Three-dimensional extracellular matrix textured biomaterials

Preparation and properties of a 3D printed nHA/PLA bone tissue engineering scaffold loaded with a β-CD-CHX combined dECM hydrogel

Jaw defects, which can result from a multitude of causes, significantly affect the physical well-being and psychological health of patients. The repair of these infected defects presents a formidable challenge in the clinical and research fields, owing to their intricate and diverse nature. This study aims to develop a personalized bone tissue engineering scaffold that synergistically offers antibacterial and osteogenic properties for treating infected maxillary defects. This study engineered a novel temperature-sensitive, sustained-release hydrogel by amalgamating β-cyclodextrin (β-CD) with chlorhexidine (CHX) and a decellularized extracellular matrix (dECM). This hydrogel was further integrated with a polylactic acid (PLA)-nano hydroxyapatite (nHA) scaffold, fabricated through 3D printing, to form a multifaceted composite scaffold (nHA/PLA/dECM/β-CD-CHX). Drug release assays revealed that this composite scaffold ensures prolonged and sustained release. Bacteriological studies confirmed that the β-CD-CHX loaded scaffold exhibits persistent antibacterial efficacy, thus effectively inhibiting bacterial growth. Moreover, the scaffold demonstrated robust mechanical strength. Cellular assays validated its superior biocompatibility, attributed to dECM and nHA components, significantly enhancing the proliferation, adhesion, and osteogenic differentiation of osteogenic precursor cells (MC3T3-E1). Consequently, the nHA/PLA/dECM/β-CD-CHX composite scaffold, synthesized via 3D printing technology, shows promise in inducing bone regeneration, preventing infection, and facilitating the repair of jaw defects, positioning itself as a potential breakthrough in bone tissue engineering.

Controllable synthesis of biomimetic nano/submicro-fibrous tubes for potential small-diameter vascular grafts

Mimicking the morphological structure of native blood vessels is critical for the development of vascular grafts. Herein, small-diameter composite vascular grafts that integrate the nanofibrous bacterial cellulose (BC) and submicrofibrous cellulose acetate (CA) were fabricated via a combined electrospinning and step-by-step in situ biosynthesis. Scanning electron microscopy (SEM) observation shows the nano/submicro-fibrous morphology and well-interconnected porous structure of the BC/CA grafts. It is found that the BC/CA graft with a suitable BC content demonstrates lower potential of thrombus formation and enhanced endothelialization as compared to the BC and CA counterparts. Western blotting and RT-qPCR results suggest that the BC/CA-2 graft promotes endothelialization by improving expressions of genes vWF-1 and CD31 and protein CD31. The in vivo tests demonstrate much lower inflammatory response to the BC/CA graft. These results suggest that the BC/CA graft shows a great potential as an artificial graft for rapid formation of an endothelial cell monolayer.

Transduction of cell and matrix geometric cues by the actin cytoskeleton

Engineered culture substrates have proven invaluable for investigating the role of cell and extracellular matrix geometry in governing cell behavior. While the mechanisms relating geometry to phenotype are complex, it is clear that the actin cytoskeleton plays a key role in integrating geometric inputs and transducing these cues into intracellular signals that drive downstream biology. Here, we review recent progress in elucidating the role of the cell and matrix geometry in regulating actin cytoskeletal architecture and mechanics. We address new developments in traditional two-dimensional culture paradigms and discuss efforts to extend these advances to three-dimensional systems, ranging from nanotextured surfaces to microtopographical systems (e.g. channels) to fully three-dimensional matrices.

Direct cell imprint lithography in superconductive carbon black polymer composites: process optimization, characterization and in vitro toxicity analysis

Cell imprint lithography (CIL) or cell replication plays a vital role in fields like biomimetic smart culture substrates, bone tissue engineering, cell guiding, cell adhesion, tissue engineering, cell microenvironments, tissue microenvironments, cell research, drug delivery, diagnostics, therapeutics and many other applications. Herein we report a new formulation of superconductive carbon black photopolymer composite and its characterization towards a CIL process technique. In this article, we demonstrated an approach of using a carbon nanoparticle-polymer composite (CPC) for patterning cells. It is observed that a 0.3 wt % load of carbon nanoparticles (CNPs) in a carbon polymer mixture (CPM) was optimal for cell-imprint replica fabrication. The electrical resistance of the 3-CPC (0.3 wt %) was reduced by 68% when compared to N-CPC (0 wt %). This method successfully replicated the single cell with sub-organelle scale. The shape of microvesicles, grooves, pores, blebs or microvilli on the cellular surface was patterned clearly. This technique delivers a free-standing cell feature substrate. In vitro evaluation of the polymer demonstrated it as an ideal candidate for biomimetic biomaterial applications. This approach also finds its application in study based on morphology, especially for drug delivery applications and for investigations based on molecular pathways.

Replication of a Tissue Microenvironment by Thermal Scanning Probe Lithography

Thermal scanning probe lithography (t-SPL) is a nanofabrication technique in which an immobilized thermolabile resist, such as polyphthalaldehyde (PPA), is locally vaporized by a heated atomic force microscope tip. Compared with other nanofabrication techniques, such as soft lithography and nanoimprinting lithography, t-SPL is more efficient and convenient as it does not involve time-consuming mask productions or complicated etching procedures, making it a promising candidate technique for the fast prototyping of nanoscale topographies for biological studies. Here, we established the direct use of PPA-coated surfaces as a cell culture substrate. We showed that PPA is biocompatible and that the deposition of allylamine by plasma polymerization on a silicon wafer before PPA coating can stabilize the immobilization of PPA in aqueous solutions. When seeded on PPA-coated surfaces, human mesenchymal stem cells (MSC) adhered, spread, and proliferated in a manner indistinguishable from cells cultured on glass surfaces. This allowed us to subsequently use t-SPL to generate nanotopographies for cell culture experiments. As a proof of concept, we analyzed the surface topography of bovine tendon sections, previously shown to induce morphogenesis and differentiation of MSC, by means of atomic force microscopy, and then "wrote" topographical data on PPA by means of t-SPL. The resulting substrate, matching the native tissue topography on the nanoscale, was directly used for MSC culture. The t-SPL substrate induced similar changes in cell morphology and focal adhesion formation in the MSC compared to native tendon sections, suggesting that t-SPL can rapidly generate cell culture substrates with complex and spatially accurate topographical signals. This technique may greatly accelerate the prototyping of models for the study of cell-matrix interactions.

PDMS Sylgard 527-Based Freely Suspended Ultrathin Membranes Exhibiting Mechanistic Characteristics of Vascular Basement Membranes

In the past, significant effort has been made to develop ultrathin membranes exhibiting physiologically relevant mechanical properties, such as thickness and elasticity of native basement membranes. However, most of these fabricated membranes have a relatively high elastic modulus, ∼MPa-GPa, relevant only to retinal and epithelial basement membranes. Vascular basement membranes exhibiting relatively low elastic modulus, ∼kPa, on the contrary, have seldom been mimicked. Membranes demonstrating high compliance, with moduli ranging in ∼kPa along with sub-microscale thicknesses have rarely been reported, and would be ideal to mimic vascular basement membranes in vitro. To address this, we fabricate ultrathin membranes demonstrating the mechanistic features exhibited by their vascular biological counterparts. Salient features of the fabricated ultrathin membranes include free suspension, physiologically relevant thickness ∼sub-micrometers, relatively low modulus ∼kPa, and sufficiently large culture area ∼20 mm². To fabricate such ultrathin membranes, undiluted PDMS Sylgard 527 was utilized as opposed to the conventional diluted polymer-solvent mixture approach. In addition, the necessity to have a sacrificial layer for releasing membranes from the underlying substrates was also eliminated in our approach. The novelty of our work lies in achieving the distinct combination of membranes having thickness in sub-micrometers and the associated elasticity in kilopascal using undiluted polymer, which past approaches with dilution have not been able to accomplish. The ultrathin membranes with average thickness of 972 nm (thick) and 570 nm (thin) were estimated to have an elastic modulus of 45 and 214 kPa, respectively. Contact angle measurements revealed the ultrathin membranes exhibited hybrophobic characteristics in unpeeled state and transformed to hydrophilic behavior when freely suspended. Human umbilical vein endothelial cells were cultured on the polymeric ultrathin membranes, and the temporal cell response to change in local compliance of the membranes was studied by evaluating the cell spread area, density, percentage area coverage, and spread rate. After 24 h, single cells, pairs, and group of three to four cells were noticed on highly compliant thick membranes, having average thickness of 972 nm and modulus of 45 kPa. On the contrary, the cell monolayer was noted on the glass slide acting as a control. For the thin membranes featuring average thickness of 570 nm and modulus of 214 kPa, the cells tend to exhibit response similar to that on control with initiation of monolayer formation. Our results indicate, the local compliance, in turn, the membrane thickness governs the cell behavior and this can have vital implications during disease initiation and progression, wound healing, and cancer cell metastasis.

Magnetic Induction of Multiscale Anisotropy in Macroporous Alginate Scaffolds

Nano- and microscale topographical cues have become recognized as major regulators of cell growth, migration, and phenotype. In tissue engineering, the complex and anisotropic architecture of culture platforms is aimed to imitate the high degree of spatial organization of the extracellular matrix and basement membrane components. Here, we developed a method of creating a novel, magnetically aligned, three-dimensional (3D) tissue culture matrix with three distinct classes of anisotropy-surface topography, microstructure, and physical properties. Alginate-stabilized magnetic nanoparticles (MNPs) were added to a cross-linked alginate solution, and an external magnetic field of about 2400 G was applied during freezing to form the aligned macroporous scaffold structure. The resultant scaffold exhibited anisotropic topographic features on the submicron scale, the directionality of the pore shape, and increased scaffold stiffness in the direction of magnetic alignment. These scaffold features were modulated by an alteration in the impregnated MNP size and concentration, as quantified by electron microscopy, advanced image processing analyses, and rheological methods. Mouse myoblasts (C2C12) cultured on the magnetically aligned scaffolds, demonstrated co-oriented morphology in the direction of the magnetic alignment. In summary, magnetic alignment introduces several degrees of anisotropy in the scaffold structure, providing diverse mechanical cues that can affect seeded cells and further tissue development. Multiscale anisotropy together with the capability of the MNP-containing alginate scaffolds to undergo reversible shape deformation in an oscillating magnetic field creates interesting opportunities for multifarious stimulation of cells and functional tissue development.

Topography on a subcellular scale modulates cellular adhesions and actin stress fiber dynamics in tumor associated fibroblasts

Cells can sense and adapt to mechanical properties of their environment. The local geometry of the extracellular matrix, such as its topography, has been shown to modulate cell morphology, migration, and proliferation. Here we investigate the effect of micro/nanotopography on the morphology and cytoskeletal dynamics of human pancreatic tumor-associated fibroblast cells (TAFs). We use arrays of parallel nanoridges with variable spacings on a subcellular scale to investigate the response of TAFs to the topography of their environment. We find that cell shape and stress fiber organization both align along the direction of the nanoridges. Our analysis reveals a strong bimodal relationship between the degree of alignment and the spacing of the nanoridges. Furthermore, focal adhesions align along ridges and form preferentially on top of the ridges. Tracking actin stress fiber movement reveals enhanced dynamics of stress fibers on topographically patterned surfaces. We find that components of the actin cytoskeleton move preferentially along the ridges with a significantly higher velocity along the ridges than on a flat surface. Our results suggest that a complex interplay between the actin cytoskeleton and focal adhesions coordinates the cellular response to micro/nanotopography.

Lamination of microfibrous PLGA fabric by electrospinning a layer of collagen-hydroxyapatite composite nanofibers for bone tissue engineering

BACKGROUND

To mimic the muscle inspired cells adhesion through proteins secretion, the lamination of collagen-hydroxyapatite nanorod (nHA) composite nanofibers has been carried out successfully on polydopamine (PDA)-coated microfibrous polylactide-co-glycolide (PLGA) fabrics. The lamination of collagen-hydroxyapatite composite nanofibers on polydopamine-coated microfibrous PLGA fabrics was carried through electrospinning the solution of collagen containing L-glutamic acid-grafted hydroxyapatite nanorods (nHA-GA) at a flow rate of 1.5 mL/h and an applied voltage of 15 kV.

RESULTS

In comparison to pristine PLGA, dopamine-coated PLGA and collagen-hydroxyapatite composite nanofiber lamination has produced more wettable surfaces and surface wettability is found to higher with dopamine-coated PLGA fabrics then pristine PLGA. The SEM micrographs have clearly indicated that the lamination of polydopamine-coated PLGA fabric with collagen-hydroxyapatite composite nanofibers has shown increased adhesion of MC3T3E1 cells in comparison to pristine PLGA fabrics.

CONCLUSION

The results of these studies have clearly demonstrated that collagen-nHA composites fibers may be used to create bioactive 3D scaffolds using PLGA as an architectural support agent.

Cell Guidance on Nanostructured Metal Based Surfaces

Metal surface nanostructuring to guide cell behavior is an attractive strategy to improve parts of medical implants, lab-on-a-chip, soft robotics, self-assembled microdevices, and bionic devices. Here, we discus important parameters, relevant trends, and specific examples of metal surface nanostructuring to guide cell behavior on metal-based hybrid surfaces. Surface nanostructuring allows precise control of cell morphology, adhesion, internal organization, and function. Pre-organized metal nanostructuring and dynamic stimuli-responsive surfaces are used to study various cell behaviors. For cells dynamics control, the oscillating stimuli-responsive layer-by-layer (LbL) polyelectrolyte assemblies are discussed to control drug delivery, coating thickness, and stiffness. LbL films can be switched "on demand" to change their thickness, stiffness, and permeability in the dynamic real-time processes. Potential applications of metal-based hybrids in biotechnology and selected examples are discussed.

The modulation effect of the convexity of silicon topological nanostructures on the growth of mesenchymal stem cells

The convexity of topological nanostructures, as analyzed by grey-level histogram and fast Fourier transformation, has important modulation effects on the size expansion and filopodia generation of mesenchymal stem cells.

Micro/Nano Multilayered Scaffolds of PLGA and Collagen by Alternately Electrospinning for Bone Tissue Engineering

The dual extrusion electrospinning technique was used to fabricate multilayered 3D scaffolds by stacking microfibrous meshes of poly(lactic acid-co-glycolic acid) (PLGA) in alternate fashion to micro/nano mixed fibrous meshes of PLGA and collagen. To fabricate the multilayered scaffold, 35 wt% solution of PLGA in THF-DMF binary solvent (3:1) and 5 wt% solution of collagen in hexafluoroisopropanol (HFIP) with and without hydroxyapatite nanorods (nHA) were used. The dual and individual electrospinning of PLGA and collagen were carried out at flow rates of 1.0 and 0.5 mL/h, respectively, at an applied voltage of 20 kV. The density of collagen fibers in multilayered scaffolds has controlled the adhesion, proliferation, and osteogenic differentiation of MC3T3-E1 cells. The homogeneous dispersion of glutamic acid-modified hydroxyapatite nanorods (nHA-GA) in collagen solution has improved the osteogenic properties of fabricated multilayered scaffolds. The fabricated multilayered scaffolds were characterized using FT-IR, X-ray photoelectron spectroscopy, and transmission electron microscopy (TEM). The scanning electron microscopy (FE-SEM) was used to evaluate the adhesion and spreads of MC3T3-E1 cells on multilayered scaffolds. The activity of MC3T3-E1 cells on the multilayered scaffolds was evaluated by applying MTT, alkaline phosphatase, Alizarin Red, von Kossa, and cytoskeleton F-actin assaying protocols. The micro/nano fibrous PLGA-Col-HA scaffolds were found to be highly bioactive in comparison to pristine microfibrous PLGA and micro/nano mixed fibrous PLGA and Col scaffolds.

Nanoscale and mechanical properties of the physiological cell-ECM microenvironment

Studying biological processes in vitro requires faithful and successful reconstitution of the in vivo extracellular matrix (ECM) microenvironment. However, the physiological basis behind in vitro studies is often forgotten or ignored. A number of diverse cell-ECM interactions have been characterized throughout the body and in disease, reflecting the heterogeneous nature of cell niches. Recently, a greater emphasis has been placed on characterizing both the chemical and physical characteristics of the ECM and subsequently mimicking these properties in the lab. Herein, we describe physiological measurement techniques and reported values for the three main physical aspects of the ECM: tissue stiffness, topography, and ligand presentation.

Short-term effects of microstructured surfaces: role in cell differentiation toward a contractile phenotype

Cell adhesion plays a key role in cell behavior, in terms of migration, proliferation, differentiation and apoptosis. All of these events concur with tissue regeneration and remodeling mechanisms, integrating a complex network of intracellular signaling modules. Morphogenetic responses, which involve changes in cell shape, proliferation and differentiation, are thought to be controlled by both biochemical and biophysical cues. Indeed, the extracellular matrix not only displays adhesive ligands necessary for cell adhesion but also plays an essential biomechanical role — responsible, for instance, for the acquisition of the contractile phenotype. The substrate topography around the forming tissues and the associated mechanical stresses that are generated regulate cellular morphology, proliferation and differentiation. Thus, the ability to tailor topographical features around cells can be a crucial design parameter in tissue engineering applications, inducing cells to exhibit the required performances.

In this work, we designed micropillared substrates using highly spaced arrays (interspacing equal to 25 μm) to evaluate the effects of topography on C2C12 myoblasts' adhesion and differentiation. Optical and fluorescence microscopy images were used to observe cell adhesion, together with Western blot analysis on vinculin and focal adhesion kinase (FAK) expression, a protein highly involved in adhesive processes. Differentiation marker (Myf5, myogenin and myosin heavy chain [MHC]) expression was also studied, in relation to the effect of different substrate topographies on the enhancement of a contractile phenotype. Our results demonstrated that microstructured surfaces may play a key role in the regeneration of functional tissues.

Reconstructing spinal dura-like tissue using electrospun poly(lactide-co-glycolide) membranes and dermal fibroblasts to seamlessly repair spinal dural defects in goats

Many neuro- and spinal surgeries involving access to the underlying nervous tissue will cause defect of spinal dural mater, further resulting in cerebrospinal fluid leakage. The current work was thus aimed to develop a package which included two layers of novel electrospun membranes, dermal fibroblasts and mussel adhesive protein for repairing spinal dural defect. The inner layer is electrospun fibrous poly(lactide-co-glycolide) membrane with oriented microstructure (O-poly(lactide-co-glycolide)), which was used as a substrate to anchor dermal fibroblasts as seed cells to reconstitute dura-like tissue via tissue engineering technique. The outer layer is chitosan-coated electrospun nonwoven poly(lactide-co-glycolide) membrane (poly(lactide-co-glycolide)-chitosan). During surgery, the inner reconstituted tissue layer was first used to directly cover dura defects, while the outer layer was placed onwards with its marginal area tightly immobilized to the surrounding normal spinal dura aided by mussel adhesive protein. Efficacy of the current design was verified in goats with spinal dural defects (0.6 cm × 0.5 cm) in lumbar. It was shown that seamless and quick sealing of the defect area with the implants was realized by mussel adhesive protein. Guided tissue growth and regeneration in the defects of goats were observed when they were repaired by the current package. Effective cerebrospinal fluid containment and anti-adhesion of the regenerated tissue to the surrounding tissue could be achieved in the current animal model. Hence, it could be ascertained that the current package could be a favorite choice for surgeries involving spinal dural defects.

The synergistic effect of micro-topography and biochemical culture environment to promote angiogenesis and osteogenic differentiation of human mesenchymal stem cells

Critical failures associated with current engineered bone grafts involve insufficient induction of osteogenesis of the implanted cells and lack of vascular integration between graft scaffold and host tissue. This study investigated the combined effects of surface microtextures and biochemical supplements to achieve osteogenic differentiation of human mesenchymal stem cells (hMSCs) and revascularization of the implants in vivo. Cells were cultured on 10μm micropost-textured polydimethylsiloxane (PDMS) substrates in either proliferative basal medium (BM) or osteogenic medium (OM). In vitro data revealed that cells on microtextured substrates in OM had dense coverage of extracellular matrix, whereas cells in BM displayed more cell spreading and branching. Cells on microtextured substrates in OM demonstrated a higher gene expression of osteoblast-specific markers, namely collagen I, alkaline phosphatase, bone sialoprotein, and osteocalcin, accompanied by substantial amount of bone matrix formation and mineralization. To further investigate the osteogenic capacity, hMSCs on microtextured substrates under different biochemical stimuli were implanted into subcutaneous pockets on the dorsal aspect of immunocompromised mice to study capacity for ectopic bone formation. In vivo data revealed greater expression of osteoblast-specific markers coupled with increased vascular invasion on microtextured substrates with hMSCs cultured in OM. Together, these data represent a novel regenerative strategy that incorporates defined surface microtextures and biochemical stimuli to direct combined osteogenesis and re-vascularization of engineered bone scaffolds for musculoskeletal repair and relevant bone tissue engineering applications.

Combined effects of substrate topography and stiffness on endothelial cytokine and chemokine secretion

Endothelial physiology is regulated not only by humoral factors, but also by mechanical factors such as fluid shear stress and the underlying cellular matrix microenvironment. The purpose of the present study was to examine the effects of matrix topographical cues on the endothelial secretion of cytokines/chemokines in vitro. Human endothelial cells were cultured on nanopatterned polymeric substrates with different ratios of ridge to groove widths (1:1, 1:2, and 1:5) and with different stiffnesses (6.7 MPa and 2.5 GPa) in the presence and absence of 1.0 ng/mL TNF-α. The levels of cytokines/chemokines secreted into the conditioned media were analyzed with a multiplexed bead-based sandwich immunoassay. Of the nanopatterns tested, the 1:1 and 1:2 type patterns were found to induce the greatest degree of endothelial cell elongation and directional alignment. The 1:2 type nanopatterns lowered the secretion of inflammatory cytokines such as IL-1β, IL-3, and MCP-1, compared to unpatterned substrates. Additionally, of the two polymers tested, it was found that the stiffer substrate resulted in significant decreases in the secretion of IL-3 and MCP-1. These results suggest that substrates with specific extracellular nanotopographical cues or stiffnesses may provide anti-atherogenic effects like those seen with laminar shear stresses by suppressing the endothelial secretion of cytokines and chemokines involved in vascular inflammation and remodeling.

Constructing a novel three-dimensional scaffold with mesoporous TiO2 nanotubes for potential bone tissue engineering

A novel 3D porous network-structured tissue engineering scaffold built of mesoporous TiO₂ nanotubes has been synthesized via the bacterial cellulose-templated sol–gel route followed by calcination.

Topography design concept of a tissue engineering scaffold for controlling cell function and fate through actin cytoskeletal modulation

The physiological role of the actin cytoskeleton is well known: it provides mechanical support and endogenous force generation for formation of a cell shape and for migration. Furthermore, a growing number of studies have demonstrated another significant role of the actin cytoskeleton: it offers dynamic epigenetic memory for guiding cell fate, in particular, proliferation and differentiation. Because instantaneous imbalance in the mechanical homeostasis is adjusted through actin remodeling, a synthetic extracellular matrix (ECM) niche as a source of topographical and mechanical cues is expected to be effective at modulation of the actin cytoskeleton. In this context, the synthetic ECM niche determines cell migration, proliferation, and differentiation, all of which have to be controlled in functional tissue engineering scaffolds to ensure proper regulation of tissue/organ formation, maintenance of tissue integrity and repair, and regeneration. Here, with an emphasis on the epigenetic role of the actin cytoskeletal system, we propose a design concept of micro/nanotopography of a tissue engineering scaffold for control of cell migration, proliferation, and differentiation in a stable and well-defined manner, both in vitro and in vivo.

Wharton's Jelly human mesenchymal stem cell contact guidance by noisy nanotopographies

The development of biomaterials ensuring proper cell adhesion, polarization, migration and differentiation represents a true enabler for successful tissue-engineering applications. Surface nanostructuring was suggested as a promising method for improving cell-substrate interaction. Here, we study Wharton's Jelly human Mesenchymal Stem Cells (WJ-hMSC) interacting with nanogratings (NGs) having a controlled amount of nanotopographical noise (nTN). Our data demonstrate that unperturbed NGs induce cell polarization, alignment and migration along NG lines. The introduction of nTN dramatically modifies this behavior and leads to a marked loss of cell polarization and directional migration, even at low noise levels. High-resolution focal adhesions (FAs) imaging showed that this behavior is caused by the release of the geometrical vinculum imposed by the NGs to FA shaping and maturation. We argue that highly anisotropic nanopatterned scaffolds can be successfully exploited to drive stem cell migration in regenerative medicine protocols and discuss the impact of scaffold alterations or wear.

Technological advances in nanoscale biomaterials: the future of synthetic vascular graft design

Currently, autologous veins are the first choice for patients in need of bypass grafting materials. However, due to either pre-existing conditions or previous bypass surgery, some patients lack the necessary amount of host tissue for such procedures. Unfortunately, current synthetic vascular grafts of less than 6 mm in diameter have been plagued by a variety of problems. For this reason, there has been significant research aimed at finding more suitable small-diameter vascular graft materials. In order to improve vascular cell functions on such synthetic materials, several techniques are currently under development that attempt to mimic the natural nanometer architecture of the vascular basement membrane. This review presents several processes including colloidal lithography, chemical etching, electrospinning and solid free-form fabrication that could play a role in the future of vascular nanostructured biomaterial development.

Topographic effect on human induced pluripotent stem cells differentiation towards neuronal lineage

Pluripotent stem cells have the potential to develop into all cell types of the adult body. Besides chemical and mechanical cues, topographical effect of surfaces could also contribute to the development of new therapies in regenerative medicine. In the present study, we tested the effects of nanograting substrates with different widths (width:350 nm/2 μm/5 μm, height: 300 nm) on human induced pluripotent stem cells (hiPSCs), in particular regarding the commitment of stem cell differentiation to desired phenotypes. We found that nuclei of hiPSCs could align and elongate in the direction of the nano/microstructure, whereas they distributed randomly on flat surfaces. The contact guidance significantly increased when the cells were cultured on the surface with smaller pitch. Gene expression profiling by real-time PCR and immunostaining showed significant up-regulation of neuronal markers on nanostructured substrates either with solely topographical cues or combined with pre-neuronal induction. A width of 350 nm, in particular, induced highest neuronal marker expression. This study demonstrates the significance of topography, especially regarding the width of the structures, in directing differentiation of hiPSCs towards the neuronal lineage. Our study suggests the potential applications of surface topography in clinical regenerative medicine for nerve injury repair.

Lotus-leaf-like topography predominates over adsorbed ECM proteins in poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) surface/cell interactions

It is well-known that extracellular matrix (ECM) proteins mediate cell/surface interactions. However, introduction of a specific surface topography may disturb the correlation between ECM proteins adsorption and cells adhesion on a given surface. In present study, lotus-leaf-like topography was introduced on the surface of a biodegradable material, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx). Protein adsorption and cell interactions with this lotus-leaf-like surface (designated PHBHHx-L) were investigated. Water contact angle data indicated that the hydrophobicity of PHBHHx was enhanced by the introduction of lotus-leaf-like topography. The adsorption of extracellular matrix proteins (fibronectin and vitronectin) on PHBHHx-L was measured by enzyme linked immunosorbent assay (ELISA). Compared with flat PHBHHx, adsorption on the PHBHHx-L surface increased by ~260% for fibronectin and ~40% for vitronectin. In contrast, fibroblast and endothelial cell adhesion and proliferation were reduced on the PHBHHx-L compared to the flat polymer surface. These results suggest that the inhibition of cell adhesion and proliferation caused by the lotus-leaf-like topography dominates over the effect of the adsorbed adhesive proteins in promoting adhesion and proliferation. It can be concluded that the lotus-leaf-like topography plays a dominant role in cell/PHBHHx-L interactions. The present findings indicate the complexity of the interplay among surface topography, adsorbed proteins, and cell-surface interactions.

Vascularized bone tissue engineering: approaches for potential improvement

Significant advances have been made in bone tissue engineering (TE) in the past decade. However, classical bone TE strategies have been hampered mainly due to the lack of vascularization within the engineered bone constructs, resulting in poor implant survival and integration. In an effort toward clinical success of engineered constructs, new TE concepts have arisen to develop bone substitutes that potentially mimic native bone tissue structure and function. Large tissue replacements have failed in the past due to the slow penetration of the host vasculature, leading to necrosis at the central region of the engineered tissues. For this reason, multiple microscale strategies have been developed to induce and incorporate vascular networks within engineered bone constructs before implantation in order to achieve successful integration with the host tissue. Previous attempts to engineer vascularized bone tissue only focused on the effect of a single component among the three main components of TE (scaffold, cells, or signaling cues) and have only achieved limited success. However, with efforts to improve the engineered bone tissue substitutes, bone TE approaches have become more complex by combining multiple strategies simultaneously. The driving force behind combining various TE strategies is to produce bone replacements that more closely recapitulate human physiology. Here, we review and discuss the limitations of current bone TE approaches and possible strategies to improve vascularization in bone tissue substitutes.

Engineering microscale topographies to control the cell-substrate interface

Cells in their in vivo microenvironment constantly encounter and respond to a multitude of signals. While the role of biochemical signals has long been appreciated, the importance of biophysical signals has only recently been investigated. Biophysical cues are presented in different forms including topography and mechanical stiffness imparted by the extracellular matrix and adjoining cells. Microfabrication technologies have allowed for the generation of biomaterials with microscale topographies to study the effect of biophysical cues on cellular function at the cell-substrate interface. Topographies of different geometries and with varying microscale dimensions have been used to better understand cell adhesion, migration, and differentiation at the cellular and sub-cellular scales. Furthermore, quantification of cell-generated forces has been illustrated with micropillar topographies to shed light on the process of mechanotransduction. In this review, we highlight recent advances made in these areas and how they have been utilized for neural, cardiac, and musculoskeletal tissue engineering application.

Nanostructured material surfaces--preparation, effect on cellular behavior, and potential biomedical applications: a review

Nanostructures play important roles in vivo, where nanoscaled features of extracellular matrix (ECM) components influence cell behavior and resultant tissue formation. This review summarizes some of the recent developments in fostering new concepts and approaches to nanofabrication, such as top-down and bottom-up and combinations of the two. As in vitro investigations demonstrate that man-made nanotopography can be used to control cell reactions to a material surface, its potential application in implant design and tissue engineering becomes increasingly evident. Therefore, we present recent progress in directing cell fate in the field of cell mechanics, which has grown rapidly over the last few years, and in various tissue-engineering applications. The main focus is on the initial responses of cells to nanostructured surfaces and subsequent influences on cellular functions. Specific examples are also given to illustrate the potential nanostructures may have for biomedical applications and regenerative medicine.

The effect of tendon surface treatment on cell attachment for potential enhancement of tendon graft healing: an ex vivo model

For both tendon allografts and autografts, the surface, initially optimized for gliding, may not be ideal to facilitate tissue integration for graft healing to host tendon or bone. As a prelude to studying tendon-bone integration, we investigated the effect of surface treatments with trypsin or mechanical abrasion on cell attachment to the tendon surface in a canine ex vivo intrasynovial tendon tissue culture model. Intrasynovial tendon allograft surfaces were seeded with cells after the following treatments: (1) no treatment, (2) mechanical abrasion, (3) trypsin, and (4) abrasion and trypsin. The area covered by cells was determined using confocal laser microscopy at one and two weeks. Results were compared to untreated extrasynovial tendon. Additional tendons were characterized with scanning electron microscopy. Tendons with trypsin treatment had significantly more surface coverage with cells than the other groups, after both one and two weeks of culture. In terms of the cellular shape and size, cells on tendons with trypsin treatment spread more and were more polygonal in shape, whereas tendons with mechanical abrasion with/without trypsin treatment contained smaller, more spindle-like cells. Surface roughening can affect cell behavior with topographical stimulation. Trypsin surface digestion exposes a mesh-like structure on the tendon surface, which could enhance cell adherence and, possibly, tendon/bone healing.

Inhibition of smooth muscle cell adhesion and proliferation on heparin-doped polypyrrole

We have investigated the application of polypyrrole (pPy) as a material to influence neointimal cell behaviour. The physico-chemical properties of pPy doped with heparin (Hep), para-toluene sulfonate, poly(2-methoxyaniline-5-sulfonic acid) (pMAS) and nitrate ions were studied in addition to cell adhesion and proliferation studies of neointimal relevant cell lines cultured on the pPy substrates. Both smooth muscle (hSMC) and endothelial (hEC) cell types adhered and proliferated best on the smooth, hydrophilic pPy/pMAS material. Moreover, pPy/Hep is able to support the proliferation of hECs on the surface but inhibits hSMC proliferation after 4 days of culture. The inhibitory effect on hSMCs is most likely due to the well-known antiproliferative effect of heparin on hSMC growth. The results presented indicate that surface exposed heparin binds to the putative heparin receptor of hSMCs and is sufficient to inhibit proliferation. The application of galvanostatically synthesized pPy/Hep to stent surfaces presents a novel bioactive control mechanism to control neointimal cell growth.

Polystyrene replicas of neuronal basal lamina act as excellent guides for regenerating neurites

Various scaffolds, natural or artificial, have been used for neural repair, including basal lamina scaffolds obtained through extraction of nerves. Here we tested whether plastic casts of such preparations could be used for neurite guidance. To this end, longitudinal micron thick sections of rat sciatic nerve were extracted with detergents and treated with Dnase, yielding an acellular basal lamina master. From the basal lamina master a polydimethylsiloxane (PDMS) mold was made. Then a polystyrene replica was made using the PDMS mold as the master. The polystyrene replica showed high similarity to the master within nanometer resolution as revealed by scanning electron microscopy. Organ cultured mouse dorsal root ganglia grown on the polystyrene replica and the master preparation exhibited guided outgrowth of neurites as assayed by two-dimensional fast Fourier transform analysis on preparations, where the neurites had been visualized by β-III-tubulin staining. The neurites aligned longitudally in the direction of the original basal lamina tubes. Thus, using inexpensive methods it is possible to make replicas of basal lamina which can be used for neurite guidance. This opens a new avenue for nerve reconstruction.

Micro- and nanoengineering approaches to control stem cell-biomaterial interactions

As our population ages, there is a greater need for a suitable supply of engineered tissues to address a range of debilitating ailments. Stem cell based therapies are envisioned to meet this emerging need. Despite significant progress in controlling stem cell differentiation, it is still difficult to engineer human tissue constructs for transplantation. Recent advances in micro- and nanofabrication techniques have enabled the design of more biomimetic biomaterials that may be used to direct the fate of stem cells. These biomaterials could have a significant impact on the next generation of stem cell based therapies. Here, we highlight the recent progress made by micro- and nanoengineering techniques in the biomaterials field in the context of directing stem cell differentiation. Particular attention is given to the effect of surface topography, chemistry, mechanics and micro- and nanopatterns on the differentiation of embryonic, mesenchymal and neural stem cells.

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

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

Carbon Nanotube Composite Scaffolds and Coatings for Tissue Engineering Applications

Carbon nanotubes (CNTs) are composed of two-dimensional hexagonal graphite sheets rolled up to form into a seamless hollow tube or cylinder of diameters ranging from 0.7 to 100 nm and length of several micrometres up to several millimetres [1, 2]. CNTs can be synthesised in two configurations, as single-walled nanotubes (SWCNTs) and multi-walled nanotubes (MWCNTs). Whereas SWCNTs are made of one tubular structure, MWCNTs consist of concentrically arranged carbon tubes with a typical spacing of ≈ 0.34 nm between the different layers. Owing to their remarkable structural characteristics (light weight, high aspect ratio, high specific surface area), as well as attractive mechanical (high stiffness and strength), electrical (high conductivity) and chemical (versatile surface chemistry, easily to functionalise) properties [2], there is increasing interest in biomedical applications of CNTs.

Engineering substrate topography at the micro- and nanoscale to control cell function

The interaction of mammalian cells with nanoscale topography has proven to be an important signaling modality in controlling cell function. Naturally occurring nanotopographic structures within the extracellular matrix present surrounding cells with mechanotransductive cues that influence local migration, cell polarization, and other functions. Synthetically nanofabricated topography can also influence cell morphology, alignment, adhesion, migration, proliferation, and cytoskeleton organization. We review the use of in vitro synthetic cell-nanotopography interactions to control cell behavior and influence complex cellular processes, including stem-cell differentiation and tissue organization. Future challenges and opportunities in cell-nanotopography engineering are also discussed, including the elucidation of mechanisms and applications in tissue engineering.

Development of dual scale scaffolds via direct polymer melt deposition and electrospinning for applications in tissue regeneration

The objective of this study was the fabrication of highly functionalized polymeric three-dimensional (3D) structures characterized by nano and microfibers for use as an extracellular matrix-like tissue engineering scaffold. A hybrid process utilizing direct polymer melt deposition (DPMD) and an electrospinning method were employed to obtain the structure. Each microfibrous layer of the scaffold was built using the DPMD process in accordance with computer-aided design modeling data considering some structural points such as pore size, pore interconnectivity and fiber diameter. Between the layers of the three-dimensional structure, polycaprolactone/collagen nanofiber matrices were deposited via an electrospinning process. To evaluate the fabricated scaffolds, chondrocytes were seeded and cultured within the developed scaffolds for 10 days, and the levels of cell adhesion and proliferation were monitored. The results showed that the polymeric scaffolds with nanofiber matrices fabricated using the proposed hybrid process provided favorable conditions for cell adhesion and proliferation. These conditions can be attributed to enhanced cytocompatibility of the scaffold due to surficial nanotopography in the scaffold, chemical composition by use of a functional biocomposite, and an enlarged inner surface of the structure for cell attachment and growth.

Upregulation of matrix and adhesion molecules induced by controlled topography

Electrostatic spinning is receiving increasing attention in the field of tissue engineering, due to its ability to produce 3-dimensional, multidirectional, microfibrous scaffolds. These structures are capable of supporting a wide range of cell growth; however, there is little knowledge relating material substrates with specific cellular interactions and responses. The aim of this research was to investigate if electrostatically spun scaffolds, with controlled topographical features, would affect the adhesion mechanisms of contacting cells. A range of electrostatically spun Tecoflex SG-80A polyurethane scaffolds was characterized in terms of inter-fibre separation, fibre diameter, surface roughness, void fraction and fibre orientation. Human embryonic lung fibroblasts and human vein endothelial cells were cultured on these scaffolds for 7, 14, 28 days, and analysed for their expression of extracellular matrix and adhesion molecules using image analysis and laser scanning confocal microscopy. There were significant differences in adhesion mechanisms between scaffolds, cell types and culture periods. Fibroblast-scaffolds were stimulated and oriented to a greater degree, and at earlier cultures, by the controlled topographical features than the endothelial cells. These conclusions confirm that cellular behaviour can be influenced by the induced scaffold topography at both molecular and cellular levels, with implications for optimum application specific tissue engineering constructs.

3D polymer scaffolds for tissue engineering

This review discusses some of the most common polymer scaffold fabrication techniques used for tissue engineering applications. Although the field of scaffold fabrication is now well established and advancing at a fast rate, more progress remains to be made, especially in engineering small diameter blood vessels and providing scaffolds that can support deep tissue structures. With this in mind, we introduce two new lithographic methods that we expect to go some way to addressing this problem.

Enhanced Functions of Vascular Cells on Nanostructured Ti for Improved Stent Applications

Vascular tissue possesses numerous nanostructured surface features, but most metallic vascular stents proposed to restore blood flow are smooth at the nanoscale. Thus, the objective of the present study was to determine in vitro vascular cell functions on nanostructured titanium (Ti) compared to conventional commercially pure (c.p.) Ti. Results of this study showed for the first time greater competitive adhesion of endothelial versus vascular smooth muscle cells on nanostructured Ti compared to conventional Ti after 4 hours. Moreover, when cultured separately, increased endothelial and vascular smooth muscle cell density was observed on nanostructured Ti compared to conventional c.p. Ti after 1, 3, and 5 days; endothelial cells formed confluent monolayers before vascular smooth muscle cells on nanostructured Ti. Results also showed greater total amounts of collagen and elastin synthesis by vascular cells when cultured on nanostructured Ti. Since a major mode of failure of conventional vascular stents is the overgrowth of smooth muscle cells compared to endothelial cells, these results suggest that while the functions of both types of vascular cells were promoted on nanostructured c.p. Ti, endothelial cell functions (of particular importance, cell density or confluence) were enhanced over that of vascular smooth muscle cells. Thus, the present in vitro study showed that vascular stents composed of nanometer c.p. Ti particles may invoke advantageous cellular responses for improved stent applications.