Surface chemistry modulates fibronectin conformation and directs integrin binding and specificity to control cell adhesion

Fibronectin in Fracture Healing: Biological Mechanisms and Regenerative Avenues

The importance of extracellular matrix (ECM) proteins in mediating bone fracture repair is evident, and fibronectin (FN) has emerged as a pivotal regulator of this process. FN is an evolutionarily conserved glycoprotein found in all tissues of the body, and functions in several stages of fracture healing. FN acts as a three-dimensional scaffold immediately following trauma, guiding the assembly of additional ECM components. Furthermore, FN regulates cellular behavior via integrin-binding and growth factor-binding domains, promoting downstream responses including cell recruitment, proliferation and differentiation. Due to its diverse functions, the development of FN-based strategies to promote fracture healing is under intense research. In this review, we discuss the recent advancements in utilizing FN-based biomaterials, showing promise in tissue engineering and regenerative medicine applications.

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.

[Experimental study on repairing rabbit skull defect with bone morphogenetic protein 2 peptide/functionalized carbon nanotube composite]

Objective

To observe and compare the effects of peptides on the repair of rabbit skull defects through two different binding modes of non-covalent and covalent, and the combination of carboxyl (-COOH) and amino (-NH ₂) groups with materials.

Methods

Twenty-one 3-month-old male ordinary New Zealand white rabbits were numbered 1 to 42 on the left and right parietal bones. They were divided into 5 groups using a random number table, the control group (group A, 6 sides) and the material group 1, 2, 3, 4 (respectively group B, C, D, E, 9 sides in each group). All animals were prepared with 12-mm-diameter skull defect models, and bone morphogenetic protein 2 (BMP-2) non-covalently bound multiwalled carbon nanotubes (MWCNT)-COOH+poly ( L-lactide) (PLLA), BMP-2 non-covalently bound MWCNT-NH ₂+PLLA, BMP-2 covalently bound MWCNT-COOH+PLLA, and BMP-2 covalently bound MWCNT-NH ₂+PLLA were implanted into the defects of groups B, C, D, and E, respectively. At 4, 8, and 12 weeks after operation, the samples were taken for CT scanning and three-dimensional reconstruction, the ratio of bone tissue regeneration volume to total volume and bone mineral density were measured, and the histological observation of HE staining and Masson trichrome staining were performed to quantitatively analyze the volume ratio of new bone tissue.

Results

CT scanning and three-dimensional reconstruction showed that with the extension of time, the defects in groups A-E were filled gradually, and the defect in group E was completely filled at 12 weeks after operation. HE staining and Masson trichrome staining showed that the volume of new bone tissue in each group gradually increased with time, and regenerated mature bone tissue appeared in groups D and E at 12 weeks after operation. Quantitative analysis showed that at 4, 8, and 12 weeks after operation, the ratio of bone tissue regeneration volume to total volume, bone mineral density, and the volume ratio of new bone tissue increased gradually over time; and at each time point, the above indexes increased gradually from group A to group E, and the differences between groups were significant ( P<0.05).

Conclusion

Through covalent binding and using -NH ₂ to bound peptides with materials, the best bone repair effect can be achieved.

Mechanistic insights into the adsorption and bioactivity of fibronectin on surfaces with varying chemistries by a combination of experimental strategies and molecular simulations

Fibronectin (Fn) is significant to the performance of biomaterials, and the chemistry of biomaterial surface play important roles in Fn adsorption and subsequent cell behavior. However, the "molecular scale" mechanism is still unclear. Herein, we combined experimental strategies with molecular simulations to solve this problem. We prepared self-assembled monolayers with varying chemistries, i.e., SAMs-CH₃, SAMs-NH₂, SAMs-COOH and SAMs-OH, and characterized Fn adsorption and cell behaviors on them. Next, Monte Carlo method and all-atom molecular dynamics simulations were employed to reveal the orientation/conformation of Fn on surfaces. We found that SAMs-CH₃ strongly adsorbed Fn via hydrophobic interactions, but show poor bioactivity as the low exposure of RGD/PHSRN motifs and the deformation of Fn. SAMs-NH₂ and SAMs-COOH could adsorb Fn efficiently via vdW interactions, electrostatic interactions, hydrogen bonds and salt bridges. Fn exhibited excellent bioactivity for cell adhesion, proliferation and osteogenic differentiation as high exposure of bioactive motifs on SAMs-NH₂, or as the activation of other inferior cell-binding motifs on SAMs-COOH. SAMs-OH showed poor Fn adsorption as the water film. However, the adsorbed Fn displayed non-negligible bioactivity due to high exposure of PHSRN motif and large degree of protein flexibility. We believe that the revealed mechanism presents great potential to rationally design Fn-activating biomaterials.

Fibronectin in development and wound healing

Fibronectin structure and composition regulate contextual cell signaling. Recent advances have been made in understanding fibronectin and its role in tissue organization and repair. This review outlines fibronectin splice variants and their functions, evaluates potential therapeutic strategies targeting or utilizing fibronectin, and concludes by discussing potential future directions to modulate fibronectin function in development and wound healing.

Influence of poly(N-isopropylacrylamide) (PIPAAm) graft density on properties of PIPAAm grafted poly(dimethylsiloxane) surfaces and their stability

A previous report shows that poly(N-isopropylacrylamide) (PIPAAm) gel grafted onto poly(dimethylsiloxane) (PDMS) (PI-PDMS) surfaces with large PIPAAm graft density (Lar-PI-PDMS), is prepared by using electron beam irradiation, demonstrating that applied mechanical stretching affects properties of the Lar-PI-PDMS surface. However, the influence of PIPAAm graft density on the properties of PI-PDMS surfaces and their stability are not understood. To provide insight into these points, the properties of PI-PDMS surfaces with low PIPAAm graft density (Low-PI-PDMS) surfaces with stretched (stretch ratio = 20%) and unstretched states were examined as stretchable temperature-responsive cell culture surface using contact angle measurement and cell attachment/detachment assays, compared to those with Lar-PI-PDMS, as previously reported. Long-term contact angle measurements (61 days) for unstretched Low-PI-PDMS and Lar-PI-PDMS surfaces indicated that the cross-linked structure of the grafted PIPAAm gel suppressed hydrophobic recovery of the basal PDMS surface. The cell attachment assay revealed that the stretched Low-PI-PDMS surface was less cell adhesive than that of the unstretched Low-PI-PDMS surface despite of a larger amount of adsorbed fibronectin (FN). The lower cell adhesiveness was possibly explained by denaturation of adsorbed FN, which was induced by the strong hydrophobic property of the stretched Low-PI-PDMS surface. The cell detachment assay revealed that dual stimuli, low temperature treatment and mechanical shrinking stress applied to the stretched Low-PI-PDMS surface promoted cell detachment compared to a single stimulus, low temperature treatment or mechanical shrinking stress. These results suggested that the PIPAAm gelgrafted PDMS surface was chemically stable and did not suffer from hydrophobic recovery. External mechanical stretching stress not only strongly dehydrated grafted PIPAAm chains, but also denatured the adsorbed FN when the grafted PIPAAm layer was extremely thin, as in Low-PI-PDMS surfaces. Thus, PI-PDMS may be utilized as a stretchable temperature-responsive cell culture surface without significant hydrophobic recovery.

Printable Organic Electronic Materials for Precisely Positioned Cell Attachment

Over the past 3 decades, there has been a vast expansion of research in both tissue engineering and organic electronics. Although the two fields have interacted little, the materials and fabrication technologies which have accompanied the rise of organic electronics offer the potential for innovation and translation if appropriately adapted to pattern biological materials for tissue engineering. In this work, we use two organic electronic materials as adhesion points on a biocompatible poly(p-xylylene) surface. The organic electronic materials are precisely deposited via vacuum thermal evaporation and organic vapor jet printing, the proven, scalable processes used in the manufacture of organic electronic devices. The small molecular-weight organics prevent the subsequent growth of antifouling polyethylene glycol methacrylate polymer brushes that grow within the interstices between the molecular patches, rendering these background areas both protein and cell resistant. Last, fibronectin attaches to the molecular patches, allowing for the selective adhesion of fibroblasts. The process is simple, reproducible, and promotes a high yield of cell attachment to the targeted sites, demonstrating that biocompatible organic small-molecule materials can pattern cells at the microscale, utilizing techniques widely used in electronic device fabrication.

Fibronectin adsorption on oxygen plasma-treated polyurethane surfaces modulates endothelial cell response

Fibronectin coating increases implant biocompatibility by enhancing surface endothelialization via integrin-mediated binding.

The Body's Cellular and Molecular Response to Protein-Coated Medical Device Implants: A Review Focused on Fibronectin and BMP Proteins

Recent years have seen a marked rise in implantation into the body of a great variety of devices: hip, knee, and shoulder replacements, pacemakers, meshes, glucose sensors, and many others. Cochlear and retinal implants are being developed to restore hearing and sight. After surgery to implant a device, adjacent cells interact with the implant and release molecular signals that result in attraction, infiltration of the tissue, and attachment to the implant of various cell types including monocytes, macrophages, and platelets. These cells release additional signaling molecules (chemokines and cytokines) that recruit tissue repair cells to the device site. Some implants fail and require additional revision surgery that is traumatic for the patient and expensive for the payer. This review examines the literature for evidence to support the possibility that fibronectins and BMPs could be coated on the implants as part of the manufacturing process so that the proteins could be released into the tissue surrounding the implant and improve the rate of successful implantation.

A Giant Extracellular Matrix Binding Protein of Staphylococcus epidermidis Binds Surface-Immobilized Fibronectin via a Novel Mechanism

Although it is normally an innocuous part of the human skin microbiota, Staphylococcus epidermidis has emerged as a major nosocomial pathogen, and implanted foreign materials are an essential risk factor for the development of an infection. The extraordinary efficiency of S. epidermidis to colonize artificial surfaces is particularly related to the ability to form biofilms. Biofilm formation itself critically depends on stable pathogen binding to extracellular host matrix components, e.g. fibronectin (Fn), covering inserted devices in vast amounts. Extracellular matrix binding protein (Embp) and its subdomains referred to as the F-repeat and the FG-repeat are critical for adherence of S. epidermidis to surface-immobilized Fn. Embp-Fn interactions preferentially occur with surface-bound, but not folded, globular Fn via binding to the F3 domain. High-resolution structure analysis of F- and FG-repeats revealed that both repeats are composed of two tightly connected triple α-helix bundles, exhibiting an elongated but rather rigid structural organization in solution. Both F- and FG-repeat possess Fn-binding capacity via interactions with type III subdomain FN12, involving residues within the C and F β-sheet. FN12 essentially supports stability of the globular Fn state, and thus these findings reasonably explain why Embp-mediated interaction of S. epidermidis necessitates Fn surface immobilization. Thus, Embp employs an uncharacterized bacterial Fn-binding mechanism to promote staphylococcal adherence.IMPORTANCE Staphylococcus epidermidis is a leading pathogen in implant-associated hospital infections. The pathogenesis critically depends on bacterial binding to ECM components, specifically fibronectin (Fn). The cell surface-localized, 1-MDa extracellular matrix binding protein (Embp) is essentially characterized by 10 F- and 40 FG-repeats. These repetitive units, each characterized by two α-helical bundles, organize themselves in a rigid, elongated form. Embp binds preferentially to surface-localized but not soluble Fn, with both F- and FG-repeats being sufficient for Fn binding and resulting bacterial adherence. Binding preferentially involves Fn type III domain, specifically residues of FN12 β-sheets C and F. Both play key role in stabilizing the globular Fn conformation, explaining the necessity of Fn surface immobilization for a subsequent interaction with Embp. In comparison to many other bacterial Fn-binding proteins using the Fn N terminus, Embp employs a previously undescribed mechanism supporting the adhesion of S. epidermidis to surface-immobilized Fn.

Titanium dental implants hydrophilicity promotes preferential serum fibronectin over albumin competitive adsorption modulating early cell response

In vitro studies have consistently shown that titanium surface wettability affects the response of osteoprogenitors, leading to important advances in the clinical osseointegration of dental implants. However, the underlying molecular mechanisms remain unknown. Since surface conditioning by blood components initiates within milliseconds after insertion, it is reasonable to hypothesize that the amount and the type of blood proteins adsorbed influences the interaction between the implant surface and osteoprogenitors. To test this hypothesis, titanium implant surfaces with different characteristics, in terms of topography and wettability, have been conditioned with selected plasma proteins. Pure fibronectin (HFN) and albumin (HSA) solutions, or their mixture at the relative plasma concentrations were allowed to adsorb on titanium surfaces for 60 min. Protein adsorption was monitored by Bradford assay, while the contribution of HSA and HFN in forming the microfilm layer at the interface was studied by Western Blot. Subsequently, the same protein-conditioned surfaces were used to culture C2C12 cells, thus studying their capacity to adhere and to spread after 3 h. Cell viability was evaluated up to 7 days, while the expression of osteogenic genes was assessed after 3 days. Under competitive adsorption conditions, hydrophilicity promotes the selectivity of titanium for HFN regardless of the surface microtopography. As a consequence of selective HFN adsorption, cells on hydrophilic surfaces displayed enhanced adhesion and spreading, as well as increased proliferation. On the other hand, selective HFN adsorption did not appreciably affect cell differentiation. These data suggest that implant surface hydrophilicity plays a key role in guiding the selective adsorption of specific proteins from blood plasma. Moreover, the selective adsorption of HFN, as a consequence of surface hydrophilicity, was found to account for early cell responses amelioration. Thus, titanium surface hydrophilicity contributes to the clinical success of dental implant by selectively controlling protein adsorption at the interface.

Characterization of the in Vitro Osteogenic Response to Submicron TiO2 Particles of Varying Structure and Crystallinity

Titanium oxide (TiO2) nano-/microparticles have been widely used in orthopedic and dental sciences because of their excellent mechanical properties, chemical stability, and ability to promote the osseointegration of implants. However, how the structure and crystallinity of TiO2 particles may affect their osteogenic activity remains elusive. Herein, we evaluated the osteogenic response to submicron amorphous, anatase, and rutile TiO2 particles with controlled size and morphology. First, the ability of TiO2 particles to precipitate apatite was assessed in an acellular medium by using a simulated body fluid (SBF). Three days after the addition to SBF, anatase and rutile TiO2 particles induced the precipitation of aggregates of nanoparticles with a platelike morphology, typical for biomimetic apatite. Conversely, amorphous TiO2 particles induced the precipitation of particles with poor Ca/P atomic ratio only after 14 days of exposure to SBF. Next, the osteogenic response to TiO2 particles was assessed in vitro by incubating MC3T3-E1 preosteoblasts with the particles. The viability and mineralization efficiency of osteoblastic cells were maintained in the presence of all the tested TiO2 particles despite the differences in the induction of apatite precipitation in SBF by TiO2 particles with different structures. Analysis of the particles' surface charge and of the proteins adsorbed onto the particles from the culture media suggested that all the tested TiO2 particles acquired a similar biological identity in the culture media. We posited that this phenomenon attenuated potential differences in osteoblast response to amorphous, anatase, and rutile particles. Our study provides an important insight into the complex relationship between the physicochemical properties and function of TiO2 particles and sheds light on their safe use in medicine.

Reversible control of biomaterial properties for dynamically tuning cell behavior

In the past decade, significant advances in chemistry and manufacturing have enabled the development of increasingly complex and controllable biomaterials. A key innovation is the design of dynamic biomaterials that allow for user-specified, reversible, temporal control over material properties. In this review, we provide an overview of recent advancements in reversible biomaterials, including control of stiffness, chemistry, ligand presentation, and topography. These systems have wide-ranging applications within biomedical engineering, including in vitro disease models and tissue-engineered scaffolds to guide multistep biological processes.

Dendritic Cells as Targets for Biomaterial-Based Immunomodulation

Various subtypes of immunocytes react against implanted biomaterials to eliminate the foreign body object from the host's body. Among these cells, dendritic cells (DCs) play a key role in early immune response, later engaging lymphocytes through antigens presentation. Due to their capability to induce tolerogenic or immunogenic responses, DCs have been considered as key therapeutic targets for immunomodulatory products. For instance, tolerogenic DCs are applied in the treatment of autoimmune diseases, rejection of allograft transplantation, and implanted biomaterial. Due to the emerging importance of DCs in immunomodulatory biomaterials, this Review summarizes DCs' responses-such as adhesion, migration, and maturation-to biomaterials. We also review some examples of key molecules and their applications in DCs' immunoengineering. These evaluations would pave the way for designing advanced biomaterials and nanomaterials to modulate the immune system, applicable in tissue engineering, transplantation, and drug delivery technologies.

Biomimetic Nanostructures with Compositional Gradient Grown by Combinatorial Matrix-Assisted Pulsed Laser Evaporation for Tissue Engineering

There is permanent progress with the fabrication of smart bioactive surfaces that could govern tissue regeneration. Thin coatings of two or more materials with compositional gradient allow the construction of arrays with different chemical and physical features on a solid substrate. With such intelligent bio-platforms, cells can be exposed to a tissue-like biomimetic micro-environment with precise characteristics that directs cells fate towards specific phenotypes. We have introduced combinatorial matrix-assisted pulsed laser evaporation (C-MAPLE) as an alternative approach for the fabrication in a single-step process of either organic or inorganic thin and nanostructured coatings with variable composition. A continuous reciprocal gradient of two biomolecules can be achieved by C-MAPLE with discrete areas exhibiting physicochemical specificity that modulates intracellular signaling events. Herein, we present a review of the current combinatorial laser strategies and methods for fabricating thin organic and inorganic films with compositional gradient with emphasis on the surface influence on cell responsiveness. In particular, the specific biological potential of surface functionalization with thin coatings of biopolymers, proteins and drugs will be discussed. Laser deposition combinatorial processes are considered an emerging unconventional technology that can be widely applied to produce composite multilayers and micro-patterns for faster cell colonization and tissue engineering.

Screening as a strategy to drive regenerative medicine research

In the field of regenerative medicine, optimization of the parameters leading to a desirable outcome remains a huge challenge. Examples include protocols for the guided differentiation of pluripotent cells towards specialized and functional cell types, phenotypic maintenance of primary cells in cell culture, or engineering of materials for improved tissue interaction with medical implants. This challenge originates from the enormous design space for biomaterials, chemical and biochemical compounds, and incomplete knowledge of the guiding biological principles. To tackle this challenge, high-throughput platforms allow screening of multiple perturbations in one experimental setup. In this review, we provide an overview of screening platforms that are used in regenerative medicine. We discuss their fabrication techniques, and in silico tools to analyze the extensive data sets typically generated by these platforms.

Chondroinduction of Mesenchymal Stem Cells on Cellulose-Silk Composite Nanofibrous Substrates: The Role of Substrate Elasticity

Smart biomaterials with an inherent capacity to elicit specific behaviors in lieu of biological prompts would be advantageous for regenerative medicine applications. In this work, we employ an electrospinning technique to model the in vivo nanofibrous extracellular matrix (ECM) of cartilage using a chondroinductive cellulose and silk polymer blend (75:25 ratio). This natural polymer composite is directly electrospun for the first time, into nanofibers without post-spun treatment, using a trifluoroacetic acid and acetic acid cosolvent system. Biocompatibility of the composite nanofibres with human mesenchymal stem cells (hMSCs) is demonstrated and its inherent capacity to direct chondrogenic stem cell differentiation, in the absence of stimulating growth factors, is confirmed. This chondrogenic stimulation could be countered biochemically using fibroblast growth factor-2, a growth factor used to enhance the proliferation of hMSCs. Furthermore, the potential mechanisms driving this chondroinduction at the cell-biomaterial interface is investigated. Composite substrates are fabricated as two-dimensional film surfaces and cultured with hMSCs in the presence of chemicals that interfere with their biochemical and mechanical signaling pathways. Preventing substrate surface elasticity transmission resulted in a significant downregulation of chondrogenic gene expression. Interference with the classical chondrogenic Smad2/3 phosphorylation pathway did not impact chondrogenesis. The results highlight the importance of substrate mechanical elasticity on hMSCs chondroinduction and its independence to known chondrogenic biochemical pathways. The newly fabricated scaffolds provide the foundation for designing a robust, self-inductive, and cost-effective biomimetic biomaterial for cartilage tissue engineering.

Proteins and Peptides as Important Modifiers of the Polymer Scaffolds for Tissue Engineering Applications-A Review

Polymer scaffolds constitute a very interesting strategy for tissue engineering. Even though they are generally non-toxic, in some cases, they may not provide suitable support for cell adhesion, proliferation, and differentiation, which decelerates tissue regeneration. To improve biological properties, scaffolds are frequently enriched with bioactive molecules, inter alia extracellular matrix proteins, adhesive peptides, growth factors, hormones, and cytokines. Although there are many papers describing synthesis and properties of polymer scaffolds enriched with proteins or peptides, few reviews comprehensively summarize these bioactive molecules. Thus, this review presents the current knowledge about the most important proteins and peptides used for modification of polymer scaffolds for tissue engineering. This paper also describes the influence of addition of proteins and peptides on physicochemical, mechanical, and biological properties of polymer scaffolds. Moreover, this article sums up the major applications of some biodegradable natural and synthetic polymer scaffolds modified with proteins and peptides, which have been developed within the past five years.

Introduction of an interface layer on hydroxyapatite whisker/poly(L-lactide) composite and its contribution for improved bioactivity and mechanical properties

A hydroxyapatite whisker (w-HA) was synthesized via dissolution-precipitation by forming calcium-ethylene diamine tetra acetic acid (Ca-EDTA) complexing. The hydroxyapatite whisker was formed with precipitation of Ca²⁺ along the c-axis due to the space inhibition of Ca-EDTA complex during refluxing. The op-w-HA (oligomeric poly(lactic acid) modified w-HA), p-w-HA (poly(L-lactide) modified w-HA) and pc-w-HA (poly(L-lactide) and cyclodextrin modified w-HA) were obtained via the surface modification of w-HA. The particle size, surface charge and biocompatibility of theses modified w-HA particles were successfully adjusted. Among these materials, pc-w-HA exhibited nearly no toxicity, better adhesion to mesenchymal stem cells (MSCs) (5 times better than w-HA) and greater osteoinductivity among the obtained materials (40% of mineralized extracellular matrix higher than w-HA) due to better surface properties. Different kinds of powders (w-HA, p-w-HA and pc-w-HA) were blended with PLLA (poly(L-Lactide)) to form a composite material, respectively. The pc-w-HA/PLLA composite showed better mechanical properties (tensile strength of the pc-w-HA/PLLA composite was 22.3% higher than that of w-HA/PLLA), which could be attributed to mainly two factors including the structure preservation of w-HA bundles and pseudorotaxane linkage between PLA-cyclodextrin and PLLA. The MSCs adhesion of the pc-w-HA/PLLA composite was much better due to balanced hydrophilicity/hydrophobicity and surface roughness. This surface modification method could provide a new and effective strategy for the preparation of bioresorbable composite material with great bioactivity and mechanical property, which has great potential in the medical device industry.

ILK supports RhoA/ROCK-mediated contractility of human intestinal epithelial crypt cells by inducing the fibrillogenesis of endogenous soluble fibronectin during the spreading process

BACKGROUND

Fibronectin (FN) assembly into an insoluble fibrillar matrix is a crucial step in many cell responses to extracellular matrix (ECM) properties, especially with regards to the integrin-related mechanosensitive signaling pathway. We have previously reported that the silencing of expression of integrin-linked kinase (ILK) in human intestinal epithelial crypt (HIEC) cells causes significant reductions in proliferation and spreading through concomitantly acquired impairment of soluble FN deposition. These defects in ILK-depleted cells are rescued by growth on exogenous FN. In the present study we investigated the contribution of ILK in the fibrillogenesis of FN and its relation to integrin-actin axis signaling and organization.

RESULTS

We show that de novo fibrillogenesis of endogenous soluble FN is ILK-dependent. This function seemingly induces the assembly of an ECM that supports increased cytoskeletal tension and the development of a fully spread contractile cell phenotype. We observed that HIEC cell adhesion to exogenous FN or collagen-I (Col-I) is sufficient to restore fibrillogenesis of endogenous FN in ILK-depleted cells. We also found that optimal engagement of the Ras homolog gene family member A (RhoA) GTPase/Rho-associated kinase (ROCK-1, ROCK-2)/myosin light chain (MLC) pathway, actin ventral stress fiber formation, and integrin adhesion complex (IAC) maturation rely primarily upon the cell's capacity to execute FN fibrillogenesis, independent of any significant ILK input. Lastly, we confirm the integrin α5β1 as the main integrin responsible for FN assembly, although in ILK-depleted cells αV-class integrins expression is needed to allow the rescue of FN fibrillogenesis on exogenous substrate.

CONCLUSION

Our study demonstrates that ILK specifically induces the initiation of FN fibrillogenesis during cell spreading, which promotes RhoA/ROCK-dependent cell contractility and maturation of the integrin-actin axis structures. However, the fibrillogenesis process and its downstream effect on RhoA signaling, cell contractility and spreading are ILK-independent in human intestinal epithelial crypt cells.

Si substituted hydroxyapatite nanorods on Ti for percutaneous implants

An ideal intraosseous transcutaneous implant should form a tight seal with soft tissue, besides a requirement of osseointegration at the bone-fixed position. Si substituted hydroxyapatite (Si-HA) nanorods releasing Si ion and simulating nanotopography of natural tissue were designed on Ti to enhance fibroblast response in vitro and biosealing with soft tissue in vivo. Si-HA nanorods were fabricated by alkali-heat treatment followed with hydrothermal treatment. The hydrothermal formation mechanism of Si-HA nanorods was explored. The surface characteristic of Si-HA nanorods was compared with pure HA nanorods. Fibroblast behaviors in vitro and skin response in vivo on different surfaces were also evaluated. The obtained results show that the substitution of Si did not significantly alter the phase component, morphology, roughness and wettability of HA, but additional Si and more Ca were released from Si-HA into medium. Comparing to pure HA nanrods and Ti substrate, Si-HA nanrods enhanced cell behaviors including proliferation, fibrotic phenotype and collagen secretion in vitro, and reduced epithelial down growth in vivo. The enhanced cell response and biosealing should be due to the releasing of Ca, Si and nanotopography of Si-HA nanorods. Si-HA nanorods can be a potential coating to accelerate skin integration for percutaneous implants in clinic.

Nanoscale Surface-Induced Unfolding of Single Fibronectin Is Restricted by Serum Albumin Crowding

Understanding nanoscale protein conformational changes at solid-liquid interfaces is critical for predicting how proteins will impact the performance of biomaterials in vivo. Crowding is an important contributor to conformational stability. Here we apply single-molecule high resolution imaging with photobleaching to directly measure dye-conjugated fibronectin's unfolding in varying conditions of crowding with human serum albumin on aminosilanized glass. Using this approach, we identify serum albumin's crowding mechanism. We find that fibronectin achieves larger degrees of unfolding when not crowded by coadsorbed serum albumin. Serum albumin does not as effectively constrict fibronectin's conformation if it is sequentially, rather than simultaneously, introduced, suggesting that serum albumin's crowding mechanism is dependent on its ability to sterically block fibronectin's unfolding during the process of adsorption. Because fibronectin's conformation is dependent on interfacial macromolecular crowding under in vitro conditions, it is important to consider the role of in vivo crowding on protein activity.

Terminal Group Modification of Carbon Nanotubes Determines Covalently Bound Osteogenic Peptide Performance

Osteogenic peptides are often introduced to improve biological activities and the osteogenic ability of artificial bone materials as an effective approach. Covalent bindings between the peptide and the host material can increase the molecular interactions and make the functionalized surface more stable. However, covalent bindings through different functional groups can bring different effects on the overall bioactivities. In this study, carboxyl and amino groups were respectively introduced onto carbon nanotubes, a nanoreinforcement for synthetic scaffold materials, which were subsequently covalently attached to the RGD/BMP-2 osteogenic peptide. MC3T3-E1 cells were cultured on scaffolds containing peptide-modified carbon nanotubes. The results showed that the peptide through the amino group binding could promote cell functions more effectively than those through carboxyl groups. The mechanism may be that the amino group could bring more positive charges to carbon nanotube surfaces, which further led to differences in the peptide conformation, protein adsorption, and targeting osteogenic effects. Our results provided an effective way of improving the bioactivities of artificial bone materials by chemically binding osteogenic peptides.

Self-assembled biomimetic Nano-Matrix for stem cell anchorage

Mesenchymal stem cells (MSCs) have been widely applied in biomedicine due to their ability to differentiate into many different cell types and their ability to synthesize a broad spectrum of growth factors and cytokines that directly and indirectly influence other cells in their vicinity. To guide MSC infiltration to a bone fracture site, we developed a novel self-assembled Nano-Matrix which can be used as an injectable scaffold to repair bone fractures. The Nano-Matrix is formed by Janus base nanotubes (JBNTs) and fibronectin (FN). JBNTs are nucleobase-derived nanotubes mimicking collagen fibers, and FN is one of the cell adhesive glycoproteins which is responsible for cell-extracellular matrix interactions and guides stem cell migration and differentiation to desired cells types. Here, we demonstrated the successful fabrication and characterization of the JBNT/FN Nano-Matrix as well as its excellent bioactivity that encouraged human MSC migration and adhesion. This work lays a solid foundation for using the Nano-Matrix as an injectable approach to improve MSC retention and function during bone fracture healing.

A glance on the role of fibronectin in controlling cell response at biomaterial interface

The bioactivity of biomaterials is closely related to cell response in contact with them. However, shortly after their insertion, materials are soon covered with proteins that constitute the biological fluids, and which render the direct surface recognition by cells almost impossible. The control of protein adsorption at the interface is therefore desirable. Extracellular matrix proteins are of particular interest in this sense, due to their well-known ability to modulate cell behavior. Particularly, fibronectin plays a leading role, being present in both healthy and injured tissues undergoing healing and regeneration. The aim of the present work is to give an overview on fibronectin and on its involvement in the control of cell behavior providing evidence of its pivotal role in the control of cell adhesion, spreading, migration, proliferation and differentiation. A deep insight into methods to enrich biomaterials surface with fibronectin will be then discussed, as well as new cues on the possibility to design tailored platforms able to specifically retain fibronectin from the surrounding extracellular milieu.

Laminin-Inspired Cell-Instructive Microenvironments for Neural Stem Cells

Laminin is a heterotrimeric glycoprotein with a key role in the formation and maintenance of the basement membrane architecture and properties, as well as on the modulation of several biological functions, including cell adhesion, migration, differentiation and matrix-mediated signaling. In the central nervous system (CNS), laminin is differentially expressed during development and homeostasis, with an impact on the modulation of cell function and fate. Within neurogenic niches, laminin is one of the most important and well described extracellular matrix (ECM) proteins. Specifically, efforts have been made to understand laminin assembly, domain architecture, and interaction of its different bioactive domains with cell surface receptors, soluble signaling molecules, and ECM proteins, to gain insight into the role of this ECM protein and its receptors on the modulation of neurogenesis, both in homeostasis and during repair. This is also expected to provide a rational basis for the design of biomaterial-based matrices mirroring the biological properties of the basement membrane of neural stem cell niches, for application in neural tissue repair and cell transplantation. This review provides a general overview of laminin structure and domain architecture, as well as the main biological functions mediated by this heterotrimeric glycoprotein. The expression and distribution of laminin in the CNS and, more specifically, its role within adult neural stem cell niches is summarized. Additionally, a detailed overview on the use of full-length laminin and laminin derived peptide/recombinant laminin fragments for the development of hydrogels for mimicking the neurogenic niche microenvironment is given. Finally, the main challenges associated with the development of laminin-inspired hydrogels and the hurdles to overcome for these to progress from bench to bedside are discussed.

Bone tissue regeneration: biology, strategies and interface studies

Nowadays, bone diseases and defects as a result of trauma, cancers, infections and degenerative and inflammatory conditions are increasing. Consequently, bone repair and replacement have been developed with improvement of orthopedic technologies and biomaterials of superior properties. This review paper is intended to sum up and discuss the most relevant studies performed in the field of bone biology and bone regeneration approaches. Therefore, the bone tissue regeneration was investigated by synthetic substitutes, scaffolds incorporating active molecules, nanomedicine, cell-based products, biomimetic fibrous and nonfibrous substitutes, biomaterial-based three-dimensional (3D) cell-printing substitutes, bioactive porous polymer/inorganic composites, magnetic field and nano-scaffolds with stem cells and bone-biomaterials interface studies.

Lineage Commitment, Signaling Pathways, and the Cytoskeleton Systems in Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) from adult tissues are promising candidates for personalized cell therapy and tissue engineering. Significant progress was achieved in our understanding of the regulation of MSCs proliferation and differentiation by different cues during the past years. Proliferation and differentiation of MSCs are sensitive to the extracellular matrix (ECM) properties, physical cues, and chemical signaling. Sheath stress, matrix stiffness, surface adhesiveness, and micro- and nanotopography define cell shape and dictate lineage commitment of MSCs even in the absence of specific chemical signals. We discuss mechanotransduction as the major route from ECM through the cytoskeleton toward signaling pathways and gene expression. All components of the cytoskeleton from primary cilium and focal adhesions (FAs) to actin, microtubules (MTs), and intermediate filaments (IFs) are involved in the mechanotransduction. Differentiation of MSCs is regulated via the complex network of interrelated signaling pathways, including RhoA/ROCK, Akt/Erk, and YAP/TAZ effectors of Hippo pathway. These pathways could be regulated both by chemical and mechanical stimuli. Attenuation of these pathways in MSCs results in specific changes in FAs and actin cytoskeleton. Besides, differentiation of MSCs affects MTs and IFs. Recent findings highlight the role of intranuclear actin in the regulation of transcription factors in response to mechanical environmental stimuli. Alterations of cytoskeletal components reflect the MSC senescence state and their migratory capacity. In this review, we discuss the relationships between the molecular interactions in signaling pathways and morphological response of cytoskeletal components and reveal the complex interrelations between cytoskeleton systems and signaling pathways during lineage commitment of MSCs. Impact Statement This review describes the complex network of relationships between mechanical and biochemical stimuli in mesenchymal stem cells (MSC) and their balance which defines the morphological changes of cell shape due to rearrangement of cytoskeletal systems during lineage commitment of MSCs.

Tunable shape memory behavior of polymer with surface modification of nanoparticles

In-situ inclusion of different nanoclays during synthesis results in different level of dispersion of nanoclays in the polymer matrix depending upon the surface modification of the nanoclay. Higher intercalation of the polymer chains within the galleries of organically modified nanoclay results better dispersion as compared to pristine nanoclay. The spectroscopic measurement shows that the extent of interaction between the nanoclay and polymer chains is higher in modified nanoclay nanocomposite which decreases the crystallinity considerably as compared to pristine clay nanocomposite. Interestingly, shape memory behavior measured at physiological temperature (37 °C) improves significantly in presence of organically modified nanoclay while it decreases in presence of unmodified nanoclay in same polyurethane matrix. Complete melting of soft segment along with restricted flipping of hard segment with temperature in presence of extensive interaction in nanocomposite with modified nanoclay helps it to achieve better shape memory behavior against flipping induced stacking of hard segment with temperature along with poor interaction decreases its shape memory behavior in nanocomposite with unmodified nanoclay. Temperature dependent nanostructure reveals the cause of variation in shape memory behavior in presence of organically modified nanoclay. Further, the cell culture studies like cell adhesion, cell viability assay and fluorescence imaging, suggest superior biomaterial of the nanocomposite with modified nanoclay as compared to other composite. Better biodegradable nature of the modified nanocomposite makes it suitable candidate for its potential biomedical applications.

Electrospun Poly(ε-caprolactone) Fiber Scaffolds Functionalized by the Covalent Grafting of a Bioactive Polymer: Surface Characterization and Influence on in Vitro Biological Response

The purpose of this study is to present the poly(caprolactone) (PCL) functionalization by the covalent grafting of poly(sodium styrene sulfonate) on electrospun scaffolds using the "grafting from" technique and evaluate the effect of the coating and surface wettability on the biological response. The "grafting from" technique required energy (thermal or UV) to induce the decomposition of the PCL (hydro)peroxides and generate radicals able to initiate the polymerization of NaSS. In addition, UV irradiation was used to initiate the radical polymerization of NaSS directly from the surface (UV direct "grafting from"). The interest of these two techniques is their easiness, the reduction of the number of process steps, and its applicability to the industry. The selected parameters allow controlling the grafting rate (i.e., degree of functionalization). The aim of the study was to compare two covalent grafting in terms of surface functionalization and hydrophilicity and their effect on the in vitro biological responses of fibroblasts. The achieved results showed the influence of the sulfonate functional groups on the cell response. In addition, outcomes highlighted that the UV direct "grafting from" method allows to moderate the amount of sulfonate groups and the surface hydrophilicity presents a considerable interest for covalently immobilizing bioactive polymers onto electrospun scaffolds designed for tissue engineering applications using efficient post-electrospinning chemical modification.

Designing stem cell niches for differentiation and self-renewal

Mesenchymal stem cells, characterized by their ability to differentiate into skeletal tissues and self-renew, hold great promise for both regenerative medicine and novel therapeutic discovery. However, their regenerative capacity is retained only when in contact with their specialized microenvironment, termed the stem cell niche Niches provide structural and functional cues that are both biochemical and biophysical, stem cells integrate this complex array of signals with intrinsic regulatory networks to meet physiological demands. Although, some of these regulatory mechanisms remain poorly understood or difficult to harness with traditional culture systems. Biomaterial strategies are being developed that aim to recapitulate stem cell niches, by engineering microenvironments with physiological-like niche properties that aim to elucidate stem cell-regulatory mechanisms, and to harness their regenerative capacity in vitro In the future, engineered niches will prove important tools for both regenerative medicine and therapeutic discoveries.

Quince seed mucilage-based scaffold as a smart biological substrate to mimic mechanobiological behavior of skin and promote fibroblasts proliferation and h-ASCs differentiation into keratinocytes

The use of biological macromolecules like quince seed mucilage (QSM), as the common curative practice has a long history in traditional folk medicine to cure wounds and burns. However, this gel cannot be applied on exudative wounds because of the high water content and non-absorption of infection of open wounds. It also limits cell-to-cell interactions and leads to the slow wound healing process. In this study to overcome these problems, a novel QSM-based hybrid scaffold modified by PCL/PEG copolymer was designed and characterized. The properties of this scaffold (PCL/QSM/PEG) were also compared with four scaffolds of PCL/PEG, PCL/Chitosan/PEG, chitosan, and QSM, to assess the role of QSM and the combined effect of polymers in improving the function of skin tissue-engineered scaffolds. It was found, the physicochemical properties play a crucial role in regulating cell behaviors so that, PCL/QSM/PEG as a smart/stimuli-responsive bio-matrix promotes not only human-adipose stem cells (h-ASCs) adhesion but also supports fibroblasts growth, via providing a porous-network. PCL/QSM/PEG could also induce keratinocytes at a desirable level for wound healing, by increasing the mechanobiological signals. Immunocytochemistry analysis confirmed keratinocytes differentiation pattern and their normal phenotype on PCL/QSM/PEG. Our study demonstrates, QSM as a differentiation/growth-promoting biological factor can be a proper candidate for design of wound dressings and skin tissue-engineered substrates containing cell.

Plasma Proteins at the Interface of Dental Implants Modulate Osteoblasts Focal Adhesions Expression and Cytoskeleton Organization

The host-material interface is a crucial relationship dictating the possibility of successful osseointegration in implant dentistry. The aim of the present study was to characterize the effects of plasma proteins pre-adsorption on the adhesion capacity of osteoblasts, which occurs immediately after implant insertion in vivo. After having pre-adsorbed human plasma proteins on a machined and microrough titanium surface, MC3T3-E1 osteoblasts adhesion was evaluated through crystal violet cell adhesion assay, immunofluorescence staining for cytoskeleton, focal adhesions and cell nuclei, and scanning electron microscopy. The pre-adsorbed protein layer markedly affected the adhesion rate of cells, as well as their morphology and the expression of focal contacts. Moreover, protein adsorption to the underlying titanium surface was found to be correlated to surface pre-wetting. Thus, the early adsorption of serum proteins to the interface of dental implants impacts cell adhesion in terms of strength and of focal adhesions expression.

Novel chitosan/agarose/hydroxyapatite nanocomposite scaffold for bone tissue engineering applications: comprehensive evaluation of biocompatibility and osteoinductivity with the use of osteoblasts and mesenchymal stem cells

Background

Nanocomposites produced by reinforcement of polysaccharide matrix with nanoparticles are widely used in engineering of biomaterials. However, clinical applications of developed novel biomaterials are often limited due to their poor biocompatibility.

Purpose

The aim of this work was to comprehensively assess biocompatibility of highly macroporous chitosan/agarose/nanohydroxyapatite bone scaffolds produced by a novel method combining freeze-drying with a foaming agent. Within these studies, blood plasma protein adsorption, osteoblast (MC3T3-E1 Subclone 4 and hFOB 1.19) adhesion and proliferation, and osteogenic differentiation of mesenchymal stem cells derived from bone marrow and adipose tissue were determined. The obtained results were also correlated with materials' surface chemistry and wettability to explain the observed protein and cellular response.

Results

Obtained results clearly showed that the developed nanocomposite scaffolds were characterized by high biocompatibility and osteoconductivity. Importantly, the scaffolds also revealed osteoinductive properties since they have the ability to induce osteogenic differentiation (Runx2 synthesis) in undifferentiated mesenchymal stem cells. The surface of biomaterials is extremely hydrophilic, prone to protein adsorption with the highest affinity toward fibronectin binding, which allows for good osteoblast adhesion, spreading, and proliferation.

Conclusion

Produced by a novel method, macroporous nanocomposite biomaterials have great potential to be used in regenerative medicine for acceleration of the bone healing process.