A Simple Nanoscale Interface Directs Alignment of a Confluent Cell Layer on Oxide and Polymer Surfaces

Fibronectin fibril alignment is established upon initiation of extracellular matrix assembly

The physical structure of the extracellular matrix (ECM) is tissue-specific and fundamental to normal tissue function. Proper alignment of ECM fibers is essential for the functioning of a variety of tissues. While matrix assembly in general has been intensively investigated, little is known about the mechanisms required for formation of aligned ECM fibrils. We investigated the initiation of fibronectin (FN) matrix assembly using fibroblasts that assemble parallel ECM fibrils and found that matrix assembly sites, where FN fibrillogenesis is initiated, were oriented in parallel at the cell poles. We show that these polarized matrix assembly sites progress into fibrillar adhesions and ultimately into aligned FN fibrils. Cells that assemble an unaligned meshwork matrix form matrix assembly sites around the cell periphery, but the distribution of matrix assembly sites in these cells could be modulated through micropatterning or mechanical stretch. While an elongated cell shape corresponds with a polarized matrix assembly site distribution, these two features are not absolutely linked, since we discovered that transforming growth factor beta (TGF-β1) enhances matrix assembly site polarity and assembly of aligned fibrils independent of cell elongation. We conclude that the ultimate orientation of FN fibrils is determined by the alignment and distribution of matrix assembly sites that form during the initial stages of cell–FN interactions.

Covalent attachment of resveratrol to stainless steel toward the development of a resveratrol-releasing bare-metal stent

Herein, we describe the covalent attachment of resveratrol, a naturally occurring antioxidant, to the surface of stainless-steel as a model for designing a novel bare-metal stent to treat coronary artery disease. Resveratrol has been shown to reduce oxidative stress in dysfunctional endothelial cells, and stimulate arterial healing. Resveratrol treatments, however, are limited by low water solubility, such that a localized delivery to the site of arterial narrowing via a coated stent presents a promising strategy for improving stent outcomes. Our attachment strategy utilizes zirconium vapor deposition to lay down a thin layer of zirconium oxide with labile hydrocarbon groups at the surface. Resveratrol can displace these hydrocarbons in aprotic solvent to afford a covalently attached layer of resveratrol. We evaluated the release of resveratrol under a range of pH levels, including physiological conditions (pH = 7.4 and 37 °C). Furthermore, we established that endothelial cells grown on a resveratrol-bound surface release elevated nitric oxide levels compared to controls, a key endothelial signaling molecule responsible for arterial health. These results are promising toward the development of a resveratrol-coated bare-metal stent to improve patient outcomes.

Controlling the Surface Chemistry of a Hydrogel for Spatially Defined Cell Adhesion

A two-step synthesis is described for activating the surface of a fully hydrated hydrogel that is of interest as a possible scaffold for neural regeneration devices. The first step exploits the water content of the hydrogel and the hydrophobicity of the reaction solvent to create a thin oxide layer on the hydrogel surface using a common titanium or zirconium alkoxide. This layer serves as a reactive interface that enables rapid transformation of the hydrophilic, cell-nonadhesive hydrogel into either a highly hydrophobic surface by reaction with an alkylphosphonic acid, or into a cell-adhesive one using a (α,ω-diphosphono)alkane. Physically imprinting a mask ("debossing") into the hydrogel, followed by a two-step surface modification with a phosphonate, allows for patterning its surface to create spatially defined, cell-adhesive regions.

Self-assembled monolayers of phosphonates promote primary chondrocyte adhesion to silicon dioxide and polyvinyl alcohol materials

The optimal solution for articular cartilage repair has not yet been identified, in part because of the challenges in achieving integration with the host. Coatings have the potential to transform the adhesive features of surfaces, but their application to cartilage repair has been limited. Self-assembled monolayer of phosphonates (SAMPs) have been demonstrated to increase the adhesion of various immortalized cell types to metal and polymer surfaces, but their effect on primary chondrocyte adhesion has not been studied. The objective of this study was to investigate the response of primary chondrocytes to SAMP coatings. We hypothesized a SAMP terminated with an α,ω-bisphosphonic acid, in particular butane-1,4-diphosphonic acid, would increase the number of adherent primary chondrocytes to polyvinyl alcohol (PVA). To test our hypothesis, we first established our ability to successfully modify silicon dioxide (SiO2) surfaces to enable chondrocytes to attach to the surface, without substantial changes in gene expression. Secondly, we applied identical chemistry to PVA, and quantified chondrocyte adhesion. SAMP modification to SiO2 increased chondrocyte adhesion by ×3 after 4 hr and ×4.5 after 24 hr. PVA modification with SAMPs increased chondrocyte adhesion by at least ×31 after 4 and 24 hours. Changes in cell morphology indicated that SAMP modification led to improved chondrocyte adhesion and spreading, without changes in gene expression. In summary, we modified SiO2 and PVA with SAMPs and observed an increase in the number of adherent primary bovine chondrocytes at 4 and 24 hr post-seeding. Mechanisms of chondrocyte interaction with SAMP-modified surfaces require further investigation.

Perforation Does Not Compromise Patterned Two-Dimensional Substrates for Cell Attachment and Aligned Spreading

Polymeric sheets were perforated by laser ablation and were uncompromised by a debris field when first treated with a thin layer of photoresist. Polymer sheets perforated with holes comprising 5, 10, and 20% of the nominal surface area were then patterned in stripes by photolithography, which was followed by synthesis in exposed regions of a cell-attractive zirconium oxide-1,4-butanediphosphonic acid interface. Microscopic and scanning electron microscopy analyses following removal of unexposed photoresist show well-aligned stripes for all levels of these perforations. NIH 3T3 fibroblasts plated on each of these perforated surfaces attached to the interface and spread in alignment with pattern fidelity in every case that is as high as that measured on a nonperforated, patterned substrate.

Cell-derived decellularized extracellular matrices

The ability to create cell-derived decellularized matrices in a dish gives researchers the opportunity to possess a bioactive, biocompatible material made up of fibrillar proteins and other factors that recapitulates key features of the native structure and composition of in vivo microenvironments. By using cells in a culture system to provide a natural ECM, decellularization allows for a high degree of customization through the introduction of selected proteins and soluble factors. The culture system, culture medium, cell types, and physical environments can be varied to provide specialized ECMs for wide-ranging applications to study cell-ECM signaling, cell migration, cell differentiation, and tissue engineering purposes. This chapter describes a procedure for performing a detergent and high pH-based extraction that leaves the native, cell-assembled ECM intact while removing cellular materials. We address common evaluation methods for assessing the ECM and its composition as well as potential uses for a decellularized ECM.

Functional Organophosphonate Interfaces for Nanotechnology: A Review

Optimization of interfaces in inorganic-organic device systems depends strongly on understanding both the molecular processes that are involved in surface modification and the effects that such modifications have on the electronic states of the material. In particular, the last several years have seen passivation and functionalization of semiconductor surfaces to be strategies by which to realize devices with superior function by controlling Fermi level energies, band-gap magnitudes, and work functions of semiconducting substrates. Among all of the synthetic routes and deposition methods available for the optimization of functional interfaces in hybrid systems, organophosphonate chemistry has been found to be a powerful tool to control at the molecular level the properties of materials in many different applications. In this Review, we focus on the relevance of organophosphonate chemistry in nanotechnology, giving an overview about some recent advances in surface modification, interface engineering, nanostructure optimization, and biointegration.

Nerve Guidance by a Decellularized Fibroblast Extracellular Matrix

Spinal cord and peripheral nerve injuries require the regeneration of nerve fibers across the lesion site for successful recovery. Providing guidance cues and soluble factors to promote neurite outgrowth and cell survival can enhance repair. The extracellular matrix (ECM) plays a key role in tissue repair by controlling cell adhesion, motility, and growth. In this study, we explored the ability of a mesenchymal ECM to support neurite outgrowth from neurons in the superior cervical ganglia (SCG). Length and morphology of neurites extended on a decellularized fibroblast ECM were compared to those on substrates coated with laminin, a major ECM protein in neural tissue, or fibronectin, the main component of a mesenchymal ECM. Average radial neurite extension was equivalent on laminin and on the decellularized ECM, but contrasted with the shorter, curved neurites observed on the fibronectin substrate. Differences between neurites on fibronectin and on other substrates were confirmed by fast Fourier transform analyses. To control the direction of neurite outgrowth, we developed an ECM with linearly aligned fibril organization by orienting the fibroblasts that deposit the matrix on a polymeric surface micropatterned with a striped chemical interface. Neurites projected from SCGs appeared to reorient in the direction of the pattern. These results highlight the ability of a mesenchymal ECM to enhance neurite extension and to control the directional outgrowth of neurites. This micropatterned decellularized ECM architecture has potential as a regenerative microenvironment for nerve repair.

Disorder-derived, strong tunneling attenuation in bis-phosphonate monolayers

Monolayers of alkyl bisphosphonic acids (bisPAs) of various carbon chain lengths (C4, C8, C10, C12) were grown on aluminum oxide (AlO(x)) surfaces from solution. The structural and electrical properties of these self-assembled monolayers (SAMs) were compared with those of alkyl monophosphonic acids (monoPAs). Through contact angle (CA) and Kelvin-probe (KP) measurements, ellipsometry, and infrared (IR) and x-ray photoelectron (XPS) spectroscopies, it was found that bisPAs form monolayers that are relatively disordered compared to their monoPA analogs. Current-voltage (J-V) measurements made with a hanging Hg drop top contact show tunneling to be the prevailing transport mechanism. However, while the monoPAs have an observed decay constant within the typical range for dense monolayers, β(mono)  =  0.85  ±  0.03 per carbon atom, a surprisingly high value, β(bis) =  1.40  ±  0.05 per carbon atom, was measured for the bisPAs. We attribute this to a strong contribution of 'through-space' tunneling, which derives from conformational disorder in the monolayer due to strong interactions of the distal phosphonic acid groups; they likely form a hydrogen-bonding network that largely determines the molecular layer structure. Since bisPA SAMs attenuate tunnel currents more effectively than do the corresponding monoPA SAMs, they may find future application as gate dielectric modification in organic thin film devices.

Priming the Surface of Orthopedic Implants for Osteoblast Attachment in Bone Tissue Engineering

The development of better orthopedic implants is incessant. While current implants can function reliably in the human body for a long period of time, there are still a significant number of cases for which the implants can fail prematurely due to poor osseointegration of the implant with native bone. Increasingly, it is recognized that it is extremely important to facilitate the attachment of osteoblasts on the implant so that a proper foundation of extracellular matrix (ECM) can be laid down for the growth of new bone tissue. In order to facilitate the osseointegration of the implant, both the physical nanotopography and chemical functionalization of the implant surface have to be optimized. In this short review, however, we explore how simple chemistry procedures can be used to functionalize the surfaces of three major classes of orthopedic implants, i.e. ceramics, metals, and polymers, so that the attachment of osteoblasts on implants can be facilitated in order to promote implant osseointegration.

Perfect nematic order in confined monolayers of spindle-shaped cells

Elongated, weakly interacting, apolar, fibroblast cells (mouse fibroblasts NIH-3T3) cultured at confluence align together, forming large domains (correlation length ∼ 500 μm) where they are perfectly ordered. We study the emergence of this mesoscopic nematic order by quantifying the ordering dynamics in a two-dimensional tissue. Cells are initially very motile and the monolayer is characterized by anomalous density fluctuations, a signature of far-from-equilibrium systems. As the cell density increases because of proliferation, the cells align with each other forming these large oriented domains while, at the same time, the cellular movements and the density fluctuations freeze. Topological defects that are characteristic of nematic phases remain trapped at long times thereby preventing the development of infinite domains. When confined within adhesive stripes of given widths (from 30 μm to 1.5 mm) cells spontaneously align with the domain edges. This orientation then propagates toward the pattern center. For widths smaller than the orientation correlation length, cells perfectly align in the direction of the stripe. Experiments performed in cross-shaped patterns show that in the situation of two competing populations, both the number of cells and the degree of alignment impact the final orientation.