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

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.

Surface Micro- and Nanoengineering: Applications of Layer-by-Layer Technology as a Versatile Tool to Control Cellular Behavior

Extracellular matrix (ECM) cues have been widely investigated for their impact on cellular behavior. Among mechanics, physics, chemistry, and topography, different ECM properties have been discovered as important parameters to modulate cell functions, activating mechanotransduction pathways that can influence gene expression, proliferation or even differentiation. Particularly, ECM topography has been gaining more and more interest based on the evidence that these physical cues can tailor cell behavior. Here, an overview of bottom-up and top-down approaches reported to produce materials capable of mimicking the ECM topography and being applied for biomedical purposes is provided. Moreover, the increasing motivation of using the layer-by-layer (LbL) technique to reproduce these topographical cues is highlighted. LbL assembly is a versatile methodology used to coat materials with a nanoscale fidelity to the geometry of the template or to produce multilayer thin films composed of polymers, proteins, colloids, or even cells. Different geometries, sizes, or shapes on surface topography can imply different behaviors: effects on the cell adhesion, proliferation, morphology, alignment, migration, gene expression, and even differentiation are considered. Finally, the importance of LbL assembly to produce defined topographical cues on materials is discussed, highlighting the potential of micro- and nanoengineered materials to modulate cell function and fate.

Micropatterned multienzyme devices with adjustable amounts of immobilized enzymes

Multienzyme microstructures of glucose oxidase (GOx) and horseradish peroxidase (HRP) were prepared by layer-by-layer deposition inside microfluidic networks on glass substrates in order to allow both site-specific deposition and control of the amount of immobilized enzymes. The obtained microstructures were characterized by scanning force microscopy for the topography of the deposited layers. The local enzyme activity was characterized by the substrate-generation/tip-collection mode and the enzyme-mediated feedback mode of the scanning electrochemical microscope (SECM). These measurements provided quantitative information about the immobilized enzyme activity as a basis for adjusting enzyme loading for multienzyme structures that realize logical operations based on enzymatic conversions. Information about local HRP activity can also be obtained by optical readout using an Amplex UltraRed fluorgenic substrate and reading with a confocal laser scanning microscope with a much higher repetition rate for image acquisition. Using these principles, a layout with HRP and GOx microstructures was realized that showed the functionality of an OR Boolean logic switch.

Chondrocyte Behavior on Micropatterns Fabricated Using Layer-by-Layer Lift-Off: Morphological Analysis

Cell patterning has emerged as an elegant tool in developing cellular arrays, bioreactors, biosensors, and lab-on-chip devices and for use in engineering neotissue for repair or regeneration. In this study, micropatterned surfaces were created using the layer-by-layer lift-off (LbL-LO) method for analyzing canine chondrocytes response to patterned substrates. Five materials were chosen based on our previous studies. These included: poly(dimethyldiallylammonium chloride) (PDDA), poly(ethyleneimine) (PEI), poly(styrene sulfonate) (PSS), collagen, and chondroitin sulfate (CS). The substrates were patterned with these five different materials, in five and ten bilayers, resulting in the following multilayer nanofilm architectures: (PSS/PDDA)₅, (PSS/PDDA)₁₀; (CS/PEI)₄/CS, (CS/PEI)₉/CS; (PSS/PEI)₅, (PSS/PEI)₁₀; (PSS/Collagen)₅, (PSS/Collagen)₁₀; (PSS/PEI)₄/PSS, (PSS/PEI)₉/PSS. Cell characterization studies were used to assess the viability, longevity, and cellular response to the configured patterned multilayer architectures. The cumulative cell characterization data suggests that cell viability, longevity, and functionality were enhanced on micropatterned PEI, PSS, collagen, and CS multilayer nanofilms suggesting their possible use in biomedical applications.

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.

From miniature to nano robots for diagnostic and therapeutic applications

This paper presents the evolution of diagnostic and therapeutic procedures as a process of convergence of technologies coming from different fields and involving different disciplines. In particular, it illustrates how modern surgery evolved thanks to fundamental biology knowledge; thus, with the introduction of imaging techniques intra-operatively and with the introduction of robotics, surgical procedures became much more predictable, precise and effective. Finally, the recent developments of optics (with CMOS and CCD technologies, and with the introduction of fiber optic technologies) allowed to "see" inside the human body, thus reducing the invasiveness of surgical procedures and making diagnostic procedures adequate for an effective early discovery of pathologies. Nowadays, we are assisting to a concrete merging between microrobotics technologies and bioengineering, with the potential to bring therapeutic tools where requested and when requested, with high precision and with very limited side effects. Furthermore, nanotechnology offers the possibility to fully implement this merging, thanks to the development of dedicated theranostic nanotools suitably fitting the considered convergence scenario.

Freely suspended cellular "backpacks" lead to cell aggregate self-assembly

Cellular “backpacks” are a new type of anisotropic, nanoscale thickness microparticle that may be attached to the surface of living cells creating a “bio-hybrid” material. Previous work has shown that these backpacks do not impair cell viability or native functions such as migration in a B and T cell line, respectively. In the current work, we show that backpacks, when added to a cell suspension, assemble cells into aggregates of reproducible size. We investigate the efficiency of backpack−cell binding using flow cytometry and laser diffraction, examine the influence of backpack diameter on aggregate size, and show that even when cell−backpack complexes are forced through small pores, backpacks are not removed from the surfaces of cells.

Magnetic Nanofilms for Biomedical Applications

Polymeric ultrathin films, also called nanofilms or nanosheets, show peculiar properties making them potentially useful for several applications in biomedicine, e.g., as nanoplasters for localized drug release or as a new solution for closing endoluminal surgical wounds. In this sense, one of most challenging issues is film control in the working environment: the possibility of including magnetic components, such as magnetic nanoparticles or nanotubes, paves the way for the effective use of nanofilms in the human body, by allowing precise positioning by an external magnetic field. State of the art and new perspectives of magnetic nanofilms for biomedical applications are here presented, including fabrication, modeling, characterization and validation.

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."

Laser printing mediated cell patterning

An approach for complex cell patterning, using laser printing, is described allowing essentially any cellular image or pattern to be rapidly fabricated.

Polymer/colloid surface micromachining: micropatterning of hybrid multilayers

Fabrication of multicomponent patterned films comprising polymer/nanoparticle multilayers using conventional lithography and bottom-up layer-by-layer nanofabrication techniques is described. The work is motivated by the potential to extend polymer surface micromachining capabilities toward construction of integrated systems by connecting discrete domains of active materials containing functional nanoparticles. Modified surfaces illustrate tunability of the physical (thickness, roughness, 3D structures) and chemical (inorganic/organic material combinations) properties of the nanocomposite micropatterns. Intriguing nanoscale phenomena were observed for the structures when the order of material deposition was changed; the final multilayer thickness and surface roughness and mechanical integrity of the patterns were found to be interdependent and related to the roughness of layers deposited earlier in the process.

Surface functionalization of living cells with multilayer patches

We demonstrate that functional polyelectrolyte multilayer (PEM) patches can be attached to a fraction of the surface area of living, individual lymphocytes. Surface-modified cells remain viable at least 48 h following attachment of the functional patch, and patches carrying magnetic nanoparticles allow the cells to be spatially manipulated using a magnetic field. The patch does not completely occlude the cellular surface from the surrounding environment; this approach allows a functional payload to be attached to a cell that is still free to perform its native functions, as suggested by preliminary studies on patch-modified T-cell migration. This approach has potential for broad applications in bioimaging, cellular functionalization, immune system and tissue engineering, and cell-based therapeutics where cell-environment interactions are critical.

Solvent-assisted patterning of polyelectrolyte multilayers and selective deposition of virus assemblies

We introduce a simple method to pattern electrostatic assemblies of viruses onto a polyelectrolyte multilayer. The increased mobility of weak polycation chains in the multilayer above a given thickness ensures the surface mobility of viruses required for spontaneous ordering of densely packed viruses atop polymeric patterns. To pattern the polyelectrolyte multilayer film, we employ a nonconventional patterning method known as solvent-assisted capillary molding for the first time on multilayer films, and demonstrate micrometer-scaled dense patterns of viruses, where the accessible feature size can be correlated by the length scale of virus and swelling property of underlying patterned polyelectrolyte multilayer. We further examine the ability to modify the top surfaces of these assemblies with biological ligands, which extends the applicability of patterned viruses to biological detection purposes. We expect that the present method described here can be generally applied to the patterning of other polyelectrolyte multilayers and combined with the ordered assembly of anisotropic nanomaterials such as polymeric nanotubes or inorganic nanowires for a broad range of applications.