Context dependence of the assembly, structure, and stability of polypeptide multilayer nanofilms

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.

Branched polymer models and the mechanism of multilayer film buildup

The "in and out diffusion" hypothesis does not provide a conclusive explanation of the buildup displayed by some polyelectrolyte multilayer film systems. Here, we report initial tests of an alternative hypothesis, on which the completion of each adsorption cycle results in an increase in the number of polymer binding sites on the film surface. Polycationic dendrimeric peptides, which can potentially bind several oppositely-charged peptides each, have been designed, synthesized and utilized in comparative film buildup experiments. Material deposited, internal film structure and film surface morphology have been studied by ultraviolet spectroscopy (UVS), circular dichroism spectroscopy (CD), quartz crystal microbalance (QCM) and atomic force microscopy (AFM). Polycations tended to contribute more to film buildup than did polyanions on quartz but not on gold. Increasing the number of branches in the dendrimeric peptides from 4 to 8 reproducibly resulted in an increase in the film growth rate on quartz but not on gold. Peptide backbones tended to adopt a β-strand conformation on incorporation into a film. Thicker films had a greater surface roughness than thin films. The data are consistent with film buildup models in which the average number of polymer binding sites will increase with each successive adsorption cycle in the range where exponential growth is displayed.

Dynamic materials from microgel multilayers

Multilayer coatings made from hydrogel microparticles (microgels) are conceptually very simple materials: thin films composed of microgel building blocks held together by polyelectrolyte "glue". However, the apparent simplicity of their fabrication and structure belies extremely complex properties, including those of "dynamic" coatings that display rapid self-healing behavior in the presence of solvent. This contribution covers our work with these materials and highlights some of the key findings regarding damage mechanisms, healing processes, film structure/composition, and how the variation of fabrication parameters can impact self-healing behavior.

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.

"In and out diffusion" hypothesis of exponential multilayer film buildup revisited

A hypothesis concerning the exponential buildup of polyelectrolyte multilayer films prepared by layer-by-layer assembly has become widely accepted in the scientific community. This model was first introduced with experimental data in Langmuir. It was subsequently described in Proceedings of the National Academy of Sciences and extended and amended in papers in Langmuir and other journals. According to the "in and out diffusion" hypothesis, as it is called, or "common rule" of exponential multilayer film buildup, as it is widely regarded, "a diffusion-based buildup mechanism ... explains most of the exponential-like growth process of polyelectrolyte multilayers reported in the literature." The present work offers an alternative viewpoint to specific elements of the hypothesis and the model as a whole.

Peptide-mediated constructs of quantum dot nanocomposites for enzymatic control of nonradiative energy transfer

A bottom-up approach for constructing colloidal semiconductor quantum dot (QDot) nanocomposites that facilitate nonradiative Förster-type resonance energy transfer (FRET) using polyelectrolyte peptides was proposed and realized. The electrostatic interaction of these polypeptides with altering chain lengths was probed for thermodynamic, structural, and morphological aspects. The resulting nanocomposite film was successfully cut with the protease by digesting the biomimetic peptide layer upon which the QDot assembly was constructed. The ability to control photoluminescence decay lifetime was demonstrated by proteolytic enzyme activity, opening up new possibilities for biosensor applications.

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."