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

Macrophage cell morphology-imprinted substrates can modulate mesenchymal stem cell behaviors and macrophage M1/M2 polarization for wound healing applications

Mesenchymal stem cells and macrophages (MQ) are two very important cells involved in the normal wound healing process. It is well understood that topological cues and mechanical factors can lead to different responses in stem cells and MQ by influencing their shape, cytoskeleton proliferation, migration, and differentiation, which play an essential role in the success or failure of biomaterial implantation and more importantly wound healing. On the other hand, the polarization of MQ from proinflammatory (M1) to prohealing (M2) phenotypes has a critical role in the acceleration of wound healing. In this study, the morphology of different MQ subtypes (M0, M1, and M2) was imprinted on a silicon surface (polydimethylsiloxane [PDMS]) to prepare a nano-topography cell-imprinted substrate with the ability to induce anti-inflammatory effects on the mouse adipose-derived stem cells (ADSCs) and RAW264.7 monocyte cell line (MO). The gene expression profiles and flow cytometry of MQ revealed that the cell shape microstructure promoted the MQ phenotypes according to the specific shape of each pattern. The ELISA results were in agreement with the gene expression profiles. The ADSCs on the patterned PDMS exhibited remarkably different shapes from no-patterned PDMS. The MOs grown on M2 morphological patterns showed a significant increase in expression and section of anti-inflammatory cytokine compared with M0 and M1 patterns. The ADSCs homing in niches heavily deformed the cytoskeletal, which is probably why the gene expression and phenotype unexpectedly changed. In conclusion, wound dressings with M2 cell morphology-induced surfaces are suggested as excellent anti-inflammatory and antiscarring dressings.

The Bumpy Road to Stem Cell Therapies: Rational Design of Surface Topographies to Dictate Stem Cell Mechanotransduction and Fate

Cells sense and respond to a variety of physical cues from their surrounding microenvironment, and these are interpreted through mechanotransductive processes to inform their behavior. These mechanisms have particular relevance to stem cells, where control of stem cell proliferation, potency, and differentiation is key to their successful application in regenerative medicine. It is increasingly recognized that surface micro- and nanotopographies influence stem cell behavior and may represent a powerful tool with which to direct the morphology and fate of stem cells. Current progress toward this goal has been driven by combined advances in fabrication technologies and cell biology. Here, the capacity to generate precisely defined micro- and nanoscale topographies has facilitated the studies that provide knowledge of the mechanotransducive processes that govern the cellular response as well as knowledge of the specific features that can drive cells toward a defined differentiation outcome. However, the path forward is not fully defined, and the "bumpy road" that lays ahead must be crossed before the full potential of these approaches can be fully exploited. This review focuses on the challenges and opportunities in applying micro- and nanotopographies to dictate stem cell fate for regenerative medicine. Here, key techniques used to produce topographic features are reviewed, such as photolithography, block copolymer lithography, electron beam lithography, nanoimprint lithography, soft lithography, scanning probe lithography, colloidal lithography, electrospinning, and surface roughening, alongside their advantages and disadvantages. The biological impacts of surface topographies are then discussed, including the current understanding of the mechanotransductive mechanisms by which these cues are interpreted by the cells, as well as the specific effects of surface topographies on cell differentiation and fate. Finally, considerations in translating these technologies and their future prospects are evaluated.

Colloidal Lithography for Photovoltaics: An Attractive Route for Light Management

The pursuit of ever-more efficient, reliable, and affordable solar cells has pushed the development of nano/micro-technological solutions capable of boosting photovoltaic (PV) performance without significantly increasing costs. One of the most relevant solutions is based on light management via photonic wavelength-sized structures, as these enable pronounced efficiency improvements by reducing reflection and by trapping the light inside the devices. Furthermore, optimized microstructured coatings allow self-cleaning functionality via effective water repulsion, which reduces the accumulation of dust and particles that cause shading. Nevertheless, when it comes to market deployment, nano/micro-patterning strategies can only find application in the PV industry if their integration does not require high additional costs or delays in high-throughput solar cell manufacturing. As such, colloidal lithography (CL) is considered the preferential structuring method for PV, as it is an inexpensive and highly scalable soft-patterning technique allowing nanoscopic precision over indefinitely large areas. Tuning specific parameters, such as the size of colloids, shape, monodispersity, and final arrangement, CL enables the production of various templates/masks for different purposes and applications. This review intends to compile several recent high-profile works on this subject and how they can influence the future of solar electricity.

Designing Nanostructured Ti6Al4V Bioactive Interfaces with Directed Irradiation Synthesis toward Cell Stimulation to Promote Host-Tissue-Implant Integration

A new generation of biomaterials are evolving from being biologically inert toward bioactive surfaces, which can further interact with biological components at the nanoscale. Here, we present directed irradiation synthesis (DIS) as a novel technology to selectively apply plasma ions to bombard any type of biomaterial and tailor the nanofeatures needed for in vitro growth stimulation. In this work, we demonstrate for the first time, the influence of physiochemical cues (e.g., self-organized topography at nanoscale) of medical grade Ti₆Al₄V results in control of cell shape, adhesion, and proliferation of human aortic smooth muscle stem cells. The control of surface nanostructures was found to be correlated to ion-beam incidence angle linked to a surface diffusive regime during irradiation synthesis with argon ions at energies below 1 keV and a fluence of 2.5 × 10¹⁷ cm^-2. Cell viability and cytoskeleton morphology were evaluated at 24 h, observing an advance cell attachment state on post-DIS surfaces. These modified surfaces showed 84% of cell biocompatibility and an increase in cytoplasmatic protusions ensuring a higher cell adhesion state. Filopodia density was promoted by a 3-fold change for oblique incidence angle DIS treatment compared to controls (e.g., no patterning) and lamellipodia structures were increased more than a factor of 2, which are indicators of cell attachment stimulation due to DIS modification. In addition, the morphology of the nanofeatures were tailored, with high fidelity control of the main DIS parameters that control diffusive and erosive regimes of self-organization. We have correlated the morphology and the influence in cell behavior, where nanoripple formation is the most active morphology for cell stimulation.

Balancing biofunctional and biomechanical properties using porous titanium reinforced by carbon nanotubes

Despite the well-known advantages of the titanium-based implant systems, they still lack an optimal balance between biofunctionality and mechanical strength, especially regarding the modulation of cellular response and a desired implant osseointegration. In this work, we fabricated a nanocomposite based on porous commercially pure grade 4 titanium (c.p. Ti) reinforced with carbon nanotubes (CNT) at 5% and 10% w/w, with the aim of obtaining a nanocomposite with lower stiffness compared to traditional titanium-based implants and with the mechanical strength and bioactivity owed by the CNT. Results obtained by scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy characterization showed that the CNT dispersed and incorporated into the porous c.p. Ti matrix. Interestingly, CNT were associated with a higher twining within neighbor Ti grains, which was indeed consistent with an increased in nano-hardness. Biological evaluation by MTT and Comet assay revealed that the nanocomposites did not induce genotoxicity and cytotoxicity on two different cells lines despite the presence of nickel at the surface. Accordingly, a purification step would be required before these CNT can be used for biomedical applications. Our results indicate that incorporation of CNT into porous c.p. Ti is a promising avenue to achieve an adequate balance between biofunctionality and mechanical strength in Ti-based scaffolds for tissue replacement. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 719-731, 2019.

Soft Lithography and Minimally Human Invasive Technique for Rapid Screening of Oral Biofilm Formation on New Microfabricated Dental Material Surfaces

Introduction

Microfabrication offers opportunities to study surface concepts focused to reduce bacterial adhesion on implants using human minimally invasive rapid screening (hMIRS). Wide information is available about cell/biomaterial interactions using eukaryotic and prokaryotic cells on surfaces of dental materials with different topographies, but studies using human being are still limited.

Objective

To evaluate a synergy of microfabrication and hMIRS to study the bacterial adhesion on micropatterned surfaces for dental materials.

Materials and Methods

Micropatterned and flat surfaces on biomedical PDMS disks were produced by soft lithography. The hMIRS approach was used to evaluate the total oral bacterial adhesion on PDMS surfaces placed in the oral cavity of five volunteers (the study was approved by the University Ethical Committee). After 24 h, the disks were analyzed using MTT assay and light microscopy.

Results

In the present pilot study, microwell structures were microfabricated on the PDMS surface via soft lithography with a spacing of 5 µm. Overall, bacterial adhesion did not significantly differ between the flat and micropatterned surfaces. However, individual analysis of two subjects showed greater bacterial adhesion on the micropatterned surfaces than on the flat surfaces.

Significance

Microfabrication and hMIRS might be implemented to study the cell/biomaterial interactions for dental materials.

Upregulation of osteogenesis of mesenchymal stem cells with virus-based thin films

A major aim of tissue engineering is to develop biomimetic scaffolding materials that can guide the proliferation, self-renewal and differentiation of multipotent stem cells into specific lineages. Cellular functions can be controlled by the interactions between cells and biomaterials. Therefore, the surface chemistry and topography of support materials play a pivotal role in modulating cell behaviors at many stages of cell growth and development. Due to their highly ordered structure and programmable surface chemistries, which provide unique topography as biomaterials, viral nanoparticles have been utilized as building blocks for targeted cell growth and differentiation. This review article discusses the fabrication of two-dimensional virus-based thin film on substrates and highlights the study of the effect of chemical and physical cues introduced by plant virus nanoparticle thin films on the promotion of osteogenic differentiation of BMSCs.

Fabrication of Plant Virus-Based Thin Films to Modulate the Osteogenic Differentiation of Mesenchymal Stem Cells

Stem cells can interact and respond to the extracellular nanoscale environment. Viral nanoparticles have been utilized as building blocks to control cell growth and differentiation. By integrating stem cell research and virus nanoparticle chemistry together, a systematic analysis of the effects of nanotopography on stem cell differentiation can be accomplished. The fabrication of thin films of the viral nanoparticles is particularly valuable for such studies. Here, we describe two methods to fabricate plant virus-based thin films and procedures to study the osteogenic differentiation of mesenchymal stem cells on plant virus-based substrates. The method makes use of wild-type tobacco mosaic virus (wt-TMV), RGD-modified TMV (TMV-RGD), turnip yellow mosaic virus (TYMV), cowpea mosaic virus (CPMV), turnip vein clearing virus (TVCV), and potato virus X (PVX) for development of bone tissue engineering biomaterials.

Nanotopography-based strategy for the precise manipulation of osteoimmunomodulation in bone regeneration

Immune cells play vital roles in regulating bone dynamics. Successful bone regeneration requires a favourable osteo-immune environment. The high plasticity and diversity of immune cells make it possible to manipulate the osteo-immune response of immune cells, thus modulating the osteoimmune environment and regulating bone regeneration. With the advancement in nanotechnology, nanotopographies with different controlled surface properties can be fabricated. On tuning the surface properties, the osteo-immune response can be precisely modulated. This highly tunable characteristic and immunomodulatory effects make nanotopography a promising strategy to precisely manipulate osteoimmunomdulation for bone tissue engineering applications. This review first summarises the effects of the immune response during bone healing to show the importance of regulating the immune response for the bone response. The plasticity of immune cells is then reviewed to provide rationales for manipulation of the osteoimmune response. Subsequently, we highlight the current types of nanotopographies applied in bone biomaterials and their fabrication techniques, and explain how these nanotopographies modulate the immune response and the possible underlying mechanisms. The effects of immune cells on nanotopography-mediated osteogenesis are emphasized, and we propose the concept of "nano-osteoimmunomodulation" to provide a valuable strategy for the development of nanotopographies with osteoimmunomodulatory properties that can precisely regulate bone dynamics.

Study on the regulation of focal adesions and cortical actin by matrix nanotopography in 3D environment

Matrix nanotopography plays an important role in regulating cell behaviors by providing spatial as well as mechanical cues for cells to sense. It has been proposed that nanoscale topography is possible to modulate the tensions which direct the formation of cytoskeleton and the organization of the membrane receptor within the cell, which in turn regulate intracellular mechanical and biochemical signaling. With current studies on this topic being performed mainly in 2D platforms, the question on how nanotopography can influence cell bahaviors in 3D environments has yet to be addressed. In this paper, we explored this question by placing cells in 3D hollow spherical polydimethylsiloxane scaffolds. After culturing rat embryonic fibroblast cells in two kinds of scaffold, one with smooth surface and the other with numerous nano-spikes, we observed that cells in the smooth scaffold have more anchoring sites and more focal adhesions than in the etched scaffold. Moreover, we found the presence of correlation between cortical actin, the important component for supporting cell attachment, and local cell geometry.

Electrically Controlled "Sponge Effect" of PEDOT:PSS Governs Membrane Potential and Cellular Growth

PSS is a highly conductive material with good thermal and chemical stability and enhanced biocompatibility that make it suitable for bioengineering applications. The electrical control of the oxidation state of PEDOT:PSS films allows modulation of peculiar physical and chemical properties of the material, such as topography, wettability, and conductivity, and thus offers a possible route for controlling cellular behavior. Through the use of (i) the electrophysiological response of the plasma membrane as a biosensor of the ionic availability; (ii) relative abundance around the cells via X-ray spectroscopy; and (iii) atomic force microscopy to monitor PEDOT:PSS film thickness relative to its oxidation state, we demonstrate that redox processes confer to PEDOT:PSS the property to modify the ionic environment at the film-liquid interface through a "sponge-like" effect on ions. Finally, we show how this property offers the capability to electrically control central cellular properties such as viability, substrate adhesion, and growth, paving the way for novel bioelectronics and biotechnological applications.

Biophysical Regulation of Cell Behavior-Cross Talk between Substrate Stiffness and Nanotopography

The stiffness and nanotopographical characteristics of the extracellular matrix (ECM) influence numerous developmental, physiological, and pathological processes in vivo. These biophysical cues have therefore been applied to modulate almost all aspects of cell behavior, from cell adhesion and spreading to proliferation and differentiation. Delineation of the biophysical modulation of cell behavior is critical to the rational design of new biomaterials, implants, and medical devices. The effects of stiffness and topographical cues on cell behavior have previously been reviewed, respectively; however, the interwoven effects of stiffness and nanotopographical cues on cell behavior have not been well described, despite similarities in phenotypic manifestations. Herein, we first review the effects of substrate stiffness and nanotopography on cell behavior, and then focus on intracellular transmission of the biophysical signals from integrins to nucleus. Attempts are made to connect extracellular regulation of cell behavior with the biophysical cues. We then discuss the challenges in dissecting the biophysical regulation of cell behavior and in translating the mechanistic understanding of these cues to tissue engineering and regenerative medicine.

Stretchable Electrochemical Sensor for Real-Time Monitoring of Cells and Tissues

Stretchable electrochemical sensors are conceivably a powerful technique that provides important chemical information to unravel elastic and curvilinear living body. However, no breakthrough was made in stretchable electrochemical device for biological detection. Herein, we synthesized Au nanotubes (NTs) with large aspect ratio to construct an effective stretchable electrochemical sensor. Interlacing network of Au NTs endows the sensor with desirable stability against mechanical deformation, and Au nanostructure provides excellent electrochemical performance and biocompatibility. This allows for the first time, real-time electrochemical monitoring of mechanically sensitive cells on the sensor both in their stretching-free and stretching states as well as sensing of the inner lining of blood vessels. The results demonstrate the great potential of this sensor in electrochemical detection of living body, opening a new window for stretchable electrochemical sensor in biological exploration.

Harmonizing HeLa cell cytoskeleton behavior by multi-Ti oxide phased nanostructure synthesized through ultrashort pulsed laser

Knowledge about cancer cell behavior on heterogeneous nanostructures is relevant for developing a distinct biomaterial that can actuate cancer cells. In this manuscript, we have demonstrated a harmonized approach of forming multi Ti-oxide phases in a nanostructure (MTOP nanostructure) for its unique cancer cell controlling behavior.Conventionally, single phases of TiO2 are used for targeted therapy and as drug carrier systems.In this research, we have shown a biomaterial that can control HeLa cells diligently using a combination of TiO, Ti3O and TiO2 phases when compared to fibroblast (NIH3T3) cells.MTOP-nanostructures are generated by varying the ionization energy in the vapor plume of the ultrashort pulse laser; this interaction with the material allows accurate tuning and composition of phases within the nanostructure. In addition, the lattice spacing of MTOP-nanostructures was analyzed as shown by HR-TEM investigations. An FESEM investigation of MTOP-nanostructures revealed a greater reduction of HeLa cells relative to fibroblast cells. Altered cell adhesion was followed by modulation of HeLa cell architecture with a significant reduction of actin stress fibers.The intricate combination of MTOP-nanostructures renders a biomaterial that can precisely alter HeLa cell but not fibroblast cell behavior, filling a void in the research for a biomaterial to modulate cancer cell behavior.

Virus Nanoparticles Mediated Osteogenic Differentiation of Bone Derived Mesenchymal Stem Cells

There are few methodologies that allow manipulating a biomaterial surface at nanometer scale, which controllably influence different cellular functions. In this study, virus nanoparticles with different structural features are selected to prepare 2D substrates with defined nanoscale topographies and the cellular responses are investigated. It is demonstrated that the viral nanoparticle based substrates could accelerate and enhance osteogenesis of bone derived mesenchymal stem cells as indicated by the upregulation of osteogenic markers, including bone morphogenetic protein-2, osteocalcin, and osteopontin, at both gene and protein expression levels. Moreover, alkaline phosphatase activity and calcium mineralization, both indicators for a -successful bone formation, are also increased in cells grown on these nanoscale possessed substrates. These discoveries and developments present a new paradigm for nanoscale engineering of a biomaterial surface.

Osteoclastogenesis/osteoblastogenesis using human bone marrow-derived cocultures on nanotopographical polymer surfaces

BACKGROUND

Optimised nanotopography with controlled disorder (NSQ50) has been shown to stimulate osteogenesis and new bone formation in vitro. Following osteointegration the implant interface must undergo constant remodeling without inducing immune response.

AIM

We aimed to assess the effect of nanotopography on bone remodelling using osteoclast and osteoblast cocultures.

MATERIALS & METHODS

We developed a novel osteoblast/osteoclast coculture using solely human bone marrow derived mesenchymal and hematopeotic progenitor cells without extraneous supplementation. The coculture was been applied to NSQ50 or flat control polycarbonate substrates and assessed using immunohistochemical and immunofluorescent microscopy, scanning electron microscopy and quantitative reverse-transcription PCR methods.

RESULTS

These confirm the presence of mature osteoclasts, osteoblasts and bone formation in coculture. Osteoblast differentiation increased on NSQ50, with no significant difference in osteoclast differentiation.

CONCLUSION

Controlled disorder nanotopography appears to be selectively bioactive. We recommend this coculture method to be a better in vitro approximation of the osseous environment encountered by implants.

Osseointegration improvement by plasma electrolytic oxidation of modified titanium alloys surfaces

Titanium (Ti) is a material frequently used in orthopedic applications, due to its good mechanical properties and high corrosion resistance. However, formation of a non-adherent fibrous tissue between material and bone drastically could affect the osseointegration process and, therefore, the mechanical stability of the implant. Modifications of topography and configuration of the tissue/material interface is one of the mechanisms to improve that process by manipulating parameters such as morphology and roughness. There are different techniques that can be used to modify the titanium surface; plasma electrolytic oxidation (PEO) is one of those alternatives, which consists of obtaining porous anodic coatings by controlling parameters such as voltage, current, anodizing solution and time of the reaction. From all of the above factors, and based on previous studies that demonstrated that bone cells sense substrates features to grow new tissue, in this work commercially pure Ti (c.p Ti) and Ti6Al4V alloy samples were modified at their surface by PEO in different anodizing solutions composed of H2SO4 and H3PO4 mixtures. Treated surfaces were characterized and used as platforms to grow osteoblasts; subsequently, cell behavior parameters like adhesion, proliferation and differentiation were also studied. Although the results showed no significant differences in proliferation, differentiation and cell biological activity, overall results showed an important influence of topography of the modified surfaces compared with polished untreated surfaces. Finally, this study offers an alternative protocol to modify surfaces of Ti and their alloys in a controlled and reproducible way in which biocompatibility of the material is not compromised and osseointegration would be improved.

Nanotopographical Surfaces for Stem Cell Fate Control: Engineering Mechanobiology from the Bottom

During embryogenesis and tissue maintenance and repair in an adult organism, a myriad of stem cells are regulated by their surrounding extracellular matrix (ECM) enriched with tissue/organ-specific nanoscale topographical cues to adopt different fates and functions. Attributed to their capability of self-renewal and differentiation into most types of somatic cells, stem cells also hold tremendous promise for regenerative medicine and drug screening. However, a major challenge remains as to achieve fate control of stem cells in vitro with high specificity and yield. Recent exciting advances in nanotechnology and materials science have enabled versatile, robust, and large-scale stem cell engineering in vitro through developments of synthetic nanotopographical surfaces mimicking topological features of stem cell niches. In addition to generating new insights for stem cell biology and embryonic development, this effort opens up unlimited opportunities for innovations in stem cell-based applications. This review is therefore to provide a summary of recent progress along this research direction, with perspectives focusing on emerging methods for generating nanotopographical surfaces and their applications in stem cell research. Furthermore, we provide a review of classical as well as emerging cellular mechano-sensing and -transduction mechanisms underlying stem cell nanotopography sensitivity and also give some hypotheses in regard to how a multitude of signaling events in cellular mechanotransduction may converge and be integrated into core pathways controlling stem cell fate in response to extracellular nanotopography.

Osteogenic response of human mesenchymal stem cells to well-defined nanoscale topography in vitro

BACKGROUND

Patterning medical devices at the nanoscale level enables the manipulation of cell behavior and tissue regeneration, with topographic features recognized as playing a significant role in the osseointegration of implantable devices.

METHODS

In this study, we assessed the ability of titanium-coated hemisphere-like topographic nanostructures of different sizes (approximately 50, 100, and 200 nm) to influence the morphology, proliferation, and osteogenic differentiation of human mesenchymal stem cells (hMSCs).

RESULTS

We found that the proliferation and osteogenic differentiation of hMSCs was influenced by the size of the underlying structures, suggesting that size variations in topographic features at the nanoscale level, independently of chemistry, can be exploited to control hMSC behavior in a size-dependent fashion.

CONCLUSION

Our studies demonstrate that colloidal lithography, in combination with coating technologies, can be exploited to investigate the cell response to well defined nanoscale topography and to develop next-generation surfaces that guide tissue regeneration and promote implant integration.

Synthetic small intestinal scaffolds for improved studies of intestinal differentiation

In vitro intestinal models can provide new insights into small intestinal function, including cellular growth and proliferation mechanisms, drug absorption capabilities, and host-microbial interactions. These models are typically formed with cells cultured on 2D scaffolds or transwell inserts, but it is widely understood that epithelial cells cultured in 3D environments exhibit different phenotypes that are more reflective of native tissue. Our focus was to develop a porous, synthetic 3D tissue scaffold with villous features that could support the culture of epithelial cell types to mimic the natural microenvironment of the small intestine. We demonstrated that our scaffold could support the co-culture of Caco-2 cells with a mucus-producing cell line, HT29-MTX, as well as small intestinal crypts from mice for extended periods. By recreating the surface topography with accurately sized intestinal villi, we enable cellular differentiation along the villous axis in a similar manner to native intestines. In addition, we show that the biochemical microenvironments of the intestine can be further simulated via a combination of apical and basolateral feeding of intestinal cell types cultured on the 3D models.

Topographically targeted osteogenesis of mesenchymal stem cells stimulated by inclusion bodies attached to polycaprolactone surfaces

AIM

Bacterial inclusion bodies (IBs) are nanostructured (submicron), pseudospherical proteinaceous particles produced in recombinant bacteria resulting from ordered protein aggregation. Being mechanically stable, several physicochemical and biological properties of IBs can be tuned by appropriate selection of the producer strain and of culture conditions. It has been previously shown that IBs favor cell adhesion and surface colonization by mammalian cell lines upon decoration on materials surfaces, but how these biomaterials could influence the behavior of mesenchymal stem cells remains to be explored.

MATERIALS & METHODS

Here, the authors vary topography, stiffness and wettability using the IBs to decorate polycaprolactone surfaces on which mesenchymal stem cells are cultured.

RESULTS

The authors show that these topographies can be used to specifically target osteogenesis from mesenchymal stem cells, and through metabolomics, they show that the cells have increased energy demand during this bone-related differentiation.

CONCLUSION

IBs as topographies can be used not only to direct cell proliferation but also to target differentiation of mesenchymal stem cells.

In vitro and in vivo response to nanotopographically-modified surfaces of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and polycaprolactone

Colloidal lithography and embossing master are new techniques of producing nanotopography, which have been recently applied to improve tissue response to biomaterials by modifying the surface topography on a nano-scale dimension. A natural polyester (Biopol), 8% 3-hydroxyvalerate-component (D400G) and a conventional biodegradable polycaprolactone (PCL) were studied, both nanostructured and native forms, in vitro and in vivo. Nanopits (100-nm deep, 120-nm diameter) on the D400G surface were produced by the embossing master technique (Nano-D400G), while nanocylinders (160-nm height, 100-nm diameter) on the PCL surface were made by the colloidal lithography technique (Nano-PCL). L929 fibroblasts were seeded on polyesters, and cell proliferation, cytotoxic effect, synthetic and cytokine production were assessed after 72 h and 7 days. Then, under general anesthesia, 3 Sprague-Dawley rats received dorsal subcutaneous implants of nanostructured and native polyesters. At 1, 4 and 12 weeks the animals were pharmacologically euthanized and implants with surrounding tissue studied histologically and histomorphometrically. In vitro results showed significant differences between D400G and PCL in Interleukin-6 production at 72 h. At 7 days, significant (P < 0.05) differences were found in Interleukin-1beta and tumor necrosis factor-alpha release for Nano-PCL when compared to Nano-D400G, and for PCL in comparison with D400G. In vivo results indicated that Nano-D400G implants produced a greater extent of inflammatory tissue than Nano-PCL at 4 weeks. The highest vascular densities were observed for Nano-PCL at 4 and 12 weeks. Chemical and topographical factors seem to be responsible for the different behaviour, and from the obtained results a prevalence of chemistry on in vitro data and nanotopography on soft tissue response in vivo are hypothesized, although more detailed investigations are necessary in this field.

Effects of UV photofunctionalization on the nanotopography enhanced initial bioactivity of titanium

This study addresses the control of the biological capabilities of titanium through specific nanosurface features and its potential modulation by UV photofunctionalization. Rat bone marrow derived osteoblasts were cultured on titanium disks with micropits alone, micropits with 100 nm nodules, micropits with 300 nm nodules, or micropits with 500 nm nodules, with or without UV treatment. After a 24 h incubation protein adsorption, as well as the attachment, retention, and spread of osteoblasts were examined in correlation with the topographical parameters of the titanium substrates. Each of the biological events was governed by a different set of multiple surface topographical factors with a distinctive pattern of regulation. For instance, without UV treatment the protein adsorption and cell attachment capability of titanium substrates increased linearly with increasing average roughness (Ra) and surface area of titanium disks, but increased polynomially with increasing nanonodule diameter. The cell retention capability increased polynomially with increasing nanonodular diameter and Ra, but increased linearly with increasing surface area. Consequently, the micropits with 300 nm nodules created the most favorable environment for this initial osteoblast behavior and response. UV treatment of the nanonodular titanium surfaces resulted in considerable enhancement of all biological events. However, the pattern of UV-mediated enhancement was disproportionate; exponential and overriding effects were observed depending upon the biological event and topographical parameter. As an example of overriding enhancement, the cell retention capability, which fluctuated with changes in various topographical parameters, became invariably high after UV treatment. The present data provide a basis for understanding how to optimize nanostructures to create titanium surfaces with increased biological capabilities and uncover a novel advantage of UV photofunctionalization of titanium substrates that synergistically increases its nanotopography enhanced biological capabilities whereby most of the initial biological events of osteoblasts were overwhelmingly enhanced beyond a simple proportional increase.

Quantitative analysis of the combined effect of substrate rigidity and topographic guidance on cell morphology

Live cells are exquisitely sensitive to both the substratum rigidity and texture. To explore cell responses to both these types of inputs in a precisely controlled fashion, we analyzed the responses of Chinese hamster ovary (CHO) cells to nanotopographically defined substrata of different rigidities, ranging from 1.8 MPa to 1.1 GPa. Parallel arrays of nanogrooves (800-nm width, 800-nm space, and 800-nm depth) on polyurethane (PU)-based material surfaces were fabricated by UV-assisted capillary force lithography (CFL) over an area of 5 mm × 3 mm. We observed dramatic morphological responses of CHO cells, evident in their elongation and polarization along the nanogrooves direction. The cells were progressively more spread and elongated as the substratum rigidity increased, in an integrin β1 dependent manner. However, the degree of orientation was independent of substratum rigidity, suggesting that the cell shape is primarily determined by the topographical cues.

Biomimetic microtopography to enhance osteogenesis in vitro

Biomimicry is being used in the next generation of biomaterials. Tuning material surface features such as chemistry, stiffness and topography allow the control of cell adhesion, proliferation, growth and differentiation. Here, microtopographical features with nanoscale depths, similar in scale to osteoclast resorption pits, were used to promote in vitro bone formation in basal medium. Primary human osteoblasts were used to represent an orthopaedically relevant cell type and analysis of adhesions, cytoskeleton, osteospecific proteins (phospho-Runx2 and osteopontin) and mineralisation (alizarin red) was performed. The results further demonstrate the potential for biomimicry in material design and show that the osteoblast response can be tuned from changes in feature size.

Synergistic effects of UV photofunctionalization and micro-nano hybrid topography on the biological properties of titanium

Titanium surfaces with micro-nano hybrid topography (nanoscale nodules in microscale pits) have been recently demonstrated to show higher biological capability than those with microtopography alone. On the other hand, UV treatment of titanium surfaces, which is called UV photofunctionalization, has recently been introduced to substantially increase the biological capability and osteoconductivity of titanium surfaces. However, synergistic effects of these two advanced surface modification technologies and regulatory factors to potentially modulate the mutual effects have never been addressed. In this study, utilization of a recently discovered controllable self-assembly of TiO(2) nanonodules has enabled the exploration of the relative contribution of different sizes of nanostructures to determine the biological capability of titanium surfaces and their relative responsiveness to UV photofunctionalization. Rat bone marrow-derived osteoblasts were cultured on titanium disks with either micropits alone, micropits with 100-nm nodules, micropits with 300-nm nodules, or micropits with 500-nm nodules, with or without UV treatment. Although UV treatment increased the attachment, spread, proliferation, and mineralization of these cells on all titanium surfaces, these effects were more accentuated (3-5 times) on nanonodular surfaces than on surfaces with micropits alone and were disproportionate depending on nanonodule sizes. For instance, on UV-treated micro-nano hybrid surfaces, cell attachment correlated with nanonodule sizes in a quadratic approximation with its peak for 300-nm nodules followed by a decline for 500-nm nodules, while cell attachment exponentially correlated with surface roughness with its plateau achieved for 300-nm nodules without a subsequent decline. Moreover, cell attachment increased in a linear correlation with the surface area, while no significant effect of the inter-irregularities space or degree of hydrophilicity was observed on cell attachment. These results suggest that the effect of UV photofunctionalization can be multiplied on micro-nano hybrid titanium surfaces compared with the surfaces with micropits alone. This multiplication is disproportionately regulated by a selected set of topographical parameters of the titanium surfaces. Among the nanonodules tested in this study, 300-nm nodules seemed to create the most effective morphological environment for responding to UV photofunctionalization. The data provide a systematic platform to effectively optimize nanostructures on titanium surfaces in order to enhance their biological capability as well as their susceptibility to UV photofunctionalization.

Human macrophage adhesion on polysaccharide patterned surfaces

Despite many advances in designing biocompatible materials, inflammation remains a problem in medical devices and implants. We report two methods, microcontact printing and photodegradation by UV exposure, to pattern dextran and hyaluronic acid on glass, as well as demonstrate their utility for use as an anti-inflammatory biomaterial. The dextran/glass patterned surface can be further modified by grafting hyaluronic acid to glass, creating a binary polysaccharide patterned surface. We used two geometries, 90 µm squares and 22 µm stripes, to study the human macrophage (THP-1) adhesion on the patterned surfaces containing dextran, hyaluronic acid and the binary pattern. The results indicate that a majority of the macrophages are non-adherent on hyaluronic acid for three day culture. The ranking of surfaces according to macrophage adhesion is 3-aminopropyl triethoxysilane-modified glass culture dish, dextranized surfaces, glass, and hyaluronic acid-modified surfaces. On the binary pattern of dextran and hyaluronic acid, macrophages preferentially attach and adhere to the dextranized area. Patterned surfaces provide an excellent platform for mimicking the complexity of the glycocalyx and investigating the interface between this surface and cells. This binary polysaccharide pattern also offers a new route to address anti-inflammatory potential of surface coatings on biomaterials in a high through-put fashion.

Cell interaction with nanopatterned surface of implants

Metals such as titanium and alloys are commonly used for manufacturing orthopedic and dental implants because their surface properties provide a biocompatible interface with peri-implant tissues. Strategies for modifying the nature of this interface frequently involve changes to the surface at the nanometer level, thereby affecting protein adsorption, cell-substrate interactions and tissue development. Recent methods to control these biological interactions at the nanometer scale on the surface of implants are reviewed. Future strategies to control peri-implant tissue healing are also discussed.

Nanoscale surfacing for regenerative medicine

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

Relative influence of surface topography and surface chemistry on cell response to bone implant materials. Part 2: Biological aspects

A current medical challenge is the replacement of tissue which can be thought of in terms of bone tissue engineering approaches. The key problem in bone tissue engineering lies in associating bone stem cells with material supports or scaffolds that can be implanted in a patient. Beside bone tissue engineering approaches, these types of materials are used daily in orthopaedics and dental practice as permanent or transitory implants such as ceramic bone filling materials or metallic prostheses. Consequently, it is essential to better understand how bone cells interact with materials. For several years, the current authors and others have developed in vitro studies in order to elucidate the mechanisms underlying the response of human bone cells to implant surfaces. This paper reviews the current state of knowledge and proposes future directions for research in this domain.

The interaction of cells and bacteria with surfaces structured at the nanometre scale

The current development of nanobiotechnologies requires a better understanding of cell-surface interactions on the nanometre scale. Recently, advances in nanoscale patterning and detection have allowed the fabrication of appropriate substrates and the study of cell-substrate interactions. In this review we discuss the methods currently available for nanoscale patterning and their merits, as well as techniques for controlling the surface chemistry of materials at the nanoscale without changing the nanotopography and the possibility of truly characterizing the surface chemistry at the nanoscale. We then discuss the current knowledge of how a cell can interact with a substrate at the nanoscale and the effect of size, morphology, organization and separation of nanofeatures on cell response. Moreover, cell-substrate interactions are mediated by the presence of proteins adsorbed from biological fluids on the substrate. Many questions remain on the effect of nanotopography on protein adsorption. We review papers related to this point. As all these parameters have an influence on cell response, it is important to develop specific studies to point out their relative influence, as well as the biological mechanisms underlying cell responses to nanotopography. This will be the basis for future research in this field. An important topic in tissue engineering is the effect of nanoscale topography on bacteria, since cells have to compete with bacteria in many environments. The limited current knowledge of this topic is also discussed in the light of using topography to encourage cell adhesion while limiting bacterial adhesion. We also discuss current and prospective applications of cell-surface interactions on the nanoscale. Finally, based on questions raised previously that remain to be solved in the field, we propose future directions of research in materials science to help elucidate the relative influence of the physical and chemical aspects of nanotopography on bacteria and cell response with the aim of contributing to the development of nanobiotechnologies.

Nanotopographical control of stem cell differentiation

Stem cells have the capacity to differentiate into various lineages, and the ability to reliably direct stem cell fate determination would have tremendous potential for basic research and clinical therapy. Nanotopography provides a useful tool for guiding differentiation, as the features are more durable than surface chemistry and can be modified in size and shape to suit the desired application. In this paper, nanotopography is examined as a means to guide differentiation, and its application is described in the context of different subsets of stem cells, with a particular focus on skeletal (mesenchymal) stem cells. To address the mechanistic basis underlying the topographical effects on stem cells, the likely contributions of indirect (biochemical signal-mediated) and direct (force-mediated) mechanotransduction are discussed. Data from proteomic research is also outlined in relation to topography-mediated fate determination, as this approach provides insight into the global molecular changes at the level of the functional effectors.

Methodologies for assessing local surface texture features that are relevant to cell attachment

In this paper, we describe techniques for extracting features from surface topography data, gathered by a 3D-microscopy system, on a length scale that is relevant for cell attachment. The feature parameters considered include standard surface roughness parameters applied to the complete surface as well as new feature parameters designed to quantify local variations in surface topography potentially influencing cell behaviour. Methodologies have been developed both to determine the degree of homogeneity or isotropy of a surface and to compare the topographies of different samples. The approaches followed include wavelet decomposition and linear and nonlinear filtering techniques. The analysis has been used to investigate the correlation between osteoblast cell attachment and structural features of titanium-coated surfaces representative of orthopaedic implants. The results confirm that there is a discernible correlation between cell orientation and the underlying surface lay.

Nanotopographical modification: a regulator of cellular function through focal adhesions

As materials technology and the field of biomedical engineering advances, the role of cellular mechanisms, in particular adhesive interactions with implantable devices, becomes more relevant in both research and clinical practice. A key tenet of medical device design has evolved from the exquisite ability of biological systems to respond to topographical features or chemical stimuli, a process that has led to the development of next-generation biomaterials for a wide variety of clinical disorders. In vitro studies have identified nanoscale features as potent modulators of cellular behavior through the onset of focal adhesion formation. The focus of this review is on the recent developments concerning the role of nanoscale structures on integrin-mediated adhesion and cellular function with an emphasis on the generation of medical constructs with regenerative applications.

FROM THE CLINICAL EDITOR

In this review, recent developments related to the role of nanoscale structures on integrin-mediated adhesion and cellular function is discussed, with an emphasis on regenerative applications.

The effect of topography of polymer surfaces on platelet adhesion

In this study, the effect of surface topography on fibrinogen and platelet adsorption was investigated. High aspect ratio surface features, in the submicron to nanometer range, were constructed on the poly- (lactic-co-glycolic-acid) (PLGA) films. The topographic surfaces were fabricated by solvent-mediated polymer casting on a master template. Fibrinogen adsorption and platelets adhesion on these topographic surfaces were quantified by enzyme linked immunosorbent assay (ELISA) and lactate dehydrogenase (LDH) assay respectively, while the activation of platelets was quantified by flow cytometric analysis using fluorescein isothiocyanate (FITC) tagging. The lowest fibrinogen adsorption amount and platelet activity was observed on surfaces with specific topographical features in the submicron range with a significant reduction in adhesion when compared to the pristine PLGA films. The topographical parameters found to induce low levels of fibrinogen adsorption and platelet response were high aspect ratio structures (>3:1) with reduced interspacing (<200 nm) or high density. The results signify that topographical manipulation of thrombogenic surfaces of biodegradable polymers is a feasible approach for reducing their thrombogenicity.

Nanoscale topography of nanocrystalline diamonds promotes differentiation of osteoblasts

The excellent mechanical, tribological and biochemical properties of diamond coatings are promising for improving orthopedic or stomatology implants. A crucial prerequisite for such applications is an understanding and control of the biological response of the diamond coatings. This study concentrates on the correlation of diamond surface properties with osteoblast behavior. Nanocrystalline diamond (NCD) films (grain size up to 200 nm, surface roughness 20 nm) were deposited on silicon substrates of varying roughnesses (1, 270 and 500 nm) and treated by oxygen plasma to generate a hydrophilic surface. Atomic force microscopy was used for topographical characterization of the films. As a reference surface, tissue culture polystyrene (PS) was used. Scanning electron microscopy and immunofluorescence staining was used to visualize cell morphological features as a function of culture time. Metabolic activity, alkaline phosphatase activity, and calcium and phosphate deposition was also monitored. The results show an enhanced osteoblast adhesion as well as increased differentiation (raised alkaline phosphatase activity and mineral deposition) on NCD surfaces (most significantly on RMS 20 nm) compared to PS. This is attributed mainly to the specific surface topography as well as to the biocompatible properties of diamond. Hence the controlled (topographically structured) diamond coating of various substrates is promising for preparation of better implants, which offer faster colonization by specific cells as well as longer-term stability.

A Novel Approach for Automated Analysis of Cell Attachment and Spreading Based on Backscattered Electron Imaging by Scanning Electron Microscopy

The development of new materials for biological application requires in vitro testing of cell/surface interactions. Cell adhesion and spreading are difficult to quantify as most materials are non-transparent and transmission microscopy cannot be used. Contrast in reflection microscopy is rather poor. We propose an alternative method for the automated screening of cell attachment and spreading using backscattered electron imaging of scanning electron microscopy. The enhanced cell contrast permits study of cell/material interactions by little differences between cells and material.

The use of nanoscale topography to modulate the dynamics of adhesion formation in primary osteoblasts and ERK/MAPK signalling in STRO-1+ enriched skeletal stem cells

The physiochemical characteristics of a material with in vivo applications are critical for the clinical success of the implant and regulate both cellular adhesion and differentiated cellular function. Topographical modification of an orthopaedic implant may be a viable method to guide tissue integration and has been shown in vitro to dramatically influence osteogenesis, inhibit bone resorption and regulate integrin mediated cell adhesion. Integrins function as force dependant mechanotransducers, acting via the actin cytoskeleton to translate tension applied at the tissue level to changes in cellular function via intricate signalling pathways. In particular the ERK/MAPK signalling cascade is a known regulator of osteospecific differentiation and function. Here we investigate the effects of nanoscale pits and grooves on focal adhesion formation in human osteoblasts (HOBs) and the ERK/MAPK signalling pathway in mesenchymal populations. Nanopit arrays disrupted adhesion formation and cellular spreading in HOBs and impaired osteospecific differentiation in skeletal stem cells. HOBs cultured on 10 microm wide groove/ridge arrays formed significantly less focal adhesions than cells cultured on planar substrates and displayed negligible differentiation along the osteospecific lineage, undergoing up-regulations in the expression of adipospecific genes. Conversely, osteospecific function was correlated to increased integrin mediated adhesion formation and cellular spreading as noted in HOBS cultured on 100 microm wide groove arrays. Here osteospecific differentiation and function was linked to focal adhesion growth and FAK mediated activation of the ERK/MAPK signalling pathway in mesenchymal populations.

A hierarchical response of cells to perpendicular micro- and nanometric textural cues

In this paper, we report on the influence of shallow micro- and nanopatterned substrata on the attachment and behavior of a human fibroblast [human telomerase transfected immortalized (hTERT)] cells. We identify a hierarchy of textural guidance cues with respect to cell alignment on these substrates. Cells were seeded and cultured for 48 h on silicon substrates patterned with two linear textures overlaid at 90 degrees, both with 24 microm pitch: a micrograting and a nanopattern of rows of 140- nm-diameter pits arranged in a rectangular array with 300 nm centre-to-centre spacing. The cell response to these textures was shown to be highly dependent on textural feature dimensions. We show that cells align to the stripes of nanopits. Stripes of 30-nm deep nanopits were also shown to elicit a stronger response from cells than 160-nm deep nanopits.

A biomimetic hierarchical scaffold: natural growth of nanotitanates on three-dimensional microporous Ti-based metals

Nanophase materials are promising alternative implant materials in tissue engineering. Here we report for the first time the large-scale direct growth of nanostructured bioactive titanates on three-dimensional (3D) microporous Ti-based metal (NiTi and Ti) scaffolds via a facile low temperature hydrothermal treatment. The nanostructured titanates show characteristics of 1D nanobelts/nanowires on a nanoskeleton layer. Besides resembling cancelous bone structure on the micro/macroscale, the 1D nanostructured titanate on the exposed surface is similar to the lowest level of hierarchical organization of collagen and hydroxyapatite. The resulting surface displays superhydrophilicity and favors deposition of hydroxyapatite and accelerates cell attachment and proliferation. The remarkable simplicity of this process makes it widely accessible as an enabling technique for applications from engineering materials treatment including energy-absorption materials and pollution-treatment materials to biotechnology.

Genomic expression of mesenchymal stem cells to altered nanoscale topographies

The understanding of cellular response to the shape of their environment would be of benefit in the development of artificial extracellular environments for potential use in the production of biomimetic surfaces. Specifically, the understanding of how cues from the extracellular environment can be used to understand stem cell differentiation would be of special interest in regenerative medicine. In this paper, the genetic profile of mesenchymal stem cells cultured on two osteogenic nanoscale topographies (pitted surface versus raised islands) are compared with cells treated with dexamethasone, a corticosteroid routinely used to stimulate bone formation in culture from mesenchymal stem cells, using 19k gene microarrays as well as 101 gene arrays specific for osteoblast and endothelial biology. The current studies show that by altering the shape of the matrix a cell response (genomic profile) similar to that achieved with chemical stimulation can be elicited. Here, we show that bone formation can be achieved with efficiency similar to that of dexamethasone with the added benefit that endothelial cell development is not inhibited. We further show that the mechanism of action of the topographies and dexamethasone differs. This could have an implication for tissue engineering in which a simultaneous, targeted, development of a tissue, such as bone, without the suppression of angiogenesis to supply nutrients to the new tissue is required. The results further demonstrate that perhaps the shape of the extracellular matrix is critical to tissue development.

Nanoscale surface topography enhances cell adhesion and gene expression of madine darby canine kidney cells

Substrate topography is one of the key factors that influence cell behavior, such as cell attachment, adhesion, proliferation and differentiation. In the present work, nanostructures were produced on polystyrene Petri dish by polarized laser irradiation with the wavelength of 266 nm and the energy of 3.0 mJ/cm2. Cell adhesion, growth and gene expression of Madine darby canine kidney (MDCK) cells cultured on smooth and nanogrooved substrates were investigated. The results indicated that cells preferred to adhere and grow on nanogrooved substrate. The distribution of cell cycle for cells on smooth substrates was different from that on nanogrooved substrate. The percentage of G1 phase cells on nanogrooved substrate (48.6 +/- 1.4%) was lower than that on smooth substrate (57.6 +/- 4.4%), while the percentage of cells on nanogrooved substrate in S (30.2 +/- 0.5%) and G2/M (21.2 +/- 1.1%) phase was higher than those on smooth substrate (25.1 +/- 1.5% and 17.3 +/- 3.3%, respectively). Moreover, the gene expression of cyclin D1 and keratin 18, which was examined by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR), was significantly enhanced by nanogrooves, with an increase of cyclin D1 mRNA by 98% and an increase of keratin 18 mRNA by 75%. In conclusion, the nanogrooved surface features on polystyrene could alter cell cycle and enhance gene expression of cyclin D1 and keratin 18 in MDCK cells, which partly explained the increased cell adhesion and growth on nanogrooved substrate.