Creation of nanostructures to study the topographical dependency of protein adsorption

Radical Scavenging, Hemocompatibility, and Antibacterial Activity against MDR Acinetobacter baumannii in Alginate-Based Aerogels Containing Lipoic Acid-Capped Silver Nanoparticles

Retaining the hemocompatibility, supporting cell growth, and exhibiting anti-inflammatory and antioxidant properties, while having antimicrobial activity, particularly against multidrug-resistant bacteria (MDR), remain a challenge when designing aerogels for biomedical applications. Here, we report that our synthesized alginate-based aerogels containing either 7.5 or 11.25 μg of lipoic acid-capped silver nanoparticles (AgNPs) showed improved hemocompatibility properties while retaining their antimicrobial effect against MDR Acinetobacter baumannii and the reference strain Escherichia coli, relative to a commercial dressing and polymyxin B, used as a reference. The differences in terms of the microstructure and nature of the silver, used as the bioactive agent, between our synthesized aerogels and the commercial dressing used as a reference allowed us to improve several biological properties in our aerogels with respect to the reference commercial material. Our aerogels showed significantly higher antioxidant capacity, in terms of nmol of Trolox equivalent antioxidant capacity per mg of aerogel, than the commercial dressing. All our synthesized aerogels showed anti-inflammatory activity, expressed as nmol of indomethacin equivalent anti-inflammatory activity per mg of aerogel, while this property was not found in the commercial dressing material. Finally, our aerogels were highly hemocompatible (less than 1% hemolysis ratio); however, the commercial material showed a 20% hemolysis rate. Therefore, our alginate-based aerogels with lipoic acid-capped AgNPs hold promise for biomedical applications.

Combining plasmon-enhanced fluorescence with Rayleigh surface acoustic waves to quantify Carcinoembryonic Antigen from human plasma

To improve the direct quantification of Carcinoembryonic Antigen (CEA) from body fluids by immunofluorescence, a surface acoustic wave (SAW) based biosensor was developed combined with an optimized silver nanostructure at the sensing region. Fluorescence signal amplification is achieved by patterning silver nanostructures using the rapid thermal annealing (RTA) method. In addition, the problem of background noise interference from nonspecific binding in human plasma is addressed by Rayleigh wave streaming at the immunoassay region, which shows a reduction in the limit of detection. The results show that the silver nanostructures significantly increase the sensor sensitivity by 49.99-fold and lower the limit of detection of CEA in phosphate buffered saline (PBS) solution to 101.94 pg/mL. The limit of detection of CEA biomarker in human plasma was successfully brought down to 11.81 ng/mL by reducing background noise using Rayleigh SAW streaming. This allows for a point-of-need sensor system to be realized in various clinical biosensing applications.

Improvement of the wound healing properties of hydrogels with N-acetylcysteine through their modification with methacrylate-containing polymers

Hydrogels with antioxidant activity have shown to significantly improve the standard of care, because they promote efficient wound healing, i.e. regeneration. N-Acetylcysteine (NAC) is an antioxidant amino acid derivative that promotes complete tissue restoration. However, NAC has anticoagulant properties that may also hinder blood coagulation, which is crucial for hydrogels for wound healing applications. To take advantage of the regenerative activity of NAC while avoiding hampering the hemostasis stage during wound healing, we modified gelatin-NAC with the methacrylate-containing polymers 2-hydroxyethyl methacrylate (H) and poly(ethylene glycol) methyl ether methacrylate (P) to produce Gel-HP-NAC. These hydrogels clotted more blood and faster than Gel and Gel-NAC hydrogels, while maintaining fluid absorption properties adequate to promote wound healing. Similarly, there were more viable human skin fibroblasts after 10 days cultured in Gel-HP-NAC compared with Gel and Gel-NAC. A mouse full-thickness skin wound model demonstrated that Gel-HP-NAC hydrogels improved the wound healing process as compared to the untreated group as proved by the increased wound closure rates and re-epithelialization. Histology of the biopsied tissues indicated more organized collagen deposits on the wounds treated with either Gel-HP-NAC or Gel-NAC than untreated wounds. Our results show that modification of NAC-containing hydrogels through methacrylate-containing polymers improved their wound healing properties, including blood-clotting, and demonstrate the potential of Gel-HP-NAC hydrogels for wound treatment and tissue regeneration.

Protein Adsorption on Surfaces Functionalized with COOH Groups Promotes Anti-inflammatory Macrophage Responses

Implants can induce a foreign body reaction that leads to chronic inflammation and fibrosis in the surrounding tissue. Macrophages help detect the foreign material, play a role in the inflammatory response, and may promote fibrosis instead of the desired tissue regeneration around implants. Implant surface properties impact macrophage responses by changing the nature of the adsorbed protein layer, but conflicting studies highlight the complexity of this relationship. In this study, the effect of surface chemistry on macrophage behavior was investigated with poly(styrene) surfaces containing common functional groups at similar surface densities. The protein layer was characterized to identify the proteins that adsorbed on the surfaces from the medium and the proteins secreted onto the surfaces by adherent macrophages. Of the surface chemistries studied, carboxylic acid (COOH) groups promoted anti-inflammatory responses from unstimulated macrophages and did not exacerbate inflammation upon stimulation. These surfaces also enhanced the adsorption of proteins involved in integrin signaling and promoted the secretion of proteins related to angiogenesis, integrin signaling, and cytokine signaling, which have been previously associated with improved biomaterial integration. Therefore, this study suggests that surface modification with COOH groups may help improve the integration of implants in the body by enhancing anti-inflammatory macrophage responses through altered protein adsorption.

How Surface Properties of Silica Nanoparticles Influence Structural, Microstructural and Biological Properties of Polymer Nanocomposites

The aim of this work was to study effect of the type of silica nanoparticles on the properties of nanocomposites for application in the guided bone regeneration (GBR). Two types of nanometric silica particles with different size, morphology and specific surface area (SSA) i.e., high specific surface silica (hss-SiO₂) and low specific surface silica (lss-SiO₂), were used as nano-fillers for a resorbable polymer matrix: poly(L-lactide-co-D,L-lactide), called PLDLA. It was shown that higher surface specific area and morphology (including pore size distribution) recorded for hss-SiO₂ influences chemical activity of the nanoparticle; in addition, hydroxyl groups appeared on the surface. The nanoparticle with 10 times lower specific surface area (lss-SiO₂) characterized lower chemical action. In addition, a lack of hydroxyl groups on the surface obstructed apatite nucleation (reduced zeta potential in comparison to hss-SiO₂), where an apatite layer appeared already after 48 h of incubation in the simulated body fluid (SBF), and no significant changes in crystallinity of PLDLA/lss-SiO₂ nanocomposite material in comparison to neat PLDLA foil were observed. The presence and type of inorganic particles in the PLDLA matrix influenced various physicochemical properties such as the wettability, and the roughness parameter note for PLDLA/lss-SiO₂ increased. The results of biological investigation show that the bioactive nanocomposites with hss-SiO₂ may stimulate osteoblast and fibroblast cells’proliferation and secretion of collagen type I. Additionally, both nanocomposites with the nanometric silica inducted differentiation of mesenchymal cells into osteoblasts at a proliferation stage in in vitro conditions. A higher concentration of alkaline phosphatase (ALP) was observed on the material modified with hss-SiO₂ silica.

Engineering Proteins at Interfaces: From Complementary Characterization to Material Surfaces with Designed Functions

Once materials come into contact with a biological fluid containing proteins, proteins are generally—whether desired or not—attracted by the material's surface and adsorb onto it. The aim of this Review is to give an overview of the most commonly used characterization methods employed to gain a better understanding of the adsorption processes on either planar or curved surfaces. We continue to illustrate the benefit of combining different methods to different surface geometries of the material. The thus obtained insight ideally paves the way for engineering functional materials that interact with proteins in a predetermined manner.

A Method for Investigation of Size-Dependent Protein Binding to Nanoholes Using Intrinsic Fluorescence of Proteins

We have developed a novel method to study the influence of surface nanotopography on human fibrinogen adsorption at a given surface chemistry. Well-ordered arrays of nanoholes with different diameters down to 45 nm and a depth of 50 nm were fabricated in silicon by electron beam lithography and reactive ion etching. The nanostructured chip was used as a model system to understand the effect of size of the nanoholes on fibrinogen adsorption. Fluorescence imaging, using the intrinsic fluorescence of proteins, was used to characterize the effect of the nanoholes on fibrinogen adsorption. Atomic force microscopy was used as a complementary technique for further characterization of the interaction. The results demonstrate that as the size of the nanoholes is reduced to 45 nm, fibrinogen adsorption is significantly increased.

Confinement effect on the structure and elasticity of proteins interfacing polymers

The ordered nanostructured surfaces provide confined environments that allow functionalization of proteins. Here, we used the nanopores of poly(methyl methacrylate) films to attach fibrinogen and lysozyme, and discussed the changes in proteins' structures and elasticity upon confinement. Fourier-transform infrared spectroscopic analysis of protein secondary structures reveals that fibrinogen undergoes less structural change and behaves less stiff when the pore size is close to the protein size. Lysozyme, on the other hand, retains its native-like structure, however, it exhibits the highest modulus in 15 nm pores due to the lower macromolecular crowding effect the protein faces compared to lysozyme within larger pores. These findings manifest the effect of confinement and crowding on the conformation and elasticity of different shaped proteins tethered on surfaces.

Cytotoxicity effects of three-dimensional graphene in NIH-3T3 fibroblasts

We present an evaluation of the in vitro cytotoxicity of 3D graphene sheets fabricated by carbonization of polydopamine (PDA) films on a template of aligned nanopore arrays (NPAs) on a stainless steel surface.

Slope-Dependent Cell Motility Enhancements at the Walls of PEG-Hydrogel Microgroove Structures

In recent years, research utilizing micro- and nanoscale geometries and structures on biomaterials to manipulate cellular behaviors, such as differentiation, proliferation, survival, and motility, have gained much popularity; however, how the surface microtopography of 3D objects, such as implantable devices, can affect these various cell behaviors still remains largely unknown. In this study, we discuss how the walls of microgroove topography can influence the morphology and the motility of unrestrained cells, in a different fashion from 2D line micropatterns. Here adhesive substrates made of tetra(polyethylene glycol) (tetra-PEG) hydrogels with microgroove structures or 2D line micropatterns were fabricated, and cell motility on these substrates was evaluated. Interestingly, despite being unconstrained, the cells exhibited drastically different migration behaviors at the edges of the 2D micropatterns and the walls of microgroove structures. In addition to acquiring a unilamellar morphology, the cells increased their motility by roughly 3-fold on the microgroove structures, compared with the 2D counterpart or the nonpatterned surface. Immunostaining revealed that this behavior was dependent on the alignment and the aggregation of the actin filaments, and by varying the slope of the microgroove walls, it was found that relatively upright walls are necessary for this cell morphology alterations. Further progress in this research will not only deepen our understanding of topography-assisted biological phenomena like cancer metastasis but also enable precise, topography-guided manipulation of cell motility for applications such as cancer diagnosis and cell sorting.

Impact of Nanotopography, Heparin Hydrogel Microstructures, and Encapsulated Fibroblasts on Phenotype of Primary Hepatocytes

Hepatocytes, the main epithelial cell type in the liver, perform most of the biochemical functions of the liver. Thus, maintenance of a primary hepatocyte phenotype is crucial for investigations of in vitro drug metabolism, toxicity, and development of bioartificial liver constructs. Here, we report the impact of topographic cues alone and in combination with soluble signals provided by encapsulated feeder cells on maintenance of the primary hepatocyte phenotype. Topographic features were 300 nm deep with pitches of either 400, 1400, or 4000 nm. Hepatocyte cell attachment, morphology and function were markedly better on 400 nm pitch patterns compared with larger scale topographies or planar substrates. Interestingly, topographic features having biomimetic size scale dramatically increased cell adhesion whether or not substrates had been precoated with collagen I. Albumin production in primary hepatocytes cultured on 400 nm pitch substrates without collagen I was maintained over 10 days and was considerably higher compared to albumin synthesis on collagen-coated flat substrates. In order to investigate the potential interaction of soluble cytoactive factors supplied by feeder cells with topographic cues in determining cell phenotype, bioactive heparin-containing hydrogel microstructures were molded (100 μm spacing, 100 μm width) over the surface of the topographically patterned substrates. These hydrogel microstructures either carried encapsulated fibroblasts or were free of cells. Hepatocytes cultured on nanopatterned substrates next to fibroblast carrying hydrogel microstructures were significantly more functional than hepatocytes cultured on nanopatterned surfaces without hydrogels or stromal cells significantly elevated albumin expression and cell junction formation compared to cells provided with topographic cues only. The simultaneous presentation of topographic biomechanical cues along with soluble signaling molecules provided by encapsulated fibroblasts cells resulted in optimal functionality of cultured hepatocytes. The provision of both topographic and soluble signaling cues could enhance our ability to create liver surrogates and inform the development of engineered liver constructs.

Deposition of organic−inorganic hybrid coatings over 316L surgical stainless steel and evaluation on vascular cells

Surface coating of metallic materials using the sol-gel technique is a suitable approach to obtain hybrid materials with improved properties for biomedical applications. In this study, an AISI 316L stainless steel surface was coated with ormosils prepared from tetraethylsiloxane and 3-glycidoxypropyltrimethoxysilane or polydimethylsiloxane. The characterization of structural and surface properties was performed by several techniques. Surface microstructure, morphology, and energy are dependent on organosilane type and content. Chemical stability of coatings was investigated by static immersion tests in phosphate buffer solution at 37 °C, and silicon leaching after 21 days was found to be in the range of ∼200−300 μg L−1. Mechanical adhesion was found to be within 1.0 and 3.7 N cm−1. The interaction of the samples and materials in the cardiovascular environment was investigated through cellular behavior. Biological assays were performed with slides to avoid any cytotoxic effects on human endothelial cells (HUVEC) and rabbit arterial smooth muscle cells (RASM). No significant alterations were observed after 24 h in the viability of RASM and HUVEC cells exposed to different coatings. No increase of HUVEC or RASM migration was observed after 24 h as evaluated by transwell migration assay. The hybrid materials showed suitable properties for potential application as biomaterials in cardiovascular environment as well as for incorporation of bioactive species with the aim to prepare drug-eluting stents.

Proteome analysis of the plasma protein layer adsorbed to a rough titanium surface

In this study a label-free proteomic approach was used to investigate the composition of the layer of protein adsorbed to rough titanium (Ti) after exposure to human blood plasma. The influence of the protein layer on the surface free energy (SFE) of the Ti was evaluated by contact angle measurements. Ti discs were incubated with blood plasma for 180 min at 37 °C, and the proteins recovered were subjected to liquid chromatography coupled to tandem mass spectrometry analysis. A total of 129 different peptides were identified and assigned to 25 distinct plasma proteins. The most abundant proteins were fibronectin, serum albumin, apolipoprotein A-I, and fibrinogen, comprising 74.54% of the total spectral counts. Moreover, the protein layer increased the SFE of the Ti (p < 0.05). The layer adsorbed to the rough Ti surface was composed mainly of proteins related to cell adhesion, molecule transportation, and coagulation processes, creating a polar and hydrophilic interface for subsequent interactions with host cells.

Comparative study of PCL-HAp and PCL-bioglass composite scaffolds for bone tissue engineering

The aim of this work is to compare the effect of hydroxyapatite (HAp) or bioglass (BG) nanoparticles in a polycaprolactone composite scaffold aimed to bone regeneration. To allow a comparison of the influence of both types of fillers, scaffolds made of PCL or composites containing up to 20 % by weight HAp or BG were obtained. Scaffolds showed acceptable mechanical properties for its use and high interconnected porosity apt for cellular colonization. To study the effect of the different materials on pre-osteoblast cells differentiation, samples with 5 % mineral reinforcement, were cultured for up to 28 days in osteogenic medium. Cells proliferated in all scaffolds. Nevertheless, differentiation levels for the selected markers were higher in pure PCL scaffolds than in the composites; inclusion of bioactive particles showed no positive effects on cell differentiation. In osteogenic culture conditions, the presence of bioactive particles is thus not necessary in order to observe good differentiation.

The influence of biomimetic topographical features and the extracellular matrix peptide RGD on human corneal epithelial contact guidance

A major focus in the field of tissue engineering is the regulation of essential cell behaviors through biophysical and biochemical cues from the local extracellular environment. The impact of nanotopographical cues on human corneal epithelial cell (HCEC) contact guidance, proliferation, migration and adhesion have previously been demonstrated. In the current report we have expanded our study of HCEC responses to include both biophysical and controlled biochemical extracellular cues. By exploiting methods for the layer-by-layer coating of substrates with reactive poly(ethylene imine)/poly(2-vinyl-4,4-dimethylazlactone)-based multilayer thin films we have incorporated a single adhesion peptide motif, Arg-Gly-Asp (RGD), on topographically patterned substrates. This strategy eliminates protein adsorption onto the surface, thus decoupling the effects of the HCEC response to topographical cues from adsorbed proteins and soluble media proteins. The direction of cell alignment was dependent on the scale of the topographical cues and, to less of an extent, the culture medium. In EpiLife® medium cell alignment to unmodified-NOA81 topographical features, which allowed protein adsorption, differed significantly from cell alignment on RGD-modified features. These results demonstrate that the surface chemical composition significantly affects how HCECs respond to topographical cues. In summary, we have demonstrated modulation of the HCEC response to environmental cues through critical substrate and soluble parameters.

Fluorescent Detection of Oral Pathogens by a Solid-Phase Immunoassay on PDMS

We have developed an array of sensors for the oral pathogen Streptococcus mutans (S. mutans) using an enzymelinked linked immunosorbent assay (ELISA) on a polydimethylsiloxane (PDMS) device. The model bacterial analyte, S. mutans, has been implicated in the initiation and progression of dental caries. The PDMS was modified with 3-aminopropyltriethoxysilance (APTS) and glutaraldehyde to covalently crosslink monoclonal anti-S. mutans immunoglobulin G (IgG) to the sensor surface. Successful IgG immobilization was verified by AFM and fluorescence imaging. Colloidal bacteria were captured on the sensor surface and labeled with immuno-active quantum dots (QDs), whose fluorescence was excited by an LED and detected by a CCD. The system was capable of detecting S. mutans concentrations as low as 6 10⁶cells/ml in a 20 &#956;l sample. This work represents a stable foundation for the development of a chair side diagnostic system capable of specific and sensitive detection of pathogens directly from oral fluid.

Surface treatment of polymeric materials controlling the adhesion of biomolecules

This review describes different strategies of surface elaboration for a better control of biomolecule adsorption. After a brief description of the fundamental interactions between surfaces and biomolecules, various routes of surface elaboration are presented dealing with the attachment of functional groups mostly thanks to plasma techniques, with the grafting to and from methods, and with the adsorption of surfactants. The grafting of stimuli-responsive polymers is also pointed out. Then, the discussion is focused on the protein adsorption phenomena showing how their interactions with solid surfaces are complex. The adsorption mechanism is proved to be dependent on the solid surface physicochemical properties as well as on the surface and conformation properties of the proteins. Different behaviors are also reported for complex multiple protein solutions.

Submicron-patterning of bulk titanium by nanoimprint lithography and reactive ion etching

Nanopatterns on titanium may enhance endosseous implant biofunctionality. To enable biological studies to prove this hypothesis, we developed a scalable method of fabricating nanogrooved titanium substrates. We defined nanogrooves by nanoimprint lithography (NIL) and a subsequent pattern transfer to the surface of ASTM grade 2 bulk titanium applying a soft-mask for chlorine-based reactive ion etching (RIE). With respect to direct write lithographic techniques the method introduced here is fast and capable of delivering uniformly patterned areas of at least 4 cm(2). A dedicated silicon nanostamp process has been designed to generate the required thickness of the soft-mask for the NIL-RIE pattern transfer. Stamps with pitch sizes from 1000 nm down to 300 nm were fabricated using laser interference lithography (LIL) and deep cryogenic silicon RIE. Although silicon nanomachining was proven to produce smaller pitch sizes of 200 nm and 150 nm respectively, successful pattern transfer to titanium was only possible down to a pitch of 300 nm. Hence, the smallest nanogrooves have a width of 140 nm. An x-ray photoelectron spectroscopy study showed that only very few contaminations arise from the fabrication process and a cytotoxicity assay on the nanopatterned surfaces confirmed that the obtained nanogrooved titanium specimens are suitable for in vivo studies in implantology research.

Fibronectin and bone morphogenetic protein-2-decorated poly(OEGMA-r-HEMA) brushes promote osseointegration of titanium surfaces

To be better used as medical implants in orthopedic and dental clinical applications, titanium and titanium-based alloys need to be capable of inducing osteogenesis. Here we describe a method that allows the facile decoration of titanium surfaces to impart an osteogenesis capacity. A Ti surface was first deposited on a poly(OEGMA-r-HEMA) film using surface-initiated atom-transfer radical polymerization (SI-ATRP) with the further step of carboxylation. The modified surfaces were resistant to cell adhesion. Fibronectin (FN) and recombinant human bone morphogenetic protein-2 (rhBMP-2) were further immobilized onto p(OEGMA-r-HEMA) matrices. Our results demonstrate that the FN- and rhBMP-2-conjugated polymer surfaces could induce the adhesion of MC3T3 cells on Ti surfaces. Moreover, the protein-tethered surface exhibited enhanced cell differentiation in terms of alkaline phosphatase activity compared to that of the pristine Ti surface at similar cell proliferation rates. This research establishes a simple modification method of Ti surfaces via Ti-thiolate self-assembled monolayers (SAMs) and SI-ATRP and identifies a dual-functional Ti surface that combines antifouling and osseointegration promotion.

Electrostatic and dispersion interactions during protein adsorption on topographic nanostructures

Recently, biomaterials research has focused on developing functional implant surfaces with well-defined topographic nanostructures in order to influence protein adsorption and cellular behavior. To enhance our understanding of how proteins interact with such surfaces, we analyze the adsorption of lysozyme on an oppositely charged nanostructure using a computer simulation. We present an algorithm that combines simulated Brownian dynamics with numerical field calculation methods to predict the preferred adsorption sites for arbitrarily shaped substrates. Either proteins can be immobilized at their initial adsorption sites or surface diffusion can be considered. Interactions are analyzed on the basis of Derjaguin-Landau-Verway-Overbeek (DLVO) theory, including electrostatic and London dispersion forces, and numerical solutions are derived using the Poisson-Boltzmann and Hamaker equations. Our calculations show that for a grooved nanostructure (i.e., groove and plateau width 8 nm, height 4 nm), proteins first contact the substrate primarily near convex edges because of better geometric accessibility and increased electric field strengths. Subsequently, molecules migrate by surface diffusion into grooves and concave corners, where short-range dispersion interactions are maximized. In equilibrium, this mechanism leads to an increased surface protein concentration in the grooves, demonstrating that the total amount of protein per surface area can be increased if substrates have concave nanostructures.

Hydrophobic nanopillars initiate mesenchymal stem cell aggregation and osteo-differentiation

Surface engineering approaches that alter the physical topography of a substrate could be used as an effective tool and as an alternative to biochemical means of directing stem cell interactions and their subsequent differentiation. In this paper we compare hydrophobic micro- vs. nanopillar type fabrication techniques for probing mesenchymal stem cell (MSC) interaction with the surface physical environment. The roles played by the topography of the nanopillar in particular influenced MSC growth and allowed for regulatory control of the stem cell fate. The nanopillar induced large 3-D cell aggregates to form on the surface which had up-regulated osteogenic specific matrix components. The ability to control MSC differentiation, using only the topographical factors, has a profound effect on both MSC biology and tissue engineering. This study aims to highlight the importance of the physical material carrier in stem cell based tissue engineering schemes.

The influence of topographic microstructures on the initial adhesion of L929 fibroblasts studied by single-cell force spectroscopy

Single-cell force spectroscopy was used to investigate the initial adhesion of L929 fibroblasts onto periodically grooved titanium microstructures (height ~6 μm, groove width 20 μm). The position-dependent local adhesion strength of the cells was correlated with their rheological behavior. Spherical cells exhibited a significantly lower Young’s modulus (<1 kPa) than that reported for spread cells, and their elastic properties can roughly be explained by the Hertz model for an elastic sphere. While in contact with the planar regions of the substrate, the cells started to adapt their shape through slight ventral flattening. The process was found to be independent of the applied contact force for values between 100 and 1,000 pN. The degree of flattening correlated with the adhesion strength during the first 60 s. Adhesion strength can be described by fast exponential kinetics as \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ C_{1} \left[ {1 - \exp \left( { - C_{2} \cdot t} \right)} \right] $$\end{document} with C₁ = 2.34 ± 0.19 nN and C₂ = 0.09 ± 0.02 s⁻¹. A significant drop in the adhesion strength of up to 50% was found near the groove edges. The effect can be interpreted by the geometric decrease of the contact area, which indicates the inability of the fibroblasts to adapt to the shape of the substrate. Our results explain the role of the substrate’s topography in contact guidance and suggest that rheological cell properties must be considered in cell adhesion modeling.

Nanoscale surfacing for regenerative medicine

Cells in most tissues reside in microenvironment surrounded with specific three-dimensional features. The extracellular matrix or substratum with which cells interact often includes topography at the nanoscale. For example, the basement membrane of many tissues displays features of pores, fibers and ridges in the nanometer range. The nanoscale topography has significant effects on cellular behavior. Knowledge of the cell-substratum interactions is crucial to the understanding of many fundamental biological questions and to regenerative medicine. Rapid advances in nanotechnology enable cellular study on engineered nanoscale surfaces. Recent findings underscore the phenomenon that mammalian cells do respond to nanosized features on a synthetic surface. This review covers the commonly used techniques of engineering nanoscale surface and the techniques which have not been adapted but are of great potential in regenerative medicine, surveys the applications of nanoscale surface in regenerative medicine including vascular, bone, neural and stem cell tissue engineering, and discusses the possible mechanisms of cellular responses to nanoscale surface. A better understanding of the interactions between cells and nanoscale surfacing will help advance the field of regenerative medicine.

Effect of surface morphology and charge on the amount and conformation of fibrinogen adsorbed onto alginate/chitosan microcapsules

We report the influence of surface morphology and charge of alginate/chitosan (ACA) microcapsules on both the amount of adsorbed protein and its secondary structural changes during adsorption. Variations in surface morphology and charge were controlled by varying alginate molecular weight and chitosan concentration. Plasma fibrinogen (Fgn) was chosen to model this adsorption to foreign surfaces. The surface of ACA microcapsules exhibited a granular structure after incubating calcium alginate beads with chitosan solution to form membranes. The surface roughness of ACA microcapsule membranes decreased with decreasing alginate molecular weight and chitosan concentration. Zeta potential measurements showed that there was a net negative charge on the surface of ACA microcapsules which decreased with decreasing alginate molecular weight and chitosan concentration. The increase in both surface roughness and zeta potential resulted in an increase in the amount of Fgn adsorbed. Moreover, the higher the zeta potential was, the stronger the protein-surface interaction between fibrinogen and ACA microcapsules was. More protein molecules adsorbed spread and had a greater conformational change on rougher surfaces for more surfaces being available for protein to attach.

Nanoparticle coatings for enhanced capture of flowing cells in microtubes

Recently, a flow-based selectin-dependent method for the capture and enrichment of specific types of cells (CD34+ hematopoetic stem and progenitor cells and human leukemia HL60) from peripheral blood was demonstrated. However, these devices depend on a monolayer of selectin protein, which has been shown to have a maximum binding efficiency as a function of surface area. A novel surface coating of colloidal silica nanoparticles was designed that alters the surface roughness resulting in increased surface area. The nanoparticles were adhered using either an inorganic titanate resinous coating or an organic polymer of poly-L-lysine. Using Alexa Fluor 647 conjugated P-selectin, an increase in protein adsorption of up to 35% when compared to control was observed. During perfusion experiments using P-selectin-coated microtubes, we observed increased cell capture and greatly decreased rolling velocity at equivalent protein concentration compared to nonparticle control. Atomic force microscopy showed increased surface roughness consistent with the nanoparticle mean diameter, suggesting a monolayer of particles. These results support the coating's potential to improve existing cell capture implantable devices for a variety of therapeutic and scientific uses.

Lamellar Surface Structures on Stainless Steel 316 LVM and their Influence on Osteoblastic Cells

In this study, nanoscaled lamellar surface structures were prepared on medical stainless steel by chemical etching of the decomposed phases and their effect on the morphology of osteoblastic cells was investigated using Field Emission Scanning Electron Microscopy. Long filopodia were grown from the cells perpendicular to the lamellar structure while almost no or only short filopodia are formed parallel to the lamellae. The results are explained by a different surface roughness parallel and perpendicular to the lamellae: During the growth process of the filopodia a nearly flat surface is recognized parallel to the lamellae while a topographical change is sensed perpendicular to the structure, which is preferred by the cells.

Human aortic endothelial cell response to 316L stainless steel material microstructure

The role of metal microstructure (e.g. grain sizes) in modulating cell adherence behavior is not well understood. This study investigates the effect of varying grain sizes of 316L stainless steel (SS) on the attachment and spreading of human aortic endothelial cells (HAECs). Four different grain size samples; from 16 to 66 microm (ASTM 9.0-4.9) were sectioned from sheets. Grain structure was revealed by polishing and etching with glycergia. Contact angle measurement was done to assess the hydrophilicity of the specimens. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the roughness and surface chemistry of the specimens. Cells were seeded on mechanically polished and chemically etched specimens followed by identification of activated focal adhesion sites using fluorescently tagged anti-pFAK (phosphorylated focal adhesion kinase). The 16 microm grain size etched specimens had significantly (P < 0.01) higher number of cells attached per cm(2) than other specimens, which may be attributed to the greater grain boundary area and associated higher surface free energy. This study shows that the underlying material microstructure may influence the HAEC behavior and may have important implications in endothelialization.

Nanoscaled periodic surface structures of medical stainless steel and their effect on osteoblast cells

Nanoscaled lamellar surface structures have been prepared on medical stainless steel AISI 316LVM surfaces by chemical etching of the decomposed phases. The effect of this structure on osteoblastic cells has been investigated. Long filopodia were developed by the cells perpendicular to the lamellar structure while almost no or only short filopodia were formed parallel to the lamellae. These results are explained in terms of a topographical influence of the nanostructure. During the growth process of the filopodia a nearly flat surface was recognized parallel to the lamellae while a topographical change was sensed perpendicular to the structure, which was preferred by the cells.

Modulation of morphology and functions of human hepatoblastoma cells by nano-grooved substrata

It is known that cellular behavior is affected by nano-patterned topography. For example, many cell types tend to align and extend along the direction of nano-grooves/ridges structures. In this study, we investigated the impact of nano-grooves/ridges on hepatocyte morphology and functions. HepG2/C3A (C3A) cells were cultured on nano-grooved silicon or polystyrene substrata with various widths (from 100 to 500 nm) and depths (from 100 to 380 nm). Nano-grooved substrates induced dramatic changes in C3A cell morphology. The cells formed spheroids on the flat substrates, while C3A cells spread and grew confluently with elongated and aligned morphology along the nano-grooves/ridges. Albumin synthesis was enhanced on the nano-grooved silicon substrates compared to the flat surface, and was decreased with increasing groove depths. Urea conversion on the shallow grooves (400 nm wide and 100 nm deep) remained at the same level of that on the flat surfaces, but was decreased on the deeper grooves. We found that the functions of hepatocytes were enhanced on the substrates with shallow grooves. The nano-grooved substrates may be applied as in vitro culture systems of hepatocytes for both diagnostic and therapeutic applications.

Effects of nano-surface properties on initial osteoblast adhesion and Ca/P adsorption ability for titanium alloys

Titanium alloys (Ti6Al4V), while subjected to high temperature surface treatment, experience altered nano-surface characteristics. The effects of such surface treatments are examined, including the initial adhesion force experienced by osteoblasts, the Ca/P adsorption capability, and the nano-surface properties, including the amounts of amphoteric Ti-OH groups, surface topography, and surface roughness. The initial adhesion force is considered a quantitative indicator of cyto-compatibility in vitro. Previously, a cyto-detacher was applied in a pioneer attempt measuring the initial adhesion force of fibroblasts on a metal surface. Presently, the cyto-detacher is further applied to evaluate the initial adhesion force of osteoblasts. Results reveal that (1) titanium alloys subjected to heat treatment could promote the adsorption capability of Ca and P; (2) titanium alloys subjected to heat treatment could have higher initial osteoblast adhesion forces; (3) the adhesion strength of osteoblasts, ranging from 38.5 to 58.9 nN (nanonewtons), appears stronger for rougher surfaces. It is concluded that the heat treatment could have impacted the biocompatibility in terms of the initial osteoblast adhesion force and Ca/P adsorption capability.

Dewetting of polystyrene thin films on poly(ethylene glycol)-modified surfaces as a simple approach for patterning proteins

A simple technique for patterning proteins utilizing dewetted polystyrene (PS) droplets is demonstrated. A polystyrene thin film was spin coated on a poly(ethylene glycol) (PEG) silane-modified surface. As the PS film dewets from the surface, upon annealing, to form droplets, the PEG-silane-modified surface is exposed, which retains its capability to resist protein adsorption, and the PS droplets allow the selective adsorption of proteins. In contrast to the undewetted flat PS film, the droplet surface had a greater amount of adsorbed proteins. Atomic force microscopy scans reveal that the roughness of the droplet surface is higher, and a multilayer of proteins results on the droplet surface. Moreover, micro- and nanoscale droplet patterns can easily be achieved by tuning the thickness of PS thin films. Because dewetting approaches for generating ordered dewetting droplets have been successfully generated by others, those approaches could be easily combined with this technique to fabricate ordered protein patterns.

Simultaneous investigation of the influence of topography and charge on protein adsorption using artificial nanopatterns

The combined influence of surface topography and charge of a polymer surface on the adsorption of the protein avidin has been investigated. Atomic force microscopy contact mode imaging and charge writing were used to create defined topographical roughness and electrostatic charge patterns on the surface of polystyrene. Increased avidin adsorption was found on nanometer-size topographical patterns, but the adsorption remained unaffected by electrostatic patterns.

Functionalized silicone nanofilaments: a novel material for selective protein enrichment

We present a simple and versatile technique of tailoring functionalized surface structures for protein enrichment and purification applications based on a superhydrophobic silicone nanofilament coating. Using amino and carboxyl group containing silanes, silicone nanofilament templates were chemically modified to mimic anionic and cationic exchange resins. Investigations on the selectivity of the functionalized surfaces toward adsorption of charged model proteins were carried out by means of fluorescence techniques. Due to a high contact area resulting from the nanoroughness of the coating, excellent protein retention characteristics under various conditions were found. The surfaces were shown to be highly stable and reusable over several retention-elution cycles. Especially the full optical transparency and the possibility to use glass substrates as support material open new opportunities for the development of optical biosensors, open geometry microfluidics, or lab-on-a-chip devices.

Wettability modification and the subsequent manipulation of protein adsorption on a Ti6Al4V alloy by means of CO2 laser surface treatment

Improvements in the wettability of the Ti6Al4V alloy following CO(2) laser treatment were identified as being due mainly to the increase in surface roughness, surface oxygen content and surface energy of the material. Untreated and mechanically roughened samples had higher amounts of adsorbed albumin and lower amounts of adsorbed fibronectin than CO(2) laser treated samples. Moreover, as the wettability of the Ti6Al4V alloy increased the adsorbed amounts of fibronectin increased, while the adsorbed amounts of albumin decreased--indicating the controllability of the CO(2) laser process. From this finding it is possible to assert that the wettability of the Ti6Al4V alloy was the prime influence on the observed changes in in vitro protein adsorption. Further, the noted considerable change in the polar component of surface energy, [Formula: see text], on the protein adsorption implied that the protein adsorption on the Ti6Al4V alloy was probably due to the polar and chemical interactions. This work has demonstrated that CO(2) laser radiation could be a suitable means to modify the wettability of the Ti6Al4V alloy and thereby manipulate protein adsorption and consequently render the material more bone cell responsive.