number of layers for most of the biomaterials. LDH-L and MTT assays were performed on chondrosarcoma cells and canine chondrocytes, respectively. A major observation was that 10-bilayer nanofilms exhibited lesser cytotoxicity towards human chondrosarcoma cells than their 5-bilayer counterparts. In the case of canine chondrocytes, BSA enhanced cell metabolic activity with increasing number of layers, underscoring the importance of the multilayer nanofilm architecture on cellular behaviour.

Secondary structure of rhBMP-2 in a protective biopolymeric carrier material

Efficient delivery of growth factors is one of the great challenges of tissue engineering. Polyelectrolyte multilayer films (PEM) made of biopolymers have recently emerged as an interesting carrier for delivering recombinant human bone morphogenetic protein 2 (rhBMP-2 noted here BMP-2) to cells in a matrix-bound manner. We recently showed that PEM made of poly(l-lysine) and hyaluronan (PLL/HA) can retain high and tunable quantities of BMP-2 and can deliver it to cells to induce their differentiation in osteoblasts. Here, we investigate quantitatively by Fourier transform infrared spectroscopy (FTIR) the secondary structure of BMP-2 in solution as well as trapped in a biopolymeric thin film. We reveal that the major structural elements of BMP-2 in solution are intramolecular β-sheets and unordered structures as well as α-helices. Furthermore, we studied the secondary structure of rhBMP-2 trapped in hydrated films and in dry films since drying is an important step for future applications of these bioactive films onto orthopedic biomaterials. We demonstrate that the structural elements were preserved when BMP-2 was trapped in the biopolymeric film in hydrated conditions and, to a lesser extent, in dry state. Importantly, its bioactivity was maintained after drying of the film. Our results appear highly promising for future applications of these films as coatings of biomedical materials, to deliver bioactive proteins while preserving their bioactivity upon storage in dry state.

Nanoporous peptide particles for encapsulating and releasing neurotrophic factors in an animal model of neurodegeneration

Neurotrophin-BDNF can be effectively encapsulated in nanoporous poly(L-glutamic acid) particles prepared via mesoporous silica templating. The loaded BDNF can be released in a sustained manner with retained biological activity. Animal experiments demonstrate the released BDNF can efficiently rescue the auditory neurons (as indicated by the arrows) in the cochlea of guinea pigs with sensorineural hearing loss.

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.

Drug releasing polymer thin films: new era of surface-mediated drug delivery

Polymer films and coatings are among the popular and most successful tools to modulate surface properties of biomaterials, specifically tissue responses and fouling behavior. Over the past decade, a novel opportunity has been widely investigated, namely utility of surface coatings in surface-mediated drug delivery. In these applications, deposited polymer films act as both a coating to modulate surface properties and a reservoir for active therapeutic cargo. The field has recently accelerated beyond the proof-of-concept reports toward delivering practical solutions and established technologies for biomedical applications. This review briefly summarizes the recent successes of polymer thin films, specifically those constructed by sequential polymer deposition technique, in surface-mediated drug delivery.

Polysaccharide-blend multilayers containing hyaluronan and heparin as a delivery system for rhBMP-2

It is shown that blend multilayers of hyaluronan (HA) and heparin (HEP) as polyanions and poly(L-lysine) (PLL) as a polycation can be used to prepare films with different thicknesses and chemical compositions. The amounts of recombinant human BMP-2 (rhBMP-2) loaded and the fraction initially released from the films depend on the film's chemical composition. The amounts of rhBMP-2 loaded in the films are much higher for HA mass fractions of more than 0.4. The bioactivity of the rhBMP-2-loaded films is investigated on C2C12 myoblasts, which differentiates into osteoblasts in contact with the films. The alkaline phosphatase expression for cells grown on nanoblend films of various compositions falls over a unique curve. This suggests that the cells "sensing" the rhBMP-2 are not influenced by the film's chemistry. The rhBMP-2 can sustain at least three successive culture sequences while remaining bioactive, thus confirming the important and protective effect of rhBMP-2. Altogether, these results indicate that crosslinked PLL/HA films have superior properties for the incorporation of rhBMP-2 and on its long-lasting bioactivity.

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."

Controlled drug release from multilayered phospholipid polymer hydrogel on titanium alloy surface

Here we describe the functionalization of a multilayered hydrogel layer on a Ti alloy with an antineoplastic agent, paclitaxel (PTX). The multilayered hydrogel was synthesized via layer-by-layer self-assembly (LbL) using selective intermolecular reactions between two water-soluble polymers, phospholipid polymer (PMBV) containing a phenylboronic acid unit and poly(vinyl alcohol) (PVA). Reversible covalent bonding between phenylboronic acid and the polyol provided the driving force for self-assembly. Poorly water-soluble PTX dissolves in PMBV aqueous solutions because PMBV is amphiphilic. Therefore, our multilayered hydrogel could be loaded with PTX at different locations to control the release profile and act as a drug reservoir. The amount of PTX incorporated in the hydrogel samples increased with the number of layers but was not directly proportional to the number of layers. However, as the step for making layers was repeated, the concentration of PTX in the PMBV layers increased. The different solubilities of PTX in PMBV and PVA aqueous solutions allow for the production of multilayered hydrogels loaded with PTX at different locations. In vitro experiments demonstrated that the location of PTX in the multilayered hydrogel influences the start and profile of PTX release. We expect that this rapid and facile LbL synthesis of multilayered hydrogels and technique for in situ loading with PTX, where the location of loading controls the release pattern, will find applications in biomedicine and pharmaceutics as a promising new technique.

Layer-by-layer films as a biomimetic reservoir for rhBMP-2 delivery: controlled differentiation of myoblasts to osteoblasts

Efficient delivery of growth or survival factors to cells is one of the most important long-term challenges of current cell-based tissue engineering strategies. The extracellular matrix acts as a reservoir for a number of growth factors through interactions with its components. In the matrix, growth factors are protected against circulating proteases and locally concentrated. Thus, the localized and long-lasting delivery of a matrix-bound recombinant human bone morphogenetic protein 2 (rhBMP-2) from a biomaterial surface would mimic in vivo conditions and increase BMP-2 efficiency by limiting its degradation. Herein, it is shown that crosslinked poly(L-lysine)/hyaluronan (HA) layer-by-layer films can serve as a reservoir for rhBMP-2 delivery to myoblasts and induce their differentiation into osteoblasts in a dose-dependent manner. The amount of rhBMP-2 loaded in the films is controlled by varying the deposition conditions and the film thickness. Its local concentration in the film is increased up to approximately 500-fold when compared to its initial solution concentration. Its adsorption on the films, as well as its diffusion within the films, is evidenced by microfluorimetry and confocal microscopy observations. A direct interaction of rhBMP-2 with HA is demonstrated by size-exclusion chromatography, which could be at the origin of the rhBMP-2 "trapping" in the film and of its low release from the films. The bioactivity of rhBMP-2-loaded films is due neither to film degradation nor to rhBMP-2 release. The rhBMP-2-containing films are extremely resistant and could sustain three successive culture sequences while remaining bioactive, thus confirming the important and protective effect of rhBMP-2 immobilization. These films may find applications in the local delivery of immobilized growth factors for tissue-engineered constructs and for metallic biomaterial surfaces, as they can be deposited on a wide range of substrates with different shapes, sizes, and composition.

Antibacterial protection of suture material by chlorhexidine-functionalized polyelectrolyte multilayer films

The formation of bacterial biofilms on the surface of implanted materials is a critical factor that may lead to chronic microbial infection and tissue necrosis. In the present study we analysed the stability of polyelectrolyte multilayer (ML) films on suture materials and the antibacterial effect obtained with chlorhexidine (CHX)-functionalized films built on different types of suture materials such as silk, polyester and copolymer of glycolide and L: -lactide. The comparison of Escherichia coli culture on glass coverslips and glass coverslips with ML and CHX showed at 24 h an inhibition of the bacterial relative luminescence (40.68%, P < 0.5) and at 48 h (99.46%, P < 0.001). In another way, simple soaking of suture material overnight in CHX digluconate 20% without polyelectrolyte films did not at all protect sutures from bacterial colonization but CHX-functionalized polyelectrolyte films, made from poly-L: -glutamic acid and poly-L: -lysine, inhibited Escherichia coli proliferation.

Coating electrospun poly(epsilon-caprolactone) fibers with gelatin and calcium phosphate and their use as biomimetic scaffolds for bone tissue engineering

Electrospinning was employed to fabricate fibrous scaffolds of poly(epsilon-caprolactone) in the form of nonwoven mats. The surfaces of the fibers were then coated with gelatin through layer-by-layer self-assembly, followed by functionalization with a uniform coating of bonelike calcium phosphate by mineralization in the 10 times concentrated simulated body fluid for 2 h. Transmission electron microscopy, water contact angle, and scanning electron microscopy measurements confirmed the presence of gelatin and calcium phosphate coating layers, and X-ray diffraction results suggested that the deposited mineral phase was a mixture of dicalcium phosphate dehydrate (a precursor to apatite) and apatite. It was also demonstrated that the incorporation of gelatin promoted nucleation and growth of calcium phosphate. The porous scaffolds could mimic the structure, composition, and biological function of bone extracellular matrix. It was found that the preosteoblastic MC3T3-E1 cells attached, spread, and proliferated well with a flat morphology on the mineralized scaffolds. The proliferation rate of the cells on the mineralized scaffolds was significantly higher (by 1.9-fold) than that on the pristine fibrous scaffolds after culture for 7 days. These results indicated that the hybrid system containing poly(epsilon-caprolactone), gelatin, and calcium phosphate could serve as a new class of biomimetic scaffolds for bone tissue engineering.

Embedded silver ions-containing liposomes in polyelectrolyte multilayers: cargos films for antibacterial agents

A new antibacterial coating made of poly(L-lysine)/hyaluronic acid (PLL/HA) multilayer films and liposome aggregates loaded with silver ions was designed. Liposomes filled with an AgNO 3 solution were first aggregated by the addition of PLL in solution. The obtained micrometer-sized aggregates were then deposited on a PLL/HA multilayer film, playing the role of a spacer with the support. Finally, HA/PLL/HA capping layers were deposited on top of the architecture to form a composite AgNO 3 coating. Release of encapsulated AgNO 3 from this composite coating was followed and triggered upon temperature increase over the transition temperature of vesicles, found to be equal to 34 degrees C. After determination of the minimal inhibitory concentration (MIC) of AgNO 3 in solution, the antibacterial activity of the AgNO 3 coating was investigated against Escherichia coli. A 4-log reduction in the number of viable E. coli cells was observed after contact for 120 min with a 120 ng/cm (2) AgNO 3 coating. In comparison, no bactericidal activity was found for PLL/HA films previously dipped in an AgNO 3 solution and for PLL/HA films with liposome aggregates containing no AgNO 3 solution. The strong bactericidal effect could be linked to the diffusion of silver ions out of the AgNO 3 coating, leading to an important bactericidal concentration close to the membrane of the bacteria. A simple method to prepare antibacterial coatings loaded with a high and controlled amount of AgNO 3 is therefore proposed. This procedure is far superior to that soaking AgNO 3 or Ag nanoparticles into a coating. In principle, other small bactericidal chemicals like antibiotics could be encapsulated by this method. This study opens a new route to modify surfaces with small solutes that are not permeating phospholipid membranes below the phase transition temperature.

Design, synthesis and applications of hyaluronic acid-paclitaxel bioconjugates

Paclitaxel (1a), a well known antitumor agent adopted mainly for the treatment of breast and ovarian cancer, suffers from significant disadvantages such as low solubility, certain toxicity and specific drug-resistance of some tumor cells. To overcome these problems extensive research has been carried out. Among the various proposed strategies, the conjugation of paclitaxel (1a) to a biocompatible polymer, such as hyaluronic acid (HA, 2), has also been considered. Coupling a bioactive compound to a biocompatible polymer offers, in general, many advantages such as better drug solubilization, better stabilization, specific localization and controlled release. Hereafter the design, synthesis and applications of hyaluronic acid-paclitaxel bioconjugates are reviewed. An overview of HA-paclitaxel combinations is also given.

Primary Neuron/Astrocyte Co-Culture on Polyelectrolyte Multilayer Films: A Template for Studying Astrocyte-Mediated Oxidative Stress in Neurons

We engineered patterned co-cultures of primary neurons and astrocytes on polyelectrolyte multilayer (PEM) films without the aid of adhesive proteins/ligands to study the oxidative stress mediated by astrocytes on neuronal cells. A number of studies have explored engineering co-culture of neurons and astrocytes predominantly using cell lines rather than primary cells owing to the difficulties involved in attaching primary cells onto synthetic surfaces. To our knowledge this is the first demonstration of patterned co-culture of primary neurons and astrocytes for studying neuronal metabolism. In our study, we used synthetic polymers, namely poly(diallyldimethylammoniumchloride) (PDAC) and sulfonated poly(styrene) (SPS) as the polycation and polyanion, respectively, to build the multilayers. Primary neurons attached and spread preferentially on SPS surfaces, while primary astrocytes attached to both SPS and PDAC surfaces. SPS patterns were formed on PEM surfaces, either by microcontact printing SPS onto PDAC surfaces or vice-versa, to obtain patterns of primary neurons and patterned co-cultures of primary neurons and astrocytes. We further used the patterned co-culture system to study the neuronal response to elevated levels of free fatty acids as compared to the response in separated monoculture by measuring the level of reactive oxygen species (ROS; a widely accepted marker of oxidative stress). The elevation in the ROS levels was observed to occur earlier in the patterned co-culture system than in the separated monoculture system. The results suggest that this technique may provide a useful tool for engineering neuronal co-culture systems, that may more accurately capture neuronal function and metabolism, and thus could be used to obtain valuable insights into neuronal cell function and perhaps even the pathogenesis of neurodegenerative diseases.

Development of an artificial neuronal network with post-mitotic rat fetal hippocampal cells by polyethylenimine

The selection of appropriate surface materials that promote cellular adhesion and growth is an important consideration when designing a simplified neuronal network in vitro. In the past, extracellular matrix proteins such as laminin (LN) or positively charged substances such as poly-l-lysine (PLL) have been used. In this study, we examined the ability of another positively charged polymer, polyethyleneimine (PEI), to promote neuronal adhesion, growth and the formation of a functional neuronal network in vitro. PEI, PLL and LN were used to produce grid-shape patterns on glass coverslips by micro-contact printing. Post-mitotic neurons from the rat fetal hippocampus were cultured on the different polymers and the viability and morphology of these neurons under serum-free culture conditions were observed using fluorescent microscopy and atomic force microscopy (AFM). We show that neurons cultured on the PEI- and PLL-coated surfaces adhered to and extended neurites along the grid-shape patterns, whereas neurons cultured on the LN-coated coverslips clustered into clumps of cells. In addition, we found that the neurons on the PEI and PLL-coated grids survived for more than 2 weeks in serum-free conditions, whereas most neurons cultured on the LN-coated grids died after 1 week. Using AFM, we observed some neurosynapse-like structures near the neuronal soma on PEI-coated coverslips. These findings indicate that PEI is a suitable surface for establishing a functional neuronal network in vitro.

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

Polyethyleneimine (PEI) is a synthetic polymer commonly used as precursor base layer in polyelectrolyte multilayer films. However, the biological properties of this cationic macromolecule are poorly understood. The aim of this experimental investigation was to evaluate in vitro the biocompatibility of PEI towards two different human cell lines. The experimental investigation was undertaken on pure titanium (Ti) and nickel-titanium (NiTi) alloy samples with an average surface roughness of Ra=0.3microm. A biological study was undertaken at day 0 (2h after seeding), day 2, day 4 and day 7 to observe the cellular response of fibroblasts and osteoblasts cell lines in terms of morphology, adhesion (as observed by scanning electron microscopy), and viability (Mosmann's test). The results showed that PEI can be successfully deposited onto Ti or NiTi alloy, but generates a detrimental cellular response on both substrates as illustrated by a decrease of both fibroblast and osteoblast adhesion and proliferation over a 7-day culture period. These results suggest that PEI is potentially cytotoxic and may not be biocompatible enough in clinical applications using high molecular weight. As a consequence, polyelectrolyte multilayer films, which are promising in prosthesis and implantology fields, could not be coated with PEI at a high molecular weight. A lower molecular weight should be considered or a more biocompatible molecular base as precursor layer of polyelectrolyte multilayer films would be better to use for a good human bio-integration.

Multifunctional polyelectrolyte multilayer films: combining mechanical resistance, biodegradability, and bioactivity

Cross-linked polyelectrolyte multilayer films (CL PEM) have an increased rigidity and are mechanically more resistant than native (e.g., uncrosslinked) films. However, they are still biodegradable, which make them interesting candidates for biomedical applications. In this study, CL PEM films have been explored for their multifunctional properties as (i) mechanically resistant, (ii) biodegradable, and (iii) bioactive films. Toward this end, we investigated drug loading into CL chitosan/hyaluronan (CHI/HA) and poly(L-lysine)/hyaluronan (PLL/HA) films by simple diffusion of the drugs. Sodium diclofenac and paclitaxel were chosen as model drugs and were successfully loaded into the films. The effect of varying the number of layers in the (CHI/HA) films as well as the cross-linker concentration on diclofenac loading were studied. Diclofenac was released from the film in about 10 h. Paclitaxel was also found to diffuse within CL films. Its activity was maintained after loading in the CL films, and cellular viability could be reduced by about 55% over 3 days. Such a simple approach may be applied to other types of cross-linked films and to other drugs. These results prove that it is possible to design multifunctional multilayer films that combine mechanical resistance, biodegradability, and bioactivity properties into a single PEM architecture.

Control of drug accessibility on functional polyelectrolyte multilayer films

A surface coating based on polylysine/hyaluronic acid multilayers was designed and acted as a reservoir for an antiproliferative agent, paclitaxel (Taxol). Absolutely no chemical modification of polyelectrolytes or of the drug was needed and the final architecture was obtained in an extremely simple way using the layer-by-layer method. The paclitaxel dose available for human colonic adenocarcinoma cells HT29 seeded on the films could be finely tuned. Moreover, the accessibility of the drugs was controlled by adding on the top of the drug reservoir a capping made of synthetic polyelectrolyte multilayers. This capping was also required to allow adhesion of HT29 cells. Paclitaxel activity was maintained after embedding in the polyelectrolyte multilayers and cellular viability could be reduced by about 80% 96 h after seeding. The strategy described in this paper could be valuable for various other drug/cell systems.

Functionalization of multilayered DNA-coatings with bone morphogenetic protein 2

The focus of the present study was to functionalize multilayered DNA-coatings with the osteoinductive factor bone morphogenetic protein 2 (BMP-2) using different loading modalities. The multilayered DNA-coatings were built up from either poly-d-lysine (PDL) or poly(allylamine hydrochloride) (PAH) and DNA using electrostatic self-assembly (ESA). The amounts of BMP-2 loaded into the multilayered DNA-coatings and its subsequent release characteristics were determined using radiolabeled BMP-2. Additionally, the effect of BMP-2 functionalized multilayered DNA-coatings on the in vitro behavior of bone marrow-derived osteoblast-like cells was evaluated in terms of proliferation, differentiation, mineralization, and cell morphology. The results demonstrate the feasibility of multilayered DNA-coatings to be functionalized by embedding BMP-2 according to three different loading modalities: superficial (s), deep (d), and double-layer (dl). BMP-2 was incorporated proportionally into the multilayered DNA-coatings as: s+(4*d)=dl. All differently loaded multilayered DNA-coatings showed an initial burst release followed by an incremental sustained release of the remaining BMP-2. In vitro experiments demonstrated that the loaded factor remained biologically active, as an accelerated calcium deposition was observed on s- and dl-loaded multilayered DNA-coatings, without affecting cell proliferation. In contrast, d-loaded multilayered DNA-coatings influenced osteoblast-like cell behavior by decreasing the deposition of calcium.

Fabrication of interdigitated micropatterns of self-assembled polymer nanofilms containing cell-adhesive materials

Micropatterns of different biomaterials with micro- and nanoscale features and defined spatial arrangement on a single substrate are useful tools for studying cellular-level interactions, and recent reports have highlighted the strong influence of scaffold compliance in determining cell behavior. In this paper, a simple yet versatile and precise patterning technique for the fabrication of interdigitated micropatterns of nanocomposite multilayer coatings on a single substrate is demonstrated through a combination of lithography and layer-by-layer (LbL) assembly processes, termed polymer surface micromachining (PSM). The first nanofilm pattern is constructed using lithography, followed by LbL multilayer assembly and lift-off, and the process is repeated with optical alignment to obtain interdigitated patterns on the same substrate. Thus, the method is analogous to surface micromachining, except that the deposition materials are polymers and biological materials that are used to produce multilayer nanocomposite structures. A key feature of the multilayers is the capability to tune properties such as stiffness by appropriate selection of materials, deposition conditions, and postdeposition treatments. Two- and four-component systems on glass coverslips are presented to demonstrate the versatility of the approach to construct precisely defined, homogeneous nanofilm patterns. In addition, an example of a complex system used as a testbed for in vitro cell adhesion and growth is provided: micropatterns of poly(sodium 4-styrenesulfonate)/poly-L-lysine hydrobromide (PSS/PLL) and secreted phospholipase A(2)/poly(ethyleneimine) (sPLA(2)/PEI) multilayers. The interdigitated square nanofilm array patterns were obtained on a single coverslip with poly(diallyldimethylammonium chloride) (PDDA) as a cell-repellent background. Cell culture experiments show that cortical neurons respond and bind specifically to the sPLA(2) micropatterns in competition with PLL micropatterns. The fabrication and the initial biological results on the nanofilm micropatterns support the usefulness of this technique for use in studies aimed at elucidating important biological structure-function relationships, but the applicability of the fabrication method is much broader and may impact electronics, photonics, and chemical microsystems.

Cyto- and histocompatibility of multilayered DNA-coatings on titanium

DNA-containing biomaterial coatings offer potential beneficial effects for both soft and hard tissue implants because of the structural properties of DNA. In the current study, the aim was to assess the in vitro cyto- and in vivo histocompatibility of multilayered DNA-coatings generated using the electrostatic self-assembly technique, with poly-D-lysine or poly(allylamine hydrochloride) as the cationic counterparts of anionic DNA. Multilayered DNA-coatings were fabricated on titanium substrates. Noncoated titanium substrates served as controls. In vitro experiments with rat primary dermal fibroblasts (RDF) assessing their viability were performed using a Live/Dead assay and an MTT-based assay. The presence of multilayered DNA-coatings did not affect RDF cell viability. On the other hand, an increased proliferation was demonstrated on both types of multilayered DNA-coatings. An in vivo rat model was used to study the soft tissue histocompatibility of subcutaneously inserted implants during implantation periods of 4 and 12 weeks. Light microscopic analysis revealed that all implants were surrounded by a fibrous capsule containing alpha-smooth muscle actin, and that the presence of a multilayered DNA-coating did not induce any adverse effects in terms of inflammation and wound healing. Histomorphometrically, no significant differences in capsule quality or thickness were observed dependent on multilayered DNA-coating or implantation period. The cyto- and histocompatibility of multilayered DNA-coatings demonstrated in this study allows their use and functionalization with appropriate compounds to modulate cell and tissue responses in dental and medical implantology.

Antifungal coating by biofunctionalized polyelectrolyte multilayered films

The surface of medical devices is a common site of bacterial and fungal adhesion, first step to the constitution of a resistant biofilm leading frequently to chronic infections. In order to prevent such complications, several physical and chemical modifications of the device surface have been proposed. Here, we experiment a new type of topical antifungal coating using the layer-by-layer technique. The nanometric multilayer film obtained by this technique is functionalized by the insertion of a chromogranin A-derived antifungal peptide (CGA 47-66, chromofungin). We show that the embedded peptide keeps its antifungal activity by interacting with the fungal membrane and penetrating into the cell. In vitro studies demonstrate that such an antifungal coating is able to inhibit the growth of yeast Candida albicans by 65% and completely stop the proliferation of filamentous fungus Neurospora crassa. The cytotoxicity of such a coating was also assessed by growing human gingival fibroblasts at its surface. Finally, the antifungal coating of poly(methylmethacrylate), a widely used material for biomedical devices, is successfully tested in an in vivo oral candidiasis rat model. Taken together, these results assessed the functionalized multilayer films containing a new potent antifungal non-toxic peptide, as a novel and promising technique for local antifungal protection.