Increased endothelial cell adhesion and elongation on micron-patterned nano-rough poly(dimethylsiloxane) films

PDMS nanoparticles-decorated PDMS substrate promotes adhesion, proliferation and differentiation of skin cells

Polydimethylsiloxane (PDMS) is known to be a common substrate for various cell culture-based applications. However, native PDMS is not very conducive for cell culture and hence, surface modification via cell adhesion moieties is generally needed to make it suitable especially for long-term cell culture. To address this issue, we propose to coat PDMS nanoparticles (NPs) on the surface of PDMS film to improve adhesion, proliferation and differentiation of skin cells. The proposed modification strategy introduces necessary nanotopography without altering the surface chemical properties of PDMS. Due to resemblance in the mechanical properties of PDMS with skin, PDMS NPs can recreate the native extracellular nanoenvironment of skin on the PDMS surface and provide anchoring sites for skin cells to adhere and grow. Human keratinocytes, representing 95% of the epidermal skin cells maintained their characteristic well-spread morphology with the formation of interconnected cell-sheets on this coated PDMS surface. Moreover, our in vitro immunofluorescence studies confirmed expression of distinctive epidermal protein markers on the coated surface indicating close resemblance with the native skin epidermis. Conclusively, our findings suggest that introducing nanotopography via PDMS NPs can be an effective strategy for emulating the native cellular functions of keratinocytes on PDMS based cell culture devices.

Effectiveness of Direct Laser Interference Patterning and Peptide Immobilization on Endothelial Cell Migration for Cardio-Vascular Applications: An In Vitro Study

Endothelial coverage of an exposed cardiovascular stent surface leads to the occurrence of restenosis and late-stent thrombosis several months after implantation. To overcome this difficulty, modification of stent surfaces with topographical or biochemical features may be performed to increase endothelial cells’ (ECs) adhesion and/or migration. This work combines both strategies on cobalt-chromium (CoCr) alloy and studies the potential synergistic effect of linear patterned surfaces that are obtained by direct laser interference patterning (DLIP), coupled with the use of Arg-Gly-Asp (RGD) and Tyr-Ile-Gly-Ser-Arg (YIGSR) peptides. An extensive characterization of the modified surfaces was performed by using AFM, XPS, surface charge, electrochemical analysis and fluorescent methods. The biological response was studied in terms of EC adhesion, migration and proliferation assays. CoCr surfaces were successfully patterned with a periodicity of 10 µm and two different depths, D (≈79 and 762 nm). RGD and YIGSR were immobilized on the surfaces by CPTES silanization. Early EC adhesion was increased on the peptide-functionalized surfaces, especially for YIGSR compared to RGD. High-depth patterns generated 80% of ECs’ alignment within the topographical lines and enhanced EC migration. It is noteworthy that the combined use of the two strategies synergistically accelerated the ECs’ migration and proliferation, proving the potential of this strategy to enhance stent endothelialization.

3D printing of self-standing and vascular supportive multimaterial hydrogel structures for organ engineering

Three dimensional printable formulation of self-standing and vascular-supportive structures using multi-materials suitable for organ engineering is of great importance and highly challengeable, but, it could advance the 3D printing scenario from printable shape to functional unit of human body. In this study, the authors report a 3D printable formulation of such self-standing and vascular-supportive structures using an in-house formulated multi-material combination of albumen/alginate/gelatin-based hydrogel. The rheological properties and relaxation behavior of hydrogels were analyzed before the printing process. The suitability of the hydrogel in 3D printing of various customizable and self-standing structures, including a human ear model, was examined by extrusion-based 3D printing. The structural, mechanical, and physicochemical properties of the printed scaffolds were studied systematically. Results supported the 3D printability of the formulated hydrogel with self-standing structures, which are customizable to a specific need. In vitro cell experiment showed that the formulated hydrogel has excellent biocompatibility and vascular supportive behavior with the extent of endothelial sprout formation when tested with human umbilical vein endothelial cells. In conclusion, the present study demonstrated the suitability of the extrusion-based 3D printing technique for manufacturing complex shapes and structures using multi-materials with high fidelity, which have great potential in organ engineering.

Potential of CO2-laser processing of quartz for fast prototyping of microfluidic reactors and templates for 3D cell assembly over large scale

Carbon dioxide (CO2)-laser processing of glasses is a versatile maskless writing technique to engrave micro-structures with flexible control on shape and size. In this study, we present the fabrication of hundreds of microns quartz micro-channels and micro-holes by pulsed CO2-laser ablation with a focus on the great potential of the technique in microfluidics and biomedical applications. After discussing the impact of the laser processing parameters on the design process, we illustrate specific applications. First, we demonstrate the use of a serpentine microfluidic reactor prepared by combining CO2-laser ablation and post-ablation wet etching to remove surface features stemming from laser-texturing that are undesirable for channel sealing. Then, cyclic olefin copolymer micro-pillars are fabricated using laser-processed micro-holes as molds with high detail replication. The hundreds of microns conical and square pyramidal shaped pillars are used as templates to drive 3D cell assembly. Human Umbilical Vein Endothelial Cells are found to assemble in a compact and wrapping way around the micro-pillars forming a tight junction network. These applications are interesting for both Lab-on-a-Chip and Organ-on-a-Chip devices.

Integration of substrate- and flow-derived stresses in endothelial cell mechanobiology

Endothelial cells (ECs) lining all blood vessels are subjected to large mechanical stresses that regulate their structure and function in health and disease. Here, we review EC responses to substrate-derived biophysical cues, namely topography, curvature, and stiffness, as well as to flow-derived stresses, notably shear stress, pressure, and tensile stresses. Because these mechanical cues in vivo are coupled and are exerted simultaneously on ECs, we also review the effects of multiple cues and describe burgeoning in vitro approaches for elucidating how ECs integrate and interpret various mechanical stimuli. We conclude by highlighting key open questions and upcoming challenges in the field of EC mechanobiology.

Using Wet Electrospun PCL/Gelatin/CNT Yarns to Fabricate Textile-Based Scaffolds for Vascular Tissue Engineering

Incorporating conductive materials in scaffolds has shown advantages in regulating adhesion, mitigation, and proliferation of electroactive cells for tissue engineering applications. Among various conductive materials, carbon nanotubes (CNTs) have shown great promises in tissue engineering because of their good mechanical properties. However, the broad application of CNTs in tissue engineering is limited by current methods to incorporate CNTs in polymers that require miscible solvents to dissolve CNTs and polymers or CNT surface modification. These methods either limit polymer selections or adversely affect the properties of polymer/CNT composites. Here, we report a novel method to fabricate polymer/CNT composite yarns by electrospinning polycaprolactone/gelatin into a bath of CNT dispersion and extracting electrospun fibers out of the bath. The concentration of CNTs in the bath affects the thermal and mechanical properties and the yarns' degradation behavior. In vitro biological test results show that within a limited range of CNT concentrations in the bath, the yarns exhibit good biocompatibility and the ability to guide cell elongation and alignment. We also report the design and fabrication of a vascular scaffold by knitting the yarns into a textile fabric and combining the textile fabric with gelatin. The scaffold has similar mechanical properties to native vessels and supports cell proliferation. This work demonstrates that the wet electrospun polymer/CNT yarns are good candidates for constructing vascular scaffolds and provides a novel method to incorporate CNTs or other functional materials into biopolymers for tissue engineering applications.

Patterned dextran ester films as a tailorable cell culture platform

The elucidation of cell-surface interactions and the development of model platforms to help uncover their underlying mechanisms remains vital to the design of effective biomaterials. To this end, dextran palmitates with varying degrees of substitution were synthesised with a multipurpose functionality: an ability to modulate surface energy through surface chemistry, and an ideal thermal behaviour for patterning. Herein, dextran palmitate films are produced by spin coating, and patterned by thermal nanoimprint lithography with nano-to-microscale topographies. These films of moderately hydrophobic polysaccharide esters with low nanoscale roughness performed as well as fibronectin coatings in the culture of bovine aortic endothelial cells. Upon patterning, they display distinct regions of roughness, restricting cell adhesion to the smoothest surfaces, while guiding multicellular arrangements in the patterned topographies. The development of biomaterial interfaces through topochemical fabrication such as this could prove useful in understanding protein and cell-surface interactions.

Surface Modification Techniques for Endothelial Cell Seeding in PDMS Microfluidic Devices

Microfluidic lab-on-a-chip cell culture techniques have been gaining popularity by offering the possibility of reducing the amount of samples and reagents and greater control over cellular microenvironment. Polydimethylsiloxane (PDMS) is the commonly used polymer for microfluidic cell culture devices because of the cheap and easy fabrication techniques, non-toxicity, biocompatibility, high gas permeability, and optical transparency. However, the intrinsic hydrophobic nature of PDMS makes cell seeding challenging when applied on PDMS surface. The hydrophobicity of the PDMS surface also allows the non-specific absorption/adsorption of small molecules and biomolecules that might affect the cellular behaviour and functions. Hydrophilic modification of PDMS surface is indispensable for successful cell seeding. This review collates different techniques with their advantages and disadvantages that have been used to improve PDMS hydrophilicity to facilitate endothelial cells seeding in PDMS devices.

Surface Engineering of Cardiovascular Devices for Improved Hemocompatibility and Rapid Endothelialization

Cardiovascular devices have been widely applied in the clinical treatment of cardiovascular diseases. However, poor hemocompatibility and slow endothelialization on their surface still exist. Numerous surface engineering strategies have mainly sought to modify the device surface through physical, chemical, and biological approaches to improve surface hemocompatibility and endothelialization. The alteration of physical characteristics and pattern topographies brings some hopeful outcomes and plays a notable role in this respect. The chemical and biological approaches can provide potential signs of success in the endothelialization of vascular device surfaces. They usually involve therapeutic drugs, specific peptides, adhesive proteins, antibodies, growth factors and nitric oxide (NO) donors. The gene engineering can enhance the proliferation, growth, and migration of vascular cells, thus boosting the endothelialization. In this review, the surface engineering strategies are highlighted and summarized to improve hemocompatibility and rapid endothelialization on the cardiovascular devices. The potential outlook is also briefly discussed to help guide endothelialization strategies and inspire further innovations. It is hoped that this review can assist with the surface engineering of cardiovascular devices and promote future advancements in this emerging research field.

Surface patterning of a novel PEG-functionalized poly-l-lactide polymer to improve its biocompatibility: Applications to bioresorbable vascular stents

Today, research in the field of bioresorbable vascular stents (BVS) not only focusses on a new material being nontoxic but also tries to enhance its biocompatibility in terms of endothelialization potential and hemocompatibility. To this end, we used picosecond laser ablation technology as a single‐step and contactless method for surface microstructuring of a bioresorbable polymer which can be utilized in stent manufacture. The method works on all materials via fast material removal, can be easily adapted for micropatterning of tubular or more complex sample shapes and scaled up by means of micropatterning of metal molds for manufacturing. Here, picosecond laser ablation was applied to a bioresorbable, biologically inactive and polyethylene glycol‐modified poly‐l‐lactide polymer (PEGylated PLLA) to generate parallel microgrooves with varying geometries. The different patterns were thoroughly evaluated by a series of cyto‐ and hemocompatibility tests revealing that all surfaces were non‐toxic and non‐hemolytic. More importantly, patterns with 20 to 25 µm wide and 6 to 7 µm deep grooves significantly enhanced endothelial cell adhesion in comparison to samples with smaller grooves. Here, human cardiac microvascular endothelial cells were found to align along the groove direction, which is thought to encourage endothelialization of intraluminal surfaces of BVS. © 2018 The Authors Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 00B: 000–000, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 624–634, 2019.

Direct Laser Interference Patterning of CoCr Alloy Surfaces to Control Endothelial Cell and Platelet Response for Cardiovascular Applications

The main drawbacks of cardiovascular bare-metal stents (BMS) are in-stent restenosis and stent thrombosis as a result of an incomplete endothelialization after stent implantation. Nano- and microscale modification of implant surfaces is a strategy to recover the functionality of the artery by stimulating and guiding molecular and biological processes at the implant/tissue interface. In this study, cobalt-chromium (CoCr) alloy surfaces are modified via direct laser interference patterning (DLIP) in order to create linear patterning onto CoCr surfaces with different periodicities (≈3, 10, 20, and 32 µm) and depths (≈20 and 800 nm). Changes in surface topography, chemistry, and wettability are thoroughly characterized before and after modification. Human umbilical vein endothelial cells' adhesion and spreading are similar for all patterned and plain CoCr surfaces. Moreover, high-depth series induce cell elongation, alignment, and migration along the patterned lines. Platelet adhesion and aggregation decrease in all patterned surfaces compared to CoCr control, which is associated with changes in wettability and oxide layer characteristics. Cellular studies provide evidence of the potential of DLIP topographies to foster endothelialization without enhancement of platelet adhesion, which will be of high importance when designing new BMS in the future.

Impact of Implant Surface Micropatterns on Epithelial Cell Behavior

PURPOSE

This study investigated the effect of topography on cell behavior by screening polydimethylsiloxane (PDMS) molds with different nanoscale micropatterns to determine the ideal surface characteristics for attachment of human epithelial cells.

MATERIALS AND METHODS

A soft PDMS mold with regular dot arrays was fabricated based on an aluminum oxide template with ordered nanotube arrays and used as a substrate for cell culture. Cell proliferation, spread, and morphology, as well as features of the extracellular matrix and the actin cytoskeleton were assessed.

DISCUSSION

Cells grown on 100-nm regular dot arrays had the highest proliferation rate and spread, with the longest pseudopodia; they showed robust actin distribution relative to the control group.

CONCLUSION

Three-dimensional PDMS microstructures with 100 nm regular dot arrays were the most effective surface for epithelial cell attachment. These findings can aid in the manufacture of superior materials for use in implants to better integrate into recipient tissue.

Nano- and microstructured materials for in vitro studies of the physiology of vascular cells

The extracellular environment of vascular cells in vivo is complex in its chemical composition, physical properties, and architecture. Consequently, it has been a great challenge to study vascular cell responses in vitro, either to understand their interaction with their native environment or to investigate their interaction with artificial structures such as implant surfaces. New procedures and techniques from materials science to fabricate bio-scaffolds and surfaces have enabled novel studies of vascular cell responses under well-defined, controllable culture conditions. These advancements are paving the way for a deeper understanding of vascular cell biology and materials-cell interaction. Here, we review previous work focusing on the interaction of vascular smooth muscle cells (SMCs) and endothelial cells (ECs) with materials having micro- and nanostructured surfaces. We summarize fabrication techniques for surface topographies, materials, geometries, biochemical functionalization, and mechanical properties of such materials. Furthermore, various studies on vascular cell behavior and their biological responses to micro- and nanostructured surfaces are reviewed. Emphasis is given to studies of cell morphology and motility, cell proliferation, the cytoskeleton and cell-matrix adhesions, and signal transduction pathways of vascular cells. We finalize with a short outlook on potential interesting future studies.

Chitosan-poly(vinyl alcohol) nanofibers by free surface electrospinning for tissue engineering applications

Deformities in tissues and organs can be treated by using tissue engineering approach offering the development of biologically functionalized scaffolds from a variety of polymer blends which mimic the extracellular matrix and allow adjusting the material properties to meet the defect architecture. In recent years, research interest has been shown towards the development of chitosan (CS) based biomaterials for tissue engineering applications, because of its minimal foreign body reactions, intrinsic antibacterial property, biocompatibility, biodegradability and ability to be molded into various geometries and forms thereby making it suitable for cell ingrowth and conduction. The present work involves the fabrication of nanofibrous scaffold from CS and poly(vinyl alcohol) blends by free-surface electrospinning method. The morphology and functional characteristics of the developed scaffolds were assessed by field emission scanning electron microscopy and fourier transformed infra-red spectra analysis. The morphological analysis showed the average fiber diameter was 269 nm and thickness of the mat was 200-300 µm. X-ray diffraction study confirmed the crystalline nature of the prepared scaffolds, whereas hydrophilic characteristic of the prepared scaffolds was confirmed by measured contact angle. The scaffolds possess an adequate biodegradable, swelling and mechanical property that is found desirable for tissue engineering applications. The cell study using umbilical cord blood-derived mesenchymal stem cells has confirmed the in vitro biocompatibility and cell supportive property of the scaffold thereby depicting their potentiality for future clinical applications.

The Systems Biocompatibility of Coronary Stenting

The coronary stent has propelled our understanding of the term "biocompatibility." Stents are expanded at sites of arterial blockage and mechanically reestablish blood flow. This simplicity belies the complex reactions that occur when a stent contacts living substrates. Biocompatible seek to elicit the intended response; stents should perform rather than merely exist. Because performance is assessed in the patient, stent biocompatibility is the multiscale examination of material and cell, and of material, structure, and device in the context of cell, tissue, and organism. This review tracks major biomaterial advances in coronary stent design and discusses biocompatibility clinical performance.

Cellular Responses Modulated by FGF-2 Adsorbed on Albumin/Heparin Layer-by-Layer Assemblies

In a typical cell culture system, growth factors immobilized on the cell culture surfaces can serve as a reservoir of bio-signaling molecules, without the need to supplement them additionally into the culture medium. In this paper, we report on the fabrication of albumin/heparin (Alb/Hep) assemblies for controlled binding of basic fibroblast growth factor (FGF-2). The surfaces were constructed by layer-by-layer adsorption of polyelectrolytes albumin and heparin and were subsequently stabilized by covalent crosslinking with glutaraldehyde. An analysis of the surface morphology by atomic force microscopy showed that two Alb/Hep bilayers are required to cover the surface of substrate. The formation of the Alb/Hep assemblies was monitored by the surface plasmon resonance (SPR), the infrared multiinternal reflection spectroscopy (FTIR MIRS) and UV/VIS spectroscopy. The adsorption of FGF-2 on the cross-linked Alb/Hep was followed by SPR. The results revealed that FGF-2 binds to the Alb/Hep assembly in a dose and time-dependent manner up to the surface concentration of 120 ng/cm². The bioactivity of the adsorbed FGF-2 was assessed in experiments in vitro, using calf pulmonary arterial endothelial cells (CPAE). CPAE cells could attach and proliferate on Alb/Hep surfaces. The adsorbed FGF-2 was bioactive and stimulated both the proliferation and the differentiation of CPAE cells. The improvement was more pronounced at a lower FGF-2 surface concentration (30 ng/cm²) than on surfaces with a higher concentration of FGF-2 (120 ng/cm²).

Contrasting biofunctionalization strategies for the enhanced endothelialization of biodegradable vascular grafts

Surface modification of biodegradable vascular grafts is an important strategy to improve the in situ endothelialization of tissue engineered vascular grafts (TEVGs) and prevent major complications associated with current synthetic grafts. Important strategies for improving endothelialization include increasing endothelial cell mobilization and increased endothelial cell capture through biofunctionalization of TEVGs. The objective of this study was to assess two biofunctionalization strategies for improving endothelialization of biodegradable polyester vascular grafts. These techniques consisted of cross-linking heparin to graft surfaces to immobilize vascular endothelial growth factor (VEGF) or antibodies against CD34 (anti-CD34Ab). To this end, heparin, VEGF, and anti-CD34Ab attachment and quantification assays confirmed the efficacy of the modification strategy. Cell attachment and proliferation on these groups were compared to unmodified grafts in vitro and in vivo. To assess in vivo graft functionality, the grafts were implanted as inferior vena cava interpositional conduits in mice. Modified vascular grafts displayed increased endothelial cell attachment and activity in vivo, according to microscopy techniques, histological results, and eNOS expression. Inner lumen diameter of the modified grafts was also better maintained than controls. Overall, while both functionalized grafts outperformed the unmodified control, grafts modified with anti-CD34Ab appeared to yield the most improved results compared to VEGF-loaded grafts.

Metastatic bladder cancer cells distinctively sense and respond to physical cues of collagen fibril-mimetic nanotopography

Tumor metastasis is characterized by enhanced invasiveness and migration of tumor cells through the extracellular matrix (ECM), resulting in extravasation into the blood and lymph and colonization at secondary sites. The ECM provides a physical scaffold consisting of components such as collagen fibrils, which have distinct dimensions at the nanoscale. In addition to the interaction of peptide moieties with tumor cell integrin clusters, the ECM provides a physical guide for tumor cell migration. Using nanolithography we set out to mimic the physical dimensions of collagen fibrils using lined nanotopographical silicon surfaces and to explore whether metastatic tumor cells are uniquely able to respond to these physical dimensions. Etched silicon surfaces containing nanoscale lined patterns with varying trench and ridge sizes (65-500 nm) were evaluated for their ability to distinguish between a non-metastatic (253 J) and a highly metastatic (253 J-BV) derivative bladder cancer cell line. Enhanced alignment was distinctively observed for the metastatic cell lines on feature sizes that mimic the dimensions of collagen fibrils (65-100 nm lines, 1:1-1:1.5 pitch). Further, these sub-100 nm lines acted as guides for migration of metastatic cancer cells. Interestingly, even at this subcellular scale, metastatic cell migration was abrogated when cells were forced to move perpendicular to these lines. Compared to flat surfaces, 65 nm lines enhanced the formation of actin stress fibers and filopodia of metastatic cells. This was accompanied by increased formation of focal contacts, visualized by immunofluorescent staining of phospho-focal adhesion kinase along the protruding lamellipodia. Simple lined nanotopography appears to be an informative platform for studying the physical cues of the ECM in a pseudo-3D format and likely mimics physical aspects of collagen fibrils. Metastatic cancer cells appear distinctively well adapted to sense these features using filopodia protrusions to enhance their alignment and migration.

Nanotopographic Biomaterials for Isolation of Circulating Tumor Cells

Circulating tumor cells (CTCs) shed from the primary tumor mass and circulating in the bloodstream of patients are believed to be vital to understand of cancer metastasis and progression. Capture and release of CTCs for further enumeration and molecular characterization holds the key for early cancer diagnosis, prognosis and therapy evaluation. However, detection of CTCs is challenging due to their rarity, heterogeneity and the increasing demand of viable CTCs for downstream biological analysis. Nanotopographic biomaterial-based microfluidic systems are emerging as promising tools for CTC capture with improved capture efficiency, purity, throughput and retrieval of viable CTCs. This review offers a brief overview of the recent advances in this field, including CTC detection technologies based on nanotopographic biomaterials and relevant nanofabrication methods. Additionally, the possible intracellular mechanisms of the intrinsic nanotopography sensitive responses that lead to the enhanced CTC capture are explored.

In vitro biocompatibility of a dentine substitute cement on human MG63 osteoblasts cells: Biodentine™ versus MTA(®)

AIM

To compare the in vitro biocompatibility of Biodentine™ and White ProRoot(®) mineral trioxide aggregate (MTA(®) ) with MG63 osteoblast-like cells and to characterize the cement surface.

METHODOLOGY

A direct contact model for MG63 osteoblast-like cells with cements was used for 1, 3 and 5 days. Four end-points were investigated: (i) cement surface characterization by atomic force microscopy (AFM), (ii) cell viability by MTT assay, (iii) protein amount quantification by Bradford assay and (iv) cell morphology by SEM. Statistical analyses were performed by analysis of variance (anova) with a repetition test method.

RESULTS

The roughness of the cements was comparable as revealed by AFM analysis. The MTT test for Biodentine™ was similar to that of MTA(®) . Biodentine™ and MTA(®) induced a similar but slight decrease in metabolic activity. The amount of total protein was significantly enhanced at day three (P < 0.05) but slightly decreased at day five for both tested samples. Biodentine™ was tolerated as well as MTA(®) in all cytotoxicity assays. SEM observations showed improvement of cell attachment and proliferation on both material surfaces following the three incubation periods.

CONCLUSION

The biocompatibility of Biodentine™ to bone cells was comparable to MTA(®) .

A novel in vitro model for microvasculature reveals regulation of circumferential ECM organization by curvature

In microvascular vessels, endothelial cells are aligned longitudinally whereas several components of the extracellular matrix (ECM) are organized circumferentially. While current three-dimensional (3D) in vitro models for microvasculature have allowed the study of ECM-regulated tubulogenesis, they have limited control over topographical cues presented by the ECM and impart a barrier for the high-resolution and dynamic study of multicellular and extracellular organization. Here we exploit a 3D fibrin microfiber scaffold to develop a novel in vitro model of the microvasculature that recapitulates endothelial alignment and ECM deposition in a setting that also allows the sequential co-culture of mural cells. We show that the microfibers' nanotopography induces longitudinal adhesion and alignment of endothelial colony-forming cells (ECFCs), and that these deposit circumferentially organized ECM. We found that ECM wrapping on the microfibers is independent of ECFCs' actin and microtubule organization, but it is dependent on the curvature of the microfiber. Microfibers with smaller diameters (100–400 µm) guided circumferential ECM deposition, whereas microfibers with larger diameters (450 µm) failed to support wrapping ECM. Finally, we demonstrate that vascular smooth muscle cells attached on ECFC-seeded microfibers, depositing collagen I and elastin. Collectively, we establish a novel in vitro model for the sequential control and study of microvasculature development and reveal the unprecedented role of the endothelium in organized ECM deposition regulated by the microfiber curvature.

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.

Strategies and techniques to enhance the in situ endothelialization of small-diameter biodegradable polymeric vascular grafts

Due to the lack of success in small-diameter (<6 mm) prosthetic vascular grafts, a variety of strategies have evolved utilizing a tissue-engineering approach. Much of this work has focused on enhancing the endothelialization of these grafts. A healthy, confluent endothelial layer provides dynamic control over homeo-stasis, influencing and preventing thrombosis and smooth muscle cell proliferation that can lead to intimal hyperplasia. Strategies to improve endothelialization of biodegradable polymeric grafts have encompassed both chemical and physical modifications to graft surfaces, many focusing on the recruitment of endothelial and endothelial progenitor cells. This review aims to provide a compilation of current and developing strategies that utilize in situ endothelialization to improve vascular graft outcomes, providing a context for the future directions of vascular tissue-engineering strategies that do not require preprocedural cell seeding.

Hypoxia Affects the Structure of Breast Cancer Cell-Derived Matrix to Support Angiogenic Responses of Endothelial Cells

Hypoxia, a common feature of the tumor environment and participant in tumor progression, is known to alter gene and protein expression of several Extracellular Matrix (ECM) proteins, many of which have roles in angiogenesis. Previously, we reported that ECM deposited from co-cultures of Neonatal Fibroblasts (NuFF) with breast cancer cells, supported 3-dimensional vascular morphogenesis. Here, we sought to characterize the hypoxic ECM and to identify whether the deposited ECM induce angiogenic responses in Endothelial Cells (ECs). NuFF and MDA-MB-231 breast cancer cells were co-cultured, subjected to alternating cycles of 24 hours of 1% (hypoxia) and 21% (atmospheric) oxygen and de-cellularized for analyses of deposited ECM. We report differences in mRNA expression profiles of matrix proteins and crosslinking enzymes relevant to angiogenesis in hypoxia-exposed co-cultures. Interestingly, overt differences in the expression of ECM proteins were not detected in the de-cellularized ECM; however, up-regulation of the cell-binding fragment of fibronecin was observed in the conditioned media of hypoxic co-cultures. Ultrastructure analyses of the de-cellularized ECM revealed differences in fiber morphology with hypoxic fibers more compact and aligned, occupying a greater percent area and having larger diameter fibers than atmospheric ECM. Examining the effect of hypoxic ECM on angiogenic responses of ECs, morphological differences in Capillary-Like Structures (CLS) formed atop de-cellularized hypoxic and atmospheric ECM were not evident. Interestingly, we found that hypoxic ECM regulated the expression of angiogenic factors and matrix metalloproteinases in CLS. Overall, we report that in vitro, hypoxia does not alter the composition of the ECM deposited by co-cultures of NuFF/MDA-MB-231, but rather alters fiber morphology, and induces vascular expression of angiogenic growth factors and metalloproteinases. Taken together, these results have important implications for understanding how the hypoxic matrix may regulate angiogenesis in tumors.

Engineering approaches for investigating tumor angiogenesis: exploiting the role of the extracellular matrix

A major paradigm shift in cancer research is the emergence of multidisciplinary approaches to investigate complex cell behaviors, to elucidate regulatory mechanisms and to identify therapeutic targets. Recently, efforts are focused on the engineering of complex in vitro models, which more accurately recapitulate the growth and progression of cancer. These strategies have proven vital for investigating and targeting the events that control tumor angiogenesis. In this review, we explore how the emerging engineering approaches are being used to unlock the complex mechanisms regulating tumor angiogenesis. Emphasis is placed on models using natural and synthetic biomaterials to generate scaffolds mimicking the extracellular matrix, which is known to play a critical role in angiogenesis. While the models presented in this review are revolutionary, improvements are still necessary and concepts for advancing and perfecting engineering approaches for modeling tumor angiogenesis are proposed. Overall, the marriage between disparate scientific fields is expected to yield significant improvements in our understanding and treatment of cancer.

Titania-polymeric powder coatings with nano-topography support enhanced human mesenchymal cell responses

Titanium implant osseointegration is dependent on the cellular response to surface modifications and coatings. Titania-enriched nanocomposite polymeric resin coatings were prepared through the application of advanced ultrafine powder coating technology. Their surfaces were readily modified to create nano-rough (<100 nm) surface nano-topographies that supported human embryonic palatal mesenchymal cell responses. Energy dispersive x-ray spectroscopy confirmed continuous and homogenous coatings with a similar composition and even distribution of titanium. Scanning electron microscopy (SEM) showed complex micro-topographies, and atomic force microscopy revealed intricate nanofeatures and surface roughness. Cell counts, mitochondrial enzyme activity reduction of yellow 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) to dark purple, SEM, and inverted fluorescence microscopy showed a marked increase in cell attachment, spreading, proliferation, and metabolic activity on the nanostructured surfaces. Reverse Transcription- Polymerase Chain Reaction (RT-PCR) analysis showed that type I collagen and Runx2 expression were induced, and Alizarin red staining showed that mineral deposits were abundant in the cell cultures grown on nanosurfaces. This enhancement in human mesenchymal cell attachment, growth, and osteogenesis were attributed to the nanosized surface topographies, roughness, and moderate wetting characteristics of the coatings. Their dimensional similarity to naturally occurring matrix proteins and crystals, coupled with their increased surface area for protein adsorption, may have facilitated the response. Therefore, this application of ultrafine powder coating technology affords highly biocompatible surfaces that can be readily modified to accentuate the cellular response.

Characterization of surface properties and cytocompatibility of ion-etched chitosan films

Surface modification of biomaterials has been highlighted by biomedical engineers as a facile method for improving cell-biomaterial interactions without the expense and time required to develop new materials. In the present study, we investigated the influence of ion-etching on the surface characteristics of chitosan films using XPS and ATR FT-IR. The physiological behavior of human dermal fibroblasts (hDFs) grown on such surfaces was studied by evaluating adhesive and proliferative properties, and by examining surface morphologies of hDFs using AFM. hDFs displayed different shapes depending on the ion-etching time. hDFs grown on chitosan films ion-etched for 5 min displayed better development of lamellipodia and filopodia around the hDF periphery than did cells grown on nonmodified chitosan film, whereas hDFs did not spread well on films ion-etched for 20 min. Films ion-etched for 5 min or less had higher NH(2) and COOH contents, leading to enhanced hDF adhesion and proliferation.

Endothelial cell responses to micropillar substrates of varying dimensions and stiffness

In the vascular niche, the extracellular matrix (ECM) provides a structural scaffold with a rich ligand landscape of essential matrix proteins that supports the organization and stabilization of endothelial cells (ECs) into functional blood vessels. Many of the physical interactions between ECs and macromolecular components of the ECM occur at both the micron and submicron scale. In addition, the elasticity of the ECM has been shown to be a critical factor in the progress of the angiogenic cascade. Here, we sought to determine the effect of substrate topography and elasticity (stiffness) on EC behavior. Utilizing a unique SiO(2) substrate with an array of micropillars, we first demonstrate that micropillars with heights >3 μm significantly decrease EC adhesion and spreading. Fibronectin (Fn) patterning of 1 μm high micropillars enabled EC adhesion onto the micropillars and promoted alignment in a single-cell chain manner. We then developed a robust method to generate a soft micropillar substrate array made of polydimethylsiloxane (PDMS), similar to the SiO(2) substrate. Finally, we examined the kinetics of EC adhesion and spreading on the soft PDMS substrates compared to the stiff SiO(2) substrates. Culturing cells on the PDMS substrates demonstrated an enhanced EC elongation and alignment when compared to stiff SiO(2) with similar topographical features. We conclude that the elongation and alignment of ECs is coregulated by substrate topography and stiffness and can be harnessed to guide vascular organization.

Selective adhesion and growth of vascular endothelial cells on bioactive peptide nanofiber functionalized stainless steel surface

Metal-based scaffolds such as stents are the most preferred treatment methods for coronary artery disease. However, impaired endothelialization on the luminal surface of the stents is a major limitation occasionally leading to catastrophic consequences in the long term. Coating the stent surface with relevant bioactive molecules is considered to aid in recovery of endothelium around the wound site. However, this strategy remains challenging due to restrictions in availability of proper bioactive signals that will selectively promote growth of endothelium and the lack of convenience for immobilization of such signaling molecules on the metal surface. In this study, we developed self-assembled peptide nanofibers that mimic the native endothelium extracellular matrix and that are securely immobilized on stainless steel surface through mussel-inspired adhesion mechanism. We synthesized Dopa-conjugated peptide amphiphile and REDV-conjugated peptide amphiphile that are self-assembled at physiological pH. We report that Dopa conjugation enabled nanofiber coating on stainless steel surface, which is the most widely used backbone of the current stents. REDV functionalization provided selective growth of endothelial cells on the stainless steel surface. Our results revealed that adhesion, spreading, viability and proliferation rate of vascular endothelial cells are remarkably enhanced on peptide nanofiber coated stainless steel surface compared to uncoated surface. On the other hand, although vascular smooth muscle cells exhibited comparable adhesion and spreading profile on peptide nanofibers, their viability and proliferation significantly decreased. Our design strategy for surface bio-functionalization created a favorable microenvironment to promote endothelial cell growth on stainless steel surface, thereby providing an efficient platform for bioactive stent development for long term treatment of cardiovascular diseases.

Do bacteria differentiate between degrees of nanoscale surface roughness?

Whereas the employment of nanotechnology in electronics and optics engineering is relatively well established, the use of nanostructured materials in medicine and biology is undoubtedly novel. Certain nanoscale surface phenomena are being exploited to promote or prevent the attachment of living cells. However, as yet, it has not been possible to develop methods that completely prevent cells from attaching to solid surfaces, since the mechanisms by which living cells interact with the nanoscale surface characteristics of these substrates are still poorly understood. Recently, novel and advanced surface characterisation techniques have been developed that allow the precise molecular and atomic scale characterisation of both living cells and the solid surfaces to which they attach. Given this additional capability, it may now be possible to define boundaries, or minimum dimensions, at which a surface feature can exert influence over an attaching living organism.This review explores the current research on the interaction of living cells with both native and nanostructured surfaces, and the role that these surface properties play in the different stages of cell attachment.

Microscale plasma-initiated patterning of electrospun polymer scaffolds

Microscale plasma-initiated patterning (μPIP) is a novel micropatterning technique used to create biomolecular micropatterns on polymer surfaces. The patterning method uses a polydimethylsiloxane (PDMS) stamp to selectively protect regions of an underlying substrate from oxygen plasma treatment resulting in hydrophobic and hydrophilic regions. Preferential adsorption of the biomolecules onto either the plasma-exposed (hydrophilic) or plasma-protected (hydrophobic) regions leads to the biomolecular micropatterns. In the current work, laminin-1 was applied to an electrospun polyamide nanofibrillar matrix following plasma treatment. Radial glial clones (neural precursors) selectively adhered to these patterned matrices following the contours of proteins on the surface. This work demonstrates that textured surfaces, such as nanofibrillar scaffolds, can be micropatterned to provide external chemical cues for cellular organization.