Protein adsorption and monocyte activation on germanium nanopyramids

Recent Advances in Polyurethane/POSS Hybrids for Biomedical Applications

Advanced organic-inorganic materials-composites, nanocomposites, and hybrids with various compositions offer unique properties required for biomedical applications. One of the most promising inorganic (nano)additives are polyhedral oligomeric silsesquioxanes (POSS); their biocompatibility, non-toxicity, and phase separation ability that modifies the material porosity are fundamental properties required in modern biomedical applications. When incorporated, chemically or physically, into polyurethane matrices, they substantially change polymer properties, including mechanical properties, surface characteristics, and bioactivity. Hence, this review is dedicated to POSS-PU composites that have recently been developed for applications in the biomedical field. First, different modes of POSS incorporation into PU structure have been presented, then recent developments of PU/POSS hybrids as bio-active composites for scaffolds, cardiovascular stents, valves, and membranes, as well as in bio-imaging and cancer treatment, have been described. Finally, characterization and methods of modification routes of polyurethane-based materials with silsesquioxanes were presented.

Layer-by-Layer Pyramid Formation from Low-Energy Ar+ Bombardment and Annealing of Ge (110)

Isolated pyramids, 30–80 nm wide and 3–20 nm tall, form during sputter-annealing cycles on the Ge (110) surface. Pyramids have four walls with {19 13 1} faceting and a steep mound at the apex. We used scanning tunneling microscopy (STM) under ultrahigh vacuum conditions to periodically image the surface at ion energies between 100 eV and 500 eV and incremental total flux. Pyramids are seen using Ar⁺ between 200 eV and 400 eV, and require Ag to be present on the sample or sample holder. We suspect that the pyramids are initiated by Ag co-sputtered onto the surface. Growth of pyramids is due to the gathering of step edges with (16 × 2) reconstruction around the pyramid base during layer-by-layer removal of the substrate, and conversion to {19 13 1} faceting. The absence of pyramids using Ar⁺ energies above 400 eV is likely due to surface damage that is insufficiently annealed.

Ultraflat Gold QCM Electrodes Fabricated with Pressure-Forming Template Stripping for Protein Studies at the Nanoscale

Single-molecule imaging of proteins using atomic force microscopy (AFM) is crucially dependent on protein attachment to ultraflat substrates. The template-stripping (TS) technique, which can be used to create large areas of atomically flat gold, has been used to great effect for this purpose. However, this approach requires an epoxy, which can swell in solution, causing surface roughening and substantially increasing the thickness of any sample, preventing its use on acoustic resonators in liquid. Diffusion bonding techniques should circumvent this problem but cannot be used on samples containing patterned features with mismatched heights because of cracking and poor transfer. Here, we describe a new technique called pressure-forming TS (PTS), which permits an ultraflat (0.35 ± 0.05 nm root-mean-square roughness) layer of gold to be transferred to the surface of a patterned substrate at low temperature and pressure. We demonstrate this technique by modifying a quartz crystal microbalance (QCM) sensor to contain an ultraflat gold surface. Standard QCM chips have substantial roughness, preventing AFM imaging of proteins on the surface after measurement. With our approach, there is no need to run samples in parallel: the modified QCM chip is flat enough to permit high-contrast AFM imaging after adsorption studies have been conducted. The PTS-QCM chips are then used to demonstrate adsorption of bovine serum albumin in comparison to rough QCM chips. The ability to attach thin layers of ultraflat metals to surfaces of heterogeneous nature without epoxy will have many applications in diverse fields where there is a requirement to observe nanoscale phenomena with multiple techniques, including surface and interfacial science, optics, and biosensing.

Argon plasma modified nanocomposite polyurethane scaffolds provide an alternative strategy for cartilage tissue engineering

Background

Children born with a small or absent ear undergo surgical reconstruction to create a suitable replacement using rib cartilage. To overcome the donor site morbidity and long-term pain of harvesting rib cartilage, synthetic materials can be a useful alternative. Medpor, is the currently used synthetic polyethylene material to replace missing facial cartilage but unfortunately it has high levels of surgical complications including infection and extrusion, making it an unsuitable replacement. New materials for facial cartilage reconstruction are required to improve the outcomes of surgical reconstruction. This study has developed a new nanomaterial with argon surface modification for auricular cartilage replacement to overcome the complications with Medpor.

Results

Polyurethanes nanocomposites scaffolds (PU) were modified with argon plasma surface modification (Ar) and compared to Medpor in vitro and in vivo. Ar scaffolds allowed for greater protein adsorption than Medpor and PU after 48 h (p < 0.05). Cell viability and DNA assays demonstrated over 14-days greater human dermal fibroblast adhesion and cell growth on Ar than PU and Medpor nanocomposites scaffolds (p < 0.05). Gene expression using RT-qPCR of collagen-I, fibronectin, elastin, and laminin was upregulated on Ar scaffolds compared to Medpor and PU after 14-days (p < 0.05). Medpor, unmodified polyurethane and plasma modified polyurethane scaffolds were subcutaneously implanted in the dorsum of mice for 12 weeks to assess tissue integration and angiogenesis. Subcutaneous implantation of Ar scaffolds in mice dorsum, demonstrated significantly greater tissue integration by H&E and Massons trichrome staining, as well as angiogenesis by CD31 vessel immunohistochemistry staining over 12-weeks (p < 0.05).

Conclusions

Argon modified polyurethane nanocomposite scaffolds support cell attachment and growth, tissue integration and angiogenesis and are a promising alternative for facial cartilage replacement. This study demonstrates polyurethane nanocomposite scaffolds with argon surface modification are a promising biomaterial for cartilage tissue engineering applications.

Electronic supplementary material

The online version of this article (10.1186/s12951-019-0477-z) contains supplementary material, which is available to authorized users.

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.

Immunological response to nitroglycerin-loaded shear-responsive liposomes in vitro and in vivo

Liposomes formulated from the 1,3-diamidophospholipid Pad-PC-Pad are shear-responsive and thus promising nano-containers to specifically release a vasodilator at stenotic arteries. The recommended preclinical safety tests for therapeutic liposomes of nanometer size include the in vitro assessment of complement activation and the evaluation of the associated risk of complement activation-related pseudo-allergy (CARPA) in vivo. For this reason, we measured complement activation by Pad-PC-Pad formulations in human and porcine sera, along with the nanopharmaceutical-mediated cardiopulmonary responses in pigs. The evaluated formulations comprised of Pad-PC-Pad liposomes, with and without polyethylene glycol on the surface of the liposomes, and nitroglycerin as a model vasodilator. The nitroglycerin incorporation efficiency ranged from 25% to 50%. In human sera, liposome formulations with 20mg/mL phospholipid gave rise to complement activation, mainly via the alternative pathway, as reflected by the rises in SC5b-9 and Bb protein complex concentrations. Formulations having a factor of ten lower phospholipid content did not result in measurable complement activation. The weak complement activation induced by Pad-PC-Pad liposomal formulations was confirmed by the results obtained by performing an in vivo study in a porcine model, where hemodynamic parameters were monitored continuously. Our study suggests that, compared to FDA-approved liposomal drugs, Pad-PC-Pad exhibits less or similar risks of CARPA.

Biological responses to immobilized microscale and nanoscale surface topographies

Cellular responses are highly influenced by biochemical and biomechanical interactions with the extracellular matrix (ECM). Due to the impact of ECM architecture on cellular responses, significant research has been dedicated towards developing biomaterials that mimic the physiological environment for design of improved medical devices and tissue engineering scaffolds. Surface topographies with microscale and nanoscale features have demonstrated an effect on numerous cellular responses, including cell adhesion, migration, proliferation, gene expression, protein production, and differentiation; however, relationships between biological responses and surface topographies are difficult to establish due to differences in cell types and biomaterial surface properties. Therefore, it is important to optimize implant surface feature characteristics to elicit desirable biological responses for specific applications. The goal of this work was to review studies investigating the effects of microstructured and nanostructured biomaterials on in vitro biological responses through fabrication of microscale and nanoscale surface topographies, physico-chemical characterization of material surface properties, investigation of protein adsorption dynamics, and evaluation of cellular responses in specific biomedical applications.

Biomimetic nanostructures for the silicone-biosystem interface: tuning oxygen-plasma treatments of polydimethylsiloxane

Polydimethylsiloxanes (PDMS) have drawn attention because of their applicability in medical implants, soft robotics and microfluidic devices. This article examines the formation of dedicated nanostructures on liquid submicrometer PDMS films when exposed to oxygen-plasma treatment. We show that by using a vinyl-terminated PDMS prepolymer with a molecular weight of 800 g/mol, one can bypass the need of solvent, copolymer, or catalyst to fabricate wrinkled films. The amplitude and periodicity of the wrinkles is tuned varying the thickness of the PDMS film between 150 and 600 nm. The duration of the plasma treatment and the oxygen pressure determine the surface morphology. The amplitude was found between 30 and 300 nm with periodicities ranging from 500 to 2800 nm. Atomic force microscopy was used to measure film thickness, amplitude and wrinkle periodicity. The hydrophobic recovery of the nanostructured PDMS surface, as assessed by dynamic contact angle measurements, scales with nanostructure’s fineness, associated with an improved biocompatibility. The mechanical properties were extracted out of 10,000 nanoindentations on 50×50-μm

Adsorption of Human Plasma Albumin and Fibronectin onto Nanostructured Black Silicon Surfaces

The protein adsorption of two human plasma proteins-albumin (Alb) and fibronectin (Fn)-onto synthetic nanostructured bactericidal material-black silicon (bSi) surfaces (that contain an array of nanopillars) and silicon wafer (nonstructured) surfaces-was investigated. The adsorption behavior of Alb and Fn onto two types of substrata was studied using a combination of complementary analytical techniques. A two-step Alb adsorption mechanism onto the bSi surface has been proposed. At low bulk concentrations (below 40 μg/mL), the Alb preferentially adsorbed at the base of the nanopillars. At higher bulk concentrations, the Alb adsorbed on the top of the nanopillars. In the case of Fn, the protein preferentially adsorbed on the top of the nanopillars, irrespective of its bulk concentration.

Nanostructured Polyaniline Coating on ITO Glass Promotes the Neurite Outgrowth of PC 12 Cells by Electrical Stimulation

A conducting polymer polyaniline (PANI) with nanostructure was synthesized on indium tin oxide (ITO) glass. The effect of electrical stimulation on the proliferation and the length of neurites of PC 12 cells was investigated. The dynamic protein adsorption on PANI and ITO surfaces in a cell culture medium was also compared with and without electrical stimulation. The adsorbed proteins were characterized using SDS-PAGE. A PANI coating on ITO surface was shown with 30-50 nm spherical nanostructure. The number of PC 12 cells was significantly greater on the PANI/ITO surface than on ITO and plate surfaces after cell seeding for 24 and 36 h. This result confirmed that the PANI coating is nontoxic to PC 12 cells. The electrical stimulation for 1, 2, and 4 h significantly enhanced the cell numbers for both PANI and ITO conducting surfaces. Moreover, the application of electrical stimulation also improved the neurite outgrowth of PC 12 cells, and the number of PC 12 cells with longer neurite lengths increased obviously under electrical stimulation for the PANI surface. From the mechanism, the adsorption of DMEM proteins was found to be enhanced by electrical stimulation for both PANI/ITO and ITO surfaces. A new band 2 (around 37 kDa) was observed from the collected adsorbed proteins when PC 12 cells were cultured on these surfaces, and culturing PC 12 cells also seemed to increase the amount of band 1 (around 90 kDa). When immersing PANI/ITO and ITO surfaces in a DMEM medium without a cell culture, the number of band 3 (around 70 kDa) and band 4 (around 45 kDa) proteins decreased compared to that of PC 12 cell cultured surfaces. These results are valuable for the design and improvement of the material performance for neural regeneration.

A polyhedral oligomeric silsesquioxane-based bilayered dermal scaffold seeded with adipose tissue-derived stem cells: in vitro assessment of biomechanical properties

BACKGROUND

Although commercial skin substitutes are widely available, its use remains challenging at surgery and postoperatively. The high cost is also prohibitive. We designed and characterized a scaffold for dermal replacement, using advanced nanocomposite materials, which are known to have unique nanoscale features that enhance cellular behavior.

METHODS

A bilayered scaffold was developed using the nanocomposite, polyhedral oligomeric silsesquioxane, incorporated into poly(caprolactone-urea)urethane, resulting in a mechanically robust bioabsorbable polymer; forming the inner layer, which was designed with a range of porosities. The removable outer layer contained nanosilver. Tensile testing, surface tension, permeability, and scanning electron microscopy were performed. Optimal pore morphology for cellular proliferation was elucidated through adipose tissue-derived stem cell culture and a cell viability assay. All tests were repeated on Integra Dermal Regeneration Template.

RESULTS

The physical construct was easy to handle and clinically applicable. Macroporosity and permeability of scaffolds was demonstrated, confirmed by scanning electron microscopy. Both tensile strength and surface tension were comparable with skin; outer layer demonstrated hydrophobicity and inner layer showed hydrophilicity. Cell assay confirmed cellular proliferation onto the scaffold, comparable with Integra.

CONCLUSIONS

We demonstrate that a porous bilayered dermal scaffold could form the basis of a new generation of skin substitute that is both mechanically robust and harbors the ability for enhancing cell regeneration.

Laminin adsorption on nanostructures: switching the molecular orientation by local curvature changes

This work addresses the influence that the nanometric features of biologically relevant surfaces have on the conformation and properties of adsorbed laminin. It was observed that the adsorption kinetics and the nanomorphology of laminin were affected by the change in local curvature of chemically homogeneous nanostructured surfaces. The nanostructured surfaces were prepared by exploiting the self-assembly process of carboxylated polystyrene NPs, with diameters of 45, 109, and 209 nm, onto a polyelectrolyte multilayer formed by alternate deposition of poly(acrylic acid) and poly(allylamine hydrochloride) on gold. The anchored polymeric NPs were finally coated with a homogeneous layer of poly(allylamine hydrochloride), providing three surfaces with different nanometric local curvature. Atomic force microscopy was employed to characterize the relevant morphological parameters of the nanostructured surfaces. Quartz crystal microbalance with dissipation monitoring was employed to determine the adsorbed mass of laminin as well as its adsorption rate as a function of the local surface curvature. A model is proposed to explain the higher and faster laminin adsorption on surfaces with lower local curvature, where a switching of laminin anchoring orientation from a side-on to an end-on geometry can be predicted by a simple curvature-dependent parameter, γ, connecting the average nanostructure height h and the macromolecule radius of gyration R(g). The results provide a framework to understand the dependence of biomolecule orientation on local nanostructure.

Self assembly of nanoislands on YSZ-(001) surface: a mechanistic approach toward a robust process

We experimentally investigate the mechanism of formation of self-assembled arrays of nanoislands surrounding dopant sources on the (001) surface of yttria-stabilized zirconia. Initially, we used lithographically defined thin-film patches of gadolinia-doped ceria (GDC) as dopant sources. During annealing at approximately one-half the melting temperature of zirconia, surface diffusion of dopants leads to the breakup of the surface around the source, creating arrays of epitaxial nanoislands with a characteristic size (~100 nm) and alignment along elastically compliant directions, <110>. The breakup relieves elastic strain energy at the expense of increasing surface energy. On the basis of understanding the mechanism of island formation, we introduce a simple and versatile powder-based doping process for spontaneous surface patterning. The new process bypasses lithography and conventional vapor-source doping, opening the door to spontaneous surface patterning of functional ceramics and other refractory materials. In addition to using GDC solid-solution powders, we demonstrate the effectiveness of the process in another system based on Eu2O3.

Fibronectin and bovine serum albumin adsorption and conformational dynamics on inherently conducting polymers: a QCM-D study

Quartz crystal microbalance with dissipation monitoring (QCM-D) was employed to characterize the adsorption of the model proteins, bovine serum albumin (BSA) and fibronectin (FN), to polypyrrole doped with dextran sulfate (PPy-DS) as a function of DS loading and surface roughness. BSA adsorption was greater on surfaces of increased roughness and was above what could be explained by the increase in surface area alone. Furthermore, the additional mass adsorbed on the rough films was concomitant with an increase in the rigidity of the protein layer. Analysis of the dynamic viscoelastic properties of the protein adlayer reveal BSA adsorption on the rough films occurs in two phases: (1) arrival and initial adsorption of protein to the polymer surface and (2) postadsorption molecular rearrangement to a more dehydrated and compact conformation that facilitates further recruitment of protein to the polymer interface, likely forming a multilayer. In contrast, FN adsorption was independent of surface roughness. However, films prepared from solutions containing the highest concentration of DS (20 mg/mL) demonstrated both an increase in adsorbed mass and adlayer viscoelasticity. This is attributed to the higher DS loading in the conducting polymer film resulting in presentation of a more hydrated molecular structure indicative of a more unfolded and bioactive conformation. Modulating the redox state of the PPy-DS polymers was shown to modify both the adsorbed mass and viscoelastic nature of FN adlayers. An oxidizing potential increased both the total adsorbed mass and the adlayer viscoelasticity. Our findings demonstrate that modification of polymer physicochemical and redox condition alters the nature of protein-polymer interaction, a process that may be exploited to tailor the bioactivity of protein through which interactions with cells and tissues may be controlled.

Parinaric acid methyl ester polymer films with hill-structured features: fabrication and different sensitivities to normal and tumor cells

Parinaric acid methyl ester (PnA-Me) polymer films with hill-structured features were fabricated by a solvent volatilization in situ cross-linking method. Moreover, nuclear magnetic resonance, Fourier transform infrared, and oxidation kinetic analyses were successfully applied to monitor the formation process of PnA-Me polymer films. The role of PnA-Me monomer concentrations for growth control of the hill structures on a glass matrix had also been investigated. Also, the results demonstrated that size control of the resulting hill structure ranging from 0.56 ± 0.18 to 19.6 ± 3.5 μm could be realized by varying the concentration of the PnA-Me monomer from 0.0117 to 1.5 mg/mL. Additionally, the effects of polymer films with different surface topographical structures on the behaviors of rat mesenchymal stem cells and human pheochromocytoma cells were measured by morphological and metabolic methods. The results revealed that the cell activity of PnA-Me films was topographical structure- and cell-type-dependent. Furthermore, the selective sensitivity of the PnA-Me films to normal and tumor cells supported the potential value as the coatings for the tissue engineering substitutes.

Single component and selective competitive protein adsorption in a patchy polymer brush: opposition between steric repulsions and electrostatic attractions

This work explores the use of "patchy" polymer brushes to control protein adsorption rates on engineered surfaces and to bind targeted species from protein mixtures with high selectivity but without invoking molecular recognition. The brushes of interest contain embedded cationic "patches" composed of isolated adsorbed poly(l-lysine) coils (PLL) that are about 10 nm in diameter and are randomly arranged on a silica substrate. Around these patches is a protein-resistant poly(ethylene glycol) (PEG) brush that is formed from the adsorption of a PLL-g-PEG graft copolymer on the remaining silica surface. Electrostatic attractions between individual cationic patches and the negative regions of approaching proteins may be energetically insufficient to bind proteins. Furthermore, protein-patch attractions are reduced by steric repulsions between proteins and the PEG brush. We show that protein adsorption, gauged by ultimate short-term coverages and by the initial protein adsorption rate, exhibits an adhesion threshold: pure PEG brushes of the architectures employed here and brushes containing sparse loadings of PLL patches do not adsorb protein. Above a critical PLL patch loading or threshold, protein adsorption proceeds, often dramatically. The PLL patch thresholds are specific to the protein of interest, allowing surfaces to be engineered to adhesively discriminate different proteins within a mixture. The separation achieved is remarkably sharp: one protein adsorbs, but the second is completely rejected from the interface. The surfaces in this study, by virtue of their well-controlled and well-characterized patchy nature, distinguish themselves from multicomponent brushes or brushes used to end-tether peptide sequences and nucleotides.

A biodegradable and biocompatible regular nanopattern for large-scale selective cell growth

A biodegradable substrate with a regular array of nanopillars fabricated by electron-beam lithography and hot embossing is used to address the mechanisms of nanotopographical control of cell behavior. Two different cell lines cultured on the nanopillars show striking differences in cell coverage. These changes are topography- and cell-dependent, and are not mediated by air bubbles trapped on the nanopattern. For the first time, a strong cell-selective effect of the same nanotopography has been clearly demonstrated on a large area; while fibroblast proliferation is inhibited, endothelial cell spreading is visibly enhanced. The reduced fibroblast proliferation indicates that a reduction of available surface area induced by nanotopography might be the main factor affecting cell growth on nanopatterns. The results presented herein pave the way towards the development of permanent vascular replacements, where non-adhesive, inert, surfaces will induce rapid in situ endothelialization to reduce thrombosis and occlusion.

The effect of surface nanometre-scale morphology on protein adsorption

BACKGROUND

Protein adsorption is the first of a complex series of events that regulates many phenomena at the nano-bio interface, e.g. cell adhesion and differentiation, in vivo inflammatory responses and protein crystallization. A quantitative understanding of how nanoscale morphology influences protein adsorption is strategic for providing insight into all of these processes, however this understanding has been lacking until now.

METHODOLOGY/PRINCIPAL FINDINGS

Here we introduce novel methods for quantitative high-throughput characterization of protein-surface interaction and we apply them in an integrated experimental strategy, to study the adsorption of a panel of proteins on nanostructured surfaces. We show that the increase of nanoscale roughness (from 15 nm to 30 nm) induces a decrease of protein binding affinity (<or=90%) and a relevant increase in adsorbed proteins (<or=500%) beyond the corresponding increase of specific area. We demonstrate that these effects are caused by protein nucleation on the surface, which is promoted by surface nanoscale pores.

CONCLUSIONS/SIGNIFICANCE

These results show that the adsorption of proteins depends significantly on surface nanostructure and that the relevant morphological parameter regulating the protein adsorption process is the nanometric pore shape. These new findings improve our understanding of the role of nanostructures as a biomaterial design parameter and they have important implications for the general understanding of cell behavior on nanostructured surfaces.

Fibronectin adsorption, cell adhesion, and proliferation on nanostructured tantalum surfaces

The interaction between dental pulp derived mesenchymal stem cells (DP-MSCs) and three different tantalum nanotopographies with and without a fibronectin coating is examined: sputter-coated tantalum surfaces with low surface roughness <0.2 nm, hut-nanostructured surfaces with a height of 2.9 +/- 0.6 nm and a width of 35 +/- 8 nm, and dome structures with a height of 13 +/- 2 nm and a width of 52 +/- 14 nm. Using ellipsometry, the adsorption and the availability of fibronectin cell-binding domains on the tantalum surfaces were examined, as well as cellular attachment, proliferation, and vinculin focal adhesion spot assembly on the respective surfaces. The results showed the highest fibronectin mass uptake on the hut structures, with a slightly higher availability of cell-binding domains and the most pronounced formation of vinculin focal adhesion spots as compared to the other surfaces. The proliferation of DP-MSCs was found to be significantly higher on dome and hut surfaces coated with fibronectin compared to the uncoated flat tantalum surfaces. Consequently, the results presented in this study indicate that fibronectin-coated nanotopographies with a vertical dimension of less than 5 nm influence cell adhesion. This rather interesting behavior is argued to originate from the more available fibronectin cell-binding domains observed on the hut structures.

Responses of fibroblasts and glial cells to nanostructured platinum surfaces

The chronic performance of implantable neural prostheses is affected by the growth of encapsulation tissue onto the stimulation electrodes. Encapsulation is associated with activation of connective tissue cells at the electrode's metallic contacts, usually made of platinum. Since surface nanotopography can modulate the cellular responses to materials, the aim of the present work was to evaluate the 'in vitro' responses of connective tissue cells to platinum strictly by modulating its surface nanoroughness. Using molecular beam epitaxy combined with sputtering, we produced platinum nanostructured substrates consisting of irregularly distributed nanopyramids and investigated their effect on the proliferation, cytoskeletal organization and cellular morphology of primary fibroblasts and transformed glial cells. Cells were cultured on these substrates and their responses to surface roughness were studied. After one day in culture, the fibroblasts were more elongated and their cytoskeleton less mature when cultured on rough substrates. This effect increased as the roughness of the surface increased and was associated with reduced cell proliferation throughout the observation period (4 days). Morphological changes also occurred in glial cells, but they were triggered by a different roughness scale and did not affect cellular proliferation. In conclusion, surface nanotopography modulates the responses of fibroblasts and glial cells to platinum, which may be an important factor in optimizing the tissue response to implanted neural electrodes.

The influence of glancing angle deposited nano-rough platinum surfaces on the adsorption of fibrinogen and the proliferation of primary human fibroblasts

We have used the glancing angle deposition (GLAD) method as a simple and fast method to generate nano-rough surfaces for protein adsorption experiments and cell assays. The surface roughness and the detailed geometrical surface morphology of the thin films were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). As the GLAD deposition angle approaches grazing incidence, sharp and whisker-like columnar protrusions are formed. Smaller and less sharp surface features appear for the thin films synthesized at higher deposition angles. By changing the GLAD deposition angle together with the total amount of mass deposited per area on the respective surfaces, the size of the surface features can be varied on the nanoscale. Using the GLAD topographies as model surfaces, we have investigated the influence of the nano-roughness on fibrinogen adsorption and on the proliferation of primary human fibroblasts. It is found that fibrinogen, an important blood protein, preferentially adheres on the whisker-like nano-rough substrates in comparison to a flat surface. Furthermore, the proliferation of the human fibroblasts is significantly reduced on the nano-rough substrates. These results demonstrate that the GLAD technique can be used to fabricate nano-rough surface morphologies that significantly influence both protein and cellular adhesion to surfaces and are therefore well suited for biological assays.

Bovine serum albumin adsorption on nano-rough platinum surfaces studied by QCM-D

The adsorption of bovine serum albumin (BSA) on platinum surfaces with a root-mean-square roughness ranging from 1.49nm to 4.62nm was investigated using quartz crystal microbalance with dissipation (QCM-D). Two different BSA concentrations, 50microg/ml and 1mg/ml, were used, and the adsorption studies were complemented by monitoring the antibody interaction with the adsorbed BSA layer. The adsorption process was significantly influenced by the surface nano-roughness, and it was observed that the surface mass density of the adsorbed BSA layer is enhanced in a non-trivial way with the surface roughness. From a close examination of the energy dissipation vs. frequency shift plot obtained by the QCM-D technique, it was additionally observed that the BSA adsorption on the roughest surface is subject to several distinct adsorption phases revealing the presence of structural changes facilitated by the nano-rough surface morphology during the adsorption process. These changes were in particular noticeable for the adsorption at the low (50microg/ml) BSA concentration. The results confirm that the nano-rough surface morphology has a significant influence on both the BSA mass uptake and the functionality of the resulting protein layer.

Surface modifications of silicon nitride for cellular biosensor applications

Thin films of silicon nitride (Si3N4) can be used in several kinds of micro-sized biosensors as a material to monitor fine environmental changes related to the process of bone formation in vitro. We found however that Si3N4 does not provide optimal conditions for osseointegration as osteoblast-like MG-63 cells tend to detach from the surface when cultured over confluence. Therefore Si3N4 was modified with self-assembled monolayers bearing functional end groups of primary amine (NH2) and carboxyl (COOH) respectively. Both these modifications enhanced the interaction with confluent cell layers and thus improve osseointegration over Si3N4. Furthermore it was observed that the NH2 functionality increased the adsorption of fibronectin (FN), promoted cell proliferation, but delayed the differentiation. We also studied the fate of pre-adsorbed and secreted FN from cells to learn more about the impact of above functionalities for the development of provisional extracellular matrix on materials interface. Taken together our data supports that Si3N4 has low tissue integration but good cellular biocompatibility and thus is appropriate in cellular biosensor applications such as the ion-sensitive field effect transistor (ISFET). COOH and NH2 chemistries generally improve the interfacial tissue interaction with the sensor and they are therefore suitable substrates for monitoring cellular growth or matrix deposition using electrical impedance spectroscopy.

Silsesquioxane nanocomposites as tissue implants

BACKGROUND

Silicone implants are being used increasingly worldwide, especially in breast augmentation procedures. The most common morbidity observed is capsular contracture, which occurs in 15 percent of cases. To overcome this problem, the authors have developed a novel nanocomposite based on polyhedral oligomeric silsesquioxane-poly(carbonate-urea)urethane (POSS-PCU) for use as tissue implants.

METHODS

These polymers were implanted in six healthy sheep (n = 6) for 36 months and a siloxane served as the positive control. After explantation, these polymers were extracted, as was the surrounding capsule, if any. Attenuated total reflectance Fourier transform infrared spectroscopy analysis was performed to look for signs of surface degradation on the polymers and histopathologic and electron microscopic examinations were performed to study the interaction between the biomaterial and the host environment in greater detail.

RESULTS

After implantation, the authors observed minimal inflammation of the nanocomposite within the sheep model as compared with the siloxane control. Contact angle measurements and fibrinogen enzyme-linked immunosorbent assay tests were then conducted on the POSS-PCU nanocomposite to determine the reason for this behavior. The increased fibrinogen adsorption on POSS-PCU, its amphilicity, and large contact-angle hysteresis indicated that POSS-PCU inhibits inflammation by adsorbing and inactivating fibrinogen on its surface. In complete contrast, the control siloxane in the same setting demonstrated very significant inflammation and degradation, resulting in capsular formation. Naturally, there was no evidence of degradation of the nanocomposite compared with the siloxane control.

CONCLUSIONS

POSS-PCU nanocomposites have enhanced interfacial biocompatibility and better biological stability as compared with conventional silicone biomaterials, thus making them safer as tissue implants.

Cell adhesion on nanofibrous polytetrafluoroethylene (nPTFE)

Here, we described the in vitro biocompatibility of a novel nanostructured surface composed of PTFE as a potential polymer for the prevention of adverse host reactions to implanted devices. The foreign body response is characterized at the tissue-material interface by several layers of macrophages and large multinucleated cells known as foreign body giant cells (FBGC), and a fibrous capsule. The nanofibers of nanofibrous PTFE (nPTFE) range in size from 20 to 30 nm in width and 3-4 mm in length. Glass surfaces coated with nPTFE (produced by jet-blowing of PTFE 601A) were tested under in vitro conditions to characterize the amount of protein adsorption, cell adhesion, and cell viability. We have shown that nPTFE adsorbs 495 +/- 100 ng of bovine serum albumin (BSA) per cm2. This level was considerably higher than planar PTFE, most likely due to the increase in hydrophobicity and available surface area, both a result of the nanoarchitecture. Endothelial cells and macrophages were used to determine the degree of cell adsorption on the surface of the nanostructured polymer. Both cell types were significantly more round and occupied less area on nPTFE as compared to tissue culture polystyrene (TCPS). Furthermore, a larger majority of the cells on the nPTFE were dead compared to TCPS, at dead-to-live ratios of 778 +/- 271 to 1 and 23 +/- 5.6 to 1, respectively. Since there was a high amount of cell death (due to either apoptosis or necrosis), and the foreign body response is a form of chronic inflammation, an 18 cytokine Luminex panel was performed on the supernatant from macrophages adherent on nPTFE and TCPS. As a positive control for inflammation, lipopolysaccharide (LPS) was added to macrophages on TCPS to estimate the maximum inflammation response of the macrophages. From the data presented with respect to IL-1, TNF-alpha, IFN-gamma, and IL-5, we concluded that nPTFE is nonimmunogenic and should not yield a huge inflammatory response in vivo, and cell death observed on the surface of nPTFE was likely due to apoptosis resulting from the inability of cells to spread on these surface. On the basis of the production of IL-1, IL-6, IL-4, and GM-CSF, we concluded that FBGC formation on nPTFE may be decreased as compared to materials known to elicit FBGC formation in vivo.

Film from peroxidation of an amino phospholipid and its biocompatibility

A new kind of phospholipid product with fluorescence was derived from autoxidation of an aminophospholipid, L-alpha-phosphatidylethanolamine dilinoleoyl in solid film state. Atomic force microscopy showed that the film product was composed of round and elliptical vesicles with diameters of about 20-45 nm. The product was difficult to dissolve in water and most organic solvents. Fourier transform infrared spectroscopy, solid-state (13)C NMR, and solid-state (31)P NMR indicated that the unsaturated double carbon bond decreased with the reaction, and polymerization within/between phospholipid molecules occurred. Endothelial cells from human vein seeded onto the film showed the highest proliferating activity compared with seeding onto Corning culture plate, glass plate, or phospholipid film with phosphorylcholine head group, as evaluated by 3-(4,5-timethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay (p < 0.001). The hemocompatibility of the film was also assessed by platelet adhesion and protein adsorption. The results suggest that the product has potential applications as a new biomaterial coating.

Guided three-dimensional growth of functional cardiomyocytes on polyethylene glycol nanostructures

We introduce well-defined nanopillar arrays of a poly(ethylene glycol) (PEG) hydrogel as a cell culture platform to guide a 3D construct of primary rat cardiomyocytes in vitro for potential tissue engineering applications. Ultraviolet (UV)-assisted capillary lithography was used to fabricate highly uniform approximately 150 nm PEG pillars with approximately 400 nm height. It was found that cell adhesion was significantly enhanced on PEG nanopillars (132 +/- 29 cells/mm2) compared to that on the bare PEG control (39 +/- 17 cells/mm2) (p < 0.05) but substantially reduced compared to that on the glass control (502 +/- 45 cells/mm2) (p < 0.01). Furthermore, in colonizing cardiomyocytes, the nanopillars stimulated self-assembled aggregates among the contacting cells with 3D growth, which is a unique feature for nanopatterned PEG hydrogels as a cell culture substrate. The 3D-grown cardiomyocytes retained their conductive and contractile properties, as evidenced by the observation of beating cardiomyocytes with robust action potential generation.

The antithrombogenic potential of a polyhedral oligomeric silsesquioxane (POSS) nanocomposite

We have developed a nanocomposite using a silica nanocomposite polyhedral oligomeric silsesquioxane (POSS) and poly(carbonate-urea)urethane (PCU) for potential use in cardiovascular bypass grafts and the microvascular component of artificial capillary beds. In this study, we sought to compare its antithrombogenicity to that of conventional polymers used in vascular bypass grafts so as to improve upon current patency rates, particularly in the microvascular setting. Using atomic force microscopy (AFM) and transmission electron microscopy (TEM), surface topography and composition were studied, respectively. The ability of the nanocomposite surface to repel both proteins and platelets in vitro was assessed using thromboelastography (TEG), fibrinogen ELISA assays, antifactor Xa assays, scanning electron microscopy (SEM), and platelet adsorption tests. TEG analysis showed a significant decrease in clot strength (one-way ANOVA, p < 0.001) and increase in clot lysis (one-way ANOVA, p < 0.0001) on the nanocomposite when compared to both poly(tetrafluoroethylene) (PTFE) and PCU. ELISA assays indicate lower adsorption of fibrinogen to the nanocomposite compared to PTFE (one-way ANOVA, p < 0.01). Interestingly, increasing the concentration of POSS nanocages within these polymers was shown to proportionately inhibit factor X activity. Platelet adsorption at 120 min was also lower compared to PTFE and PCU (two-way ANOVA, p < 0.05). SEM images showed a "speckled" morphologic pattern with Cooper grades I platelet adsorption morphology on the nanocomposite compared to PTFE with grade IV morphology. On the basis of these results, we concluded that POSS nanocomposites possess greater thromboresistance than PTFE and PCU, making it an ideal material for the construction of both bypass grafts and microvessels.

Fabrication of nanostructures of polyethylene glycol for applications to protein adsorption and cell adhesion

A simple method was developed to fabricate polyethylene glycol (PEG) nanostructures using capillary lithography mediated by ultraviolet (UV) exposure. Acrylate-containing PEG monomers, such as PEG dimethacrylate (PEG-DMA, MW = 330), were photo-cross-linked under UV exposure to generate patterned structures. In comparison to unpatterned PEG films, hydrophobicity of PEG nanostructure modified surfaces was significantly enhanced. This could be attributed to trapped air in the nanostructures as supported by water contact angle measurements. Proteins (fibronectin, immunoglobulin, and albumin) and cells (fibroblasts and P19 EC cells) were examined on the modified surfaces to test for the level of protein adsorption and cell adhesion. It was found that proteins and cells preferred to adhere on nanostructured PEG surfaces in comparison to unpatterned PEG films; however, this level of adhesion was significantly lower than that of glass controls. These results suggest that capillary lithography can be used to fabricate PEG nanostructures capable of modifying protein and cell adhesive properties of surfaces.

Osteoblast attachment to a textured surface in the absence of exogenous adhesion proteins

The present study investigated whether osteoblasts could attach to a culture substratum through a surface texture-dependent mechanism. Four test groups were used: (A) untextured, and three texture groups with maximum feature sizes of (B) <0.5 microm, (C) 2 microm, and (D) 4 microm, respectively. All surfaces were coated with the nonadhesive protein bovine serum albumin (BSA). Osteoblasts were allowed to adhere in serum-free medium for either 1 or 4 h, at which time nonadherent cells were removed. At 4 h, untextured surface A exhibited no cell attachment, while textured surfaces B, C, and D exhibited 9%, 32%, and 16% cell adhesion, respectively. At 16 h of incubation, adherent osteoblasts on textured surface C exhibited focal adhesion contacts and microfilament stress-fiber bundles. These results indicate that microtextured surfaces in the absence of exogenous adhesive proteins can facilitate osteoblast adhesion.

Influence of systematically varied nanoscale topography on the morphology of epithelial cells

With the knowledge that cells can react to lithographically manufactured nanometer-sized surface objects, our interest concerned whether cells would respond to surface structures of systematically increasing size. Our approach to answer this question was to fabricate surfaces with the same surface chemistry and similar surface roughness but increasing size of structural features. To fabricate large areas of patterned surfaces, required for cell culture studies, we used colloidal lithography utilizing colloidal particles as a template for surface nanostructuring. The fabricated surfaces contained hemispherical nanopillars with diameters ranging from 60 to 170 nm. Changes in cell morphology of a pancreatic epithelial cell line (AR4-2J) were studied by evaluating cell area and cell shape. The latter was studied by applying the cell shape classification method using three shape descriptors. The pancreatic cells responded in a systematic way to the surface nanostructures. The cells spread more and became more nonround when cultured on surfaces with increasing size of the topographic features. Index Terms-Biological cells, image analysis, nanotechnology, shape measurement, surfaces.

Fibrinogen adsorption and platelet interactions on polymer membranes

The hemocompatibility of four different wettable polymer membranes, namely Cuprophan (CE), polyether-polycarbonate (PC-PE), polysulfone (PSU), and polyetherimide (PEI), was investigated with respect to fibrinogen (Fng) adsorption and platelet adhesion/activation. In order to estimate the polar and dispersion components of the surface free energy, contact angles using water/vapor and water/n-hexadecane systems were measured. Adsorption of fibrinogen was studied using fluorescence-labeled protein. The adsorption isotherms showed that the amount and the affinity of adsorbed Fng increased with decreasing surface wettability of the membranes, which correlates with the dispersion and polar components of the surface free energy. The conformational changes of adsorbed Fng were detected by measuring the difference between monoclonal antibody binding to the conformation-sensitive epitope in the D-domain and the binding of polyclonal anti-Fng antibody. The anticipated conformational/orientational changes were greater for PEI and PSU membranes (the least wettable membranes) and negligible for the more wettable PC-PE and CE membranes. In addition, a possible relationship with the degree of platelet activation was found, showing negligible platelet adhesion on PC-PE and CE, but high platelet adhesion on PEI and PSU. Furthermore, platelets were spread to a large extent on PEI, while the formation of aggregates was observed on PSU. This may correspond to the anticipated differences in the conformational state of Fng on both membranes.

Growth of connective tissue progenitor cells on microtextured polydimethylsiloxane surfaces

Growth of human connective tissue progenitor cells (CTPs) was characterized on smooth and microtextured polydimethylsiloxane (PDMS) surfaces. Human bone-marrow-derived cells were cultured for 9 days under conditions promoting osteoblastic differentiation on smooth PDMS surfaces and on PDMS post microtextures that were 6 microm high and 5, 10, 20, and 40 microm in diameter, respectively. Glass tissue-culture dishes were used as controls. The number of viable cells was determined, and an alkaline phosphatase stain was used as a marker for osteoblastic phenotype. CTPs attached, proliferated, and differentiated on all surfaces. Cells on the smooth PDMS and control surfaces spread and proliferated as colonies in proximity to other cells and migrated in random directions, with cell process lengths of up to 80 microm. In contrast, cells on the PDMS post microtextures grew as sparsely distributed networks of cells, with processes, occasionally up to 300 microm, that appeared to interact with the posts. Cell counts revealed that there were fewer (50%) CTPs on the smooth PDMS surface than were on the glass control surfaces. However, there were consistently more (>144%) CTPs on the PDMS post textures than on the controls. In particular, the 10-microm-in-diameter posts (268%) exhibited a significantly (p < 0.05) greater cell number than did the smooth PDMS.

Analysis of connective tissue progenitor cell behavior on polydimethylsiloxane smooth and channel micro-textures

Growth of human connective tissue progenitor cells (CTPs) was characterized on smooth and microtextured polydimethylsiloxane (PDMS) surfaces. Human bone marrow derived cells were cultured for nine days under conditions promoting osteoblastic differentiation on Smooth PDMS and PDMS Channel microtextures (11 microm high, 45 microm wide channels, and separated by 5 microm wide ridges). Glass tissue culture dish surfaces were used as controls. Cell numbers per colony, cell density within colonies, alignment of cells, area of colonies, and colony shapes were determined as a function of substrate surface topography. An alkaline phosphatase stain was used as a marker for osteoblastic phenotype. CTPs attached, proliferated, and differentiated on all surfaces with cell process lengths of up to 80 microm. Cells on the Smooth PDMS and control surfaces spread and proliferated as colonies in proximity to other cells and migrated in random directions creating colonies that covered significantly larger areas (0.96 and 1.05 mm(2), respectively) than colonies formed on PDMS Channel textures (0.64 mm(2)). In contrast, cells on PDMS Channel textures spread, proliferated, aligned along the channel axis, and created colonies that were more dense, and with lengths of longest colony axes that were significantly longer (3252 microm) than those on the Smooth PDMS (1265 microm) and control surfaces (1319 microm). Cells on PDMS Channel textures were aligned at an angle of 14.44 degrees relative to the channel axis, and the resulting colonies exhibited a significantly higher aspect ratio (13.72) compared to Smooth PDMS (1.57) and control surfaces (1.51).