Detection of interfacial phenomena with osteoblast-like cell adhesion on hydroxyapatite and oxidized polystyrene by the quartz crystal microbalance with dissipation

Cell-Specific Impacts of Surface Coating Composition on Extracellular Vesicle Secretion

Biomaterial properties have recently been shown to modulate extracellular vesicle (EV) secretion and cargo; however, the effects of substrate composition on EV production remain underexplored. This study investigates the impacts of surface coatings composed of collagen I (COLI), fibronectin (FN), and poly l-lysine (PLL) on EV secretion for applications in therapeutic EV production and to further understanding of how changes in the extracellular matrix microenvironment affect EVs. EV secretion from primary bone marrow-derived mesenchymal stromal cells (BMSCs), primary adipose-derived stem cells (ASCs), HEK293 cells, NIH3T3 cells, and RAW264.7 cells was characterized on the different coatings. Expression of EV biogenesis genes and cellular adhesion genes was also analyzed. COLI coatings significantly decreased EV secretion in RAW264.7 cells, with associated decreases in cell viability and changes in EV biogenesis-related and cell adhesion genes at day 4. FN coatings increased EV secretion in NIH3T3 cells, while PLL coatings increased EV secretion in ASCs. Surface coatings had significant effects on the capacity of EVs derived from RAW264.7 and NIH3T3 cells to impact in vitro macrophage proliferation. Overall, surface coatings had different cell-specific effects on EV secretion and in vitro functional capacity, thus highlighting the potential of substrate coatings to further the development of clinical EV production systems.

Analytical investigation of nano-bio interfacial protein mediation for fibroblast adhesion on hydroxyapatite nanoparticles

A quartz crystal microbalance with dissipation (QCM-D) analysis was used to investigate fetal bovine serum (FBS) protein preadsorption on a hydroxyapatite (HAp) surface and the subsequent adhesion process of fibroblasts as compared with the case of oxidized poly(styrene) (PSox). The results showed that the preadsorption of FBS proteins on HAp promoted the subsequent initial cell adhesion ability. Moreover, the measured frequency (Δf) and dissipation shift (ΔD) curves, ΔD-Δf plots and viscoelastic analysis were used to study the initial cell adhesion process in real time. It was suggested that FBS-HAp showed sensitive changes in mass and viscoelasticity as compared with FBS-PSox, which realized the in situ reflection of the cell adhesion state, and the interfacial reactions between the cells and FBS-HAp surfaces such as dehydration and binding occurred to promote the initial cell adhesion and spreading. The viscoelastic analysis of the interface layer showed that the adhered cells on FBS-HAp could secrete some viscous substances such as extracellular matrix (ECM) proteins at the interfaces to provide good adhesion behaviors, and the Voigt-based viscoelastic model could clearly reveal the cellular interfacial viscoelasticity depending on the substrate surface. In addition, the morphology of cells was observed by confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM), and it was found that the pseudopodia were more uniformly stretched on FBS-HAp than on FBS-PSox. Furthermore, the state of the interfacial protein layer was analyzed by localized Fourier-transform infrared (FT-IR) spectroscopy and fluorescence microscopy (FLM), and it was indicated that the type of substrate affects the formation state of ECM proteins, resulting in changes in cell adhesion properties and morphology. The abundant formation of connective proteins (i.e., collagen type I) on FBS-HAp promoted subsequent pseudopodia formation and cell spreading. Therefore, the initial adhesion properties of fibroblasts on the FBS-HAp surface were systematically studied, which is of great importance for understanding the interfacial interaction between biomaterials and cells, and has great application value in biomedical fields.

Practical Use of Quartz Crystal Microbalance Monitoring in Cartilage Tissue Engineering

Quartz crystal microbalance (QCM) is a real-time, nanogram-accurate technique for analyzing various processes on biomaterial surfaces. QCM has proven to be an excellent tool in tissue engineering as it can monitor key parameters in developing cellular scaffolds. This review focuses on the use of QCM in the tissue engineering of cartilage. It begins with a brief discussion of biomaterials and the current state of the art in scaffold development for cartilage tissue engineering, followed by a summary of the potential uses of QCM in cartilage tissue engineering. This includes monitoring interactions with extracellular matrix components, adsorption of proteins onto biomaterials, and biomaterial–cell interactions. In the last part of the review, the material selection problem in tissue engineering is highlighted, emphasizing the importance of surface nanotopography, the role of nanofilms, and utilization of QCM as a “screening” tool to improve the material selection process. A step-by-step process for scaffold design is proposed, as well as the fabrication of thin nanofilms in a layer-by-layer manner using QCM. Finally, future trends of QCM application as a “screening” method for 3D printing of cellular scaffolds are envisioned.

Biosensors for Studies on Adhesion-Mediated Cellular Responses to Their Microenvironment

Cells interact with their microenvironment by constantly sensing mechanical and chemical cues converting them into biochemical signals. These processes allow cells to respond and adapt to changes in their environment, and are crucial for most cellular functions. Understanding the mechanism underlying this complex interplay at the cell-matrix interface is of fundamental value to decipher key biochemical and mechanical factors regulating cell fate. The combination of material science and surface chemistry aided in the creation of controllable environments to study cell mechanosensing and mechanotransduction. Biologically inspired materials tailored with specific bioactive molecules, desired physical properties and tunable topography have emerged as suitable tools to study cell behavior. Among these materials, synthetic cell interfaces with built-in sensing capabilities are highly advantageous to measure biophysical and biochemical interaction between cells and their environment. In this review, we discuss the design of micro and nanostructured biomaterials engineered not only to mimic the structure, properties, and function of the cellular microenvironment, but also to obtain quantitative information on how cells sense and probe specific adhesive cues from the extracellular domain. This type of responsive biointerfaces provides a readout of mechanics, biochemistry, and electrical activity in real time allowing observation of cellular processes with molecular specificity. Specifically designed sensors based on advanced optical and electrochemical readout are discussed. We further provide an insight into the emerging role of multifunctional micro and nanosensors to control and monitor cell functions by means of material design.

Interfacial Effect of Hydration Structures of Hydroxyapatite Nanoparticle Films on Protein Adsorption and Cell Adhesion States

The synthesized elliptical hydroxyapatite (E-HAp) and needle-like HAp (N-HAp) nanoparticles (NPs) were electrophoretically deposited on a gold (Au) substrate. A comparative study of the hydration layers on E-HAp, N-HAp, and Au films was achieved to investigate the interfacial effect of the hydration layers on the conformation of the adsorbed fibrinogen (Fgn) and fibroblast adhesion properties. As a result, the ratios of three types of hydration layer states (free water, intermediate water, nonfreezing water) analyzed by a Fourier transform infrared (FT-IR) spectral deconvolution of the O-H stretching absorption band were investigated. The ratio of the bonding water state (i.e., intermediate and nonfreezing water molecules) is almost the same between two HAp films, and the E-HAp film with an elliptical shape and smaller particle size exhibited the smallest ratio of nonfreezing water, which can suppress the denaturation of the adsorbed protein. Subsequently, FT-IR spectral deconvolution results of the amide I band of the adsorbed Fgn on the E-HAp film indicated the higher proportion of α-helix and β-sheet structures as compared with those on the N-HAp and Au films, suggesting that the smaller proportion of nonfreezing waters would play a significant role in the stereoscopic Fgn conformation. In the culture of fibroblasts, FT-IR spectra of the adhered cells on the E-HAp, N-HAp, and Au films exhibited different absorbance intensities of the amide A, I, II, and III bands, suggesting a different amount of collagen-producing states by the cells, which were also supported by immunostaining results of the collagen type I. Therefore, the different hydration structures on the films clearly influenced the conformation of the adsorbed protein, and the preferential conformation was found at the interfaces between the fibroblasts and the underground E-HAp films.

Peptide-functionalized supported lipid bilayers to construct cell membrane mimicking interfaces

Supported lipid bilayers (SLB) functionalized with bioactive molecules can be effectively used to study the interaction of cells with different molecules for fundamental research or to develop biosynthetic systems for various biomedical applications. In this study, RGD and Osteocalcin mimetic (OSN) peptides were used as model molecules for functionalization of otherwise passive SLBs to evaluate cell-surface interactions via real-time monitoring in quartz crystal microbalance with dissipation. Similar platforms were also used in cell culture environment. It was seen that low density of mobile RGD peptides on SLB platforms preserved their biological activity and promoted cell adhesion more efficiently than high number of immobile, physisorbed peptides. Even though nonspecific protein and cell attachment was promoted, cells did not spread well on OSN-coated control surfaces. The stability of SLBs produced with different lipids were evaluated in various medium conditions. Enrichment with different lipids increased the stability of SLB to pure PC bilayer.

A Cryosectioning Technique for the Observation of Intracellular Structures and Immunocytochemistry of Tissues in Atomic Force Microscopy (AFM)

The use of cryosectioning facilitates the morphological analysis and immunocytochemistry of cells in tissues in atomic force microscopy (AFM). The cantilever can access all parts of a tissue sample in cryosections after the embedding medium (sucrose) has been replaced with phosphate-buffered saline (PBS), and this approach has enabled the production of a type of high-resolution image. The images resembled those obtained from freeze-etching replica electron microscopy (EM) rather than from thin-section EM. The AFM images showed disks stacked and enveloped by the cell membrane in rod photoreceptor outer segments (ROS) at EM resolution. In addition, ciliary necklaces on the surface of connecting cilium, three-dimensional architecture of synaptic ribbons, and the surface of the post-synaptic membrane facing the active site were revealed, which were not apparent using thin-section EM. AFM could depict the molecular binding of anti-opsin antibodies conjugated to a secondary fluorescent antibody bound to the disk membrane. The specific localization of the anti-opsin binding sites was verified through correlation with immunofluorescence signals in AFM combined with confocal fluorescence microscope. To prove reproducibility in other tissues besides retina, cryosectioning-AFM was also applied to elucidate molecular organization of sarcomere in a rabbit psoas muscle.

Effective segregation of cytocompatible chitosan molecules in a silica-surfactant nanostructure formation process

Segregated nanostructures of Chi molecules by a silica-surfactant self-assembly film formation process were successfully prepared, and it is shown that their self-organization affects the cytocompatibility.

Effective Surface Functionalization of Carbon Fibers for Fiber/Polymer Composites with Tailor-Made Interfaces

Composites between carbon fibers (CFs) and heterogeneous materials have been widely studied and their fabrication techniques have been developed. However, their hydrophobic surfaces make it difficult to disperse CFs into hydrophilic resins, which results in weak junctions with ceramics. To develop high-strength composite fibers, it is important to design interfacial chemical bonds. Thus, surface-modification techniques of CFs have recently become the main focus and their interfaces have been characterized by various analytical methods. In this Minireview, various techniques that modify the CF surface by coating with inorganic polymers (metal oxide compounds) are highlighted, and the applications of novel nanocomposite fibers are also described. Furthermore, interfacial bonds between CFs and polymer resins are reviewed and discussed in terms of CF-reinforced plastics and their future prospects.

Impact of polyelectrolytes and their corresponding multilayers to human primary endothelial cells

The layer-by-layer technique, which allows simple preparation of polyelectrolyte multilayers, came into the focus of research for development of functionalized medical devices. Numerous literature exist that concentrate on the film build-up and the behaviour of cells on polyelectrolyte multilayers. However, in case of very soft polyelectrolyte multilayers, studies of the cell behaviour on these films are sometimes misleading with regard to clinical applications because cells do not die due to cytotoxicity but due to apoptosis by missing cell adhesion. It turns out that the adhesion in vitro, and thus, the viability of cells on polyelectrolyte multilayers is mostly influenced by their mechanical properties. In order to decide, which polyelectrolyte multilayers are suitable for implants, we take this problem into account by putting the substrates with soft films on top of pre-cultured human primary endothelial cells ('reverse assay'). Hence, the present work aims giving a more complete and reliable study of typical polyelectrolyte multilayers with regard to clinical applications. In particular, coatings consisting of hyaluronic acid and chitosan as natural polymers and sulfonated polystyrene and polyallylamine hydrochlorite as synthetic polymers were studied. The adsorption of polyelectrolytes was characterized by physico-chemical methods which show regular buildup. Biological examination of the native or modified polyelectrolyte multilayers was based on their effect to cell adhesion and morphology of endothelial cells by viability assays, immunostaining and scanning electron microscopy. Using the standard method, which is typically applied in literature--seeding cells on top of films--shows that the best adhesion and thus, viability can be achieved using sulfonated polystyrene/polyallylamine hydrochlorite. However, putting the films on top of endothelial cells reveals that hyaluronic acid/chitosan may also be suitable for clinical applications: This result is especially remarkable, since hyaluronic acid and chitosan mediate per se no cytotoxic effects, whereas the individual polyelectrolytes, sulfonated polystyrene and polyallylamine hydrochlorite, and their complexes show slight cytotoxicity.

Nano/microstructural effect of hydroxyapatite nanocrystals on hepatocyte cell aggregation and adhesion

Hepatocyte cell aggregation and adhesion to HAp nanocrystals covered with SU-8 polymer micropatterns by nano/microfabrication techniques is demonstrated. The surface roughness and wettability of the HAp nanocrystals are significantly different from those of the SU-8 polymer. QCM-D and microscopic observation clearly reveal that the cells realize the surface properties to form aggregation and preferentially adhere to the HAp nanocrystals at 2 h after seeding, indicating the importance of the microstructures as well as the interfacial phenomena at a nanometer scale.