Stable Cell Adhesion Research Articles

Bioprinting of Stable Bionic Interfaces Using Piezoresistive Hydrogel Organoelectronics.

Bionic tissues offer an exciting frontier in biomedical research by integrating biological cells with artificial electronics, such as sensors. One critical hurdle is the development of artificial electronics that can mechanically harmonize with biological tissues, ensuring a robust interface for effective strain transfer and local deformation sensing. In this study, a highly tissue-integrative, soft mechanical sensor fabricated from a composite piezoresistive hydrogel. The composite not only exhibits exceptional mechanical properties, with elongation at the point of fracture reaching up to 680%, but also maintains excellent biocompatibility across multiple cell types. Furthermore, the material exhibits bioadhesive qualities, facilitating stable cell adhesion to its surface. A unique advantage of the formulation is the compatibility with 3D bioprinting, an essential technique for fabricating stable interfaces. A multimaterial sensorized 3D bionic construct is successfully bioprinted, and it is compared to structures produced via hydrogel casting. In contrast to cast constructs, the bioprinted ones display a high (87%) cell viability, preserve differentiation ability, and structural integrity of the sensor-tissue interface throughout the tissue development duration of 10 d. With easy fabrication and effective soft tissue integration, this composite holds significant promise for various biomedical applications, including implantable electronics and organ-on-a-chip technologies.

STABILITY OF BIOFUNCTIONALIZED HIGH-PERFORMANCE OXIDE CERAMICS AGAINST RADIATION STERILIZATION

While high-performance ceramics like alumina and zirconia exhibit excellent wear resistance, they provide poor osseointegration capacity. As osseointegration is crucial for non-cemented joint prostheses, new techniques have been successfully developed for biofunctionalizing high-performance ceramic surfaces. Stable cell adhesion can be achieved by covalently bound specific peptides. In this study we investigate the effect of sterilization processes on organo-chemically functionalized surfaces.To enhance the performance of alumina-toughened zirconia ceramics (ATZ), a 3-aminopropyldiisopropylethoxysilane (APDS) monolayer was applied and coupled with cyclo-RGD peptides (cRGD) by using bifunctional crosslinker bis(sulfosuccinimidyl)suberat (BS³). The samples were sterilized using e-beam or gamma-sterilization at 25 kGy, either before or after biofunctionalization with cRGD. Functionalization stability was investigated by contact angle measurements. The functionality of cRGD after sterilization was demonstrated using proliferation tests and cytotoxicity assays. Immunofluorescence staining (pFAK, Actin, DAPI) was conducted to evaluate the adhesion potential between the samples and human mesenchymal stem cells (hMSCs).Functionalized samples before and after sterilization showed no significant difference regarding their contact angles. A proliferation test demonstrated that the cells on functionalized samples proliferate significantly more than on untreated samples before and after sterilization. hMSCs showed a significant higher proliferation on gamma sterilized samples compared to all other groups after 14 days. It was confirmed that the samples did not exhibit cytotoxic behavior before or after sterilization. Fluorescence microscopy demonstrated that both, cells on sterilized and on non-sterilized samples, expressed high levels of pFAK-Y397.The investigated functionalization enables improved adhesion and proliferation of hMSCs and is stable against the investigated sterilization processes. This is of importance as the option of having a sterile product enables the start of the translation of this biofunctional coating towards preclinical and subsequently first-in-man applications.Acknowledgments: We acknowledge the financial support of the Federal Ministry of Education and Research, BMBF (13GW0452A-C).

The Force-Dependent Mechanism of an Integrin α4β7-MAdCAM-1 Interaction.

The interaction between integrin α4β7 and mucosal vascular addressin cell-adhesion molecule-1 (MAdCAM-1) facilitates the adhesion of circulating lymphocytes to the surface of high endothelial venules in inflammatory bowel diseases (IBDs). Lymphocyte adhesion is a multistep cascade involving the tethering, rolling, stable adhesion, crawling, and migration of cells, with integrin α4β7 being involved in rolling and stable adhesions. Targeting the integrin α4β7-MAdCAM-1 interaction may help decrease inflammation in IBDs. This interaction is regulated by force; however, the underlying mechanism remains unknown. Here, we investigate this mechanism using a parallel plate flow chamber and atomic force microscopy. The results reveal an initial increase in the lifetime of the integrin α4β7-MAdCAM-1 interaction followed by a decrease with an increasing force. This was manifested in a two-state curve regulated via a catch-bond-slip-bond conversion regardless of Ca2+ and/or Mg2+ availability. In contrast, the mean rolling velocity of cells initially decreased and then increased with the increasing force, indicating the flow-enhanced adhesion. Longer tether lifetimes of single bonds and lower rolling velocities mediated by multiple bonds were observed in the presence of Mg2+ rather than Ca2+. Similar results were obtained when examining the adhesion to substrates co-coated with chemokine CC motif ligand 25 and MAdCAM-1, as opposed to substrates coated with MAdCAM-1 alone. In conclusion, the integrin α4β7-MAdCAM-1 interaction occurs via ion- and cytokine-dependent flow-enhanced adhesion processes and is regulated via a catch-bond mechanism.

Improving dental epithelial junction on dental implants with bioengineered peptides.

Introduction: The functionalization of titanium (Ti) and titanium alloys (Ti6Al4V) implant surfaces via material-specific peptides influence host/biomaterial interaction. The impact of using peptides as molecular linkers between cells and implant material to improve keratinocyte adhesion is reported. Results: The metal binding peptides (MBP-1, MBP-2) SVSVGMKPSPRP and WDPPTLKRPVSP were selected via phage display and combined with laminin-5 or E-cadherin epithelial cell specific peptides (CSP-1, CSP-2) to engineer four metal-cell specific peptides (MCSPs). Single-cell force spectroscopy and cell adhesion experiments were performed to select the most promising candidate. In vivo tests using the dental implant for rats showed that the selected bi functional peptide not only enabled stable cell adhesion on the trans-gingival part of the dental implant but also arrested the unwanted apical migration of epithelial cells. Conclusion: The results demonstrated the outstanding performance of the bioengineered peptide in improving epithelial adhesion to Ti based implants and pointed towards promising new opportunities for applications in clinical practice.

Shigella IpaA mediates actin bundling through diffusible vinculin oligomers with activation imprint

Upon activation, vinculin reinforces cytoskeletal anchorage during cell adhesion. Activating ligands classically disrupt intramolecular interactions between the vinculin head and tail domains that bind to actin filaments. Here, we show that Shigella IpaA triggers major allosteric changes in the head domain, leading to vinculin homo-oligomerization. Through the cooperative binding of its three vinculin-binding sites (VBSs), IpaA induces a striking reorientation of the D1 and D2 head subdomains associated with vinculin oligomerization. IpaA thus acts as a catalyst producing vinculin clusters that bundle actin at a distance from the activation site and trigger the formation of highly stable adhesions resisting the action of actin relaxing drugs. Unlike canonical activation, vinculin homo-oligomers induced by IpaA appear to keep a persistent imprint of the activated state in addition to their bundling activity, accounting for stable cell adhesion independent of force transduction and relevant to bacterial invasion.

Stimulus-Responsive, Gelatin-Containing Supramolecular Nanofibers as Switchable 3D Microenvironments for Cells.

Polymer- and/or protein-based nanofibers that promote stable cell adhesion have drawn increasing attention as well-defined models of the extracellular matrix. In this study, we fabricated two classes of stimulus-responsive fibers containing gelatin and supramolecular crosslinks to emulate the dynamic cellular microenvironment in vivo. Gelatin enabled cells to adhere without additional surface functionalization, while supramolecular crosslinks allowed for the reversible switching of the Young’s modulus through changes in the concentration of guest molecules in culture media. The first class of nanofibers was prepared by coupling the host–guest inclusion complex to gelatin before electrospinning (pre-conjugation), while the second class of nanofibers was fabricated by coupling gelatin to polyacrylamide functionalized with host or guest moieties, followed by conjugation in the electrospinning solution (post-conjugation). In situ AFM nano-indentation demonstrated the reversible switching of the Young’s modulus between 2–3 kPa and 0.2–0.3 kPa under physiological conditions by adding/removing soluble guest molecules. As the concentration of additives does not affect cell viability, the supramolecular fibers established in this study are a promising candidate for various biomedical applications, such as standardized three-dimensional culture matrices for somatic cells and the regulation of stem cell differentiation.

Two-Dimensional Metal-Organic Framework-Based Cellular Scaffolds with High Protein Adsorption, Retention, and Replenishment Capabilities.

Metal-organic frameworks (MOFs) are porous materials with adsorption, storage, and separation capabilities due to their high specific surface areas and large pore volumes. MOFs are thus used in biomedical applications, and MOF nanoparticles have been widely studied as nanocarriers for drug delivery systems. Several research groups recently reported that specific MOF nanoparticles can adsorb and retain proteins, suggesting to us that MOF nanoparticles may have advantages as novel cell culture scaffolds. However, MOF nanoparticles cannot be used as two-dimensional scaffolds for cells. We therefore established a bottom-up technique to construct two-dimensional MOFs [MIL-53 (Al)] on polymer films. The developed two-dimensional MIL-53 (Al) film [fMIL-53 (Al)] exhibited high serum protein adsorption, retention, and replenishment capabilities as compared to conventional cell culture scaffolds. β-Galactosidase, used as a model protein, adsorbed on fMIL-53 (Al) exhibited original enzymatic activity, indicating that proteins are not denatured during the adsorption process. The viability of mouse myoblast cells (C2C12) cultured on fMIL-53 (Al) was 100%, indicating the cell compatibility of fMIL-53 (Al). Importantly, C2C12 cells cultured on serum protein-preadsorbed fMIL-53 (Al) exhibited excellent long-term adhesion, morphology, and proliferation even in a medium lacking serum proteins, demonstrating an important advantage of fMIL-53 (Al) as a cell culture scaffold, given that conventional cell culture scaffolds typically require a serum-containing medium to support stable cell adhesion and proliferation. To our knowledge, this is the first report regarding the application of MOFs as cell culture scaffolds and will serve as a starting point for studying two- and three-dimensional MOF-based cellular scaffolds for cell culture systems and for in vitro and in vivo tissue engineering.

Thermoplastic elastomer enhanced interface adhesion and bending durability for flexible organic solar cells

Stable interface adhesion and bending durability of flexible organic solar cells (FOSCs) is a basic requirement for its real application in wearable electronics. Unfortunately, the device performance always degraded during continuous bending. Here, we revealed the weak interface adhesion force between MoO3 hole transporting layer (HTL) and the organic photoactive layer was the main reason of poor bending durability. The insertion of an interface bonding layer with a thermoplastic elastomer, polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) effectively improved the interface adhesion force of MoO3 HTL and the active layer and decreased the modulus, which ensured higher than 90% of the initial efficiency remaining after 10000 bending. Meanwhile, the FOSCs gave an efficiency of 14.18% and 16.15% for the PM6:Y6 and PM6:L8-BO devices, which was among the highest performance of FOSCs. These results demonstrated the potential of improving the mechanical durability of FOSCs through thermoplastic elastomer interface modification.

Condensed ECM-based nanofilms on highly permeable PET membranes for robust cell-to-cell communications with improved optical clarity

The properties of a semipermeable porous membrane, including pore size, pore density, and thickness, play a crucial role in creating a tissue interface in a microphysiological system (MPS) because it dictates multicellular interactions between different compartments. The small pore-sized membrane has been preferentially used in an MPS for stable cell adhesion and the formation of tissue barriers on the membrane. However, it limited the applicability of the MPS because of the hindered cell transmigration via sparse through-holes and the optical translucence caused by light scattering through pores. Thus, there remain unmet challenges to construct a compartmentalized MPS without those drawbacks. Here we report a submicrometer-thickness (∼500 nm) fibrous extracellular matrix (ECM) film selectively condensed on a large pore-sized track-etched (TE) membrane (10 µm-pores) in an MPS device, which enables the generation of functional tissue barriers simultaneously achieving optical transparency, intercellular interactions, and transmigration of cells across the membrane. The condensed ECM fibers uniformly covering the surface and 10 µm-pores of the TE membrane permitted sufficient surface areas where a monolayer of the human induced pluripotent stem cell-derived brain endothelial cells is formed in the MPS device. The functional maturation of the blood–brain barrier (BBB) was proficiently achieved due to astrocytic endfeet sheathing the brain endothelial cells through 10 µm pores of the condensed-ECM-coated TE (cECMTE) membrane. We also demonstrated the extravasation of human metastatic breast tumor cells through the human BBB on the cECMTE membrane. Thus, the cECMTE membrane integrated with an MPS can be used as a versatile platform for studying various intercellular communications and migration, mimicking the physiological barriers of an organ compartment.

Improvement of wound healing by the development of ECM-inspired biomaterial coatings and controlled protein release.

Implant design has evolved from biochemically inert substrates, minimizing cell and protein interaction, towards sophisticated bioactive substrates, modulating the host response and supporting the regeneration of the injured tissue. Important aspects to consider are the control of cell adhesion, the discrimination of bacteria and non-local cells from the desired tissue cell type, and the stimulation of implant integration and wound healing. Here, the extracellular matrix acts as a role model providing us with inspiration for sophisticated designs. Within this scope, small bioactive peptides have proven to be miscellaneously deployable for the mediation of surface, cell and matrix interactions. Combinations of adhesion ligands, proteoglycans, and modulatory proteins should guide multiple aspects of the regeneration process and cooperativity between the different extracellular matrix components, which bears the chance to maximize the therapeutic efficiency and simultaneously lower the doses. Hence, efforts to include multiple of these factors in biomaterial design are well worth. In the following, multifunctional implant coatings based on bioactive peptides are reviewed and concepts to implement strong surface anchoring for stable cell adhesion and a dynamic delivery of modulator proteins are discussed.

Cell-Laden Gelatin Methacryloyl Bioink for the Fabrication of Z-Stacked Hydrogel Scaffolds for Tissue Engineering

Hydrogel-based scaffolds have been widely used to fabricate artificial tissues capable of replacing tissues and organs. However, several challenges inherent in fabricating tissues of large size and complex morphology using such scaffolds while ensuring cell viability remain. To address this problem, we synthesized gelatin methacryloyl (GelMA) based bioink with cells for fabricating a scaffold with superior characteristics. The bioink was grafted onto a Z-stacking bioprinter that maintained the cells at physiological temperature during the printing process, without exerting any physical pressure on the cells. Various parameters, such as the bioink composition and light exposure time, were optimized. The printing accuracy of the scaffolds was evaluated using photorheological studies. The internal morphology of the scaffolds at different time points was analyzed using electron microscopy. The Z-stacked scaffolds were fabricated using high-speed printing, with the conditions optimized to achieve high model reproducibility. Stable adhesion and high proliferation of cells encapsulated within the scaffold were confirmed. We introduced various strategies to improve the accuracy and reproducibility of Z-stack GelMA bioprinting while ensuring that the scaffolds facilitated cell adhesion, encapsulation, and proliferation. Our results demonstrate the potential of the present method for various applications in tissue engineering.

Comprehensive Evaluation of Stable Neuronal Cell Adhesion and Culture on One-Step Modified Polydimethylsiloxane Using Functionalized Pluronic

Polydimethylsiloxane (PDMS) is a popular and property-advantageous material for developing biomedical microsystems and advancing cell microengineering. The requirement of constructing a robust cell-adhesive PDMS interface drives the exploration of simple, straightforward, and applicable surface modification methods. Here, a comprehensive evaluation of highly stable neuronal cell adhesion and culture on the PDMS surface modified in one step using functionalized Pluronic is presented. According to multiple comparative tests, this modification is sufficiently verified to enable more significant cell adhesion and spreading in both quantity and stability, higher neuronal differentiation and viability/growth, more complete formation of the neuronal network, and stabler neuronal cell culture than the common coating tools on the PDMS substrate. The comparable and even superior cellular effects of this modification on PDMS to the standard coating of polystyrene for in vitro neurological research are demonstrated. Long-term microfluidic neuron culture with stable adhesion and high differentiation on the modified PDMS interface is accomplished, too. The achievement provides a detailed experimental demonstration of this simple and effective modification for strengthening neuronal cell culture on the PDMS substrate, which is useful for potential applications in the fields of neurobiology, neuron microengineering, and brain-on-a-chip.

Dual-functional alginate crosslinker: Independent control of crosslinking density and cell adhesive properties of hydrogels via separate conjugation pathways

Alginate is an abundant natural polysaccharide widely utilized in various biomedical applications. Alginate also possesses numerous hydroxyl and carboxylate functional groups that allow chemical modifications to introduce different functionalities. However, it is difficult to apply various chemical reactions to alginate due to limited solubility in organic solvents. Herein, functional moieties for radical polymerization and cell adhesion were separately conjugated to hydroxyl and carboxylate groups of alginate, respectively, in order to independently control the crosslinking density and cell adhesive properties of hydrogels. Sodium counterions of alginate are first substituted with tetrabutylammonium ions to facilitate the dissolution in an organic solvent, followed by in situ conjugations of (1) cell adhesion molecules (CAM) via carbodiimide-mediated amide formation and (2) methacrylate via ring-opening nucleophilic reaction. The resulting CAM-linked methacrylic alginate was able to not only crosslink different monomers to form hydrogels with varying mechanical properties, but also induce stable cell adhesion to the hydrogels.

Mussel‐Inspired Biocoating for Improving the Adhesion of Dental Pulp Stem Cells in Dental Pulp Regeneration

Dental pulp engineering possesses a promising perspective to replacing lost pulp in the root canal and restoring its functions. Stable adhesion of dental pulp stem cells (DPSCs) on the root canal dentin wall is a key element required for reconstruction of a functional odontoblast layer in dental pulp regeneration. To address this challenge, dopamine-modified hyaluronic acid (DA-HA) is coated on dentin to obtain a stable adhesion of DPSCs. The dopamine segment provides adhesion ability to the coating, and the hyaluronic acid increases the biocompatibility. The results show that DPSCs can adhere on the DA-HA coated dentin slice better than those without coating. Simultaneously, DPSCs proliferation can be further promoted on the prepared coating. Therefore, the DA-HA coating may provide a possible way to immobilize odontoblast cell onto dentin surface for pulp regeneration.

Stable cell adhesion affects mesenchymal stem cell sheet fabrication: Effects of fetal bovine serum and human platelet lysate.

Cell sheet technology exploits temperature responsive cell culture dishes (TRCDs) as versatile cell harvesting methods to yield contiguous cell monolayers robustly held together by cell-cell junctions, receptors, and endogenous extracellular matrix. More than 15 years of clinical data using autologous-sourced cell sheets demonstrate enhanced therapeutic properties through increased cell retention at target tissue sites. Recently, several preclinical studies have also been reported using mesenchymal stem cell (MSC) sheets in wound healing, cardiac ischemia therapies, and pancreatic regeneration. However, optimized MSC sheet fabrication conditions have not yet been reported. In this study, we identified specific conditions for reliable human MSC sheet fabrication by comparing cell growth media supplements (fetal bovine serum [FBS] and human platelet lysate [hPL]). Human umbilical cord-derived MSCs cultured in FBS and hPL exhibit different actin cytoskeletal structures related to their cell morphologies and adhesion. MSCs cultured in FBS media showed stable cell adhesion on TRCDs with flattened cell shapes and aligned actin cytoskeletal structure. This stable cell adhesion enables production of consistent MSC cell sheets, with controlled cell sheet detachment. Conversely, cell sheet fabrication in hPL media exhibits poor reproducibility being more sensitive to temperature- and culture time-induced release due to weak cell adhesion. These findings suggest that stable MSC adhesion to TRCDs is important to reliable MSC sheet fabrication methods and that MSC growth media supplementation directly affects cell adhesion during culture.

Surface modifications to polydimethylsiloxane substrate for stabilizing prolonged bone marrow stromal cell culture

Polydimethylsiloxane (PDMS) has been extensively used as a supporting material for studies of cell mechanobiology, cell micropatterning and microscale-cell analysis in microfluidic chips due to its numerous advantages, such as low cytotoxicity, ease of modification, inexpensive costs and biocompatibility. However, the innate hydrophobicity of PDMS often poses a problem for stable cell adhesion, seriously limiting its applicability for prolonged cell culture. UV exposure and protein coating are suboptimal solutions, while chemical surface functionalization is often associated with laborious procedures and producing environmental toxics. Plasma treatment can render a hydrophilic substrate by altering the surface chemistry, but such effect is often short-lived due to its tendency to hydrophobic recovery. Variation of physical properties of the substratum are known to influence cell behaviour. Nevertheless, the combination of varying PDMS substratum properties via base:curing agent ratio and plasma treatment to stabilize the long-term culture of bone marrow derived stromal cells (BMSCs) still remain poorly understood. In this study, we developed a protocol to maintain the hydrophilicity of the plasma-treated PDMS over a range of substratum properties. This study demonstrated that varying the substratum properties of PDMS can enhance the stability of BMSC culture for at least three weeks, while plasma treatment with or without additional collagen coating further enhanced such effect. The changes in the physical properties of PDMS have rendered difference in BMSCs adhesion, proliferation and in-vitro plasticity, thereby offering a simple and effective strategy for PDMS surface modification to enable long term cell analysis in PDMS-based culture platform.

Integrins outside focal adhesions transmit tensions during stable cell adhesion.

Integrins coupled with other proteins form protein complexes named focal adhesions (FA) which are considered as the primary sites for cellular forces transduction during cell stable adhesion. Cell traction forces transmitted by FAs and integrin tensions inside FAs have been extensively studied. However, it remains unknown whether integrins outside FAs can transmit tension, and if so, what is the tension range. We previously developed a tension sensor named tension gauge tether (TGT). To calibrate integrin tensions outside FAs, here we applied multiplex TGT (mTGT) to simultaneously monitor integrin tensions at separate levels. mTGT unambiguously revealed that integrins outside FAs also transmit tension after FA formation. These tensions are mainly located in the range of 43 ~ 54 pN which is lower than integrin tensions inside FAs. Integrin tensions both inside and outside FAs substantially contribute to bulk cellular forces and they respond independently to actin and myosin II inhibition, serum deprivation and microtubule inhibition, indicating their different tension sources and independent dynamics. Our work identified integrin tensions outside FAs and calibrated the tension range for the first time. We also demonstrated that mTGT is a valuable tool to monitor integrin tension profile in a broad detection range of 10 ~ 60 pN.

Enhanced In Vitro Biocompatibility of Chemically Modified Poly(dimethylsiloxane) Surfaces for Stable Adhesion and Long-term Investigation of Brain Cerebral Cortex Cells.

Studies on the mammalian brain cerebral cortex have gained increasing importance due to the relevance of the region in controlling critical higher brain functions. Interactions between the cortical cells and surface extracellular matrix (ECM) proteins play a pivotal role in promoting stable cell adhesion, growth, and function. Poly(dimethylsiloxane) (PDMS) based platforms have been increasingly used for on-chip in vitro cellular system analysis. However, the inherent hydrophobicity of the PDMS surface has been unfavorable for any long-term cell system investigations due to transitory physical adsorption of ECM proteins on PDMS surfaces followed by eventual cell dislodgement due to poor anchorage and viability. To address this critical issue, we employed the (3-aminopropyl)triethoxysilane (APTES) based cross-linking strategy to stabilize ECM protein immobilization on PDMS. The efficiency of surface modification in supporting adhesion and long-term viability of neuronal and glial cells was analyzed. The chemically modified surfaces showed a relatively higher cell survival with an increased neurite length and neurite branching. These changes were understood in terms of an increase in surface hydrophilicity, protein stability, and cell-ECM protein interactions. The modification strategy could be successfully applied for stable cortical cell culture on the PDMS microchip for up to 3 weeks in vitro.

Design of a Vitronectin-Based Recombinant Protein as a Defined Substrate for Differentiation of Human Pluripotent Stem Cells into Hepatocyte-Like Cells.

Maintenance and differentiation of human pluripotent stem cells (hPSCs) usually requires culture on a substrate for cell adhesion. A commonly used substratum is Matrigel purified from Engelbreth—Holm—Swarm sarcoma cells, and consists of a complex mixture of extracellular matrix proteins, proteoglycans, and growth factors. Several studies have successfully induced differentiation of hepatocyte-like cells from hPSCs. However, most of these studies have used Matrigel as a cell adhesion substrate, which is not a defined culture condition. In an attempt to generate a substratum that supports undifferentiated properties and differentiation into hepatic lineage cells, we designed novel substrates consisting of vitronectin fragments fused to the IgG Fc domain. hPSCs adhered to these substrates via interactions between integrins and the RGD (Arg-Gly-Asp) motif, and the cells maintained their undifferentiated phenotypes. Using a previously established differentiation protocol, hPSCs were efficiently differentiated into mesendodermal and hepatic lineage cells on a vitronectin fragment-containing substrate. We found that full-length vitronectin did not support stable cell adhesion during the specification stage. Furthermore, the vitronectin fragment with the minimal RGD-containing domain was sufficient for differentiation of human induced pluripotent stem cells into hepatic lineage cells under completely defined conditions that facilitate the clinical application of cells differentiated from hPSCs.

Molecular architecture and function of the hemidesmosome.

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.