Polyelectrolyte multilayers with a tunable Young's modulus: influence of film stiffness on cell adhesion

Presenting dual-functional peptides on implant surface to direct in vitro osteogenesis and in vivo osteointegration

The complex biological process of osseointegration and the bio-inertness of bone implants are the major reasons for the high failure rate of long-term implants, and have also promoted the rapid development of multifunctional implant coatings in recent years. Herein, through the special design of peptides, we use layer-by-layer assembly technology to simultaneously display two peptides with different biological functions on the implant surface to address this issue. A variety of surface characterization techniques (ellipsometry, atomic force microscopy, photoelectron spectroscopy, dissipation-quartz crystal microbalance) were used to study in detail the preparation process of the dual peptide functional coating and the physical and chemical properties, such as the composition, mechanical modulus, stability, and roughness of the coating. Compared with single peptide functional coatings, dual-peptide functionalized coatings had much better performances on antioxidant, cellular adhesion in early stage, proliferation and osteogenic differentiation in long term, as well as in vivo osteogenesis and osseointegration capabilities. These findings will promote the development of multifunctional designs in bone implant coatings, as a coping strategy for the complexity of biological process during osteointegration.

Recent Developments in Layer-by-Layer Assembly for Drug Delivery and Tissue Engineering Applications

Surfaces with biological functionalities are of great interest for biomaterials, tissue engineering, biophysics, and for controlling biological processes. The layer-by-layer (LbL) assembly is a highly versatile methodology introduced 30 years ago, which consists of assembling complementary polyelectrolytes or biomolecules in a stepwise manner to form thin self-assembled films. In view of its simplicity, compatibility with biological molecules, and adaptability to any kind of supporting material carrier, this technology has undergone major developments over the past decades. Specific applications have emerged in different biomedical fields owing to the possibility to load or immobilize biomolecules with preserved bioactivity, to use an extremely broad range of biomolecules and supporting carriers, and to modify the film's mechanical properties via crosslinking. In this review, the focus is on the recent developments regarding LbL films formed as 2D or 3D objects for applications in drug delivery and tissue engineering. Possible applications in the fields of vaccinology, 3D biomimetic tissue models, as well as bone and cardiovascular tissue engineering are highlighted. In addition, the most recent technological developments in the field of film construction, such as high-content liquid handling or machine learning, which are expected to open new perspectives in the future developments of LbL, are presented.

Thickness Gradient in Polymer Coating by Reactive Layer-by-Layer Assembly on Solid Substrate

The study describes a simple yet robust methodology for forming gradients in polymer coatings with nanometer-thickness precision. The thickness gradients of 0-20 nm in the coating are obtained by a reactive layer-by-layer assembly of polyester and polyethylenimine on gold substrates. Three parameters are important in forming thickness gradients: (i) the incubation time, (ii) the incubation concentration of the polymer solutions, and (iii) the tilt angle of the gold substrate during the dipping process. After examining these parameters, the characterization of the anisotropic surface obtained under the best conditions is presented in the manuscript. The thickness profile and nanomechanical characterization of the polymer gradients are characterized by atomic force microscopy. The roughness analysis has demonstrated that the coating exhibited decreasing roughness with increasing thickness. On the other hand, Young's moduli of the thin and thick coatings are 0.50 and 1.4 MPa, respectively, which assured an increase in mechanical stability with increasing coating thickness. Angle-dependent infrared spectroscopy reveals that the C-O-C ester groups of the polyesters exhibit a perpendicular orientation to the surface, while the C≡C groups are parallel to the surface. The surface properties of the polymer gradients are explored by fluorescence microscopy, proving that the dye's fluorescence intensity increases as the coating thickness increases. The significant benefit of the suggested methodology is that it promises thickness control of gradients in the coating as a consequence of the fast reaction kinetics between layers and the reaction time.

Supramolecular presentation of bioinstructive peptides on soft multilayered nanobiomaterials stimulates neurite outgrowth

Peptide amphiphiles (PAs) have emerged as effective molecular building blocks for creating self-assembling nanobiomaterials for multiple biomedical applications. Herein, we report a straightforward approach to assemble soft bioinstructive platforms to recreate the native neural extracellular matrix (ECM) aiming for neuronal regeneration based on the electrostatic-driven supramolecular presentation of laminin-derived IKVAV-containing self-assembling PA (IKVAV-PA) on biocompatible multilayered nanoassemblies. Spectroscopic and microscopic techniques show that the co-assembly of positively charged low-molecular-weight IKVAV-PA with oppositely charged high-molecular-weight hyaluronic acid (HA) triggers the formation of ordered β-sheet structures denoting a one-dimensional nanofibrous network. The successful functionalization of poly(L-lysine)/HA layer-by-layer nanofilms with an outer positively charged layer of self-assembling IKVAV-PA is demonstrated by the quartz crystal microbalance with dissipation monitoring and the nanofibrous morphological properties revealed by atomic force microscopy. The bioactive ECM-mimetic supramolecular nanofilms promote the enhancement of primary neuronal cells' adhesion, viability, and morphology when compared to the PA without the IKVAV sequence and PA-free biopolymeric multilayered nanofilms, and stimulate neurite outgrowth. The nanofilms hold great promise as bioinstructive platforms for enabling the assembly of customized and robust multicomponent supramolecular biomaterials for neural tissue regeneration.

Elastic moduli of polyelectrolyte multilayer films regulate endothelium-blood interaction under dynamic conditions

A broad spectrum of biomaterials has been explored in order to design cardiovascular implants of sufficient hemocompatibility. Most of them were extensively tested for the ability to facilitate repopulation by patient cells. It was shown that stiffness, surface roughness, or hydrophilicity of polyelectrolyte films have an impact on adhesion, proliferation, and differentiation of cells. At the same time, it is still unknown how these properties influence cell functionality and as a consequence interactions with blood components under dynamic conditions. In this study, we aimed to determine the impact of chemical cross-linking of Chitosan (Chi) and Chrondroitin Sulphate (CS) on endothelium-blood cross-talk. We have found that the morphology of the endothelium monolayer was not altered by changes in coating properties. However, free radical generation by endothelial cells varied depending on the elastic properties of the coating. Simultaneously, we have observed a significant decrease in the level of adhering and circulating active platelets as well as aggregates when the endothelium monolayer was formed on stiffer films than on the other coating variants. Moreover, the same type of films has promoted significantly higher adhesion of blood morphotic elements when they were not functionalized by endothelium. The observed changes in hemocompatibility indicate the importance of a design of coatings that will promote cellularization in vivo in a relatively short time and which will regulate cell function.

Physical Chemistry Study of Collagen-Based Multilayer Films

The surface properties of a biomaterial play an important role in cell behavior, e.g., recolonization, proliferation, and migration. Collagen is known to favor wound healing. In this study, collagen (COL)-based layer-by-layer (LbL) films were built using different macromolecules as a partner, i.e., tannic acid (TA), a natural polyphenol known to establish hydrogen bonds with protein, heparin (HEP), an anionic polysaccharide, and poly(sodium 4-styrene sulfonate) (PSS), an anionic synthetic polyelectrolyte. To cover the whole surface of the substrate with a minimal number of deposition steps, several parameters of the film buildup were optimized, such as the pH value of the solutions, the dipping time, and the salt (sodium chloride) concentration. The morphology of the films was characterized by atomic force microscopy. Built at an acidic pH, the stability of COL-based LbL films was studied when in contact with a physiological medium as well as the TA release from COL/TA films. In contrast to COL/PSS and COL/HEP LbL films, COL/TA films showed a good proliferation of human fibroblasts. These results validate the choice of TA and COL as components of LbL films for biomedical coatings.

Interplay between integrins and cadherins to control bone differentiation upon BMP-2 stimulation

Introduction: Upon BMP-2 stimulation, the osteoblastic lineage commitment in C2C12 myoblasts is associated with a microenvironmental change that occurs over several days. How does BMP-2 operate a switch in adhesive machinery to adapt to the new microenvironment and to drive bone cell fate is not well understood. Here, we addressed this question for BMP-2 delivered either in solution or physically bound of a biomimetic film, to mimic its presentation to cells via the extracellular matrix (ECM). Methods: Biommetics films were prepared using a recently developed automated method that enable high content studies of cellular processes. Comparative gene expressions were done using RNA sequencing from the encyclopedia of the regulatory elements (ENCODE). Gene expressions of transcription factors, beta chain (1, 3, 5) integrins and cadherins (M, N, and Cad11) were studied using quantitative PCR. ECM proteins and adhesion receptor expressions were also quantified by Western blots and dot blots. Their spatial organization in and around cells was studied using immuno-stainings. The individual effect of each receptor on osteogenic transcription factors and alkaline phosphatase expression were studied using silencing RNA of each integrin and cadherin receptor. The organization of fibronectin was studied using immuno-staining and quantitative microscopic analysis. Results: Our findings highlight a switch of integrin and cadherin expression during muscle to bone transdifferentiation upon BMP-2 stimulation. This switch occurs no matter the presentation mode, for BMP-2 presented in solution or via the biomimetic film. While C2C12 muscle cells express M-cadherin and Laminin-specific integrins, the BMP-2-induced transdifferentiation into bone cells is associated with an increase in the expression of cadherin-11 and collagen-specific integrins. Biomimetic films presenting matrix-bound BMP-2 enable the revelation of specific roles of the adhesive receptors depending on the transcription factor. Discussion: While β3 integrin and cadherin-11 work in concert to control early pSMAD1,5,9 signaling, β1 integrin and Cadherin-11 control RunX2, ALP activity and fibronectin organization around the cells. In contrast, while β1 integrin is also important for osterix transcriptional activity, Cadherin-11 and β5 integrin act as negative osterix regulators. In addition, β5 integrin negatively regulates RunX2. Our results show that biomimetic films can be used to delinate the specific events associated with BMP-2-mediated muscle to bone transdifferentiation. Our study reveals how integrins and cadherins work together, while exerting distinct functions to drive osteogenic programming. Different sets of integrins and cadherins have complementary mechanical roles during the time window of this transdifferentiation.

Chemical Strategies for Dendritic Magneto-plasmonic Nanostructures Applied to Surface-Enhanced Raman Spectroscopy

Chemical analyses in the field using surface-enhanced Raman scattering (SERS) protocols are expected to be part of several analytical procedures applied to water quality monitoring. To date, these endeavors have been supported by developments in SERS substrate nanofabrication, instrumentation portability, and the internet of things. Here, we report distinct chemical strategies for preparing magneto-plasmonic (Fe₃ O₄  : Au) colloids, which are relevant in the context of trace-level detection of water contaminants due to their inherent multifunctionality. The main objective of this research is to investigate the role of poly(amidoamine) dendrimers (PAMAMs) in the preparation of SERS substrates integrating both functionalities into single nanostructures. Three chemical routes were investigated to design magneto-plasmonic nanostructures that translate into different ways for assessing SERS detection by using distinct interfaces. Hence, a series of magneto-plasmonic colloids have been characterized and then assessed for their SERS activity by using a model pesticide (thiram) dissolved in aqueous samples.

Tailored Polyelectrolyte Multilayer Systems by Variation of Polyelectrolyte Composition and EDC/NHS Cross-Linking: Physicochemical Characterization and In Vitro Evaluation

The layer-by-layer (LbL) self-assembly technique is an effective method to immobilize components of the extracellular matrix (ECM) such as collagen and heparin onto, e.g., implant surfaces/medical devices with the aim of forming polyelectrolyte multilayers (PEMs). Increasing evidence even suggests that cross-linking influences the physicochemical character of PEM films since mechanical cues inherent to the substrate may be as important as its chemical nature to influence the cellular behavior. In this study, for the first-time different collagen/heparin films have been prepared and cross-linked with EDC/NHS chemistry. Quartz crystal microbalance, zeta potential analyzer, diffuse reflectance Fourier transform infrared spectroscopy, atomic force microscopy and ellipsometry were used to characterize film growth, stiffness, and topography of different film systems. The analysis of all data proves a nearly linear film growth for all PEM systems, the efficacy of cross-linking and the corresponding changes in the film rigidity after cross-linking and an appropriate surface topography. Furthermore, preliminary cell culture experiments illustrated those cellular processes correlate roughly with the quantity of newly created covalent amide bonds. This allows a precise adjustment of the physicochemical properties of the selected film architecture regarding the desired application and target cells. It could be shown that collagen improves the biocompatibility of heparin containing PEMs and due to their ECM-analogue nature both molecules are ideal candidates intended to be used for any biomedical application with a certain preference to improve the performance of bone implants or bone augmentation strategies.

Engineering of a Microscale Niche for Pancreatic Tumor Cells Using Bioactive Film Coatings Combined with 3D-Architectured Scaffolds

Two-photon polymerization has recently emerged as a promising technique to fabricate scaffolds for three-dimensional (3D) cell culture and tissue engineering. Here, we combined 3D-printed microscale scaffolds fabricated using two-photon polymerization with a bioactive layer-by-layer film coating. This bioactive coating consists of hyaluronic acid and poly(l-lysine) of controlled stiffness, loaded with fibronectin and bone morphogenic proteins 2 and 4 (BMP2 and BMP4) as matrix-bound proteins. Planar films were prepared using a liquid handling robot directly in 96-well plates to perform high-content studies of cellular processes, especially cell adhesion, proliferation, and BMP-induced signaling. The behaviors of two human pancreatic cell lines PANC1 (immortalized) and PAN092 (patient-derived cell line) were systematically compared and revealed important context-specific cell responses, notably in response to film stiffness and matrix-bound BMPs (bBMPs). Fibronectin significantly increased cell adhesion, spreading, and proliferation for both cell types on soft and stiff films; BMP2 increased cell adhesion and inhibited proliferation of PANC1 cells and PAN092 on soft films. BMP4 enhanced cell adhesion and proliferation of PANC1 and showed a bipolar effect on PAN092. Importantly, PANC1 exhibited a strong dose-dependent BMP response, notably for bBMP2, while PAN092 was insensitive to BMPs. Finally, we proved that it is possible to combine a microscale 3D Ormocomp scaffold fabricated using the two-photon polymerization technique with the bioactive film coating to form a microscale tumor tissue and mimic the early stages of metastatic cancer.

Differential bioactivity of four BMP-family members as function of biomaterial stiffness

While a soft film itself is not able to induce cell spreading, BMP-2 presented via such soft film (so called "matrix-bound BMP-2") was previously shown to trigger cell spreading, migration and downstream BMP-2 signaling. Here, we used thin films of controlled stiffness presenting matrix-bound BMPs to study the effect of four BMP members (BMP-2, 4, 7, 9) on cell adhesion and differentiation of skeletal progenitors. We performed automated high-content screening of cellular responses, including cell number, cell spreading area, SMAD phosphorylation and alkaline phosphatase activity. We revealed that the cell response to bBMPs is BMP-type specific, and involved certain BMP receptors and beta chain integrins. In addition, this response is stiffness-dependent for several receptors. The basolateral presentation of the BMPs allowed us to discriminate the specificity of cellular response, especiallyd the role of type I and II BMP receptors and of β integrins in a BMP-type and stiffness-dependent manner. Notably, BMP-2 and BMP-4 were found to have distinct roles, while ALK5, previously known as a TGF-β receptor was revealed to be involved in the BMP-pathway.

Xanthan-gelatin and xanthan-gelatin-keratin wound dressings for local delivery of Vitamin C

Recently, functional dressings that can protect the wound area from dehydration and bacterial infection and support healing have gained importance in place of passive dressings. This study aimed to develop temporary and regenerative xanthan/gelatin (XGH) and keratin/xanthan/gelatin hydrogels (KXGHs) that have high absorption capacity and applicability as a wound dressing that can provide local delivery of Vitamin C (VC). Firstly, xanthan/gelatin hydrogels were produced by crosslinking with different glycerol concentrations and characterized to determine the hydrogel composition. According to their weight ratios, xanthan, gelatin, and glycerol hydrogels are named. If their weight ratio is 1:1:2 (w/w/w), the group name is selected as X1:GEL1:GLY2. X1:GEL1:GLY2 hydrogel was selected for biocompatibility, mechanical property, water vapor transmission rate (WVTR), and porosity. The addition of keratin to X1:GEL1:GLY2 improved L929 fibroblasts viability and increased protein release. Water vapor transmission of XGHs and KXGHs was between 3059.09 ± 126 and 4523 ± 133 g m^-2 d^-1; therefore, they can be suitable for granulating, low to moderate exudate wounds. XGH and KXGHs loaded with VC had higher water uptake, making it more convenient for exudate wounds. VC was released for 100 h, and VC containing XGHs and KXGHs increased the collagen synthesis of L929 fibroblasts. All of the hydrogels (XGH, KXGH, and VC-KXGHs) inhibited the bacteria transmission. In conclusion, our results suggest that VC-XGH and VC-KXGH can be candidates for temporary wound dressing materials for skin wounds.

Facile Polyphenol-Europium Assembly Enabled Functional Poly(l-Lactic Acid) Nanofiber Mats with Enhanced Antioxidation and Angiogenesis for Accelerated Wound Healing

Burns, trauma, surgery and chronic diabetic ulcers are the most common reasons causing skin wounds in clinic. Thus, developing a functional wound dressing has been an imperative issue. Herein, functional wound dressing (poly(l-lactic acid) PLLA-((tanic acid (TA)/europium (Eu))_n ) is fabricated through a facile polyphenol-europium ion assembly to ameliorate wound microenvironment via scavenging excessive reactive oxygen species (ROS) and promoting angiogenesis. The physicochemical characterization indicates that the multicycle assembled TA/Eu is uniformly deposited on PLLA-(TA/Eu)_n nanofiber mats surface. In vitro 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant tests display good antioxidant ability by scavenging more than 75% ROS, and significantly increasing the antioxidant enzyme levels in vivo. Cytocompatibility experiments illustrate that PLLA-(TA/Eu)_n nanofiber mats can promote the adhesion and proliferation of human umbilical vein endothelial cells (HUVECs) and L929 cells. Meanwhile, real-time quantitative polymerase chain reaction (PCR) (RT-qPCR) and western blot assays illustrate that it can stimulate proangiogenesis by elevating the expression of angiogenesis-related genes and proteins. In vivo Sprague-Dawley (SD) rats experiments indicate that PLLA-(TA/Eu)_n nanofiber mats can significantly promote wound healing by improving both angiogenesis and antioxidant activity. Taken together, the functional PLLA-(TA/Eu)_n nanofiber mats can offer significant promise as wound dressing for accelerated wound healing.

Rebuilding the hematopoietic stem cell niche: Recent developments and future prospects

Hematopoietic stem cells (HSCs) have proven their clinical relevance in stem cell transplantation to cure patients with hematological disorders. Key to their regenerative potential is their natural microenvironment - their niche - in the bone marrow (BM). Developments in the field of biomaterials enable the recreation of such environments with increasing preciseness in the laboratory. Such artificial niches help to gain a fundamental understanding of the biophysical and biochemical processes underlying the interaction of HSCs with the materials in their environment and the disturbance of this interplay during diseases affecting the BM. Artificial niches also have the potential to multiply HSCs in vitro, to enable the targeted differentiation of HSCs into mature blood cells or to serve as drug-testing platforms. In this review, we will introduce the importance of artificial niches followed by the biology and biophysics of the natural archetype. We will outline how 2D biomaterials can be used to dissect the complexity of the natural niche into individual parameters for fundamental research and how 3D systems evolved from them. We will present commonly used biomaterials for HSC research and their applications. Finally, we will highlight two areas in the field of HSC research, which just started to unlock the possibilities provided by novel biomaterials, in vitro blood production and studying the pathophysiology of the niche in vitro. With these contents, the review aims to give a broad overview of the different biomaterials applied for HSC research and to discuss their potentials, challenges and future directions in the field. STATEMENT OF SIGNIFICANCE: Hematopoietic stem cells (HSCs) are multipotent cells responsible for maintaining the turnover of all blood cells. They are routinely applied to treat patients with hematological diseases. This high clinical relevance explains the necessity of multiplication or differentiation of HSCs in the laboratory, which is hampered by the missing natural microenvironment - the so called niche. Biomaterials offer the possibility to mimic the niche and thus overcome this hurdle. The review introduces the HSC niche in the bone marrow and discusses the utility of biomaterials in creating artificial niches. It outlines how 2D systems evolved into sophisticated 3D platforms, which opened the gateway to applications such as, expansion of clinically relevant HSCs, in vitro blood production, studying niche pathologies and drug testing.

Polyelectrolyte Multilayer Films Based on Natural Polymers: From Fundamentals to Bio-Applications

Natural polymers are of great interest in the biomedical field due to their intrinsic properties such as biodegradability, biocompatibility, and non-toxicity. Layer-by-layer (LbL) assembly of natural polymers is a versatile, simple, efficient, reproducible, and flexible bottom-up technique for the development of nanostructured materials in a controlled manner. The multiple morphological and structural advantages of LbL compared to traditional coating methods (i.e., precise control over the thickness and compositions at the nanoscale, simplicity, versatility, suitability, and flexibility to coat surfaces with irregular shapes and sizes), make LbL one of the most useful techniques for building up advanced multilayer polymer structures for application in several fields, e.g., biomedicine, energy, and optics. This review article collects the main advances concerning multilayer assembly of natural polymers employing the most used LbL techniques (i.e., dipping, spray, and spin coating) leading to multilayer polymer structures and the influence of several variables (i.e., pH, molar mass, and method of preparation) in this LbL assembly process. Finally, the employment of these multilayer biopolymer films as platforms for tissue engineering, drug delivery, and thermal therapies will be discussed.

Embedding Collagen in Multilayers for Enzyme-Assisted Mineralization: A Promising Way to Direct Crystallization in Confinement

The biogenic calcium phosphate (CaP) crystallization is a process that offers elegant materials design strategies to achieve bioactive and biomechanical challenges. Indeed, many biomimetic approaches have been developed for this process in order to produce mineralized structures with controlled crystallinity and shape. Herein, we propose an advanced biomimetic approach for the design of ordered hybrid mineralized nano-objects with highly anisotropic features. For this purpose, we explore the combination of three key concepts in biomineralization that provide a unique environment to control CaP nucleation and growth: (i) self-assembly and self-organization of biomacromolecules, (ii) enzymatic heterogeneous catalysis, and (iii) mineralization in confinement. We use track-etched templates that display a high density of aligned monodisperse pores so that each nanopore may serve as a miniaturized mineralization bioreactor. We enhance the control of the crystallization in these systems by coassembling type I collagen and enzymes within the nanopores, which allows us to tune the main characteristics of the mineralized nano-objects. Indeed, the synergy between the gradual release of one of the mineral ion precursors by the enzyme and the role of the collagen in the regulation of the mineralization allowed to control their morphology, chemical composition, crystal phase, and mechanical stability. Moreover, we provide clear insight into the prominent role of collagen in the mineralization process in confinement. In the absence of collagen, the fraction of crystalline nano-objects increases to the detriment of amorphous ones when increasing the degree of confinement. By contrast, the presence of collagen-based multilayers disturbs the influence of confinement on the mineralization: platelet-like crystalline hydroxyapatite form, independently of the degree of confinement. This suggests that the incorporation of collagen is an efficient way to supplement the lack of confinement while reinforcing mechanical stability to the highly anisotropic materials. From a bioengineering perspective, this biomineralization-inspired approach opens up new horizons for the design of anisotropic mineralized nano-objects that are highly sought after to develop biomaterials or tend to replicate the complex structure of native mineralized extracellular matrices.

Substrate stiffness differentially impacts autophagy of endothelial cells and smooth muscle cells

Stiffening of blood vessels is one of the most important characteristics in the process of many cardiovascular pathologies such as atherosclerosis, angiosteosis, and vascular aging. Increased stiffness of the vascular extracellular matrix drives artery pathology and alters phenotypes of vascular cell. Understanding how substrate stiffness impacts vascular cell behaviors is of great importance to the biomaterial design in tissue engineering, regenerative medicine, and medical devices. Here we report that changing substrate stiffness has a significant impact on the autophagy of vascular endothelial cells (VECs) and smooth muscle cells (VSMCs). Interestingly, our findings demonstrate that, with the increase of substrate stiffness, the autophagy level of VECs and VSMCs showed differential changes: endothelial autophagy levels reduced, leading to the reductions in a range of gene expression associated with endothelial function; while, autophagy levels of VSMCs increased, showing a transition from contractile to the synthetic phenotype. We further demonstrate that, by inhibiting cell autophagy, the expressions of endothelial functional gene were further reduced and the expression of VSMC calponin increased, suggesting an important role of autophagy in response of the cells to the challenge of microenvironment stiffness changing. Although the underlying mechanism requires further study, this work highlights the relationship of substrate stiffness, autophagy, and vascular cell behaviors, and enlightening the design principles of surface stiffness of biomaterials in cardiovascular practical applications.

Impacts of Mechanical Stiffness of Bacteriophage-Loaded Hydrogels on Their Antibacterial Activity

The elaboration of efficient hydrogel-based materials with antimicrobial properties requires a refined control of defining their physicochemical features, which includes mechanical stiffness, so as to properly mediate their antibacterial activity. In this work, we design hydrogels consisting of polyelectrolyte multilayer films for the loading of T4 and φX174 bacteria-killing viruses, also called bacteriophages. We investigate the antiadhesion and bactericidal performances of this biomaterial against Escherichia coli, with a specific focus on the effects of chemical cross-linking of the hydrogel matrix, which, in turn, mediates the hydrogel stiffness. Depending on the latter and on phage replication features, it is found that the hydrogels loaded with the bacteria-killing viruses make both contact killing (targeted bacteria are those adhered at the hydrogel surface) and release killing (planktonic bacteria are the targets) possible with ca. 20-80% efficiency after only 4 h of incubation at 25 °C as compared to cases where hydrogels are free of viruses. We further demonstrate the lack of dependence of virus diffusion within the hydrogel and of the maximal viral storage capacity on the hydrogel mechanical properties. In addition to the evidenced bacteriolytic activity of the phages loaded in the hydrogels, the antimicrobial property of the phage-loaded materials is shown to be partly controlled by the chemistry of the hydrogel skeleton and, more specifically, by the mobility of the peripheral free polycationic components, known for their ability to weaken and permeabilize membranes of bacteria, the latter then becoming "easier" targets for the viruses.

Introducing a biomimetic coating for graphene neuroelectronics: towardin-vivoapplications

Electronic micro and nano-devices are suitable tools to monitor the activity of many individual neurons over mesoscale networks. However the inorganic materials currently used in microelectronics are barely accepted by neural cells and tissues, thus limiting both the sensor lifetime and efficiency. In particular, penetrating intracortical probes face high failure rate because of a wide immune response of cells and tissues. This adverse reaction called gliosis leads to the rejection of the implanted probe after few weeks and prevent long-lasting recordings of cortical neurons. Such acceptance issue impedes the realization of many neuro-rehabilitation projects. To overcome this, graphene and related carbon-based materials have attracted a lot of interest regarding their positive impact on the adhesion and regeneration of neurons, and their ability to provide high-sensitive electronic devices, such as graphene field effect transistor (G-FET). Such devices can also be implemented on numerous suitable substrates including soft substrates to match the mechanical compliance of cells and tissues, improving further the biocompatibility of the implants. Thus, using graphene as a coating and sensing device material could significantly enhance the acceptance of intracortical probes. However, such a thin monolayer of carbon atoms could be teared off during manipulation and insertion within the brain, and could also display degradation over time. In this work, we have investigated the ability to protect graphene with a natural, biocompatible and degradable polymeric film derivated from hyaluronic acid (HA). We demonstrate that HA-based coatings can be deposited over a wide range of substrates, including intracortical probes and graphene FET arrays without altering the underlying device material, its biocompatibility and sensitivity. Moreover, we show that this coating can be monitoredin situby quantifying the number of deposited charges with the G-FET arrays. The reported graphene functionalization offers promising alternatives for improving the acceptance of various neural interfaces.

Nanoparticles in Polyelectrolyte Multilayer Layer-by-Layer (LbL) Films and Capsules—Key Enabling Components of Hybrid Coatings

Originally regarded as auxiliary additives, nanoparticles have become important constituents of polyelectrolyte multilayers. They represent the key components to enhance mechanical properties, enable activation by laser light or ultrasound, construct anisotropic and multicompartment structures, and facilitate the development of novel sensors and movable particles. Here, we discuss an increasingly important role of inorganic nanoparticles in the layer-by-layer assembly—effectively leading to the construction of the so-called hybrid coatings. The principles of assembly are discussed together with the properties of nanoparticles and layer-by-layer polymeric assembly essential in building hybrid coatings. Applications and emerging trends in development of such novel materials are also identified.

Green and Tunable Animal Protein-Free Microcarriers for Cell Expansion

Cell culture on microcarriers emerges as an alternative of two-dimensional culture to produce large cell doses, which are required for cell-based therapies. Herein, we report a versatile and easy solvent-free greener fabrication process to prepare microcarriers based on a biosourced and compostable polymer. The preparation of the microcarrier core, which is based on poly(L-lactide) crystallization from a polymer blend, allows us to easily tune the density, porosity, and size of the microparticles. A bioadhesive coating based on biopolymers, devoid of animal protein and optimized to improve cell adhesion, is then successfully deposited on the surface of the microcarriers. The ability of these new microcarriers to expand human adipose-derived stromal cells with good yield, in semistatic and dynamic conditions, is demonstrated. Finally, bead-to-bead cell transfer is shown to increase the yield of cell production without having to stop the culture. These microcarriers are therefore a promising and efficient green alternative to currently existing systems.

Layer-By-Layer Assemblies of Biopolymers: Build-Up, Mechanical Stability and Molecular Dynamics

Rapid development of versatile layer-by-layer technology has resulted in important breakthroughs in the understanding of the nature of molecular interactions in multilayer assemblies made of polyelectrolytes. Nowadays, polyelectrolyte multilayers (PEM) are considered to be non-equilibrium and highly dynamic structures. High interest in biomedical applications of PEMs has attracted attention to PEMs made of biopolymers. Recent studies suggest that biopolymer dynamics determines the fate and the properties of such PEMs; however, deciphering, predicting and controlling the dynamics of polymers remains a challenge. This review brings together the up-to-date knowledge of the role of molecular dynamics in multilayers assembled from biopolymers. We discuss how molecular dynamics determines the properties of these PEMs from the nano to the macro scale, focusing on its role in PEM formation and non-enzymatic degradation. We summarize the factors allowing the control of molecular dynamics within PEMs, and therefore to tailor polymer multilayers on demand.

Polyelectrolyte Multilayer Capsule (PEMC)-Based Scaffolds for Tissue Engineering

Tissue engineering (TE) is a highly multidisciplinary field that focuses on novel regenerative treatments and seeks to tackle problems relating to tissue growth both in vitro and in vivo. These issues currently involve the replacement and regeneration of defective tissues, as well as drug testing and other related bioapplications. The key approach in TE is to employ artificial structures (scaffolds) to support tissue development; these constructs should be capable of hosting, protecting and releasing bioactives that guide cellular behaviour. A straightforward approach to integrating bioactives into the scaffolds is discussed utilising polyelectrolyte multilayer capsules (PEMCs). Herein, this review illustrates the recent progress in the use of CaCO3 vaterite-templated PEMCs for the fabrication of functional scaffolds for TE applications, including bone TE as one of the main targets of PEMCs. Approaches for PEMC integration into scaffolds is addressed, taking into account the formulation, advantages, and disadvantages of such PEMCs, together with future perspectives of such architectures.

A closer physico-chemical look to the Layer-by-Layer electrostatic self-assembly of polyelectrolyte multilayers

The fabrication of polyelectrolyte multilayer films (PEMs) using the Layer-by-Layer (LbL) method is one of the most versatile approaches for manufacturing functional surfaces. This is the result of the possibility to control the assembly process of the LbL films almost at will, by changing the nature of the assembled materials (building blocks), the assembly conditions (pH, ionic strength, temperature, etc.) or even by changing some other operational parameters which may impact in the structure and physico-chemical properties of the obtained multi-layered films. Therefore, the understanding of the impact of the above mentioned parameters on the assembly process of LbL materials plays a critical role in the potential use of the LbL method for the fabrication of new functional materials with technological interest. This review tries to provide a broad physico-chemical perspective to the study of the fabrication process of PEMs by the LbL method, which allows one to take advantage of the many possibilities offered for this approach on the fabrication of new functional nanomaterials.

Recent Advances in Hybrid Biomimetic Polymer-Based Films: from Assembly to Applications

Biological membranes, in addition to being a cell boundary, can host a variety of proteins that are involved in different biological functions, including selective nutrient transport, signal transduction, inter- and intra-cellular communication, and cell-cell recognition. Due to their extreme complexity, there has been an increasing interest in developing model membrane systems of controlled properties based on combinations of polymers and different biomacromolecules, i.e., polymer-based hybrid films. In this review, we have highlighted recent advances in the development and applications of hybrid biomimetic planar systems based on different polymeric species. We have focused in particular on hybrid films based on (i) polyelectrolytes, (ii) polymer brushes, as well as (iii) tethers and cushions formed from synthetic polymers, and (iv) block copolymers and their combinations with biomacromolecules, such as lipids, proteins, enzymes, biopolymers, and chosen nanoparticles. In this respect, multiple approaches to the synthesis, characterization, and processing of such hybrid films have been presented. The review has further exemplified their bioengineering, biomedical, and environmental applications, in dependence on the composition and properties of the respective hybrids. We believed that this comprehensive review would be of interest to both the specialists in the field of biomimicry as well as persons entering the field.

Enzyme assisted peptide self-assemblies trigger cell adhesion in high density oxime based host gels

Peptide supramolecular self-assemblies are recognized as important components in responsive hydrogel based materials with applications in tissue engineering and regenerative medicine. Studying the influence of hydrogel matrices on the self-assembly behavior of peptides and interaction with cells is essential to guide the future development of engineered biomaterials. In this contribution, we present a PEG based host hydrogel material generated by oxime click chemistry that shows cellular adhesion behavior in response to enzyme assisted peptide self-assembly (EASA) within the host gel. This hydrogel prepared from poly(dimethylacrylamide-co-diacetoneacrylamide), poly(DMA-DAAM) with high molar fractions (49%) of DAAM and dialkoxyamine PEG cross-linker, was studied in the presence of embedded enzyme alkaline phosphatase (AP) and a non-adhesive cell behavior towards NIH 3T3 fibroblasts was observed. When brought into contact with a Fmoc-FFpY peptide solution (pY: phosphorylated tyrosine), the gel forms intercalated Fmoc-FFY peptide self-assemblies upon diffusion of Fmoc-FFpY into the cross-linked hydrogel network as was confirmed by circular dichroism, fluorescence emission spectroscopy and confocal microscopy. Nevertheless, the mechanical properties do not change significantly after the peptide self-assembly in the host gel. This enzyme assisted peptide self-assembly promotes fibroblast cell adhesion that can be enhanced if Fmoc-F-RGD peptides are added to the pre-gelator Fmoc-FFpY peptide solution. Cell adhesion results mainly from interactions of cells with the non-covalent peptide self-assemblies present in the gel despite the fact that the mechanical properties are very close to those of the native host gel. This result is in contrast to numerous studies which showed that the mechanical properties of a substrate are key parameters of cell adhesion. It opens up the possibility to develop a diverse set of hybrid materials to control cell fate in culture due to tailored self-assemblies of peptides responding to the environment provided by the host guest gel.

Preparation of Polymeric Films of PVDMA-PEI Functionalized with Fatty Acids for Studying the Adherence and Proliferation of Langerhans β-Cells

This study reports the synthesis of thin polymeric films by the layer-by-layer deposition and covalent cross-linking of polyvinyl dimethylazlactone and polyethylene imine, which were functionalized with lauric (12-C), myristic (14-C), and palmitic (16-C) saturated fatty acids, whose high levels in the bloodstream are correlated with insulin resistance and the potential development of type 2 diabetes mellitus. Aiming to assess the effect of the fatty acids on the adhesion and proliferation of Langerhans β-cells, all prepared films (35 and 35.5 bilayers with and without functionalization with the fatty acids) were characterized in terms of their physical, chemical, and biological properties by a battery of experimental techniques including 1H and 13C NMR, mass spectrometry, attenuated total reflectance-Fourier transform infrared spectroscopy, field emission scanning electron microscopy, atomic force microscopy, cell staining, and confocal laser scanning microscopy among others. In general, the developed films were found to be nanometric, transparent, resistant against manipulation, chemically reactive, and highly cytocompatible. On the other hand, in what the effect of the fatty acids is concerned, palmitic acid was found to impair the proliferation of the cultured β-cells, contrary to its homologues which did not alter this biological process. In our opinion, the multidisciplinary study presented here might be of interest for the research community working on the development of cytocompatible 2D model substrates for the safe and reproducible characterization of cell responses.

Microchannel Molding Combined with Layer-by-Layer Approach for the Formation of Three-Dimensional Tube-like Structures by Endothelial Cells

The development of a functional in vitro model for microcirculation is an unresolved challenge, with major impact for the creation and regeneration of organs in the tissue engineering. The absence of prevascularized engineered tissues limits enormously their efficacy and integration. Therefore, in this study, the in vitro formation of tubular-like structures with human umbilical vein endothelial cells (HUVECs) is investigated thanks to three-dimensional polycarbonate (PC) microchannel (μCh) scaffolds, surface biofunctionalized with hyaluronic acid/chitosan (HA/CHI) layer-by-layer (LbL) films grafted with adhesive (RGD) and angiogenic (SVV and QK) peptides, alone and in combination. The importance of this work lies in the formation of capillaries in the order of tens of μm, developing spontaneous microvessels, without the complexity of microfluidic approaches, and in a short time-scale. Ellipsometry, confocal laser scanning microscopy, and fluorospectrometry are used to characterize the biofunctionalized microchannels. PC-μCh scaffolds functionalized with (HA/CHI)_12.5 film (PC-LbL) and further grafted with RGD and QK peptides (PC-RGD+QK) or with RGD and SVV peptides (PC-RGD+SVV) are then tested for in vitro blood vessel formation. These assays evidence a rapid formation of tubular-like structures after 2 h of incubation. Moreover, a coculture system involving HUVECs and human pericytes derived from placenta (hPCs-PL) stabilizes the tubes for a longer time.

Pipette-like action of a reusable and NIR light-responsive film for the aspiration and removal of viable cancer cells

A reusable and NIR light-responsive composite membrane is developed to capture/release viable cancer cells.

Hyaluronic Acid: Incorporating the Bio into the Material

In the last few decades, hyaluronic acid (HA) has become increasingly employed as a biomaterial in both clinical and research applications. The abundance of HA in many tissues, together with its amenability to chemical modification, has made HA an attractive material platform for a wide range of applications including regenerative medicine, drug delivery, and scaffolds for cell culture. HA has traditionally been appreciated to modulate tissue mechanics and remodeling through its distinctive biophysical properties and ability to organize other matrix proteins. However, HA can influence cell behavior in much more direct and specific ways by engaging cellular HA receptors, which can trigger signals that influence cell survival, proliferation, adhesion, and migration. In turn, cells modify HA by regulating synthesis and degradation through a dedicated arsenal of enzymes. Optimal design of HA-based biomaterials demands full consideration of these diverse modes of regulation. This review summarizes how HA-based signaling regulates cell behavior and discusses how these signals can be leveraged to create cell-instructive biomaterials.

Preventing S. aureus biofilm formation on titanium surfaces by the release of antimicrobial β-peptides from polyelectrolyte multilayers

Staphylococcus aureus infections represent the major cause of titanium based-orthopaedic implant failure. Current treatments for S. aureus infections involve the systemic delivery of antibiotics and additional surgeries, increasing health-care costs and affecting patient's quality of life. As a step toward the development of new strategies that can prevent these infections, we build upon previous work demonstrating that the colonization of catheters by the fungal pathogen Candida albicans can be prevented by coating them with thin polymer multilayers composed of chitosan (CH) and hyaluronic acid (HA) designed to release a β-amino acid-based peptidomimetic of antimicrobial peptides (AMPs). We demonstrate here that this β-peptide is also potent against S. aureus (MBPC = 4 μg/mL) and characterize its selectivity toward S. aureus biofilms. We demonstrate further that β-peptide-containing CH/HA thin-films can be fabricated on the surfaces of rough planar titanium substrates in ways that allow mammalian cell attachment and permit the long-term release of β-peptide. β-Peptide loading on CH/HA thin-films was then adjusted to achieve release of β-peptide quantities that selectively prevent S. aureus biofilms on titanium substrates in vitro for up to 24 days and remained antimicrobial after being challenged sequentially five times with S. aureus inocula, while causing no significant MC3T3-E1 preosteoblast cytotoxicity compared to uncoated and film-coated controls lacking β-peptide. We conclude that these β-peptide-containing films offer a novel and promising localized delivery approach for preventing orthopaedic implant infections. The facile fabrication and loading of β-peptide-containing films reported here provides opportunities for coating other medical devices prone to biofilm-associated infections. STATEMENT OF SIGNIFICANCE: Titanium (Ti) and its alloys are used widely in orthopaedic devices due to their mechanical strength and long-term biocompatibility. However, these devices are susceptible to bacterial colonization and the subsequent formation of biofilms. Here we report a chitosan and hyaluronic acid polyelectrolyte multilayer-based approach for the localized delivery of helical, cationic, globally amphiphilic β-peptide mimetics of antimicrobial peptides to inhibit S. aureus colonization and biofilm formation. Our results reveal that controlled release of this β-peptide can selectively kill S. aureus cells without exhibiting toxicity toward MC3T3-E1 preosteoblast cells. Further development of this polymer-based coating could result in new strategies for preventing orthopaedic implant-related infections, improving outcomes of these titanium implants.

Microfluidic Shear Assay to Distinguish between Bacterial Adhesion and Attachment Strength on Stiffness-Tunable Silicone Substrates

Tuning surface composition and stiffness is now an established strategy to improve the integration of medical implants. Recent evidence suggests that matrix stiffness affects bacterial adhesion, but contradictory findings have been reported in the literature. Distinguishing between the effects of bacterial adhesion and attachment strength on these surfaces may help interpret these findings. Here, we develop a precision microfluidic shear assay to quantify bacterial adhesion strength on stiffness-tunable and biomolecule-coated silicone materials. We demonstrate that bacteria are more strongly attached to soft silicones, compared to stiff silicones; as determined by retention against increasing shear flows. Interestingly, this effect is reduced when the surface is coated with matrix biomolecules. These results demonstrate that bacteria do sense and respond to stiffness of the surrounding environment and that precisely defined assays are needed to understand the interplay among surface mechanics, composition, and bacterial binding.

The mechanics of single cross-links which mediate cell attachment at a hydrogel surface

The response of cultured cells to the mechanical properties of hydrogel substrates depends ultimately on the response of single crosslinks to external forces exerted at cell attachment points. We prepared hydrogels by co-polymerization of poly(ethylene glycol diacrylate) (PEGDA) and carboxy poly(ethylene glycol) acrylate (ACPEG-COOH) and confirmed fibroblast spreading on the hydrogel after the ACPEG linker was functionalized with the RGD cell adhesive motif. We performed specific force spectroscopy experiments on the same ACPEG linkers in order to probe the mechanics of single cross-links which mediate the cell attachment and spreading. Measurements were performed with tips of an atomic force microscope (AFM) functionalized with streptavidin and ACPEG linkers functionalized with biotin. We compared hydrogels of varying elastic modulus between 4 and 41 kPa which exhibited significant differences in cell spreading. An effective spring constant for the displacement of single cross-links at the hydrogel surface was derived from the distributions of rupture force and molecular stiffness. A factor of ten in the elastic modulus E of the hydrogel corresponded to a factor of five in the effective spring constant k of single crosslinks, indicating a transition in scaling with the mesh size ξ from the macroscopic E∝ξ^-3 to the molecular k∝ξ^-2. The quantification of stiffness and deformation at the molecular length scale contributes to the discussion of mechanisms in force-regulated phenomena in cell biology.

Immobilized Transforming Growth Factor-Beta 1 in a Stiffness-Tunable Artificial Extracellular Matrix Enhances Mechanotransduction in the Epithelial Mesenchymal Transition of Hepatocellular Carcinoma

Cancer progression is regulated by multiple factors of extracellular matrix (ECM). Understanding how cancer cells integrate multiple signaling pathways to achieve specific behaviors remains a challenge because of the lack of appropriate models to copresent and modulate ECM properties. Here we proposed a strategy to build a thin biomaterial matrix by poly(l-lysine) and hyaluronan as an artificial stiffness-tunable ECM. Transforming growth factor-beta 1 (TGF-β1) was used as a biochemical cue to present in an immobilized and spatially controlled manner, with a high loading efficiency of 90%. Either soft matrix with immobilized TGF-β1 (i-TGF) or bare stiff matrix could only promote HCC cells to form the epithelial phenotype, whereas stiff matrix with i-TGF was the only condition to induce the mesenchymal phenotype. Further investigation revealed that i-TGF increased the specific TGF-β1 receptor (TβRI) expression to activate PI3K pathway. i-TGF-TβRI interactions also promoted HCC cell adhesion to enlarge contact area for stiffness sensing, resulting in the raising expression of the mechano-sensor (β1 integrin). Mechanotransduction would then be enhanced by the β1 integrin/vinculin/p-FAK pathway, leading to a noble PI3K activation. Using our model, a novel mechanism was discovered to elucidate regulation of cell fates by coupling mechanotransduction and biochemical signaling.

Bioengineered Braided Micro-Nano (Multiscale) Fibrous Scaffolds for Tendon Reconstruction

A braided multiscale fibrous scaffold consisting of aligned PCL micro/collagen-bFGFnano fibers was fabricated (mPCL-nCol-bFGF) to mimic native tendon tissue architecture which was further coated with alginate to aid in prevention of peritendinous adhesion. The bFGF release kinetics showed a sustained release of growth factors for a period of 20 days. Further, in vitro cell viability, attachment, and proliferation were performed using rabbit tenocytes under static and dynamic conditions. mPCL-nCol-bFGF showed a higher cell proliferation and enhanced expression of tenogenic markers compared to mPCL-nCol (braided scaffold without bFGF). When subjected to dynamic stimulation in a bioreactor, mPCL-nCol-bFGF-DS (braided scaffold with bFGF after dynamic stimulation) showed enhanced cellular proliferation and tenogenic marker expression, compared to mPCL-nCol-bFGF. The in vivo studies of the cell seeded scaffold after dynamic stimulation in Achilles tendon defect model showed tendon tissue regeneration with aligned collagen morphology within 12 weeks of implantation.

Self-assembled phosphate-polyamine networks as biocompatible supramolecular platforms to modulate cell adhesion

The modulation of cell adhesion via biologically inspired materials plays a key role in the development of realistic platforms to envisage not only mechanistic descriptions of many physiological and pathological processes but also new biointerfacial designs compatible with the requirements of biomedical devices. In this work, we show that the cell adhesion and proliferation of three different cell lines can be easily manipulated by using a novel biologically inspired supramolecular coating generated via dip coating of the working substrates in an aqueous solution of polyallylamine in the presence of phosphate anions-a simple one-step modification procedure. Our results reveal that selective cell adhesion can be controlled by varying the deposition time of the coating. Cell proliferation experiments showed a cell type-dependent quasi-exponential growth demonstrating the nontoxic properties of the supramolecular platform. After reaching a certain surface coverage, the supramolecular films based on phosphate-polyamine networks displayed antiadhesive activity towards cells, irrespective of the cell type. However and most interestingly, these antiadherent substrates developed strong adhesive properties after thermal annealing at 37 °C for 3 days. These results were interpreted based on the changes in the coating hydrophilicity, topography and stiffness, with the latter being assessed by atomic force microscopy imaging and indentation experiments. The reported approach is simple, robust and flexible, and would offer opportunities for the development of tunable, biocompatible interfacial architectures to control cell attachment for various biomedical applications.

Tunable Adhesion for Bio-Integrated Devices

With the rapid development of bio-integrated devices and tissue adhesives, tunable adhesion to soft biological tissues started gaining momentum. Strong adhesion is desirable when used to efficiently transfer vital signals or as wound dressing and tissue repair, whereas weak adhesion is needed for easy removal, and it is also the essential step for enabling repeatable use. Both the physical and chemical properties (e.g., moisture level, surface roughness, compliance, and surface chemistry) vary drastically from the skin to internal organ surfaces. Therefore, it is important to strategically design the adhesive for specific applications. Inspired largely by the remarkable adhesion properties found in several animal species, effective strategies such as structural design and novel material synthesis were explored to yield adhesives to match or even outperform their natural counterparts. In this mini-review, we provide a brief overview of the recent development of tunable adhesives, with a focus on their applications toward bio-integrated devices and tissue adhesives.

On the Infectivity of Bacteriophages in Polyelectrolyte Multilayer Films: Inhibition or Preservation of Their Bacteriolytic Activity?

Antibiotic resistance in bacterial cells has motivated the scientific community to design new and efficient (bio)materials with targeted bacteriostatic and/or bactericide properties. In this work, a series of polyelectrolyte multilayer films differing in terms of polycation-polyanion combinations are constructed according to the layer-by-layer deposition method. Their capacities to host T4 and φx174 phage particles and maintain their infectivity and bacteriolytic activity are thoroughly examined. It is found that the macroscopic physicochemical properties of the films, which includes film thickness, swelling ratio, or mechanical stiffness (as derived by atomic force microscopy and spectroscopy measurements), do not predominantly control the selectivity of the films for hosting infective phages. Instead, it is evidenced that the intimate electrostatic interactions locally operational between the loaded phages and the polycationic and polyanionic PEM components may lead to phage activity reduction and preservation/enhancement, respectively. It is argued that the underlying mechanism involves the screening of the phage capsid receptors (operational in cell recognition/infection processes) because of the formation of either polymer-phage hetero-assemblies or polymer coating surrounding the bioactive phage surface.

Interactions of bioactive molecules with thin dendritic glycopolymer layers

The authors report on highly swellable, stable layers of spherical dendritic glycopolymers, composed of hyperbranched poly(ethylene imine) (PEI) as core and two different maltose shells (A = dense shell and B = open shell). These glycopolymers are cross-linked and attached with poly(ethylene-alt-maleic anhydride) (PEMA) or citric acid on SiO_x substrates. The swelling and adsorption of biomolecules were analyzed by spectroscopic ellipsometry and quartz crystal microbalance with dissipation. The swelling degree and complexation with the drug molecule adenosine triphosphate (ATP) were found to be up to 10 times higher for dendritic glycopolymer layers cross-linked with PEMA than for layers cross-linked with citric acid. ATP complexation by electrostatic interaction with the PEI cores was confirmed by x-ray photoelectron spectroscopy analysis. Complexation led to partial collapsing, stiffening, and increase of polymer layer viscosity of the PEMA cross-linked layers. From modeling of ellipsometric data, it was deduced that ATP complexation preferably takes place at the polymer layer-solution interface. The size effect of the adsorbates was investigated by comparing ATP complexation with the adsorption of larger vitamin B12 and human serum albumin (HSA) protein. PEI-Mal A cross-linked with PEMA was found to be resistant toward B12 and HSA adsorption due to the diffusion barrier of the polymer layer. Thus, the authors present potentially biocompatible polymer surfaces for drug loading and their surface supported release.

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.

Automated Buildup of Biomimetic Films in Cell Culture Microplates for High-Throughput Screening of Cellular Behaviors

An automatic method is established for layer-by-layer (LbL) assembly of biomimetic coatings in cell culture microplates using a commercial liquid-handling robot. Highly homogeneous thin films are formed at the bottom of each microwell. The LbL film-coated microplates are compatible with common cellular assays, using microplate readers and automated microscopes. Cellular adhesion is screened on crosslinked and peptide-functionalized LbL films and stem cell differentiation in response to increasing doses of bone morphogenetic proteins (2, 4, 7, 9). This method paves the way for future applications of LbL films in cell-based assays for regenerative medicine and high-throughput drug screening.