Cellular responses to chemical and morphologic aspects of biomaterial surfaces. I. A novel in vitro model system

The determining role of nanoscale mechanical twinning on cellular functions of nanostructured materials

Considering that micromotions generated at the bone-implant interface under physiological loading introduce mechanical strain on the tissue and surface of the implant and that strain can be introduced during processing of the biomedical device, we elucidate here the interplay between mechanically-induced nanoscale twinning in austenitic stainless steel on osteoblast functions. Mechanically-induced nanoscale twinning significantly impacted cell attachment, cell-substrate interactions, proliferation, and subsequent synthesis of prominent proteins (fibronectin, actin, and vinculin). Twinning was beneficial in favorably modulating cellular activity and contributed to small differences in hydrophilicity and nanoscale roughness in relation to the untwinned surface.

Alternative methods for assessing biocompatibility and function of implant materials

Biocompatibility testing is used to evaluate the host response to implantable materials and to assess their ability to perform in applications in which they are intended to interact with biological systems. In compliance with international and/or national standards, such assessment is based mainly on the results of experimental implantation into animal tissues. However, the development of in vitro experimental techniques creates new opportunities to observe and to understand the interaction of biomaterials with host tissue. The state-of-the-art application of alternative methods in biocompatibility testing is presented in this review article. It is discussed with respect to the Three Rs concept (reduction, refinement, replacement) of Russell & Burch. Perspectives on alternative methods in biocompatibility studies are discussed with regard to the possible role of biomaterials in tissue engineering.

Understanding the impact of grain structure in austenitic stainless steel from a nanograined regime to a coarse-grained regime on osteoblast functions using a novel metal deformation-annealing sequence

Metallic biomedical devices with nanometer-sized grains (NGs) provide surfaces that are different from their coarse-grained (CG) (tens of micrometer) counterparts in terms of increased fraction of grain boundaries (NG>50%; CG<2-3%). The novel concept of 'phase-reversion' involving a controlled deformation-annealing sequence is used to obtain a wide range of grain structures, starting from the NG regime to the CG regime, to demonstrate that the grain structure significantly impacts cellular interactions and osteoblast functions. The uniqueness of this concept is the ability to address the critical aspect of cellular activity in nanostructured materials, because a range of grain sizes from NG to CG are obtained in a single material using an identical set of parameters. This is in addition to a high strength/weight ratio and superior wear and corrosion resistance. These multiple attributes are important for the long-term stability of biomedical devices. Experiments on the interplay between grain structure from the NG regime to CG in austenitic stainless steel on osteoblast functions indicated that cell attachment, proliferation, viability, morphology and spread varied with grain size and were favorably modulated on the NG and ultrafine-grain structure. Furthermore, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on the NG surface. The differences in the cellular response with change in grain structure are attributed to grain structure and degree of hydrophilicity. The study lays the foundation for a new branch of nanostructured materials for biomedical applications.

The alignment of MC3T3-E1 osteoblasts on steps of slip traces introduced by dislocation motion

Bone tissue shows a highly anisotropic microstructure comprising biological apatite and collagen fibrils produced by the mutual activities of bone cells, which dominates its mechanical function. Accordingly, directional control of osteoblasts is crucial for forming anisotropic bone tissue. A new approach was proposed for controlling cell directionality by using crystallographic slip traces caused by dislocation glide. Dislocations were introduced into α-titanium single crystals by plastic deformation of (011¯0)[21¯1¯0] slip system, inducing a step-like structure with acute angles between the surface normal and the slip plane. Topographical properties of step patterning, including step interval and step height, could be controlled by varying the compressive plastic strain. The step geometry introduced by plastic deformation strongly influenced osteoblast elongation, and it aligned preferentially along slip traces. Ti substrates under 10% plastic strain with step height of approximately 300 nm and step interval of 10 μm induced osteoblast alignment most successfully. Actin stress fibers elongated parallel to slip traces, with polarized vinculin accumulation between steps.

Computational modeling of in vitro biological responses on polymethacrylate surfaces

The objective of this research was to examine the capabilities of QSPR (Quantitative Structure Property Relationship) modeling to predict specific biological responses (fibrinogen adsorption, cell attachment and cell proliferation index) on thin films of different polymethacrylates. Using 33 commercially available monomers it is theoretically possible to construct a library of over 40,000 distinct polymer compositions. A subset of these polymers were synthesized and solvent cast surfaces were prepared in 96 well plates for the measurement of fibrinogen adsorption. NIH 3T3 cell attachment and proliferation index were measured on spin coated thin films of these polymers. Based on the experimental results of these polymers, separate models were built for homo-, co-, and terpolymers in the library with good correlation between experiment and predicted values. The ability to predict biological responses by simple QSPR models for large numbers of polymers has important implications in designing biomaterials for specific biological or medical applications.

Primary human osteoblast culture on 3D porous collagen-hydroxyapatite scaffolds

There is a need in tissue-engineering for 3D scaffolds that mimic the natural extracellular matrix of bone to enhance cell adhesion, proliferation, and differentiation. The scaffold is also required to be degradable. A highly porous scaffold has been developed to incorporate two of the extracellular components found in bone-collagen and hydroxyapatite (HA). The scaffold's collagen component is an afibrillar monomeric type I atelocollagen extracted from foetal calf's skin. This provided a novel environment for the inclusion of HA powder. Five hundred thousand primary human osteoblasts were seeded onto 4 mm cubed scaffolds that varied in ratio of HA to collagen. Weight ratios of 1:99, 25:75, 50:50, and 75:25 hydroxyapatite:collagen (HA:Collagen) were analysed. The scaffolds plus cells were cultured for 21 days. DNA assays and live/dead viability staining demonstrated that all of the scaffolds supported cell proliferation and viability. An alkaline phosphatase assay showed similar osteoblast phenotype maintenance on all of the 3D scaffolds analysed at 21 days. MicroCT analysis demonstrated an increase in total sample volume (correlating to increase in unmineralised matrix production). An even distribution of HA throughout the collagen matrix was observed using this technique. Also at 3 weeks, reductions in the percentage of the mineralised phase of the constructs were seen. These results indicate that each of the ratios of HA/collagen scaffolds have great potential for bone tissue engineering.

Biological significance of nanograined/ultrafine-grained structures: Interaction with fibroblasts

Given the need to develop high strength/weight ratio bioimplants with enhanced cellular response, we describe here a study focused on the processing-structure-functional property relationship in austenitic stainless steel that was processed using an ingenious phase reversion approach to obtain an nanograined/ultrafine-grained (NG/UFG) structure. The cellular activity between fibroblast and NG/UFG substrate is compared with the coarse-grained (CG) substrate. A comparative investigation of NG/UFG and CG structures illustrated that cell attachment, proliferation, viability, morphology and spread are favorably modulated and significantly different from the conventional CG structure. These observations were further confirmed by expression levels of vinculin and associated actin cytoskeleton. Immunofluorescence studies demonstrated increased vinculin concentrations associated with actin stress fibers in the outer regions of the cells and cellular extensions on NG/UFG substrate. These observations suggest enhanced cell-substrate interaction and activity. The cellular attachment response on NG/UFG substrate is attributed to grain size and hydrophilicity and is related to more open lattice in the positions of high-angle grain boundaries.

Cellular response of preosteoblasts to nanograined/ultrafine-grained structures

Metallic materials with submicron- to nanometer-sized grains provide surfaces that are different from conventional polycrystalline materials because of the large proportion of grain boundaries with high free energy. In the study described here, the combination of cellular and molecular biology, materials science and engineering advances our understanding of cell-substrate interactions, especially the cellular activity between preosteoblasts and nanostructured metallic surfaces. Experiments on the effect of nano-/ultrafine grains have shown that cell attachment, proliferation, viability, morphology and spread are favorably modulated and significantly different from conventional coarse-grained structures. Additionally, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on nanograined/ultrafine-grained substrate. These observations suggest enhanced cell-substrate interaction and activity. The differences in the cellular response on nanograined/ultrafine-grained and coarse-grained substrates are attributed to grain size and degree of hydrophilicity. The outcomes of the study are expected to reduce challenges to engineer bulk nanostructured materials with specific physical and surface properties for medical devices with improved cellular attachment and response. The data lay the foundation for a new branch of nanostructured materials for biomedical applications.

Myotube formation on micro-patterned glass: intracellular organization and protein distribution in C2C12 skeletal muscle cells

Proliferation and fusion of myoblasts are needed for the generation and repair of multinucleated skeletal muscle fibers in vivo. Studies of myocyte differentiation, cell fusion, and muscle repair are limited by an appropriate in vitro muscle cell culture system. We developed a novel cell culture technique [two-dimensional muscle syncytia (2DMS) technique] that results in formation of myotubes, organized in parallel much like the arrangement in muscle tissue. This technique is based on UV lithography-produced micro-patterned glass on which conventionally cultured C2C12 myoblasts proliferate, align, and fuse to neatly arranged contractile myotubes in parallel arrays. Combining this technique with fluorescent microscopy, we observed alignment of actin filament bundles and a perinuclear distribution of glucose transporter 4 after myotube formation. Newly formed myotubes contained adjacently located MyoD-positive and MyoD-negative nuclei, suggesting fusion of MyoD-positive and MyoD-negative cells. In comparison, the closely related myogenic factor Myf5 did not exhibit this pattern of distribution. Furthermore, cytoplasmic patches of MyoD colocalized with bundles of filamentous actin near myotube nuclei. At later stages of differentiation, all nuclei in the myotubes were MyoD negative. The 2DMS system is thus a useful tool for studies on muscle alignment, differentiation, fusion, and subcellular protein localization.

Human fibroblast and human bone marrow cell response to lithographically nanopatterned adhesive domains on protein rejecting substrates

The separate influence of topographical and chemical cues on cell attachment and spreading are well documented; however, that of duel-cue substrates is less so. In this study graft copolymers that sterically stabilize biological surfaces were employed alongside nanotopographical features fabricated by colloidal lithography. This resulted in the production of a range of substrates whereby the effect of chemistry and or topography on both on human fibroblast and bone marrow cell adhesion and spreading could be observed. The current studies indicate an enhancement of cell response as a consequence of modifications in material topography, whereas the current selected chemical cues inhibited cell function. Critically, in combination, topography modulated the effects of chemical environment.

The effect of combined simulated microgravity and microgrooved surface topography on fibroblasts

This study evaluated in vitro the differences in morphological behaviour between fibroblast cultured on smooth and microgrooved substrata (groove depth: 0.5 microm, width: 1, 2, 5, and 10 microm), which were subjected to simulated microgravity. The aim of the study was to clarify which of these parameters was more dominant to determine cell behaviour. Morphological characteristics were investigated using scanning electron microscopy and fluorescence microscopy in order to obtain qualitative information on cell alignment and area. Confocal laser scanning microscopy visualised distribution of actin filaments and focal adhesion points. Finally, expression of collagen type I, fibronectin, and alpha1- and beta1-integrin were investigated by PCR. Microscopy and image analysis showed that the fibroblasts aligned along the groove direction on all textured surfaces. On the smooth substrata, cells had spread out in a random fashion. The alignment of cells cultured on grooved surfaces decreased under simulated microgravity, especially after 24 h of culturing. Cell surface area on grooved substrata were significantly smaller than on smooth substrata, but simulated microgravity on the grooved groups resulted in an enlargement of cell area. ANOVA was performed on all main parameters: topography, gravity force, and time. In this analysis, all parameters proved significant. In addition, gene levels were reduced by microgravity particularly those of beta1-integrin and fibronectin. From our data it is concluded that the fibroblasts primarily adjust their shape according to morphological environmental cues like substratum surface whilst a secondary, but significant, role is played by microgravity conditions.

Cell/surface interactions and adhesion on Ti-6Al-4V: Effects of surface texture

This paper presents the results of an experimental study of the effects of surface texture on the interactions between human osteo-sarcoma (HOS) cells and Ti-6Al-4V. These include the Ti-6Al-4V with polished (smooth); Al(2)O(3) blasted (rough); and laser micro-grooved geometries with controlled spacings and depths. Immuno-fluorescence staining of adhesion proteins (actin and vinculin) was used to study the spreading and adhesion of HOS cells in 2 day culture experiments. Quantitative measures of adhesion were also obtained using an enzymatic detachment assay. The results are discussed within the context of existing theories of cell adhesion. The implications of the results are also examined for the design of textured surfaces in biomedical systems.

Cell/surface interactions on laser micro-textured titanium-coated silicon surfaces

This paper examines the effects of nano-scale titanium coatings, and micro-groove/micro-grid patterns on cell/surface interactions on silicon surfaces. The nature of the cellular attachment and adhesion to the coated/uncoated micro-textured surfaces was elucidated by the visualization of the cells and relevant cytoskeletal & focal adhesion proteins through scanning electron microscopy and immunofluorescence staining. Increased cell spreading and proliferation rates are observed on surfaces with 50 nm thick Ti coatings. The micro-groove geometries have been shown to promote contact guidance, which leads to reduced scar tissue formation. In contrast, smooth surfaces result in random cell orientations and the increased possibility of scar tissue formation. Immunofluorescence cell staining experiments also reveal that the actin stress fibers are aligned along the groove dimensions, with discrete focal adhesions occurring along the ridges, within the grooves and at the ends of the cell extensions. The implications of the observed cell/surface interactions are discussed for possible applications of silicon in implantable biomedical systems.

Human osteosarcoma cell adhesion behaviour on hydroxyapatite integrated chitosan-poly(acrylic acid) polyelectrolyte complex

A novel degradable composite system has been prepared by integrating hydroxyapatite, Ca(10)(PO(4))(6)(OH)(2), (HAP) in a polyelectrolyte complex matrix of chitosan (CHI) and poly(acrylic acid) (PAA). The composite was formulated by integrating 80 wt.% HAP in the polyelectrolyte complex matrix of CHI and PAA in the ratio 40/60 (designated as CPH). The composite could be easily fabricated into clinically significant shapes by a simple moulding procedure intended for bone graft applications. The adhesion behaviour of human osteosarcoma (HOS) cells on this degradable composite system was studied by selecting the polyelectrolyte complex, CHI/PAA 40/60 (designated as CP) as control sample. Light microscopic observations show that cells around CPH retained the typical morphology of HOS cells while cells around the polyelectrolyte complex showed a cytotoxic effect. The adhesion behaviour as well as morphological responses of the seeded cells was further investigated by scanning electron microscopy. The scanning electron micrographs of the polyelectrolyte complex, CP, showed the presence of rounded cells with raised nuclear regions, indicating delayed spreading; cells adhered on CPH were flattened with filopodia and showed good attachment and spreading, indicating better adhesion onto the HAP integrated composite. Comparing the MTT assay for quantitative evaluation of cell viability, CPH showed a higher percentage of metabolically active cells compared to CP.

A mouse strain difference in tumorigenesis induced by biodegradable polymers

The use of poly-L-lactic acid (PLLA) surgical implants for repair of bone fractures has gained popularity in the past decade. The aim of this study was to evaluate the in vivo effect of PLLA plates on subcutaneous tissue in two mouse strains, BALB/cJ and SJL/J, which have higher and lower tumorigenicity, respectively. Gap-junctional intercellular communication and protein expression of connexin 43 were significantly suppressed, whereas secretion of transforming growth factor-beta1 and expression of extracellular matrix, insulin-like growth factor binding protein 3, and cysteine-rich intestinal protein 2 were significantly increased in PLLA-implanted BALB/cJ mice when compared with BALB/cJ controls. Finally, tumors were formed after implantation of cultured cells from the more-tumorigenic BALB/cJ, but not SJL/J, mice into nude mice.

The effect of combined hypergravity and microgrooved surface topography on the behaviour of fibroblasts

This study evaluated in vitro the differences in morphological behaviour between fibroblast cultured on smooth and micro-grooved substrata (groove depth: 1 mum, width: 1, 2, 5, 10 microm), which undergo artificial hypergravity by centrifugation (10, 24 and 50 g; or 1 g control). The aim of the study was to clarify which of these parameters was more important to determine cell behaviour. Morphological characteristics were investigated using scanning electron microscopy and fluorescence microscopy in order to obtain qualitative information on cell spreading and alignment. Confocal laser scanning microscopy visualised distribution of actin filaments and vinculin anchoring points through immunostaining. Finally, expression of collagen type I, fibronectin, and alpha(1)- and beta(1)-integrin were investigated by PCR. Microscopy and image analysis showed that the fibroblasts aligned along the groove direction on all textured surfaces. On the smooth substrata (control), cells spread out in a random fashion. The alignment of cells cultured on grooved surfaces increased with higher g-forces until a peak value at 25 g. An ANOVA was performed on the data, for all main parameters: topography, gravity force, and time. In this analysis, all parameters proved significant. In addition, most gene levels were reduced by hypergravity. Still, collagen type 1 and fibronectin are seemingly unaffected by time or force. From our data it is concluded that the fibroblasts primarily adjust their shape according to morphological environmental cues like substratum surface whilst a secondary, but significant, role is played by hypergravity forces.

In vitro study of the interaction of polyalkilimide and polyvinyl alcohol hydrogels with cells

Hydrogels are a class of polymers that in the last decade have had a great development and application for soft tissue augmentation, due to their similarity to this tissue for their high water content. The in vitro effects of polyalkylmide hydrogel (pAI) and polyvinyl alcohol hydrogel (pVOH) on human lymphocytes and U937 cells viability, apoptosis and cell shape were investigated. Cell viability was always higher than 70%, thus showing the hydrogels were not cytotoxic for both cell lines. Some differences were, however, found. At short time, lymphocytes were very sensitive to the hydrogels incubation, while at long time, U937 cells were the most sensitive cells. Other differences on cell viability were related to the time of incubation, to the type of hydrogel and to the polymers concentration. Cell viability decreased only at the longest time of incubation and with the highest hydrogel concentration. Accordingly, cell death by apoptosis increased; necrosis was never observed in the cultures. Concentration- and hydrogel-dependent modifications of cell shape (bigger cell volume, elongations of cells) were observed in a few percentage of viable cells. In conclusion, the very high in vitro degree of biocompatibility shown by both hydrogels encourages their use as dermal fillers.

A computational approach to predicting cell growth on polymeric biomaterials

A predictive model that can correlate the chemical composition of a biomaterial with the biological response of cells that are in contact with that biomaterial would represent a major advance and would facilitate the rational design of new biomaterials. As a first step toward this goal, we report here on the use of Logical Analysis of Data (LAD) to model the effect of selected polymer properties on the growth of two different cell types, rat lung fibroblasts (RLF, a transformed cell line), and normal foreskin fibroblasts (NFF, nontransformed human cells), on 112 surfaces obtained from a combinatorially designed library of polymers. LAD is a knowledge extraction methodology, based on using combinatorics, optimization, and Boolean logic. LAD was trained on a subset of 62 polymers and was then used to predict cell growth on 50 previously untested polymers. Experimental validation indicated that LAD correctly predicted the high and low cell growth polymers and found optimal ranges for polymer chemical composition, surface chemistry, and bulk properties. Particularly noteworthy is that LAD correctly identified high-performing polymer surfaces, which surpassed commercial tissue culture polystyrene as growth substratum for normal foreskin fibroblasts. Our results establish the feasibility of using computational modeling of cell growth on flat polymeric surfaces to identify promising "lead" polymers for applications that require either high or low cell growth.

Cellular Response to Gelatin- and Fibronectin-Coated Multilayer Polyelectrolyte Nanofilms

Surface engineering is a critical effort in defining substrates for cell culture and tissue engineering. In this context, multilayer self-assembly is an attractive method for creating novel composites with specialized chemical and physical properties that is currently drawing attention for potential application in this area. In this work, effects of thickness, surface roughness, and surface material of multilayer polymer nanofilms on the growth of rat aortic smooth muscle cells were studied. Polyelectrolyte multilayers (PEMs) electrostatically constructed from poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) (PSS) with gelatin, fibronectin, and PSS surface coatings were evaluated for interactions with smooth muscle cells (SMCs) in an in vitro environment. The results prove that PEMs terminated with cell-adhesive proteins promote the attachment and further growth of SMCs, and that this property is dependent upon the number of layers in the underlying multilayer film architecture. Cell roundness and number of pseudopodia were also influenced by the number of layers in the nanofilms. These findings are significant in that they demonstrate that both surface coatings and underlying architecture of nanofilms affect the morphology and growth of SMCs, which means additional degrees of freedom are available for design of biomaterials. This work supports the excellent potential of nanoassembled ultrathin films for biosurface engineering, and points to a novel perspective for controlling cell-material interaction that can lead to an elegant system for defining the extracellular in vitro environment.

Tissue-engineering approaches for axonal guidance

Owing to the profound impact of nervous system damage, extensive studies have been carried out aimed at facilitating axonal regeneration following injury. Tissue engineering, as an emerging and rapidly growing field, has received extensive attention for nervous system axonal guidance. Numerous engineered substrates containing oriented extracellular matrix molecules, cells or channels have displayed potential of supporting axonal regeneration and functional recovery. Most attempts are focused on seeking new biomaterials, new cell sources, as well as novel designs of tissue-engineered neuronal bridging devices, to generate safer and more efficacious neuronal tissue repairs.

Effects of surface undulations of biphasic calcium phosphate tablets on human osteoblast behavior

In this work, the in vitro behavior of human osteoblast cells on the undulated surfaces of biphasic calcium phosphate tablets was investigated. The tablets were produced by uniaxial pressing with convex cylindrical undulations occupying only half of the surface area; the other half was flat. Chemical and physical characterization was performed by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). XRD and FTIR analyses revealed the presence of hydroxyapatite (HA) and alpha-tricalcium phosphate (alpha-TCP) in a well-defined ratio. Moreover, microtopography, evaluated by SEM and AFM, was similar on the flat region and on that with undulations. However, surface undulations induced different cellular arrangements, confirming the influence of the macrotopography on the cells orientation.

The effect of surface chemistry and nanotopography of titanium nitride (TiN) films on 3T3-L1 fibroblasts

The cell-material interaction of 3T3-L1 fibroblasts with TiN films was studied in vitro. TiN films were deposited onto glass substrates to thicknesses of 0.2 and 1.0 microm by pulsed dc reactive magnetron sputtering. For comparison TiN films were deposited by closed field unbalanced magnetron sputter ion plating by Teer Coatings Ltd. (Hartlebury, UK) to result in TiN films with similar surface chemistries but having increased topographical features. TiN films were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The cell-material interaction was examined morphologically by monitoring fibroblast attachment and growth and comparing to a control substrate. At early time points increased numbers of 3T3-L1 fibroblasts were found to preferentially attach to TiN films with an increase in the percentage of surface interstitial nitrogen and also with decreased topographical features. At later time points the presence of nanotopography appeared to play a greater role than the effects of surface chemistry and resulted in increased numbers of attached 3T3-L1 fibroblasts. The results show that by changing the deposition route and parameters to produce TiN films, the resultant films can be used to investigate the cellular response to surfaces of differing chemistry and topography.

Effects of multigrooved surfaces on osteoblast-like cellsin vitro: Scanning electron microscopic observation and mRNA expression of osteopontin and osteocalcin

This study evaluated the behavior of osteoblast-like cells on multigrooved surfaces consisting of a combination of microgrooves and macrogrooves. A polystyrene substrate was fabricated with multigrooves with 90-degree, V-shaped microgrooves with a 2-microm pitch cut on trapezoidal macrogrooves, which had a 50-microm ridge width, a 50-microm wall width, a 50-microm bottom width, and 25-microm depth. Smooth polystyrene substrates were also prepared as controls. Rat bone marrow cells were cultured as osteoblast-like cells on the substrates for morphological evaluation using a scanning electron microscope, and for biochemical evaluation using the quantitative reverse transcriptase-polymerase chain reaction technique for osteopontin and osteocalcin mRNA expression. After 8 days of incubation, the osteoblast-like cells were aligned parallel to the surface grooves on the multigrooved substrates. After 16 days of incubation, a dense mineralized extracellular matrix (ECM) was produced along the multigrooves. The ECM on the multigrooved surface appeared oriented more in the direction of the grooves than on the smooth surface, and trapezoid-shaped macrogrooves of the ECM were cast upside down. Although there were not significant differences, the osteopontin and osteocalcin mRNA expressions of the osteoblast-like cells on the multigrooved surfaces tended to be higher than on smooth surfaces. These results suggest that multigrooves could be used to control the orientation of mineralized ECM as well as of cells, and also to enhance the production of mineralized ECM.

Interactions between MC3T3-E1 cells and textured Ti6Al4V surfaces

This paper presents the results of an experimental study of the interactions between MC3T3-E1 (mouse calvarian) cells and textured Ti6Al4V surfaces, including surfaces produced by laser microgrooving; blasting with alumina particles; and polishing. The multiscale interactions between MC3T3-E1 cells and these textured surfaces are studied using a combination of optical scanning transmission electron microscopy and atomic force microscopy. The potential cytotoxic effects of microchemistry on cell-surface interactions also are considered in studies of cell spreading and orientation over 9-day periods. These studies show that cells on microgrooved Ti6Al4V geometries that are 8 or 12 microm deep undergo contact guidance and limited cell spreading. Similar contact guidance is observed on the surfaces of diamond-polished surfaces on which nanoscale grooves are formed due to the scratching that occurs during polishing. In contrast, random cell orientations are observed on alumina-blasted Ti6Al4V surfaces. The possible effects of surface topography are discussed for scar-tissue formation and improved cell-surface integration.

Cell orientation and cytoskeleton organisation on ground titanium surfaces

A stable connection between the biomaterial surface and the surrounding tissue is one of the most important prerequisites for the long-term success of implants. Therefore, a strong adhesion of the cells on the biomaterial surface is required. Beside the surface composition the surface topography influences the properties of the adherent cells. The quality of the connection between the cell and the biomaterial is-among other factors-determined by the dimensions of the surface topography. Osteoblasts and fibroblast-like cells in contact with a ground biomaterial surface spread in the direction of the surface structures. These aligned cells provide a more favourable adhesion behaviour than a spherically shaped cell. To determine the influence of the surface structure on the cell alignment and cytoskeleton organisation or arrangement, substrate discs of cp-titanium were ground, producing different roughness of the substrates. The oriented cells had a higher density of focal contacts when they were in contact with the edges of the grooves and showed a better organisation of the cytoskeleton and stronger actin fibres. These changes of the aligned cells depend on the peak to valley height of the surface structures.

Transforming growth factor-beta 1, 2, and 3 can inhibit epithelial tissue outgrowth on smooth and microgrooved substrates

In this study, we describe the influence of parallel surface microgrooves, and of TGF-beta, on the outgrowth of corneal epithelial tissue. Microgrooves (depth 1 microm, width 1-10 microm) were made in polystyrene culturing surfaces. These surfaces were left untreated, or loaded with TGF-beta 1, 2, or 3 (6.0 ng/cm(2)). Subsequently, epithelial explants from bovine corneas were placed on the experimental surfaces. After 9 days of culturing, tissue outgrowth was evaluated. Furthermore, the tissue cultures were analyzed histologically. It was shown that epithelial tissue grew from the explants over all experimental surfaces. On microgrooved surfaces outgrowth proceeded in the direction of the grooves, rather than perpendicular to the grooves. The addition of each type of TGF-beta resulted in a reduction of outgrowth. However, outgrowth remained directed by the grooves. Further, the explants had shrunk after TGF treatment. Histology showed that this shrinkage was not related to alpha-smooth muscle actin expression in the explants. We conclude that microgrooves can direct, and TGF-betas can inhibit the outgrowth of epithelial tissue. This finding could be useful in biomaterial applications where the growth of epithelial tissue needs to be discouraged.

Topographical and physicochemical modification of material surface to enable patterning of living cells

Precise control of the architecture of multiple cells in culture and in vivo via precise engineering of the material surface properties is described as cell patterning. Substrate patterning by control of the surface physicochemical and topographic features enables selective localization and phenotypic and genotypic control of living cells. In culture, control over spatial and temporal dynamics of cells and heterotypic interactions draws inspiration from in vivo embryogenesis and haptotaxis. Patterned arrays of single or multiple cell types in culture serve as model systems for exploration of cell-cell and cell-matrix interactions. More recently, the patterned arrays and assemblies of tissues have found practical applications in the fields of Biosensors and cell-based assays for Drug Discovery. Although the field of cell patterning has its origins early in this century, an improved understanding of cell-substrate interactions and the use of microfabrication techniques borrowed from the microelectronics industry have enabled significant recent progress. This review presents the important early discoveries and emphasizes results of recent state-of-the-art cell patterning methods. The review concludes by illustrating the growing impact of cell patterning in the areas of bioelectronic devices and cell-based assays for drug discovery.

Testing of skeletal implant surfaces with human fetal osteoblasts

The effect of standard orthopaedic implant materials on osteoblast proliferation and differentiation was investigated using a human osteoblast cell culture system. Human fetal osteoblasts 1.19 were cultured on stainless steel, cobalt-chrome-molybdenum, and commercially pure titanium for 12 days. Tissue culture polystyrene was used as a control. Cell proliferation was measured by electronic cell counting and by a colorimetric proliferation assay. To assess the degree of differentiation, levels of alkaline phosphatase activity, collagen Type I, and osteocalcin production were measured. Osteocalcin gene expression was measured by reverse transcriptase-polymerase chain reaction. Electronic cell counting and proliferation assays showed lower cell numbers and delayed proliferation on stainless steel and cobalt-chrome-molybdenum compared with titanium and polystyrene. Alkaline phosphatase and osteocalcin were measured higher on titanium than on stainless steel or cobalt-chrome-molybdenum. Differences in collagen Type I production were not found. Reverse transcriptase-polymerase chain reaction showed the highest osteocalcin gene expression on titanium. The human fetal osteoblast cell line 1.19 provides a rapidly proliferating and differentiating system for testing biomaterials in which differences in osteoblast proliferation and differentiation on orthopaedic implant materials could be revealed, suggesting that the chemistry of biomaterials has a dynamic effect on proliferation and differentiation of human osteoblasts.

Modulation of epithelial tissue and cell migration by microgrooves

We used a polystyrene substratum to study the response of migrating epithelium to 1- or 5-microm depth microgrooves with groove/ridge widths of 1, 2, 5, or 10 microm. The migration of a tissue sheet was enhanced along the microgrooves, while migration across the microgrooves was inhibited. Changing the depth of the microgrooves had a greater effect on migration than alteration of the groove/ridge width. The migration of epithelial cells from a confluent monolayer culture followed a similar pattern to that of intact epithelial tissue. Cellular extensions generally followed the microgroove direction by tracking along the top of the ridges or following the ridge walls, as revealed by scanning electron microscopy. Actin filaments within the basal cell layer of the tissue were aligned with the microgrooves, unlike filaments in the superficial layers that did not appear to be affected by the presence of underlying microgrooves. The basal cell layer of the tissue conformed to the contours of the microgroove following migration. However, the ultrastructure of the tissue above the ridges resembled that of tissue on a flat surface. We concluded that surface microgrooves have the potential to direct the migration of immediately adjacent epithelial tissue, the effect of which is to guide epithelial tissue on the surface of implanted biomaterials.

Surface characterization of poly(methyl methacrylate) microgrooved for contact guidance of mammalian cells

High-resolution patterns of grooves have been made in poly(methyl methacrylate) films, PMMA, by an electron-beam microlithographic process. The surface of films processed over a large width was characterized in terms of chemical composition (X-ray photoelectron spectroscopy (XPS). time of flight secondary ion mass spectroscopy), wettability (sessile drop) and topography (atomic force microscopy). Collagen adsorption was also studied (radiocounting, XPS) as such or in competition with Pluronic F68. The chemical alteration of the surface induced by the electron-beam irradiation disappeared after the dissolution involved in the development process. W138 human fibroblasts cultivated on microgrooved substrata (grooves 1 microm deep and 0.5-10 microm wide) showed a strong orientation parallel to the grooves. The contact guidance is induced by the topography of the surface and not by the alternation of zones with different physico-chemical properties. It may be explained in terms of probability of successful substratum contact by cell protrusions.

A comparison of the inflammatory response to a polydimethylsiloxane implant in male and female Balb/c mice

The implantation of biomaterials elicits a host response that influences the long-term behavior of implanted medical devices. This foreign body response is governed by cells of the immune system. Because sexual dimorphism in the immune system is well-established, a comparative study of the foreign body response in male and female mice was initiated. Eight-week-old male and female Balb/c mice received two subcutaneous implants in the interscapular region of a smooth peroxide-catalyzed polydimethylsiloxane (PDMS) and were sacrificed at 2, 14, 42, 70, and 105 days after implantation (n = 6 per sex per time point). Controls for each time point underwent the surgical procedure but received no implant. Tissue from the implant or surgical site was fixed, processed, and paraffin-embedded for histopathological evaluation and immunohistochemical (IHC) staining for tumor necrosis factor-alpha TNF-alpha) and interleukin-1 beta (IL-1beta). In control animals, an inflammatory response was observed at 2 days that was decreased by 14 days and absent after 42 days. At 2 and 14 days after PDMS implantation, a mild to moderate inflammatory reaction was observed around implants. The peak response was seen at 14 days, and granulation tissue, composed primarily of fibroblasts, macrophages, and neutrophils, was first observed at this time. After 105 days, the implantation site was surrounded by mature connective tissue, which had minimal numbers of macrophages and neutrophils, with severity scores that did not differ significantly in males and females. The immunostaining for TNF-alpha and IL-1beta followed similar temporal patterns, with both reaching a peak at the two week time point and remaining elevated, compared to level of expression in the controls, throughout the 105 day observation period. Staining for both cytokines in the implanted animals was generally higher in females than in males, although this difference was significant only for IL-1beta. These results suggest subtle differences between males and females in the activity of peri-implant inflammatory cells.

Development of biodegradable polyesterurethane membranes with different surface morphologies for the culture of osteoblasts

To evaluate the biocompatibility of biodegradable polyesterurethane membranes with different surface morphologies for their possible use as orthopedic biomaterials, rat osteoblasts were cultured on smooth, sunken, and particulate polyesterurethane membranes. A close interaction between cells and exposed particles on the particulate membranes was found. Cells on the particulate surfaces were well spread and flattened and had the greatest adhesion while cells on the smooth surfaces were more rounded, less spread, and less adhered. In addition, in order to investigate their in vivo degradation rates, the morphologic changes in retrieved membranes from 2, 4, and 8 weeks after subcutaneous implantation were observed by scanning electron microscopy and their average molecular weight changes were determined by gel permeation chromatography. These analyses showed that smooth membranes, compared with the two other surface membrane types, had the greatest rate and degree of molecular weight change. In contrast, the molecular weight of particulate membranes, which favor the osteoblast culture, had not changed significantly at 8 weeks postimplantation. Thus particulate polyesterurethane membrane surfaces may be of use as an orthopedic biomaterial, and polyesterurethane membranes certainly provide an ideal system for further study of the relative contributions to biocompatibility and degradation derived from surface morphology.

Qualitative and quantitative study of human osteoblast adhesion on materials with various surface roughnesses

We quantitatively evaluated the adhesion of human osteoblasts on orthopedic metallic substrates (Ti6Al4V alloy) with various surface roughnesses at several times after inoculation and studied its correlation with qualitative changes in the expression of adhesion proteins and with parameters extensively describing the surface topographies. Cells were orientated in a parallel order on polished surfaces. This orientation was not affected by residual grooves after polishing. On sandblasted surfaces the cells never attained confluence and had a stellate shape, and the cell layer had no particular organization. Extracellular matrix (fibronectin, type I collagen, osteopontin) and cytoskeletal protein (actin, vinculin) orientation reflected the cell layer organization. In our experiment human osteoblasts expressed alpha3beta1 integrin but not alpha2beta1 integrin. In addition to currently analyzed roughness magnitude parameters, we calculated roughness organization parameters (fractal dimension parameters) of the substrates. We observed lower adhesion and proliferation on less organized surfaces (i.e., sandblasted ones). The significant statistical correlation observed between fractal dimension parameters (describing surface roughness organization) and cell parameters adds a new concept to the studies of substratum roughness influence on cell behavior. An attempt at modelization of the cell-surface interaction was made that includes the influence of fractal dimensions parameters.

Contact guidance of rat fibroblasts on various implant materials

Providing a substrate surface with micrometer-sized parallel grooves influences the behavior of cells growing on such substrates in vitro. Cells elongate in the direction of the groove and migrate guided by the grooves. It has been suggested that cellular alignment on microgrooves is predominantly dependent on groove dimensions and that surface chemical variation of the substrate material has little effect. Therefore we seeded primary rat dermal fibroblasts (RDF) on smooth and microgrooved (groove width 1-10 microm, depth 0.5 microm) polystyrene (PS), poly-L-lactic acid (PLA), silicone (SIL), and titanium (Ti) substrates. The production process was found to be more accurate for PS and PLA than for SIL and Ti substrates. A proliferation study, scanning electron microscopy, confocal laser scanning microscopy, and transmission electron microscopy revealed differences between RDF behavior on the materials. Our conclusions are (1) the accuracy of microtexture production by casting depends greatly on the material used; (2) even if no sharp discontinuities are present, microtextures still are potent tools for inducing contact guidance; and (3) besides surface texture, surface chemistry has a definitive influence on cell morphology.

Contact guidance of rat fibroblasts on various implant materials

Providing a substrate surface with micrometer-sized parallel grooves influences the behavior of cells growing on such substrates in vitro. Cells elongate in the direction of the groove and migrate guided by the grooves. It has been suggested that cellular alignment on microgrooves is predominantly dependent on groove dimensions and that surface chemical variation of the substrate material has little effect. Therefore we seeded primary rat dermal fibroblasts (RDF) on smooth and microgrooved (groove width 1-10 microm, depth 0.5 microm) polystyrene (PS), poly-L-lactic acid (PLA), silicone (SIL), and titanium (Ti) substrates. The production process was found to be more accurate for PS and PLA than for SIL and Ti substrates. A proliferation study, scanning electron microscopy, confocal laser scanning microscopy, and transmission electron microscopy revealed differences between RDF behavior on the materials. Our conclusions are (1) the accuracy of microtexture production by casting depends greatly on the material used; (2) even if no sharp discontinuities are present, microtextures still are potent tools for inducing contact guidance; and (3) besides surface texture, surface chemistry has a definitive influence on cell morphology.

Attachment of fibroblasts on smooth and microgrooved polystyrene

In this study rat dermal fibroblasts (RDFs) were cultured on smooth or microgrooved (1-20 microm wide, 0.5-5.4 microm deep) substrates. Polystyrene microgrooved substrates were produced by solvent casting on molds that had been produced by photolithographic techniques. We investigated the attachment of RDFs with various analytical techniques. Light microscopy and image analysis showed that RDFs were oriented on most microgrooves. The rate of orientation effectively was increased by an increase of groove depth. An analysis of confluent layers of RDF showed that at confluency microgrooves were able to support greater numbers of cells. However, the largest numbers of cells were not found on the narrowest and deepest microgrooves even though such microgrooves have the largest total surface and induce the strongest alignment. Interference reflection microscopy (IRM) showed that the RDFs form focal adhesions where the cell membrane is only 10 nm from the substrate. IRM also showed that RDFs follow the contours of shallow and wide microgrooves but bridge the grooves on deeper and narrower ones. This could explain why such grooves are not able to increase the numerical cell adhesion to a greater degree. The absence of contact between cells and the bottom of the grooves is a very important factor in establishing contact guidance.

Attachment of fibroblasts on smooth and microgrooved polystyrene

In this study rat dermal fibroblasts (RDFs) were cultured on smooth or microgrooved (1-20 microm wide, 0.5-5.4 microm deep) substrates. Polystyrene microgrooved substrates were produced by solvent casting on molds that had been produced by photolithographic techniques. We investigated the attachment of RDFs with various analytical techniques. Light microscopy and image analysis showed that RDFs were oriented on most microgrooves. The rate of orientation effectively was increased by an increase of groove depth. An analysis of confluent layers of RDF showed that at confluency microgrooves were able to support greater numbers of cells. However, the largest numbers of cells were not found on the narrowest and deepest microgrooves even though such microgrooves have the largest total surface and induce the strongest alignment. Interference reflection microscopy (IRM) showed that the RDFs form focal adhesions where the cell membrane is only 10 nm from the substrate. IRM also showed that RDFs follow the contours of shallow and wide microgrooves but bridge the grooves on deeper and narrower ones. This could explain why such grooves are not able to increase the numerical cell adhesion to a greater degree. The absence of contact between cells and the bottom of the grooves is a very important factor in establishing contact guidance.

Microgrooved subcutaneous implants in the goat

We investigated the behavior of microgrooved implants in soft tissue using polystyrene implantable disks, either smooth or microgrooved (1-10 microm) on both sides. The implants were placed subcutaneously in a goat for 1, 4, or 12 weeks. Light and transmission electron microscopy showed that fibrous capsule formation around the implants was fairly uniform. After 1 week the implants were covered with a fibrous capsule about 80 microm thick. The collagen matrix was loose, and many inflammatory cells were present. After 4 weeks the matrix was more dense and contained many newly formed blood vessels. At the implant surface a layer of inflammatory cells about 10 microm thick had accumulated. Finally, after 12 weeks the matrix had densified. One cellular layer of inflammatory cells was present at the implant surface. We carried out histomorphometric measurements of capsule thickness, inflammatory layer thickness, and the number of blood vessels. Capsule thickness appeared not to decrease with time. Further, these measurements showed that there were no differences in tissue reaction between smooth and microgrooved implants. On the basis of our observations, we suggest that 1 microm deep and 1-10 microm wide microgrooves do not influence tissue response around polystyrene implants in soft tissue.

Polymer surface chemistry and bone cell migration

Implant devices for orthopaedic applications may be improved if the surface of the biomaterial provides for osteointegration. To understand the effect of hydrophilicity on colonisation by human bone derived (HBD) cells, we compared untreated polystyrene (PS) and a sulfuric acid-treated PS surface for mechanisms of cell migration. The chemical composition of the acid-treated PS surface was analysed by monochromatic X-ray photoelectron spectroscopy and found to contain various oxidatively produced groups and a minor amount of sulfonate groups. It was found that migration of HBD cells on both PS and acid-treated PS surface was dependent on the presence of vitronectin (Vn) and was higher on the hydrophilic acid-treated surface. Minimal migration of HBD cells occurred on either surface in the absence of Vn, even when fibronectin was present in the culture medium. Using radiolabelled protein, it was shown that Vn adsorption onto the acid-treated surface was two to three fold greater than that on the hydrophobic PS. When HBD cells were seeded onto a patterned surface in a medium containing Vn, the cells preferentially colonised the hydrophilic region and few, if any, cells traversed the haptotactic boundary from the hydrophilic to the hydrophobic side. Thus the enhanced HBD cell migration seen on the acid-treated PS compared with the untreated PS surface and the haptotactic boundary phenomenon, relate to Vn adsorption.

Fabrication and selective surface modification of 3-dimensionally textured biomedical polymers from etched silicon substrates

A new method is described for producing biomedically relevant polymers with precisely defined micron scale surface texture in the x, y, and z planes. Patterned Si templates were fabricated using photolithography to create a relief pattern in photoresist with lateral dimensions as small as 1 micron. Electroless Ni was selectively deposited in the trenches of the patterned substrate. The Ni served as a resilient mask for transferring the patterns onto the Si substrate to depths of up to 8.5 microns by anisotropic reactive ion etching with a fluorine-based plasma. The 3-dimensional (3-D) textured silicon substrates were used as robust, reusable molds for pattern transfer onto poly (dimethyl siloxane), low density poly (ethylene), poly (L-lactide), and poly (glycolide) by either casting or injection molding. The fidelity of the pattern transfer from the silicon substrates to the polymers was 90 to 95% in all three planes for all polymers for more than 60 transfers from a single wafer, as determined by scanning electron microscopy and atomic force microscopy. Further, the 3-D textured polymers were selectively modified to coat proteins either in the trenches or on the mesas by capillary modification or selective coating techniques. These selectively patterned 3-D polymer substrates may be useful for a variety of biomaterial applications.

Cellular responses to chemical and morphologic aspects of biomaterial surfaces. II. The biosynthetic and migratory response of bone cell populations

The biosynthetic and migratory response of bone cells to changes in both surface composition and morphology of polystyrene (PS) substrates was examined. A system was devised wherein micromachined silicon wafers were used as templates to solvent-cast PS replicas [using 0, 1, or 2 wt % styrene (S) monomer additions] with either 0.5- or 5.0- microns-deep surface grooves. Smooth replicas (0% S) served as the control surfaces. The chemical and morphologic characteristics of the nine unique model biomaterial surfaces (MBSs) produced using this system were documented and were found to be distinct. For the biosynthetic studies, bone cells isolated from neonatal rat calvaria were plated onto the MBSs and labeled at postconfluence with [14C]proline for 24 h. Total DNA per surface, total newly synthesized collagenous (CP), and noncollagenous protein (NCP) (cell associated and secreted) were determined. Cell-associated CP was found to increase significantly for the bone cells cultured on the substrates with 0.5-micron grooves and 2% S (P < .05). Cell-associated NCP was found to be elevated for all 2% S substrates and for the 0.5-micron grooves substrates with 1% S. For the migration studies, bone cells were plated first onto 5-mm nitrocellulose disks that were attached to standard Petri dishes using a plasma clot. At confluence, the disks were removed aseptically and placed on the replicas. The cellular area occupied as a result of the outward migration of the bone cells was measured after 4 days of culture using an image analysis system. An average velocity for the leading edge of bone cell populations on each of the nine MBSs was calculated: Cells on surfaces with either 1% S or 5.0-microns grooves displayed significantly higher velocities than did the control cultures. A significant interaction effect between chemistry and morphology was observed. The biosynthetic and migratory responses of in vitro cultures of bone cells were not predictable from the observations of the cellular responses to the individual features, but appeared to depend on cellular responses to more than one substrate factor.