RGD peptide-conjugated poly(dimethylsiloxane) promotes adhesion, proliferation, and collagen secretion of human fibroblasts

Covalent Immobilization of Collagen Type I to a Polydimethylsiloxane Surface for Preventing Cell Detachment by Retaining Collagen Molecules under Uniaxial Cyclic Mechanical Stretching Stress

Surface modification of polydimethylsiloxane (PDMS) with an extracellular matrix (ECM) is useful for enhancing stable cell attachment. However, few studies have investigated the correlation between the stability of deposited ECM and cell behavior on the PDMS surfaces in external stretched cell culture systems. Herein, covalent collagen type I (Col)-immobilized PDMS surfaces were fabricated using 3-aminopropyl-trimethoxysilane, glutaraldehyde, and Col molecules. The immobilized collagen molecules on the PDMS surface were more stable and uniform than the physisorbed collagen. The cells stably adhered to the Col-immobilized surface and proliferated even under uniaxial cyclic mechanical stretching stress (UnCyMSt), whereas the cells gradually detached from the Col-physisorbed PDMS surface, accompanied by a decrease in the number of deposited collagen molecules. Moreover, the immobilization of collagen molecules enhanced cell alignment under the UnCyMSt. This study reveals that cell adhesion, proliferation, and alignment under the UnCyMSt can be attributed to the retention of collagen molecules on the PDMS surface.

Influence of Aerosolization on Endothelial Cells for Efficient Cell Deposition in Biohybrid and Regenerative Applications

The endothelialization of gas exchange membranes can increase the hemocompatibility of extracorporeal membrane oxygenators and thus become a long-term lung replacement option. Cell seeding on large or uneven surfaces of oxygenator membranes is challenging, with cell aerosolization being a possible solution. In this study, we evaluated the endothelial cell aerosolization for biohybrid lung application. A Vivostat^® system was used for the aerosolization of human umbilical vein endothelial cells with non-sprayed cells serving as a control. The general suitability was evaluated using various flow velocities, substrate distances and cell concentrations. Cells were analyzed for survival, apoptosis and necrosis levels. In addition, aerosolized and non-sprayed cells were cultured either static or under flow conditions in a dynamic microfluidic model. Evaluation included immunocytochemistry and gene expression via quantitative PCR. Cell survival for all tested parameters was higher than 90%. No increase in apoptosis and necrosis levels was seen 24 h after aerosolization. Spraying did not influence the ability of the endothelial cells to form a confluent cell layer and withstand shear stresses in a dynamic microfluidic model. Immunocytochemistry revealed typical expression of CD31 and von Willebrand factor with cobble-stone cell morphology. No change in shear stress-induced factors after aerosolization was reported by quantitative PCR analysis. With this study, we have shown the feasibility of endothelial cell aerosolization with no significant changes in cell behavior. Thus, this technique could be used for efficient the endothelialization of gas exchange membranes in biohybrid lung applications.

Effects of RGD-fused silk fibroin in a solution format on fibroblast proliferation and collagen production

BACKGROUND

Collagen production in fibroblasts is important for skin tissue repair. Cell-adhesive Arg-Gly-Asp (RGD) peptides immobilized on scaffolds stimulate fibroblast collagen production, but RGD peptides in solution exhibit opposite effects. Transgenic silkworm technology enables the design of fusion positions for RGD peptides in silk fibroin molecules. The effect of RGD-fused silk fibroin in solution on fibroblast cell activity remains unclear.

OBJECTIVE

To clarify the effects of RGD peptides fused to silk fibroin heavy (H)-chain or light (L)-chain on fibroblast proliferation and collagen production when RGD-fused silk fibroin proteins were added to the culture medium.

METHODS

Silk fibers with RGD-fused H-chains (H-RGD) or L-chains (L-RGD) were degummed, dissolved, and dialyzed to prepare H-RGD or L-RGD aqueous solutions, respectively. These solutions were added to the fibroblast medium, and their proliferation and collagen production were quantified.

RESULTS

Both L- and H-RGD stimulated fibroblast proliferation at a similar level, even in a solution format, but L-RGD promoted fibroblast collagen production significantly, indicating the synergistic effect of the native H-chain and RGD-fused L-chain.

CONCLUSION

RGD-fused silk fibroin in solution stimulated fibroblast proliferation and collagen production, depending on the fusion position of the peptides.

RNA-Seq analysis of a Pax3-expressing myoblast clone in-vitro and effect of culture surface stiffness on differentiation

Skeletal muscle satellite cells cultured on soft surfaces (12 kPa) show improved differentiation than cells cultured on stiff surfaces (approximately 100 kPa). To better understand the reasons for this, we performed an RNA-Seq analysis for a single satellite cell clone (C1F) derived from the H2k^b-tsA58 immortomouse, which differentiates into myotubes under tightly regulated conditions (withdrawal of ɣ-interferon, 37 °C). The largest change in overall gene expression occurred at day 1, as cells switched from proliferation to differentiation. Surprisingly, further analysis showed that proliferating C1F cells express Pax3 and not Pax7, confirmed by immunostaining, yet their subsequent differentiation into myotubes is normal, and enhanced on softer surfaces, as evidenced by significantly higher expression levels of myogenic regulatory factors, sarcomeric genes, enhanced fusion and improved myofibrillogenesis. Levels of mRNA encoding extracellular matrix structural constituents and related genes were consistently upregulated on hard surfaces, suggesting that a consequence of differentiating satellite cells on hard surfaces is that they attempt to manipulate their niche prior to differentiating. This comprehensive RNA-Seq dataset will be a useful resource for understanding Pax3 expressing cells.

Strategy for Conjugating Oligopeptides to Mesoporous Silica Nanoparticles Using Diazirine-Based Heterobifunctional Linkers

Successful strategies for the attachment of oligopeptides to mesoporous silica with pores large enough to load biomolecules should utilize the high surface area of pores to provide an accessible, protective environment. A two-step oligopeptide functionalization strategy is examined here using diazirine-based heterobifunctional linkers. Mesoporous silica nanoparticles (MSNPs) with average pore diameter of ~8 nm and surface area of ~730 m²/g were synthesized and amine-functionalized. Tetrapeptides Gly-Gly-Gly-Gly (GGGG) and Arg-Ser-Ser-Val (RSSV), and a peptide comprised of four copies of RSSV (4RSSV), were covalently attached via their N-terminus to the amine groups on the particle surface by a heterobifunctional linker, sulfo-succinimidyl 6-(4,4′-azipentanamido)hexanoate (sulfo-NHS-LC-diazirine, or SNLD). SNLD consists of an amine-reactive NHS ester group and UV-activable diazirine group, providing precise control over the sequence of attachment steps. Attachment efficiency of RSSV was measured using fluorescein isothiocyanate (FITC)-tagged RSSV (RSSV-FITC). TGA analysis shows similar efficiency (0.29, 0.31 and 0.26 mol peptide/mol amine, respectively) for 4G, RSSV and 4RSSV, suggesting a generalizable method of peptide conjugation. The technique developed here for the conjugation of peptides to MSNPs provides for their attachment in pores and can be translated to selective peptide-based separation and concentration of therapeutics from aqueous process and waste streams.

Versatility of unsaturated polyesters from electrospun macrolactones: RGD immobilization to increase cell attachment

Poly(globalide) (PGl), an aliphatic polyester derived from unsaturated macrocylic lactone, can be cross-linked during electrospinning and drug-loaded for regenerative medicine applications. However, it lacks intrinsic recognition sites for cell adhesion and proliferation. In order to improve their cell adhesiveness, and therefore their therapeutic potential, we aimed to functionalize electrospun PGl fibers with RGD sequence generating a biomimetic scaffold. First, an amine compound was attached to the surface double bonds of the PGl fibers. Subsequently, the amino groups were coupled with RGD sequences. X-ray photoelectron spectroscopy (XPS) analysis confirmed the functionalization. The obtained fibers were more hydrophilic, as observed by contact angle analysis, and presented smaller Young's modulus, although similar tensile strength compared with non-functionalized cross-linked fibers. In addition, the functionalization process did not significantly alter fibers morphology, as observed by scanning electron microscopy (SEM). Finally, in vitro analysis evidenced the increase in human mesenchymal stromal cells (hMSC) adhesion (9.88 times higher DNA content after 1 day of culture) and proliferation (3.57 times higher DNA content after 8 days of culture) compared with non-functionalized non-cross-linked fibers. This is the first report demonstrating the functionalization of PGl fibers with RGD sequence, improving PGl therapeutic potential and further corroborating the use of this highly versatile material toward regenerative medicine applications.

The fibrillin-1 RGD motif posttranscriptionally regulates ERK1/2 signaling and fibroblast proliferation via miR-1208

Fibrillin-1 is an extracellular matrix protein which contains one conserved RGD integrin-binding motif. It constitutes the backbone of microfibrils in many tissues, and mutations in fibrillin-1 cause various connective tissue disorders. Although it is well established that fibrillin-1 interacts with several RGD-dependent integrins, very little is known about the associated intracellular signaling pathways. Recent published evidence identified a subset of miRNAs regulated by fibrillin-1 RGD-cell adhesion, with miR-1208 among the most downregulated. The present study shows that the downregulated miR-1208 controls fibroblast proliferation. Inhibitor experiments revealed that fibrillin-1 RGD suppressed miR-1208 expression via c-Src kinase and the downstream JNK signaling. Bioinformatic prediction and experimental target sequence validation demonstrated four miR-1208 binding sites on the ERK2 mRNA and one on the MEK1 mRNA. ERK2 and MEK1 are critical proliferation-promoting kinases. Decreased miR-1208 levels elevated the total and phosphorylated ERK1/2 and MEK1/2 protein levels and the phosphorylated to total ERK1/2 ratio. Together, the data demonstrate a novel outside-in signaling mechanism explaining how fibrillin-1 RGD-cell binding regulates fibroblast proliferation.

A low-cost uniaxial cell stretcher for six parallel wells

Cells in the lungs, the heart, and numerous other organs, are constantly exposed to dynamic forces and deformations. To mimic these dynamic mechanical loading conditions and to study the resulting cellular responses such as morphological changes or the activation of biochemical signaling pathways, cells are typically seeded on flexible 2D substrates that are uniaxially or biaxially stretched. Here, we present an open-source cell stretcher built from parts of an Anet A8 3D printer. The cell stretcher is controlled by a fully programmable open-source software using GCode and Python. Up to six flexible optically clear substrates can be stretched simultaneously, allowing for comparative multi-batch biological studies including microscopic image analysis. The cell yield from the cell culture area of 4 cm2 per substrate is sufficient for Western-blot protein analysis. As a proof-of-concept, we study the activation of the Yes-associated protein (YAP) mechanotransduction pathway in response to increased cytoskeletal tension induced by uniaxial stretching of epithelial cells. Our data support the previously observed activation of the YAP transcription pathway by stretch-induced increase in cytoskeletal tension and demonstrate the suitability of the cell stretcher to study complex mechano-biological processes.

A Versatile Surface Modification Method via Vapor-phase Deposited Functional Polymer Films for Biomedical Device Applications

For last two decades, the demand for precisely engineered three-dimensional structures has increased continuously for the developments of biomaterials. With the recent advances in micro- and nano-fabrication techniques, various devices with complex surface geometries have been devised and produced in the pharmaceutical and medical fields for various biomedical applications including drug delivery and biosensors. These advanced biomaterials have been designed to mimic the natural environments of tissues more closely and to enhance the performance for their corresponding biomedical applications. One of the important aspects in the rational design of biomaterials is how to configure the surface of the biomedical devices for better control of the chemical and physical properties of the bioactive surfaces without compromising their bulk characteristics. In this viewpoint, it of critical importance to secure a versatile method to modify the surface of various biomedical devices. Recently, a vapor phase method, termed initiated chemical vapor deposition (iCVD) has emerged as damage-free method highly beneficial for the conformal deposition of various functional polymer films onto many kinds of micro- and nano-structured surfaces without restrictions on the substrate material or geometry, which is not trivial to achieve by conventional solution-based surface functionalization methods. With proper structural design, the functional polymer thin film via iCVD can impart required functionality to the biomaterial surfaces while maintaining the fine structure thereon. We believe the iCVD technique can be not only a valuable approach towards fundamental cell-material studies, but also of great importance as a platform technology to extend to other prospective biomaterial designs and material interface modifications for biomedical applications.

Surface-directed engineering of tissue anisotropy in microphysiological models of musculoskeletal tissue

Here, we present an approach to model and adapt the mechanical regulation of morphogenesis that uses contractile cells as sculptors of engineered tissue anisotropy in vitro. Our method uses heterobifunctional cross-linkers to create mechanical boundary constraints that guide surface-directed sculpting of cell-laden extracellular matrix hydrogel constructs. Using this approach, we engineered linearly aligned tissues with structural and mechanical anisotropy. A multiscale in silico model of the sculpting process was developed to reveal that cell contractility increases as a function of principal stress polarization in anisotropic tissues. We also show that the anisotropic biophysical microenvironment of linearly aligned tissues potentiates soluble factor-mediated tenogenic and myogenic differentiation of mesenchymal stem cells. The application of our method is demonstrated by (i) skeletal muscle arrays to screen therapeutic modulators of acute oxidative injury and (ii) a 3D microphysiological model of lung cancer cachexia to study inflammatory and oxidative muscle injury induced by tumor-derived signals.

Effects of physicochemical properties of polyacrylamide (PAA) and (polydimethylsiloxane) PDMS on cardiac cell behavior

In vitro cell culture is commonly applied in laboratories around the world. Cultured cells are either of primary origin or established cell lines. Such transformed cell lines are increasingly replaced by pluripotent stem cell derived organotypic cells with more physiological properties. The quality of the culture conditions and matrix environment is of considerable importance in this regard. In fact, mechanical cues of the extracellular matrix have substantial effects on the cellular physiology. This is especially true if contractile cells such as cardiomyocytes are cultured. Therefore, elastic biomaterials have been introduced as scaffolds in 2D and 3D culture models for different cell types, cardiac cells among them. In this review, key aspects of cell-matrix interaction are highlighted with focus on cardiomyocytes and chemical properties as well as strengths and potential pitfalls in using two commonly applied polymers for soft matrix engineering, polyacrylamide (PAA) and polydimethylsiloxane (PDMS) are discussed.

Review of silicone surface modification techniques and coatings for antibacterial/antimicrobial applications to improve breast implant surfaces

Silicone implants are widely used in the medical field for plastic or reconstructive surgeries for the purpose of soft tissue issues. However, as with any implanted object, healthcare-associated infections are not completely avoidable. The material suffers from a lack of biocompatibility and is often subject to bacterial/microbial infections characterized by biofilm growth. Numerous strategies have been developed to either prevent, reduce, or fight bacterial adhesion by providing an antibacterial property. The present review summarizes the diverse approaches to deal with bacterial infections on silicone surfaces along with the different methods to activate/oxidize the surface before any surface modifications. It includes antibacterial coatings with antibiotics or nanoparticles, covalent attachment of active bacterial molecules like peptides or polymers. Regarding silicone surfaces, the activation step is essential to render the surface reactive for any further modifications using energy sources (plasma, UV, ozone) or chemicals (acid solutions, sol-gel strategies, chemical vapor deposition). Meanwhile, corresponding work on breast silicone prosthesis is discussed. The latter is currently in the line of sight for causing severe capsular contractures. Specifically, to that end, besides chemical modifications, the antibacterial effect can also be achieved by physical surface modifications by adjusting the surface roughness and topography for instance.

MechanoBioTester: A Decoupled Multistimulus Cell Culture Device for Studying Complex Microenvironments In Vitro

Increasingly being recognized is the role of the complex microenvironment to regulate cell phenotype; however, the cell culture systems used to study these effects in vitro are lagging. The complex microenvironment is host to a combination of biological interactions, chemical factors, and mechanical stimuli. Many devices have been designed to probe the effects of one mechanical stimulus, but few are capable of systematically interrogating all combinations of mechanical stimuli with independent control. To address this gap, we have developed the MechanoBioTester platform, a decoupled, multi-stimulus cell culture model for studying the cellular response to complex microenvironments in vitro. The system uses an engineered elastomeric chamber with a specially defined region for incorporating different target materials to act as the cell culture substrate. We have tested the system with several target materials including: polydimethylsiloxane elastomer, polyacrylamide gel, poly(1,8-octanediol citrate) elastomer, and type I collagen gel for both 2D and 3D co-culture. Additionally, when the chamber is connected to a flow circuit and our stretching device, stimuli in the form of fluid flow, cyclic stretch, and hydrostatic pressure are able to be imparted with independent control. We validated the device using experimental and computational methods to define a range of capabilities relevant to physiological microenvironments. The MechanoBioTester platform promises to function as a model system for mechanobiology, biomaterial design, and drug discovery applications that focus on probing the impact of a complex microenvironment in an in vitro setting. The protocol described within provides the details characterizing the MechanoBioTester system, the steps for fabricating the MechanoBioTester chamber, and the procedure for operating the MechanoBioTester system to stimulate cells.

EndOxy: Dynamic Long-Term Evaluation of Endothelialized Gas Exchange Membranes for a Biohybrid Lung

In the concept of a biohybrid lung, endothelial cells seeded on gas exchange membranes form a non-thrombogenic an anti-inflammatory surface to overcome the lacking hemocompatibility of today's oxygenators during extracorporeal membrane oxygenation. To evaluate this concept, the long-term stability and gas exchange performance of endothelialized RGD-conjugated polydimethylsiloxane (RGD-PDMS) membranes was evaluated. Human umbilical vein endothelial cells (ECs) were cultured on RGD-PDMS in a model system under physiological wall shear stress (WSS) of 0.5 Pa for up to 33 days. Gas exchange performance was tested with three biological replicates under elevated WSS of 2.5 Pa using porcine blood adjusted to venous values following ISO 7199 and blood gas analysis. EC morphology was assessed by immunocytochemistry (n = 3). RGD-PDMS promoted endothelialization and stability of endothelialized membranes was shown for at least 33 days and for a maximal WSS of 2.5 Pa. Short-term exposure to porcine blood did not affect EC integrity. The gas transfer tests provided evidence for the oxygenation and decarboxylation of the blood across endothelialized membranes with a decrease of transfer rates over time that needs to be addressed in further studies with larger sample sizes. Our results demonstrate the general suitability of RGD-PDMS for biohybrid lung applications, which might enable long-term support of patients with chronic lung failure in the future.

Current Applications of Biopolymer-based Scaffolds and Nanofibers as Drug Delivery Systems

BACKGROUND

The high surface-to-volume ratio of polymeric nanofibers makes them an effective vehicle for the release of bioactive molecules and compounds such as growth factors, drugs, herbal extracts and gene sequences. Synthetic polymers are commonly used as sensors, reinforcements and energy storage, whereas natural polymers are more prone to mimicking an extracellular matrix. Natural polymers are a renewable resource and classified as an environmentally friendly material, which might be used in different techniques to produce nanofibers for biomedical applications such as tissue engineering, implantable medical devices, antimicrobial barriers and wound dressings, among others. This review sheds some light on the advantages of natural over synthetic polymeric materials for nanofiber production. Also, the most important techniques employed to produce natural nanofibers are presented. Moreover, some pieces of evidence regarding toxicology and cell-interactions using natural nanofibers are discussed. Clearly, the potential extrapolation of such laboratory results into human health application should be addressed cautiously.

Rapid and Robust Coating Method to Render Polydimethylsiloxane Surfaces Cell-Adhesive

Polydimethylsiloxane (PDMS) is a synthetic material with excellent properties for biomedical applications because of its easy fabrication method, high flexibility, permeability to oxygen, transparency, and potential to produce high-resolution structures in the case of lithography. However, PDMS needs to be modified to support homogeneous cell attachments and spreading. Even though many physical and chemical methods, like plasma treatment or extracellular matrix coatings, have been developed over the last decades to increase cell-surface interactions, these methods are still very time-consuming, often not efficient enough, complex, and can require several treatment steps. To overcome these issues, we present a novel, robust, and fast one-step PDMS coating method using engineered anchor peptides fused to the cell-adhesive peptide sequence (glycine-arginine-glycine-aspartate-serine, GRGDS). The anchor peptide attaches to the PDMS surface predominantly by hydrophobic interactions by simply dipping PDMS in a solution containing the anchor peptide, presenting the GRGDS sequence on the surface available for cell adhesion. The binding performance and kinetics of the anchor peptide to PDMS are characterized, and the coatings are optimized for efficient cell attachment of fibroblasts and endothelial cells. Additionally, the applicability is proven using PDMS-based directional nanotopographic gradients, showing a lower threshold of 5 μm wrinkles for fibroblast alignment.

Polydimethylsiloxane materials with supraphysiological elasticity enable differentiation of myogenic cells

Myogenic differentiation during muscle regeneration is guided by various physical and biochemical factors. Recently, substratum elasticity has gained attention as a physical signal that influences both cell differentiation and tissue regeneration. In this work, we investigated the influence of substratum elasticity on proliferation and differentiation of myogenic cells, mouse myoblasts of the C2C12 cell line and mouse primary myoblasts derived from satellite cells-muscle stem cells playing key role in muscle regeneration. Materials with different elastic moduli within the MPa scale based on polydimethylsiloxane (PDMS) were used as cell substratum and characterized for surface roughness, wettability, and micromechanical characteristics. We found that surface properties of PDMS substrates are alter nonlinearly with the increase of the material's elastic modulus. Using this system we provide an evidence that materials with elastic modulus higher than that of physiological skeletal muscle tissue do not perturb myogenic differentiation of both types of myoblasts; thus, can be used as biomaterials for muscle tissue engineering. PDMS materials with elasticity within the range of 2.5-4 MPa may transiently limit the proliferation of myoblasts, but not the efficiency of their differentiation. Direct correlation between substratum elasticity and myogenic differentiation efficiency was not observed but the other surface properties of the PDMS materials such as nanoroughness and wettability were also diverse.

Biomimetic Designer Scaffolds Made of D,L-Lactide-ɛ-Caprolactone Polymers by 2-Photon Polymerization

IMPACT STATEMENT

In tissue engineering (TE), the establishment of cell targeting materials, which mimic the conditions of the physiological extracellular matrix (ECM), seems to be a mission impossible without advanced materials and fabrication techniques. With this in mind we established a toolbox based on (D,L)-lactide-ɛ-caprolactone methacrylate (LCM) copolymers in combination with a nano-micromaskless lithography technique, the two-photon polymerization (2-PP) to mimic the hierarchical structured and complex milieu of the natural ECM. To demonstrate the versatility of this toolbox, we choose two completely different application scenarios in bone and tumor TE to show the high potential of this concept in therapeutic and diagnostic application.

Combinational Effects of Polymer Viscoelasticity and Immobilized Peptides on Cell Adhesion to Cell-selective Scaffolds

Immobilization of functional peptides on polymer material is necessary to produce cell-selective scaffolds. However, the expected effects of peptide immobilization differ considerably according to the properties of selected polymers. To understand such combinational effects of peptides and polymers, varieties of scaffolds including a combination of six types of poly(ε-caprolactone-co-D,L-lactide) and four types of cell-selective adhesion peptides were fabricated and compared. On each scaffold, the scaffold properties (i.e. mechanical) and their biological functions (i.e. fibroblast-/endothelial cell-/smooth muscle cell-selective adhesion) were measured and compared. The results showed that the cell adhesion performances of the peptides were considerably enhanced or inhibited by the combination of peptide and polymer properties. In the present study, we illustrated the combinational property effects of peptides and polymers using multi-parametric analyses. We provided an example of determining the best scaffold performance for tissue-engineered medical devices based on quantitative data-driven analyses.

Native extracellular matrix-derived semipermeable, optically transparent, and inexpensive membrane inserts for microfluidic cell culture

Semipermeable cell culture membranes are commonly used in multilayered microfluidic devices to mimic the basement membrane in vivo and to create compartmentalized microenvironments for physiological cell growth and differentiation. However, existing membranes are predominantly made up of synthetic polymers, providing limited capacity to replicate cellular interactions with native extracellular matrices that play a crucial role in the induction of physiological phenotypes. Here we describe a new type of cell culture membranes engineered from native extracellular matrix (ECM) materials that are thin, semipermeable, optically transparent, and amenable to integration into microfluidic cell culture devices. Facile and cost-effective fabrication of these membranes was achieved by controlled sequential steps of vitrification that transformed three-dimensional (3D) ECM hydrogels into structurally stable thin films. By modulating the composition of the ECM, our technique provided a means to tune key membrane properties such as optical transparency, stiffness, and porosity. For microfluidic cell culture, we constructed a multilayered microdevice consisting of two parallel chambers separated by a thin membrane insert derived from different types of ECM. This study showed that our ECM membranes supported attachment and growth of various types of cells (epithelial, endothelial, and mesenchymal cells) under perfusion culture conditions. Our data also revealed the promotive effects of the membranes on adhesion-associated intracellular signaling that mediates cell-ECM interactions. Moreover, we demonstrated the use of these membranes for constructing compartmentalized microfluidic cell culture systems to induce physiological tissue differentiation or to replicate interfaces between different tissue types. Our approach provides a robust platform to produce and engineer biologically active cell culture substrates that serve as promising alternatives to conventional synthetic membrane inserts. This strategy may contribute to the development of physiologically relevant in vitro cell culture models for a wide range of applications.

Mussel-inspired deposition of copper on titanium for bacterial inhibition and enhanced osseointegration in a periprosthetic infection model

Periprosthetic infection represents one of the most devastating complications in orthopedic surgeries.

Antibacterial activity and osseointegration of silver-coated poly(ether ether ketone) prepared using the polydopamine-assisted deposition technique

PEEK-PDA-Ag substrates may be a promising orthopaedic implant material due to the outstanding biocompatibility and antibacterial properties.

Investigation of human cell response to covalently attached RADA16-I peptide on silicon surfaces

We described a modification of the ionic (RADARADARADARADA)(1) peptide or RADA16-I with 4-azidophenyl isothiocyanate via a specific and gentle reaction. The azidated peptide was covalently immobilized on an alkyne-terminated monolayer on Si(111) via the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction. Detailed characterization using Impedance spectroscopy (IS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy demonstrated high coverage of the RADA 16-I peptide on silicon surfaces. Scanning electron microscopy (SEM) and methyl tetrazole sulfate (MTS) assay were used to characterize the morphology and proliferation ability of human fibroblast cells on surfaces. Cell adhesion assay was performed to examine cell-substrate interactions. Significant differences in fibroblast cell morphology, adhesion, and viability were observed on the RADA16-I peptide modified surfaces compared to the control surfaces. These results may suggest a potential application of RADA16-I peptide modified surfaces in biomedical applications.

Combinational Effect of Cell Adhesion Biomolecules and Their Immobilized Polymer Property to Enhance Cell-Selective Adhesion

Although surface immobilization of medical devices with bioactive molecules is one of the most widely used strategies to improve biocompatibility, the physicochemical properties of the biomaterials significantly impact the activity of the immobilized molecules. Herein we investigate the combinational effects of cell-selective biomolecules and the hydrophobicity/hydrophilicity of the polymeric substrate on selective adhesion of endothelial cells (ECs), fibroblasts (FBs), and smooth muscle cells (SMCs). To control the polymeric substrate, biomolecules are immobilized on thermoresponsive poly(N-isopropylacrylamide-co-2-carboxyisopropylacrylamide) (poly(NIPAAm-co-CIPAAm))-grafted glass surfaces. By switching the molecular conformation of the biomolecule-immobilized polymers, the cell-selective adhesion performances are evaluated. In case of RGDS (Arg-Gly-Asp-Ser) peptide-immobilized surfaces, all cell types adhere well regardless of the surface hydrophobicity. On the other hand, a tri-Arg-immobilized surface exhibits FB-selectivity when the surface is hydrophilic. Additionally, a tri-Ile-immobilized surface exhibits EC-selective cell adhesion when the surface is hydrophobic. We believe that the proposed concept, which is used to investigate the biomolecule-immobilized surface combination, is important to produce new biomaterials, which are highly demanded for medical implants and tissue engineering.

Reconstruction of vascular structure with multicellular components using cell transfer printing methods

Natural vessel has three types of concentric cell layers that perform their specific functions. Here, the fabrication of vascular structure is reported by transfer printing of three different cell layers using thermosensitive hydrogels. Tetronic-tyramine and RGD peptide are co-crosslinked to prepare cell adhesive and thermosensitive hydrogels. The hydrogel increases its diameter by 1.26 times when the temperature reduces from 37 °C to 4 °C. At optimized seeding density, three types of cells form monolayers on the hydrogel, which is then transferred to the target surface within 3 min. Three monolayers are simultaneously transferred on one substrate with controlled shape and arrangement. The same approach is applied onto nanofiber scaffolds that are cultured for more than 5 d. Every type of monolayer shows proliferation and migration on nanofiber scaffolds, and the formation of robust cell-cell contact is revealed by CD31 staining in endothelial cell layer. A vascular structure with multicellular components is fabricated by transfer of three monolayers on nanofibers that are manually rolled with the diameter and length of the tube being approximately 3 mm and 12 mm, respectively. Collectively, it is concluded that the tissue transfer printing is a useful tool for constructing a vascular structure and mimicking natural structure of different types of tissues.

Mechanical load and mechanical integrity of lung cells - experimental mechanostimulation of epithelial cell- and fibroblast-monolayers

Experimental mechanostimulation of soft biologic tissue is widely used to investigate cellular responses to mechanical stress or strain. Reactions on mechanostimulation are investigated in terms of morphological changes, inflammatory responses and apoptosis/necrosis induction on a cellular level. In this context, the analysis of the mechanical characteristics of cell-layers might allow to indicate patho-physiological changes in the cell-cell contacts. Recently, we described a device for experimental mechanostimulation that allows simultaneous measurement of the mechanical characteristics of cell-monolayers. Here, we investigated how cultivated lung epithelial cell- and fibroblast-monolayers behave mechanically under different amplitudes of biaxial distension. The cell monolayers were sinusoidally deflected to 5%, 10% or 20% surface gain and their mechanical properties during mechanostimulation were analyzed. With increasing stimulation amplitudes more pronounced reductions of cell junctions were observed. These findings were accompanied by a substantial loss of monolayer rigidity. Pulmonary fibroblast monolayers were initially stiffer but were stronger effected by the mechanostimulation compared to epithelial cell-monolayers. We conclude that, according to their biomechanical function within the pulmonary tissue, epithelial cells and fibroblasts differ with respect to their mechanical characteristics and tolerance of mechanical load.

Hydrogel scaffolds as in vitro models to study fibroblast activation in wound healing and disease

Wound healing results from complex signaling between cells and their environment in response to injury. Fibroblasts residing within the extracellular matrix (ECM) of various connective tissues are critical for matrix synthesis and repair. Upon injury or chronic insult, these cells activate into wound-healing cells, called myofibroblasts, and repair the damaged tissue through enzyme and protein secretion. However, misregulation and persistence of myofibroblasts can lead to uncontrolled accumulation of matrix proteins, tissue stiffening, and ultimately disease. Extracellular cues are important regulators of fibroblast activation and have been implicated in their persistence. Hydrogel-based culture models have emerged as useful tools to examine fibroblast response to ECM cues presented during these complex processes. In this Mini-Review, we will provide an overview of these model systems, which are built upon naturally-derived or synthetic materials, and mimic relevant biophysical and biochemical properties of the native ECM with different levels of control. Additionally, we will discuss the application of these hydrogel-based systems for the examination of fibroblast function and fate, including adhesion, migration, and activation, as well as approaches for mimicking both static and temporal aspects of extracellular environments. Specifically, we will highlight hydrogels that have been used to investigate the effects of matrix rigidity, protein binding, and cytokine signaling on fibroblast activation. Last, we will describe future directions for the design of hydrogels to develop improved synthetic models that mimic the complex extracellular environment.

On-chip investigation of cell-drug interactions

Investigation of cell-drug interaction is of great importance in drug discovery but continues to pose significant challenges to develop robust, fast and high-throughput methods for pharmacologically profiling of potential drugs. Recently, cell chips have emerged as a promising technology for drug discovery/delivery, and their miniaturization and flow-through operation significantly reduce sample consumption while dramatically improving the throughput, reliability, resolution and sensitivity. Herein we review various types of miniaturized cell chips used in investigation of cell-drug interactions. The design and fabrication of cell chips including material selection, surface modification, cell trapping/patterning, concentration gradient generation and mimicking of in vivo environment are presented. Recent advances of on-chip investigations of cell-drug interactions, in particular the high-throughput screening, cell sorting, cytotoxicity testing, drug resistance analysis and pharmacological profiling are examined and discussed. It is expected that this survey can provide thoughtful basics and important applications of on-chip investigations of cell-drug interactions, thus greatly promoting research and development interests in this area.

Piezoelectric fiber-composite-based cantilever sensor for electric-field-induced strain measurement in soft electroactive polymer

Polymeric materials have been widely used in electronic and electromechanical transducer applications. Because of their low elastic modulus, it is quite challenging to accurately characterize the electric-field-induced strain and elastic modulus by conventional contact methods. In this paper, a piezoelectric lead zirconate titanate (PZT) fiber-composite-based cantilever strain sensor has been investigated to accurately characterize the electric-field-induced strain response in the out-of-plane direction of soft electroactive polymer samples. By choosing appropriate substrate material and the thickness ratio of the fiber composite to the substrate, this strain sensor can be optimized to provide high sensitivity and high flexibility simultaneously. The high voltage sensitivity can be attributed to partial decoupling of the longitudinal and transverse piezoelectric responses, the improved piezoelectric coefficient and small dielectric permittivity. The high flexibility is due to the reduced flexural spring constant of the composite-based cantilever device. Both theoretical modeling of the PZT fiber-composite-based cantilever device and experimental verification are performed in this work. The results indicate that the piezoelectric PZT fiber-composite-based cantilever strain sensor can accurately characterize the electric-field-induced small strain in electroactive soft polymers with high reliability.

Capture and printing of fixed stromal cell membranes for bioactive display on PDMS surfaces

Poly(dimethylsiloxane) (PDMS) has emerged as an extremely useful polymer for various biological applications. The conjugation of PDMS with bioactive molecules to create functional surfaces is feasible yet limited to a single-molecule display with imprecise localization of the molecules on PDMS. Here we report a robust technique that can transfer and print the membrane surface of glutaraldehyde-fixed stromal cells intact onto a PDMS substrate using an intermediate polyvinylalcohol (PVA) film as a transporter system. The cell-PVA film capturing the entirety of surface molecules can be peeled off and subsequently printed onto PDMS while maintaining the spatial display of the original cell surface molecules. Proof-of-concept studies are described using human bone marrow stromal cell membranes including a demonstration of the bioactivity of transferred membranes to capture and adhere hematopoietic cells. The presented process is applicable to virtually any adherent cell and can broaden the functional display of biomolecules on PDMS for biotechnology applications.

A method to measure mechanical properties of pulmonary epithelial cell layers

The lung has a huge inner alveolar surface composed of epithelial cell layers. The knowledge about mechanical properties of lung epithelia is helpful to understand the complex lung mechanics and biomechanical interactions. Methods have been developed to determine mechanical indices (e.g., tissue elasticity) which are both very complex and in need of costly equipment. Therefore, in this study, a mechanostimulator is presented to dynamically stimulate lung epithelial cell monolayers in order to determine their mechanical properties based on a simple mathematical model. First, the method was evaluated by comparison to classical tensile testing using silicone membranes as substitute for biological tissue. Second, human pulmonary epithelial cells (A549 cell line) were grown on flexible silicone membranes and stretched at a defined magnitude. Equal secant moduli were determined in the mechanostimulator and in a conventional tension testing machine (0.49 ± 0.05 MPa and 0.51 ± 0.03 MPa, respectively). The elasticity of the cell monolayer could be calculated by the volume-pressure relationship resulting from inflation of the membrane-cell construct. The secant modulus of the A549 cell layer was calculated as 0.04 ± 0.008 MPa. These findings suggest that the mechanostimulator may represent an adequate device to determine mechanical properties of cell layers.

Synthesis of macroporous poly(dimethylsiloxane) scaffolds for tissue engineering applications

Macroporous, biostable scaffolds with controlled porous architecture were prepared from poly(dimethylsiloxane) (PDMS) using sodium chloride particles and a solvent casting and particulate leaching technique. The effect of particulate size range and overall porosity on the resulting structure was evaluated. Results found 90% v/v scaffolds and particulate ranges above 100 μm to have the most optimal open framework and porosity. Resulting hydrophobic PDMS scaffolds were coated with fibronectin and evaluated as a platform for adherent cell culture using human mesenchymal stem cells. Biocompatibility of PDMS scaffolds was also evaluated in a rodent model, where implants were found to be highly biocompatible and biostable, with positive extracellular matrix deposition throughout the scaffold. These results demonstrate the suitability of macroporous PDMS scaffolds for tissue engineering applications where strong integration with the host is desired.

Functional porous hydrogels to study angiogenesis under the effect of controlled release of vascular endothelial growth factor

Angiogenesis occurs through a cascade of events controlled by complex multiple signals that are orchestrated according to specific spatial patterns and temporal sequences. Vascularization is a central issue in most tissue engineering applications. However, only a better insight into spatio-temporal signal presentation can help in controlling and guiding angiogenesis in vivo. To this end, versatile and accessible material platforms are required in order to study angiogenic events in a systematic way. In this work we report a three-dimensional porous polyethylene glycol (PEG) diacrylate hydrogel bioactivated with heparin that is able to deliver vascular endothelial growth factor (VEGF) in a sustained and controlled manner. The efficiency of the material has been tested both in vitro and in vivo. In particular, the VEGF released from the hydrogel induces cell proliferation when tested on HUVECs, retains its bioactivity up to 21days, as demonstrated by Matrigel assay, and, when implanted on a chorion allantoic membrane, the hydrogel shows superior angiogenic potential in stimulating new vessel formation compared with unfunctionalized hydrogels. Moreover, in the light of potential tissue regeneration studies, the proposed hydrogel has been modified with adhesion peptides (RGD) to enable cell colonization. The porous hydrogel reported here can be used as a valid tool to characterize angiogenesis, and, possibly, other biological processes, in different experimental set-ups.