Decoupling geometrical and chemical cues directing epidermal stem cell fate on polymer brush-based cell micro-patterns

Navigating the Immunological Crossroads: Mesenchymal Stem/Stromal Cells as Architects of Inflammatory Harmony in Tissue-Engineered Constructs

In the dynamic landscape of tissue engineering, the integration of tissue-engineered constructs (TECs) faces a dual challenge-initiating beneficial inflammation for regeneration while avoiding the perils of prolonged immune activation. As TECs encounter the immediate reaction of the immune system upon implantation, the unique immunomodulatory properties of mesenchymal stem/stromal cells (MSCs) emerge as key navigators. Harnessing the paracrine effects of MSCs, researchers aim to craft a localized microenvironment that not only enhances TEC integration but also holds therapeutic promise for inflammatory-driven pathologies. This review unravels the latest advancements, applications, obstacles, and future prospects surrounding the strategic alliance between MSCs and TECs, shedding light on the immunological symphony that guides the course of regenerative medicine.

Supercharged Protein Nanosheets for Cell Expansion on Bioemulsions

Cell culture at liquid-liquid interfaces, for example, at the surface of oil microdroplets, is an attractive strategy to scale up adherent cell manufacturing while replacing the use of microplastics. Such a process requires the adhesion of cells at interfaces stabilized and reinforced by protein nanosheets displaying not only high elasticity but also presenting cell adhesive ligands able to bind integrin receptors. In this report, supercharged albumins are found to form strong elastic protein nanosheets when co-assembling with the co-surfactant pentafluorobenzoyl chloride (PFBC) and mediate extracellular matrix (ECM) protein adsorption and cell adhesion. The interfacial mechanical properties and elasticity of supercharged nanosheets are characterized by interfacial rheology, and behaviors are compared to those of native bovine serum albumin, human serum albumin, and α-lactalbumin. The impact of PFBC on such assembly is investigated. ECM protein adsorption to resulting supercharged nanosheets is then quantified via surface plasmon resonance and fluorescence microscopy, demonstrating that the dual role supercharged albumins are proposed to play as scaffold protein structuring liquid-liquid interfaces and substrates for the capture of ECM molecules. Finally, the adhesion and proliferation of primary human epidermal stem cells are investigated, at pinned droplets, as well as on bioemulsions stabilized by corresponding supercharged nanosheets. This study demonstrates the potential of supercharged proteins for the engineering of biointerfaces for stem cell manufacturing and draws structure-property relationships that will guide further engineering of associated systems.

Design of an Integrated Microvascularized Human Skin-on-a-Chip Tissue Equivalent Model

Tissue-engineered skin constructs have been under development since the 1980s as a replacement for human skin tissues and animal models for therapeutics and cosmetic testing. These have evolved from simple single-cell assays to increasingly complex models with integrated dermal equivalents and multiple cell types including a dermis, epidermis, and vasculature. The development of micro-engineered platforms and biomaterials has enabled scientists to better recreate and capture the tissue microenvironment in vitro, including the vascularization of tissue models and their integration into microfluidic chips. However, to date, microvascularized human skin equivalents in a microfluidic context have not been reported. Here, we present the design of a novel skin-on-a-chip model integrating human-derived primary and immortalized cells in a full-thickness skin equivalent. The model is housed in a microfluidic device, in which a microvasculature was previously established. We characterize the impact of our chip design on the quality of the microvascular networks formed and evidence that this enables the formation of more homogenous networks. We developed a methodology to harvest tissues from embedded chips, after 14 days of culture, and characterize the impact of culture conditions and vascularization (including with pericyte co-cultures) on the stratification of the epidermis in the resulting skin equivalents. Our results indicate that vascularization enhances stratification and differentiation (thickness, architecture, and expression of terminal differentiation markers such as involucrin and transglutaminase 1), allowing the formation of more mature skin equivalents in microfluidic chips. The skin-on-a-chip tissue equivalents developed, because of their realistic microvasculature, may find applications for testing efficacy and safety of therapeutics delivered systemically, in a human context.

Chemistry and engineering of brush type polymers: Perspective towards tissue engineering

In tissue engineering, it is imperative to control the behaviour of cells/stem cells, such as adhesion, proliferation, propagation, motility, and differentiation for tissue regeneration. Surfaces that allow cells to behave in this way are critical as support materials in tissue engineering. Among these surfaces, brush-type polymers have an important potential for tissue engineering and biomedical applications. Brush structure and length, end groups, bonding densities, hydrophilicity, surface energy, structural flexibility, thermal stability, surface chemical reactivity, rheological and tribological properties, electron and energy transfer ability, cell binding and absorption abilities for various biological molecules of brush-type polymers were increased its importance in tissue engineering applications. In addition, thanks to these functional properties and adjustable surface properties, brush type polymers are used in different high-tech applications such as electronics, sensors, anti-fouling, catalysis, purification and energy etc. This review comprehensively highlights the use of brush-type polymers in tissue engineering applications. Considering the superior properties of brush-type polymer structures, it is believed that in the future, it will be an effective tool in structure designs containing many different biomolecules (enzymes, proteins, etc.) in the field of tissue engineering.

The physico-chemistry of adhesions of protein resistant and weak polyelectrolyte brushes to cells and tissues

The non-specific adhesion of polymers and soft tissues is of great interest to the field of biomedical engineering, as it will shed light on some of the processes that regulate interactions between scaffolds, implants and nanoparticles with surrounding tissues after implantation or delivery. In order to promote adhesion to soft tissues, a greater understanding of the relationship between polymer chemistry and nanoscale adhesion mechanisms is required. In this work, we grew poly(dimethylaminoethyl methacrylate) (PDMAEMA), poly(acrylic acid) (PAA) and poly(oligoethylene glycol methacrylate) (POEGMA) brushes from the surface of silica beads, and investigated their adhesion to a variety of substrates via colloidal probe-based atomic force microscopy (AFM). We first characterised adhesion to a range of substrates with defined surface chemistry (self-assembled monolayers (SAMs) with a range of hydrophilicities, charge and hydrogen bonding), before studying the adhesion of brushes to epithelial cell monolayers (primary keratinocytes and HaCaT cells) and soft tissues (porcine epicardium and keratinized gingiva). Adhesion assays to SAMs reveal the complex balance of interactions (electrostatic, van der Waals interactions and hydrogen bonding) regulating the adhesion of weak polyelectrolyte brushes. This resulted in particularly strong adhesion of PAA brushes to a wide range of surface chemistries. In turn, colloidal probe microscopy on cell monolayers highlighted the importance of the glycocalyx in regulating non-specific adhesions. This was also reflected by the adhesive properties of soft tissues, in combination with their mechanical properties. Overall, this work clearly demonstrates the complex nature of interactions between polymeric biomaterials and biological samples and highlights the need for relatively elaborate models to predict these interactions.

Binary polymer brush patterns from facile initiator stickiness for cell culturing

We report a new initiator stickiness method to fabricate micropatterned binary polymer brush surfaces, which are ideal platforms for studying cell adhesion behavior. The atom transfer radical polymerization (ATRP) initiator, ω-mercaptoundecyl bromoisobutyrate (MUDBr), is found to adsorb on several hosting polymer brushes, including poly[oligo(ethylene glycol)methyl ether methacrylate] (POEGMA), poly(2-hydroxyethyl methacrylate) (PHEMA), and poly(glycidyl methacrylate) (PGMA) brushes. Based on the initiator stickiness, micropatterned initiator molecules are printed onto a layer of homogenous hosting polymer brushes via microcontact printing (μCP), and then, vertically, a patterned second layer of polymer brushes is grown from the initiator areas. With this simple, fast, and additive method, we demonstrate the fabrication of various binary polymer brushes, and show their applications for patterning cell microarrays and controlling cell orientation. This new approach to generating binary polymer brushes shows great potential for the manipulation of interfacial phenomena, facilitating a range of applications from semiconductors and lubrication to fundamental cell biology studies.

Organically modified hydroxyapatite (ormoHAP) nanospheres stimulate the differentiation of osteoblast and osteoclast precursors: a co-culture study

Isolated nanospheres consisting of organically modified hydroxyapatite (ormoHAP), prepared by an electric field-assisted ion double migration process, were embedded in foamed gelatin to form a composite scaffold. Degradation rates have been demonstrated to correlate with the crosslinking degree (40%, 80%) as well as with the mineral content of the scaffolds (0%, 20%, 40%). A human co-culture model of osteoblasts and osteoclasts, derived from bone marrow stromal cells and monocytes, respectively, without external addition of the factors RANKL and M-CSF, was run for up to 42 d in order to characterize the action of the ormoHAP-gelatin scaffolds on the co-culture. Examination was performed by quantitative biochemical methods (DNA, LDH, ALP, TRAP5b), gene expression analysis (ALP, BSP II, RANKL, IL-6, VTNR, CTSK, TRAP, OSCAR, CALCR) and confocal laser scanning microscopy (cell nuclei, actin, CD68, TRAP). Results confirm that ormoHAP embedded in the gelatin matrix enhanced TRAP 5b activity. As a feedback, ALP activity and gene expression of BSP II of osteoblasts increased. Finally, a sequence of cell cross-talk actions is suggested, which can explain the behavior of the formed vital co-culture and moreover the influence of the presence and concentration of ormoHAP.

Core-independent approach for polymer brush-functionalised nanomaterials with a fluorescent tag for RNA delivery

A core-independent approach for the design of polymer brush-functionalised nanomaterials with a fluorescent tag for RNA delivery.

Micro-/Nano-Scales Direct Cell Behavior on Biomaterial Surfaces

Cells are the smallest living units of a human body's structure and function, and their behaviors should not be ignored in human physiological and pathological metabolic activities. Each cell has a different scale, and presents distinct responses to specific scales: Vascular endothelial cells may obtain a normal function when regulated by the 25 µm strips, but de-function if the scale is removed; stem cells can rapidly proliferate on the 30 nm scales nanotubes surface, but stop proliferating when the scale is changed to 100 nm. Therefore, micro and nano scales play a crucial role in directing cell behaviors on biomaterials surface. In recent years, a series of biomaterials surface with micro and/or nano scales, such as micro-patterns, nanotubes and nanoparticles, have been developed to control the target cell behavior, and further enhance the surface biocompatibility. This contribution will introduce the related research, and review the advances in the micro/nano scales for biomaterials surface functionalization.

Controlled Arrangement of Neuronal Cells on Surfaces Functionalized with Micropatterned Polymer Brushes

Conventional in vitro cultures are useful to represent simplistic neuronal behavior; however, the lack of organization results in random neurite spreading. To overcome this problem, control over the directionality of SH-SY5Y cells was attained, utilizing photolithography to pattern the cell-repulsive anionic brush poly(potassium 3-sulfopropyl methacrylate) (PKSPMA) into tracks of 20, 40, 80, and 100 μm width. These data validate the use of PKSPMA brush coatings for a long-term culture of the SH-SY5Y cells, as well as providing a methodology by which the precise deposition of PKSPMA can be utilized to achieve a targeted control over the SH-SY5Y cells. Specifically, the PKSPMA brush patterns prevented cell attachment, allowing the SH-SY5Y cells to grow only on noncoated glass (gaps of 20, 50, 75, and 100 μm width) at different cell densities (5000, 10 000, and 15 000 cells/cm2). This research demonstrates the importance of achieving cell directionality in vitro, while these simplistic models could provide new platforms to study complex neuron-neuron interactions.

Substrate-Independent Micropatterning of Polymer Brushes Based on Photolytic Deactivation of Chemical Vapor Deposition Based Surface-Initiated Atom-Transfer Radical Polymerization Initiator Films

Precise microscale arrangement of biomolecules and cells is essential for tissue engineering, microarray development, diagnostic sensors, and fundamental research in the biosciences. Biofunctional polymer brushes have attracted broad interest in these applications. However, patterning approaches to creating microstructured biointerfaces based on polymer brushes often involve tedious, expensive, and complicated procedures that are specifically designed for model substrates. We report a substrate-independent, facile, and scalable technique with which to prepare micropatterned biofunctional brushes with the ability to generate binary chemical patterns. Employing chemical vapor deposition (CVD) polymerization, a functionalized polymer coating decorated with 2-bromoisobutyryl groups that act as atom-transfer radical polymerization (ATRP) initiators was prepared and subsequently modified using UV light. The exposure of 2-bromoisobutyryl groups to UV light with wavelengths between 187 and 254 nm resulted in selective debromination, effectively eliminating the initiation of ATRP. In addition, when coatings incorporating both 2-bromoisobutyryl and primary amine groups were irradiated with UV light, the amines retained their functionality after UV treatment and could be conjugated to activated esters, facilitating binary chemical patterns. In contrast, polymer brushes were selectively grown from areas protected from UV treatment, as confirmed by atomic force microscopy, time-of-flight secondary ion mass spectrometry, and imaging ellipsometry. Furthermore, spatial control over biomolecular adhesion was achieved in three ways: (1) patterned nonfouling brushes resulted in nonspecific protein adsorption to areas not covered with polymer brushes; (2) patterned brushes decorated with active binding sides gave rise to specific protein immobilization on areas presenting polymer brushes; (3) and primary amines were co-patterned along with clickable polymer brushes bearing pendant alkyne groups, leading to bifunctional reactivity. Because this novel technique is independent of the original substrate's physicochemical properties, it can be extended to technologically relevant substrates such as polystyrene, polydimethylsiloxane, polyvinyl chloride, and steel. With further work, the photolytic deactivation of CVD-based initiator coatings promises to advance the utility of patterned biofunctional polymer brushes across a spectrum of biomedical applications.

Surface-Initiated Poly(oligo(2-alkyl-2-oxazoline)methacrylate) Brushes

Polymer brushes are particularly performant antifouling coatings, owing to their high grafting density that prevents unwanted biomacromolecules to diffuse through the coating and adhere to the underlying substrate. In addition to this structural feature, polymer brushes require a relatively high level of hydrophilicity and a globally neutral structure to display ultrahigh protein resistance. Poly(2-alkyl-2-oxaolines) are attractive building blocks for such coatings as they can display relatively high hydrophilicity, owing to their amide repeat units, but can also be side-chain and end-chain functionalized relatively readily. However, poly(2-alkyl-2-oxazolines) have not yet been introduced through a radical-mediated grafting from polymer brush structure that would confer the high level of grafting density that is the hallmark of highly protein resistant brushes. Here, we present the formation of a series of poly(oligo(2-alkyl-2-oxazoline)methacrylate) brushes generated via a grafting from approach, via atom transfer radical polymerization. We characterize the chemical structure of the resulting coatings via ellipsometry, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. We show that allyl end groups can be introduced as a side chain of these brushes to allow functionalization via thiol-ene chemistry. We demonstrate the excellent protein resistance of these coatings in single protein solutions as well as serum solutions at concentration typically used for cell culture. Finally, we demonstrate the feasibility of using these brushes for the micropatterning of cells and the generation of cell-based assays.

Recent Advances in Engineering the Stem Cell Microniche in 3D

Conventional 2D cell culture techniques have provided fundamental insights into key biochemical and biophysical mechanisms responsible for various cellular behaviors, such as cell adhesion, spreading, division, proliferation, and differentiation. However, 2D culture in vitro does not fully capture the physical and chemical properties of the native microenvironment. There is a growing body of research that suggests that cells cultured on 2D substrates differ greatly from those grown in vivo. This article focuses on recent progress in using bioinspired 3D matrices that recapitulate as many aspects of the natural extracellular matrix as possible. A range of techniques for the engineering of 3D microenvironment with precisely controlled biophysical and chemical properties, and the impact of these environments on cellular behavior, is reviewed. Finally, an outlook on future challenges for engineering the 3D microenvironment and how such approaches would further our understanding of the influence of the microenvironment on cell function is provided.

Neural and Aneural Regions Generated by the Use of Chemical Surface Coatings

The disordered environment found in conventional neural cultures impedes various applications where cell directionality is a key process for functionality. Neurons are highly specialized cells known to be greatly dependent on interactions with their surroundings. Therefore, when chemical cues are incorporated on the surface material, a precise control over neuronal behavior can be achieved. Here, the behavior of SH-SY5Y neurons on a variety of self-assembled monolayers (SAMs) and polymer brushes both in isolation and combination to promote cellular spatial control was determined. APTES and BIBB coatings promoted the highest cell viability, proliferation, metabolic activity, and neuronal maturation, while low cell survival was seen on PKSPMA and PMETAC surfaces. These cell-attractive and repulsive surfaces were combined to generate a binary BIBB-PKSPMA coating, whereby cellular growth was restricted to an exclusive neural region. The utility of these coatings when precisely combined could act as a bioactive/bioinert surface resulting in a biomimetic environment where control over neuronal growth and directionality can be achieved.

Engineered Microenvironments to Direct Epidermal Stem Cell Behavior at Single-Cell Resolution

Mammalian epidermis is maintained through proliferation of stem cells and differentiation of their progeny. The balance between self-renewal and differentiation is controlled by a variety of interacting intrinsic and extrinsic factors. Although the nature of these interactions is complex, they can be modeled in a reductionist fashion by capturing single epidermal stem cells on micropatterned substrates and exposing them to individual stimuli, alone or in combination, over defined time points. These studies have shown that different extrinsic stimuli trigger a common outcome-initiation of terminal differentiation-by activating different signaling pathways and eliciting different transcriptional responses.

Microtechnologies for Cell Microenvironment Control and Monitoring

A great breadth of questions remains in cellular biology. Some questions cannot be answered using traditional analytical techniques and so demand the development of new tools for research. In the near future, the development of highly integrated microfluidic analytical platforms will enable the acquisition of unknown biological data. These microfluidic systems must allow cell culture under controlled microenvironment and high throughput analysis. For this purpose, the integration of a variable number of newly developed micro- and nano-technologies, which enable control of topography and surface chemistry, soluble factors, mechanical forces and cell–cell contacts, as well as technology for monitoring cell phenotype and genotype with high spatial and temporal resolution will be necessary. These multifunctional devices must be accompanied by appropriate data analysis and management of the expected large datasets generated. The knowledge gained with these platforms has the potential to improve predictive models of the behavior of cells, impacting directly in better therapies for disease treatment. In this review, we give an overview of the microtechnology toolbox available for the design of high throughput microfluidic platforms for cell analysis. We discuss current microtechnologies for cell microenvironment control, different methodologies to create large arrays of cellular systems and finally techniques for monitoring cells in microfluidic devices.

Differential integrin expression regulates cell sensing of the matrix nanoscale geometry

The nanoscale geometry and topography of the extra-cellular matrix (ECM) is an important parameter controlling cell adhesion and phenotype. Similarly, integrin expression and the geometrical maturation of adhesions they regulate have been correlated with important changes in cell spreading and phenotype. However, how integrin expression controls the nanoscale sensing of the ECM geometry is not clearly understood. Here we develop a new nanopatterning technique, electrospun nanofiber lithography (ENL), which allows the production of a quasi-2D fibrous nanopattern with controlled dimensions (250-1000nm) and densities. ENL relies on electrospun fibres to act as a mask for the controlled growth of protein-resistant polymer brushes. SEM, AFM and immunofluorescence imaging were used to characterise the resulting patterns and the adsorption of the extra-cellular matrix protein fibronectin to the patterned fibres. The control of adhesion formation was studied, as well as the remodelling and deposition of novel matrix. Cell spreading was found to be regulated by the size of fibres, similarly to previous observations made on circular nanopatterns. However, cell shape and polarity were more significantly affected. These changes correlated with important cytoskeleton reorganisation, with a gradual decrease in stress fibre formation as the pattern dimensions decrease. Finally, the differential expression of αvβ3 and α5β1 integrins in engineered cell lines was found to be an important mediator of cell sensing of the nanoscale geometry of the ECM.

STATEMENT OF SIGNIFICANCE

The novel nanofiber patterns developed in this study, via ENL, mimic the geometry and continuity of natural matrices found in the stroma of tissues, whilst preserving a quasi-2D character (to facilitate imaging and for comparison with other 2D systems such as micropatterned monolayers and circular nanopatches generated by colloidal lithography). These results demonstrate that the nanoscale geometry of the ECM plays an important role in regulating cell adhesion and that this is modulated by integrin expression. This is an important finding as it implies that the knowledge of the biochemical context underlying the integrin-mediated adhesive machinery of specific cell types should allow better design of biomaterials and biointerfaces. Indeed, changes in integrin expression are often associated with the control of cell proliferation and differentiation.

Polymer brush: a promising grafting approach to scaffolds for tissue engineering

Polymer brush is a soft material unit tethered covalently on the surface of scaffolds. It can induce functional and structural modification of a substrate’s properties. Such surface coating approach has attracted special attentions in the fields of stem cell biology, tissue engineering, and regenerative medicine due to facile fabrication, usability of various polymers, extracellular matrix (ECM)-like structural features, and in vivo stability. Here, we summarized polymer brush-based grafting approaches comparing self-assembled monolayer (SAM)-based coating method, in addition to physico-chemical characterization techniques for surfaces such as wettability, stiffness/elasticity, roughness, and chemical composition that can affect cell adhesion, differentiation, and proliferation. We also reviewed recent advancements in cell biological applications of polymer brushes by focusing on stem cell differentiation and 3D supports/implants for tissue formation. Understanding cell behaviors on polymer brushes in the scale of nanometer length can contribute to systematic understandings of cellular responses at the interface of polymers and scaffolds and their simultaneous effects on cell behaviors for promising platform designs.

The Effect of Size and Geometry of Poly(acrylamide) Brush-Based Micropatterns on the Behavior of Cells

In this study, the fabrication, detailed characterization, and application of long-term stable micropatterned bio-interfaces of passivating poly(acrylamide) (PAAm) brushes on transparent gold for application in the study of cell-surface interactions is reported. The micropatterns were fabricated by microcontact printing of an initiator for surface-initiated atom transfer radical polymerization (SI-ATRP), SI-ATRP of acrylamide, and subsequently backfilling of the unfunctionalized areas of 400-2500 μm(2) size and systematically altered number of corners with octadecanethiol. As verified by surface plasmon resonance spectroscopy, the physisorption of fibronectin (FN) was restricted to the adhesive areas. Exploiting this platform, the effect of micropattern geometry and size of cell-adhesive FN areas surrounded by passivating PAAm brushes on transparent gold substrates on the attachment of cells and cytoskeleton alignment was investigated at the single-cell level. Exceptional long-term stability of the patterned PAAm brushes and arrays of adhesive areas, in which human pancreatic tumor cells (Patu 8988T) and fibroblast cells (NIH 3T3) were confined for more than one week, was observed. Adhesive areas of 1600 μm(2) or less constrained the cell shape and caused focal adhesions to accumulate in the corners of the pattern. These changes were most obvious for the PatuT cells in adhesive areas of ∼900 μm(2), in which the actin filaments were aligned, following the boundary of the pattern, and merged in the focal adhesions concentrated in the corners of the pattern. NIH 3T3 cells possessed a larger cell area, which led to an optimal cytoskeleton alignment in adhesive patterns of ∼1600 μm(2). The alignment of the cytoskeleton was found to be less pronounced in cells on larger adhesive areas, where the PatuT cells spread similarly to cells on unpatterned substrates. By contrast, the NIH 3T3 cells were found to stretch even on larger adhesive areas, spanning from one corner to the other. The long-term stability under cell culture conditions of the patterns introduced here will also be useful for long-term studies of single and multiple cells, cell motility in toxicity assays, and stem cell differentiation.

Failure mechanisms in denture adhesives

OBJECTIVE

The mechanical properties of bio adhesives in oral care application are expected to be critical in defining the stability and release of devices such as dentures from the oral tissue. A multiscale experimental mechanical approach is used to evaluate the performance of denture adhesive materials.

METHODS

The inherent mechanical behavior of denture fixatives was examined by separating adhesive material from a representative polymethyl methacrylate (PMMA) surface using atomic force microscopy (AFM) approaches and compared to macroscopic mechanical testing.

RESULTS

Failure of denture adhesive material was found to be critically dependent on the formation of fibrillar structures within the adhesive. Small scale mechanical testing provided evidence for the mechanical properties of the fibrillar structures formed within the adhesive in macroscopic mechanical testing and indicated the importance of the forces required to fail the adhesive at these small length scales in controlling both the maximum forces sustained by the bulk material as well as the ease of separating the adhesive from PMMA surfaces.

SIGNIFICANCE

Our results are important in defining the performance of denture fixative materials and their control of adhesive behavior, allowing the potential to tune properties required in the adhesion and removal of dentures.

Study of thiol–ene chemistry on polymer brushes and application to surface patterning and protein adsorption

The functionalisation and patterning of polymer brushes via thiol–ene chemistry is studied via ellipsometry, XPS and AFM.

Cell sensing of physical properties at the nanoscale: Mechanisms and control of cell adhesion and phenotype

The chemistry, geometry, topography and mechanical properties of biomaterials modulate biochemical signals (in particular ligand-receptor binding events) that control cells-matrix interactions. In turn, the regulation of cell adhesion by the biochemical and physical properties of the matrix controls cell phenotypes such as proliferation, motility and differentiation. In particular, nanoscale geometrical, topographical and mechanical properties of biomaterials are essential to achieve control of the cell-biomaterials interface. The design of such nanoscale architectures and platforms requires understanding the molecular mechanisms underlying adhesion formation and the assembly of the actin cytoskeleton. This review presents some of the important molecular mechanisms underlying cell adhesion to biomaterials mediated by integrins and discusses the nanoscale engineered platforms used to control these processes. Such nanoscale understanding of the cell-biomaterials interface offers exciting opportunities for the design of biomaterials and their application to the field of tissue engineering.

STATEMENT OF SIGNIFICANCE

Biomaterials design is important in the fields of regenerative medicine and tissue engineering, in particular to allow the long term expansion of stem cells and the engineering of scaffolds for tissue regeneration. Cell adhesion to biomaterials often plays a central role in regulating cell phenotype. It is emerging that physical properties of biomaterials, and more generally the microenvironment, regulate such behaviour. In particular, cells respond to nanoscale physical properties of their matrix. Understanding how such nanoscale physical properties control cell adhesion is therefore essential for biomaterials design. To this aim, a deeper understanding of molecular processes controlling cell adhesion, but also a greater control of matrix engineering is required. Such multidisciplinary approaches shed light on some of the fundamental mechanisms via which cell adhesions sense their nanoscale physical environment.

A Role of Myocardin Related Transcription Factor-A (MRTF-A) in Scleroderma Related Fibrosis

In scleroderma (systemic sclerosis, SSc), persistent activation of myofibroblast leads to severe skin and organ fibrosis resistant to therapy. Increased mechanical stiffness in the involved fibrotic tissues is a hallmark clinical feature and a cause of disabling symptoms. Myocardin Related Transcription Factor-A (MRTF-A) is a transcriptional co-activator that is sequestered in the cytoplasm and translocates to the nucleus under mechanical stress or growth factor stimulation. Our objective was to determine if MRTF-A is activated in the disease microenvironment to produce more extracellular matrix in progressive SSc. Immunohistochemistry studies demonstrate that nuclear translocation of MRTF-A in scleroderma tissues occurs in keratinocytes, endothelial cells, infiltrating inflammatory cells, and dermal fibroblasts, consistent with enhanced signaling in multiple cell lineages exposed to the stiff extracellular matrix. Inhibition of MRTF-A nuclear translocation or knockdown of MRTF-A synthesis abolishes the SSc myofibroblast enhanced basal contractility and synthesis of type I collagen and inhibits the matricellular profibrotic protein, connective tissue growth factor (CCN2/CTGF). In MRTF-A null mice, basal skin and lung stiffness was abnormally reduced and associated with altered fibrillar collagen. MRTF-A has a role in SSc fibrosis acting as a central regulator linking mechanical cues to adverse remodeling of the extracellular matrix.

Cell-imprinted substrates act as an artificial niche for skin regeneration

Bioinspired materials can mimic the stem cell environment and modulate stem cell differentiation and proliferation. In this study, biomimetic micro/nanoenvironments were fabricated by cell-imprinted substrates based on mature human keratinocyte morphological templates. The data obtained from atomic force microscopy and field emission scanning electron microscopy revealed that the keratinocyte-cell-imprinted poly(dimethylsiloxane) casting procedure could imitate the surface morphology of the plasma membrane, ranging from the nanoscale to the macroscale, which may provide the required topographical cell fingerprints to induce differentiation. Gene expression levels of the genes analyzed (involucrin, collagen type I, and keratin 10) together with protein expression data showed that human adipose-derived stem cells (ADSCs) seeded on these cell-imprinted substrates were driven to adopt the specific shape and characteristics of keratinocytes. The observed morphology of the ADSCs grown on the keratinocyte casts was noticeably different from that of stem cells cultivated on the stem-cell-imprinted substrates. Since the shape and geometry of the nucleus could potentially alter the gene expression, we used molecular dynamics to probe the effect of the confining geometry on the chain arrangement of simulated chromatin fibers in the nuclei. The results obtained suggested that induction of mature cell shapes onto stem cells can influence nucleus deformation of the stem cells followed by regulation of target genes. This might pave the way for a reliable, efficient, and cheap approach of controlling stem cell differentiation toward skin cells for wound healing applications.

Polymer brush coatings regulating cell behavior: passive interfaces turn into active

Material technology platforms able to modulate the communication with cells at the interface of biomaterials are being increasingly experimented. Progress in the fabrication of supports is simultaneously introducing new surface modification strategies aimed at turning these supports from passive to active components in engineered preparations. Among these platforms, polymer brushes are arising not only as coatings determining the physical and (bio)chemical surface properties of biomaterials, but also as smart linkers between surfaces and biological cues. Their peculiar properties, especially when brushes are synthesized by "grafting-from" methods, enable closer mimicking of the complex and heterogeneous biological microenvironments. Inspired by the growing interest in this field of materials science, we summarize here the most prominent and recent advances in the synthesis of "grafted-from" polymer brush surfaces to modulate the response of adhering cells.

Probing the weak interaction of proteins with neutral and zwitterionic antifouling polymers

Protein-polymer interactions are of great interest in a wide range of scientific and technological applications. Neutral poly(ethylene glycol) (PEG) and zwitterionic poly(sulfobetaine methacrylate) (pSBMA) are two well-known nonfouling materials that exhibit strong surface resistance to proteins. However, it still remains unclear or unexplored how PEG and pSBMA interact with proteins in solution. In this work, we examine the interactions between two model proteins (bovine serum albumin and lysozyme) and two typical antifouling polymers of PEG and pSBMA in aqueous solution using fluorescence spectroscopy, atomic force microscopy and nuclear magnetic resonance. The effect of protein:polymer mass ratios on the interactions is also examined. Collective data clearly demonstrate the existence of weak hydrophobic interactions between PEG and proteins, while there are no detectable interactions between pSBMA and proteins. The elimination of protein interaction with pSBMA could be due to an enhanced surface hydration of zwitterionic groups in pSBMA. New evidence is given to demonstrate the interactions between PEG and proteins, which are often neglected in the literature because the PEG-protein interactions are weak and reversible, as well as the structural change caused by hydrophobic interaction. This work provides a better fundamental understanding of the intrinsic structure-activity relationship of polymers underlying polymer-protein interactions, which are important for designing new biomaterials for biosensor, medical diagnostics and drug delivery applications.