Cell shape and spreading of stromal (mesenchymal) stem cells cultured on fibronectin coated gold and hydroxyapatite surfaces

Chitosan/Hyaluronan and Alginate-Nanohydroxyapatite Biphasic Scaffold as a Promising Matrix for Osteoarthritis Disorders

Purpose

Regenerative medicine offers new techniques for osteoarthritis (OA) disorders, especially while considering simultaneous chondral and subchondral regenerations.

Methods

Chitosan and hyaluronan were chemically bound as the chondral phase and the osteogenic layer was prepared with alginate and nano-hydroxyapatite (nHAP). These scaffolds were fixed by fibrin glue as a biphasic scaffold and then examined.

Results

Scanning electron microscopy (SEM) confirmed the porosity of 61.45±4.51 and 44.145±2.81 % for the subchondral and chondral layers, respectively. The composition analysis by energy dispersive X-ray (EDAX) indicated the various elements of both hydrogels. Also, their mechanical properties indicated that the highest modulus and resistance values corresponded to the biphasic hydrogel as 108.33±5.56 and 721.135±8.21 kPa, despite the same strain value as other groups. Their individual examinations demonstrated the proteoglycan synthesis of the chondral layer and also, the alkaline phosphatase (ALP) activity of the subchondral layer as 13.3±2.2 ng. After 21 days, the cells showed a mineralized surface and a polygonal phenotype, confirming their commitment to bone and cartilage tissues, respectively. Immunostaining of collagen I and II represented greater extracellular matrix (ECM) secretion in the biphasic composite group due to the paracrine effect of the two cell types on each other.

Conclusion

For the first time, the ability of this biphasic scaffold to regenerate both tissue types was evaluated and the results showed satisfactory cellular commitment to bone and cartilage tissues. Thus, this scaffold can be considered a new strategy for the preparation of implants for OA.

Relationship of matrix stiffness and cell morphology in regulation of osteogenesis and adipogenesis of BMSCs

BACKGROUNDS

Matrix stiffness has been found to regulate cell morphology, while both cell morphology and matrix stiffness are verified as important factors directing BMSCs (bone marrow mesenchymal stem cells) differentiation. This study aimed to investigate whether matrix stiffness depended on cell morphology to regulate osteogenesis and adipogenesis of BMSCs on 2D substrates.

METHODS AND RESULTS

First, we seeded BMSCs on tissue culture plates (TCPs) with different fibronectin (FN) concentrations and cytoskeleton inhibitor cytochalasin D, and FN was found to promote cell spreading and osteogenesis while inhibiting adipogenesis of BMSCs through F-actin reorganization. Based on these, we modulated BMSCs morphology on 0.5 kPa and 32 kPa CytoSoft® substrates through FN. High concentration of FN (300 μg/ml) coated on 0.5 kPa substrates promoted cell spreading to similar levels with 32 kPa substrates coated with 100 μg/ml of FN, and cells in both groups dominantly commit osteogenesis. On the other hand, low FN concentration (30 μg/ml) on 32 kPa substrates induced restricted cell morphology similar with 0.5 kPa substrates coated with 100 μg/ml of FN, and cells in both groups mainly commit adipogenesis. Immunofluorescence indicated nuclear translocation and higher intensity of YAP/TAZ when cells spread to larger areas, regardless of matrix stiffness. However, when cell spreading areas were fixed as similar levels, matrix stiffness didn't significantly affect YAP/TAZ intensity or location.

CONCLUSIONS

Matrix stiffness failed to regulate BMSCs differentiation and YAP/TAZ activity without corresponding cell morphology. Cell spreading area could mediate effects of matrix stiffness on osteogenesis and adipogenesis of BMSCs.

Combinatorial fluorapatite-based scaffolds substituted with strontium, magnesium and silicon ions for mending bone defects

In bone tissue engineering, ionic doping using bone-related minerals such as magnesium (Mg) or strontium (Sr) is a promising strategy to make up for the inherent disadvantages (low solubility) of various apatite-based materials (such as fluorapatite (FAp) and hydroxyapatite (HA)). Therefore, some studies in recent years have tried to address the lack-of-methodology to improve the properties of bioceramics in the field. Even though the outcome of the studies has shown some promises, the influence of doped elements on the structures and properties of in-vitro and in-vivo mineralized FAp has not been investigated in detail so far. Thus, it is still an open question mark in the field. In this work, strontium modified fluorapatite (Sr-FAp), magnesium and silicon modified fluorapatite (Mg-SiFAp) bioceramics were synthesized using a mechanical alloying methodology. Results showed that the doped elements could decrease the crystallinity of FAp (56%) to less than 45% and 39% for Sr-FAp and Mg-SiFAp, respectively. Moreover, in-vitro studies revealed that Sr-FAp significantly enhanced osteogenic differentiation of hMSCs, after 21 days of culture, compared to Mg-SiFAp at both osteogenic and normal media. Then, in vivo bone formation in a defect of rat femur filled with a Sr-FAp and Mg-SiFAp compared to empty defect was investigated. Histological analysis revealed an increase in bone formation three weeks after implanting Sr-FAp compared to Mg-SiFAp and the empty defect. These results suggest that compared to magnesium and silicon, strontium ion significantly promotes bone formation in fluorapatite, making it appropriate for filling bone defects.

SERS-Active 3D Interconnected Nanocarbon Web toward Nonplasmonic in Vitro Sensing of HeLa Cells and Fibroblasts

A noninvasive intracellular component analysis technique is important in cancer treatment and the initial identification of cancer. Carbon nanomaterials/nanostructures, such as carbon nanotubes and graphene, have little to no surface enhanced Raman scattering (SERS) ability. Because of these structures' low Raman responses, they are conjugated with gold or silver to attain the SERS-active ability to detect normal fibroblasts and HeLa cancer cells. To the best of our knowledge, the effectiveness of the individual use of carbon nanomaterials as a nonplasmonic SERS-active platform for in vitro cancer/normal cell detection has not been investigated to date. Here, for the first time, we introduce a unique nonplasmonic SERS-based biosensing platform that uses a biocompatible self-assembled three-dimensional interconnected nanocarbon web (INW) for in vitro detection and differentiation of HeLa cells and fibroblasts. The sub-10-nm morphology of the INW facilitates the endocytic uptake of INW clusters to the cells, and its SERS functionality introduces live cell Raman sensing. The INW platform has achieved an enhancement factor (EF) of 3.66 × 10⁴ and 9.10 × 10³ with crystal violet and Rhodamine 6G dyes, respectively, significant in comparison to the EF of graphene surfaces (2-17). The results of the time-based Raman spectroscopy of live HeLa cells and fibroblasts revealed chemical fingerprints of intracellular components, such as DNA/RNA, proteins, and lipids. The components' spectroscopic differences facilitate and elucidate the specification of each cell. The highest Raman enhancement achieved was fourfold for fibroblasts (protein) and sixfold for HeLa cells (DNA). Furthermore, the SERS spectra along with scanning electron microscopy and fluorescence microscopy analysis of the immobilized cells after 24 and 48 h shed light on the health of fibroblasts and HeLa cells. A photon energy-induced ionization achieved with a femtosecond laser fabricated a biocompatible INW platform with the designated unique attributes. This simple, label-free, in vitro diagnosis approach for HeLa cells and fibroblasts has strong potential for cancer research.

Immobilization of Aluminum Hydroxide Particles on Quartz Crystal Microbalance Sensors to Elucidate Antigen-Adjuvant Interaction Mechanisms in Vaccines

Aluminum hydroxide (AH) salts are the most widely used adjuvants in vaccine formulation. They trigger immunogenicity from antigenic subunits that would otherwise suffer from a lack of efficiency. Previous studies focusing on antigen-AH interaction mechanisms, performed with model proteins, suggested that electrostatic interactions and phosphate-hydroxyl ligand exchanges drive protein adsorption on AH. We however recently evidenced that NaCl, used in vaccine formulation, provokes AH particle aggregation. This must be taken into account to interpret data related to protein adsorption on AH. Here, we report on the successful development and use of a stable AH-coated surface to explore the mechanisms of protein adsorption by means of ultrasensitive surface analysis tools. Bovine serum albumin (BSA) adsorption was studied at different pHs and ionic strengths (I) using quartz crystal microbalance. The results show that protein adsorption on the AH adjuvant cannot be explained solely by electrostatic interactions and ligand exchanges. Hence, a higher adsorption was observed at pH 3 compared to pH 7, although AH and BSA respectively undergo repulsive and attractive electrostatic interactions at these pH values. Almost no effect of I on adsorption was moreover noted at pH 7. These new developments and observations not only suggest that other mechanisms govern protein adsorption on AH but also offer a new platform for the study of antigen adsorption in the context of vaccine formulation. Immobilizing particles on QCM sensors also enriches the range of applications for which QCM can be exploited, especially in colloid science.

Optimization of the use of a pharmaceutical grade xeno-free medium for in vitro expansion of human mesenchymal stem/stromal cells

Human bone marrow-derived mesenchymal stem/stromal cells (hMSCs) are considered promising therapeutic agents in the field of cell therapy and regenerative medicine, mainly due to their relative facility to be isolated, multi-differentiation potential, and immunomodulatory role. However, their application in clinics requires a crucial step of in vitro expansion. Most of the protocols for hMSCs in vitro culture use foetal bovine serum as medium supplement that, being from animal origin, presents several safety concerns and may initiate xenogeneic immune responses after cells transplantation. This work reports the optimization of a pharmaceutical-grade xeno-free strategy for hMSCs in vitro expansion based on the supplementation of basal medium with a pharmaceutical-grade human plasma-derived supplement for cell culture (SCC) and 2 human growth factors (bFGF and TGFβ1), plus a coating of human plasma fibronectin (Fn). After 4 weeks in culture, this strategy improves hMSCs expansion yield about 4.3-fold in comparison with foetal bovine serum supplementation and 4.5-fold compared with a commercially available xeno-free medium. hMSCs expanded in SCC-based formulation maintained their phenotype and differentiation capacity into osteogenic, adipogenic, and chondrogenic lineages, without alterations in cell karyotype. Overall, the SCC-based medium appears to be an excellent alternative for the xeno-free expansion of hMSCs as therapeutic agents for clinical applications.

Xeno-Free Strategies for Safe Human Mesenchymal Stem/Stromal Cell Expansion: Supplements and Coatings

Human mesenchymal stem/stromal cells (hMSCs) have generated great interest in regenerative medicine mainly due to their multidifferentiation potential and immunomodulatory role. Although hMSC can be obtained from different tissues, the number of available cells is always low for clinical applications, thus requiring in vitro expansion. Most of the current protocols for hMSC expansion make use of fetal bovine serum (FBS) as a nutrient-rich supplement. However, regulatory guidelines encourage novel xeno-free alternatives to define safer and standardized protocols for hMSC expansion that preserve their intrinsic therapeutic potential. Since hMSCs are adherent cells, the attachment surface and cell-adhesive components also play a crucial role on their successful expansion. This review focuses on the advantages/disadvantages of FBS-free media and surfaces/coatings that avoid the use of animal serum, overcoming ethical issues and improving the expansion of hMSC for clinical applications in a safe and reproducible way.

Fibroblast-Cytophilic and HeLa-Cytotoxic Dual Function Carbon Nanoribbon Network Platform

Carbon nanomaterials have emerged as a promising material in cancer diagnosis and therapy. Carbon nanomaterials/nanostructures (C-C molecular structure) act as a carrier/skeleton and require further surface modification through functionalization with chemicals or biomolecules to attain cell response. We report the synthesis of a novel carbon nanoribbon network (CNRN) platform that possesses a combination of C-C and C-O bond architecture. The bioactive CNRN showed enhanced ability for cell adhesion. Most importantly, it induced opposite cell responses from healthy cells and cancerous cells, cytophilic to fibroblasts but cytotoxic to HeLa cells. Ultrafast laser ionization under ambient conditions transforms nonbioresponsive C-C bond of graphite to C-C and C-O bonds, forming a self-assembled CNRN platform. The morphology, nanochemistry, and functionality on modulating fibroblast and HeLa adhesion and proliferation of the fabricated CNRN platforms were investigated. The results of in vitro studies suggested that the CNRN platforms not only attracted but also actively accelerated the adhesion and proliferation of both fibroblasts and HeLa cells. The proliferation rate of fibroblasts and HeLa cells is 91 and 98 times greater compared with that of a native graphite substrate, respectively. The morphology of the cells over a period of 24 to 48 h revealed that the CNRN platform induced an apoptosis-like cytotoxic function on HeLa cells, whereas fibroblasts experienced a cytophilic effect and formed a tissuelike structure. The degree of cytotoxic or cytophilic effect can be further enhanced by adjusting parameters such as the ratio of C-C bonds to C-O bonds, the nanoribbon width, and the nanovoid porosity of the CNRN platforms, which could be tuned by careful control of laser ionization. In a nutshell, for the first time, pristine carbon nanostructures free from biochemical functionalization demonstrate dual function, cytophilic to fibroblast cells and cytotoxic to HeLa cells.

Biofunctionalized 3-D Carbon Nano-Network Platform for Enhanced Fibroblast Cell Adhesion

Carbon nanomaterials have been investigated for various biomedical applications. In most cases, however, these nanomaterials must be functionalized biologically or chemically due to their biological inertness or possible cytotoxicity. Here, we report the development of a new carbon nanomaterial with a bioactive phase that significantly promotes cell adhesion. We synthesize the bioactive phase by introducing self-assembled nanotopography and altered nano-chemistry to graphite substrates using ultrafast laser. To the best of our knowledge, this is the first time that such a cytophilic bio-carbon is developed in a single step without requiring subsequent biological/chemical treatments. By controlling the nano-network concentration and chemistry, we develop platforms with different degrees of cell cytophilicity. We study quantitatively and qualitatively the cell response to nano-network platforms with NIH-3T3 fibroblasts. The findings from the in vitro study indicate that the platforms possess excellent biocompatibility and promote cell adhesion considerably. The study of the cell morphology shows a healthy attachment of cells with a well-spread shape, overextended actin filaments, and morphological symmetry, which is indicative of a high cellular interaction with the nano-network. The developed nanomaterial possesses great biocompatibility and considerably stimulates cell adhesion and subsequent cell proliferation, thus offering a promising path toward engineering various biomedical devices.

Keratin mediated attachment of stem cells to augment cardiomyogenic lineage commitment

The objective of this work was to develop a simple surface modification technique using keratin derived from human hair for efficient cardiomyogenic lineage commitment of human mesenchymal stem cells (hMSCs). Keratin was extracted from discarded human hair containing both the acidic and basic components along with the heterodimers. The extracted keratin was adsorbed to conventional tissue culture polystyrene surfaces at different concentration. Keratin solution of 500μg/ml yielded a well coated layer of 12±1nm thickness with minimal agglomeration. The keratin coated surfaces promoted cell attachment and proliferation. Large increases in the mRNA expression of known cardiomyocyte genes such as cardiac actinin, cardiac troponin and β-myosin heavy chain were observed. Immunostaining revealed increased expression of sarcomeric α-actinin and tropomyosin whereas Western blots confirmed higher expression of tropomyosin and myocyte enhancer factor 2C in cells on the keratin coated surface than on the non-coated surface. Keratin promoted DNA demethylation of the Atp2a2 and Nkx2.5 genes thereby elucidating the importance of epigenetic changes as a possible molecular mechanism underlying the increased differentiation. A global gene expression analysis revealed a significant alteration in the expression of genes involved in pathways associated in cardiomyogenic commitment including cytokine and chemokine signaling, cell-cell and cell-matrix interactions, Wnt signaling, MAPK signaling, TGF-β signaling and FGF signaling pathways among others. Thus, adsorption of keratin offers a facile and affordable yet potent route for inducing cardiomyogenic lineage commitment of stem cells with important implications in developing xeno-free strategies in cardiovascular regenerative medicine.

Tooth Tissue Engineering: The Importance of Blood Products as a Supplement in Tissue Culture Medium for Human Pulp Dental Stem Cells

One of the goals in using cells for tissue engineering (TE) and cell therapy consists of optimizing the medium for cell culture. The present study compares three different blood product supplements for improved cell proliferation and protection against DNA damage in cultured human dental pulp stem cells for tooth TE applications. Human cells from dental pulp were first characterized as adult stem cells (ectomesenchymal mixed origin) by flow cytometry. Next, four different cell culture conditions were tested: I, supplement-free; II, supplemented with fetal bovine serum; III, allogeneic human serum; and IV, autologous human serum. Cultured cells were then characterized for cell proliferation, mineralized nodule formation, and colony-forming units (CFU) capability. After 28 days in culture, the comet assay was performed to assess possible damage in cellular DNA. Our results revealed that Protocol IV achieved higher cell proliferation than Protocol I (p = 0.0112). Protocols II and III resulted in higher cell proliferation than Protocol I, but no statistical differences were found relative to Protocol IV. The comet assay revealed less cell damage in cells cultured using Protocol IV as compared to Protocols II and III. The damage percentage observed on Protocol II was significantly higher than all other protocols. CFUs capability was highest using Protocol IV (p = 0.0018) and III, respectively, and the highest degree of mineralization was observed using Protocol IV as compared to Protocols II and III. Protocol IV resulted in significantly improved cell proliferation, and no cell damage was observed. These results demonstrate that human blood product supplements can be used as feasible supplements for culturing adult human dental stem cells.

Fibronectin-Alginate microcapsules improve cell viability and protein secretion of encapsulated Factor IX-engineered human mesenchymal stromal cells

Continuous delivery of proteins by engineered cells encapsu-lated in biocompatible polymeric microcapsules is of considerable therapeutic potential. However, this technology has not lived up to expectations due to inadequate cell--matrix interactions and subsequent cell death. In this study we hypoth-esize that the presence of fibronectin in an alginate matrix may enhance the viability and functionality of encapsulated human cord blood-derived mesenchymal stromal cells (MSCs) expressing the human Factor IX (FIX) gene. MSCs were encapsulated in alginate-PLL microcapsules containing 10, 100, or 500 μg/ml fibronectin to ameliorate cell survival. MSCs in microcapsules with 100 and 500 μg/ml fibronectin demonstrated improved cell viability and proliferation and higher FIX secretion compared to MSCs in non-supplemented microcapsules. In contrast, 10 μg/ml fibronectin did not significantly affect the viability and protein secretion from the encapsulated cells. Differentiation studies demonstrated osteogenic (but not chondrogenic or adipogenic) differentiation capability and efficient FIX secretion of the enclosed MSCs in the fibronectin-alginate suspension culture. Thus, the use of recombinant MSCs encapsulated in fibronectin-alginate microcapsules in basal or osteogenic cultures may be of practical use in the treatment of hemophilia B.

Development of complex-shaped liver multicellular spheroids as a human-based model for nanoparticle toxicity assessment in vitro

The emergence of human-based models is incontestably required for the study of complex physiological pathways and validation of reliable in vitro methods as alternative for in vivo studies in experimental animals for toxicity assessment. With this objective, we have developed and tested three dimensional environments for cells using different types of hydrogels including transglutaminase-cross-linked gelatin, collagen type I, and growth-factor depleted Matrigel. Cells grown in Matrigel exhibited the greatest cell proliferation and spheroid diameter. Moreover, analysis of urea and albumin biosynthesis revealed that the created system allowed the immortalized liver cell line HepG2 to re-establish normal hepatocyte-like properties which were not observed under the conditions of conventional cell cultures. This study presents a scalable technology for production of complex-shaped liver multicellular spheroids as a system which improves the predictive value of cell-based assays for safety and risk assessment. The time- and dose-dependent toxicity of nanoparticles demonstrates a higher cytotoxic effect when HepG2 cells grown as monolayer than embedded in hydrogels. The experimental setup provided evidence that the cell environment has significant influence on cell sensitivity and that liver spheroid is a useful and novel tool to examine nanoparticle dosing effect even at the level of in vitro studies. Therefore, this system can be applied to a wide variety of potentially hostile compounds in basic screening to provide initial warning of adverse effects and trigger subsequent analysis and remedial actions.

Nanostructured hydroxyapatite surfaces-mediated adsorption alters recognition of BMP receptor IA and bioactivity of bone morphogenetic protein-2

Highly efficient loading of bone morphogenetic protein-2 (BMP-2) onto carriers with desirable performance is still a major challenge in the field of bone regeneration. Till now, the nanoscaled surface-induced changes of the structure and bioactivity of BMP-2 remains poorly understood. Here, the effect of nanoscaled surface on the adsorption and bioactivity of BMP-2 was investigated with a series of hydroxyapatite surfaces (HAPs): HAP crystal-coated surface (HAP), HAP crystal-coated polished surface (HAP-Pol), and sintered HAP crystal-coated surface (HAP-Sin). The adsorption dynamics of recombinant human BMP-2 (rhBMP-2) and the accessibility of the binding epitopes of adsorbed rhBMP-2 for BMP receptors (BMPRs) were examined by a quartz crystal microbalance with dissipation. Moreover, the bioactivity of adsorbed rhBMP-2 and the BMP-induced Smad signaling were investigated with C2C12 model cells. A noticeably high mass-uptake of rhBMP-2 and enhanced recognition of BMPR-IA to adsorbed rhBMP-2 were found on the HAP-Pol surface. For the rhBMP-2-adsorbed HAPs, both ALP activity and Smad signaling increased in the order of HAP-Sin<HAP<HAP-Pol. Furthermore, hybrid molecular dynamics and steered molecular dynamics simulations validated that BMP-2 tightly anchored on the HAP-Pol surface with a relative loosened conformation, but the HAP-Sin surface induced a compact conformation of BMP-2. In conclusion, the nanostructured HAPs can modulate the way of adsorption of rhBMP-2, and thus the recognition of BMPR-IA and the bioactivity of rhBMP-2. These findings can provide insightful suggestions for the future design and fabrication of rhBMP-2-based scaffolds/implants.

STATEMENT OF SIGNIFICANCE

This study provides strong evidences that nanoscaled HAPs yield extraordinary influence on the adsorption behaviors and bioactivity of rhBMP-2. It has been found that the surface roughness and crystallinity played a crucial role in governing the way of rhBMP-2 binding to HAPs, and thus the conformation, recognition of BMPR-IA and bioactivity of adsorbed rhBMP-2. It is also for the first time to correlate numerical modeling and experimental results of the bioactivity of rhBMP-2 on nanostructured HAPs. This work can pave an avenue for the wider uses of rhBMP-2 in clinical applications and arouse broad interests among researchers in the fields of nano-biotechnology, biomaterials and bone tissue engineering.

Modulating Mesenchymal Stem Cell Behavior Using Human Hair Keratin-Coated Surfaces

Human mesenchymal stem cells (hMSCs) have shown great potential for therapeutic purposes. However, the low frequencies of hMSCs in the body and difficulties in expanding their numbers in vitro have limited their clinical use. In order to develop an alternative strategy for the expansion of hMSCs in vitro, we coated tissue culture polystyrene with keratins extracted from human hair and studied the behavior of cells from 2 donors on these surfaces. The coating resulted in a homogeneous distribution of nanosized keratin globules possessing significant hydrophilicity. Results from cell attachment assays demonstrated that keratin-coated surfaces were able to moderate donor-to-donor variability when compared with noncoated tissue culture polystyrene. STRO-1 expression was either sustained or enhanced on hMSCs cultured on keratin-coated surfaces. This translated into significant increases in the colony-forming efficiencies of both hMSC populations, when the cells were serially passaged. Human hair keratins are abundant and might constitute a feasible replacement for other biomaterials that are of animal origin. In addition, our results suggest that hair keratins may be effective in moderating the microenvironment sufficiently to enrich hMSCs with high colony-forming efficiency ex vivo, for clinical applications.

Effect of the Materials Properties of Hydroxyapatite Nanoparticles on Fibronectin Deposition and Conformation

Hydroxyapatite (HAP, Ca₁₀(PO₄)₆(OH)₂) nanoparticles with controlled materials properties have been synthesized through a two-step hydrothermal aging method to investigate fibronectin (Fn) adsorption. Two distinct populations of HAP nanoparticles have been generated: HAP1 particles had smaller size, plate-like shape, lower crystallinity, and more negative ζ potential than HAP2 particles. We then developed two-dimensional platforms containing HAP and Fn and analyzed both the amount and the conformation of Fn via Förster resonance energy transfer (FRET) at various HAP concentrations. Our FRET analysis reveals that larger amounts of more compact Fn molecules were adsorbed onto HAP1 than onto HAP2 particles. Additionally, our data show that the amount of compact Fn adsorbed increased with increasing HAP concentration due to the formation of nanoparticle agglomerates. We propose that both the surface chemistry of single nanoparticles and the size and morphology of HAP agglomerates play significant roles in the interaction of Fn with HAP. Collectively, our findings suggest that the HAP-induced conformational changes of Fn, a critical mechanotransducer protein involved in the communication of cells with their environment, will ultimately affect downstream cellular behaviors. These results have important implications for our understanding of organic-inorganic interactions in physiological and pathological biomineralization processes such as HAP-related inflammation.

Use of precisely sculptured thin film (STF) substrates with generalized ellipsometry to determine spatial distribution of adsorbed fibronectin to nanostructured columnar topographies and effect on cell adhesion

Sculptured thin film (STF) substrates consist of nanocolumns with precise orientation, intercolumnar spacing, and optical anisotropy, which can be used as model biomaterial substrates to study the effect of homogenous nanotopogrophies on the three-dimensional distribution of adsorbed proteins. Generalized ellipsometry was used to discriminate between the distributions of adsorbed FN either on top of or within the intercolumnar void spaces of STFs, afforded by the optical properties of these precisely crafted substrates. Generalized ellipsometry indicated that STFs with vertical nanocolumns enhanced total FN adsorption two-fold relative to flat control substrates and the FN adsorption studies demonstrate different STF characteristics influence the degree of FN immobilization both on top and within intercolumnar spaces, with increasing spacing and surface area enhancing total protein adsorption. Mouse fibroblasts or mouse mesenchymal stem cells were subsequently cultured on STFs, to investigate the effect of highly ordered and defined nanotopographies on cell adhesion, spreading, and proliferation. All STF nanotopographies investigated in the absence of adsorbed FN were found to significantly enhance cell adhesion relative to flat substrates; and the addition of FN to STFs was found to have cell-dependent effects on enhancing cell-material interactions. Furthermore, the amount of FN adsorbed to the STFs did not correlate with comparative enhancements of cell-material interactions, suggesting that nanotopography predominantly contributes to the biocompatibility of homogenous nanocolumnar surfaces. This is the first study to correlate precisely defined nanostructured features with protein distribution and cell-nanomaterial interactions. STFs demonstrate immense potential as biomaterial surfaces for applications in tissue engineering, drug delivery, and biosensing.

Thin polymer brush decouples biomaterial's micro-/nanotopology and stem cell adhesion

Surface morphology and chemistry of polymers used as biomaterials, such as tissue engineering scaffolds, have a strong influence on the adhesion and behavior of human mesenchymal stem cells. Here we studied semicrystalline poly(ε-caprolactone) (PCL) substrate scaffolds, which exhibited a variation of surface morphologies and roughness originating from different spherulitic superstructures. Substrates were obtained by varying the parameters of the thermal processing, that is, crystallization conditions. The cells attached to these polymer substrates adopted different morphologies responding to variations in spherulite density and size. In order to decouple substrate topology effects on the cells, sub-100 nm bioadhesive polymer brush coatings of oligo(ethylene glycol) methacrylates were grafted from PCL and functionalized with fibronectin. On surfaces featuring different surface textures, dense and sub-100 nm thick brush coatings determined the response of cells, irrespective to the underlying topology. Thus, polymer brushes decouple substrate micro-/nanoscale surface topology and the adhesion of stem cells.

Functional morphometric analysis in cellular behaviors: shape and size matter

Cellular morphogenesis in response to biophysical and topographical cues provides insights into cytoskeletal status, biointerface communications, and phenotypic adaptations in an incessant signaling feedback that governs cellular fate. Morphometric characterization is an important element in the study of the dynamic cellular behaviors, in their interactive response to environmental influence exerted by culture system. They collectively serve to reflect cellular proliferation, migration, and differentiation, which may serve as prognostic indices for clinical and pathological diagnosis. Various parameters are proposed to categorize morphological adaptations in relation to cellular function. In this review, the underlying principles, assumptions, and limitations of morphological characterizations are discussed. The significance, challenges, and implications of quantitative morphometric characterization of cell shapes and sizes in determining cellular functions are discussed.

In vitro proliferation and osteogenic differentiation of mesenchymal stem cells on nanoporous alumina

Cell adhesion, migration, and proliferation are significantly affected by the surface topography of the substrates on which the cells are cultured. Alumina is one of the most popular implant materials used in orthopedics, but few data are available concerning the cellular responses of mesenchymal stem cells (MSCs) grown on nanoporous structures. MSCs were cultured on smooth alumina substrates and nanoporous alumina substrates to investigate the interaction between surface topographies of nanoporous alumina and cellular behavior. Nanoporous alumina substrates with pore sizes of 20 nm and 100 nm were used to evaluate the effect of pore size on MSCs as measured by proliferation, morphology, expression of integrin β1, and osteogenic differentiation. An MTT assay was used to measure cell viability of MSCs on different substrates, and determined that cell viability decreased with increasing pore size. Scanning electron microscopy was used to investigate the effect of pore size on cell morphology. Extremely elongated cells and prominent cell membrane protrusions were observed in cells cultured on alumina with the larger pore size. The expression of integrin β1 was enhanced in MSCs cultured on porous alumina, revealing that porous alumina substrates were more favorable for cell growth than smooth alumina substrates. Higher levels of osteoblastic differentiation markers such as alkaline phosphatase, osteocalcin, and mineralization were detected in cells cultured on alumina with 100 nm pores compared with cells cultured on alumina with either 20 nm pores or smooth alumina. This work demonstrates that cellular behavior is affected by variation in pore size, providing new insight into the potential application of this novel biocompatible material for the developing field of tissue engineering.

Acoustic sensing of the initial adhesion of chemokine-stimulated cancer cells

Chemokines together with their receptors play important roles in tumor metastasis. Intracellular signals stimulated by chemokines regulate the initial adhesion of cancer cells, which controls the subsequent cell spreading and migration. Until now, the nature of initial cell adhesion has been understood very poorly, since conventional assays are static and could not provide dynamic information. In order to address this issue, we adopt an acoustic sensor, quartz crystal microbalance (QCM), to monitor the attachment of chemokine-stimulated cancer cells in real-time. As a model, the chemokine CXCL12 was used to stimulate three human breast cancer cell lines expressing different levels of its receptor CXCR4, which triggers intracellular signaling pathways that activate integrins across cell membrane. Interaction between cellular integrins and adhesion molecules (CAMs) pre-coated on sensor surfaces were in situ monitored by QCM of which the frequency was sensitive to the mechanical connection of cells to the sensor surface. The ratio of frequency shift under stimulation to that without stimulation indicated the number and strength of integrin-CAM binding stimulated by the chemokine. The cell-surface binding was found to be enhanced by CXCL12, which depends on the CAM type and levels of chemokine and receptor, and was significantly inhibited by a blocker of the chemokine pathway. The binding of integrin with intercellular adhesion molecule was also found to be strong and in good correlated with the chemotactic indexes obtained by the classical Boyden chamber assay. This research suggests that acoustic sensing of initial cell adhesion could provide a dynamic insight into cell interfacial phenomena.

Self-assembled monolayers with different chemical group substrates for the study of MCF-7 breast cancer cell line behavior

The interactions between cancer cells and the extracellular matrix (ECM) are important with respect to a number of cell behavoirs, yet remain unclear. In this study, self-assembled monolayers with different terminal chemical groups (hydroxyl (-OH), carboxyl (-COOH), animo (-NH2), mercapto (-SH), and methyl (-CH3)) were employed as substrates for the culture of MCF-7 cells to examine effects on cell behavior. Cell spreading was investigated by scanning electron microscopy, tallin expression by immunofluorescence, proliferation rate by counting cell numbers, cell cycle by flow cytometry, metabolism by high-performance liquid chromatography and cell migration by live cell imaging. Annexin V-FITC (fluorescein isothiocyanate) and JC-1 assays were performed to determine cell apoptosis and mitochondrial membrane potential, respectively. Our results demonstrate the varied behaviors of MCF-7 cells in response to different chemical groups. Specifically, NH2 and COOH terminal functional groups promote proliferation, the production of lactic acid and mobility of MCF-7 cells; SH and OH terminal groups enhance the expression and distribution of tallin but result in weak cell proliferation, metabolism, spreading and mobility. These results are meaningful for uncovering the interactions between the ECM and cancer cells; they are potentially useful for designing novel cancer treatment strategies.

The interplay between nanostructured carbon-grafted chitosan scaffolds and protein adsorption on the cellular response of osteoblasts: structure-function property relationship

The rapid adsorption of proteins occurs during the early stages of biomedical device implantation into physiological systems. In this regard, the adsorption of proteins is a strong function of the nature of a biomedical device, which ultimately governs the biological functions. The objective of this study was to elucidate the interplay between nanostructured carbon-modified (graphene oxide and single-walled carbon nanohorn) chitosan scaffolds and consequent protein adsorption and biological function (osteoblast function). We compare and contrast the footprint of protein adsorption on unmodified chitosan and nanostructured carbon-modified chitosan. A comparative analysis of cell-substrate interactions using an osteoblast cell line (MC3T3-E1) implied that biological functions were significantly enhanced in the presence of nanostructured carbon, compared with unmodified chitosan. The difference in their respective behaviors is related to the degree and topography of protein adsorption on the scaffolds. Furthermore, there was a synergistic effect of nanostructured carbon and protein adsorption in terms of favorably modulating biological functions, including cell attachment, proliferation and viability, with the effect being greater on nanostructured carbon-modified scaffolds. The study also underscores that protein adsorption is favored in nanostructured carbon-modified scaffolds such that bioactivity and biological function are promoted.

Enhanced mechanical strength and biocompatibility of electrospun polycaprolactone-gelatin scaffold with surface deposited nano-hydroxyapatite

In this study for the first time, we compared physico-chemical and biological properties of polycaprolactone-gelatin-hydroxyapatite scaffolds of two types: one in which the nano-hydroxyapatite (n-HA) was deposited on the surface of electrospun polycaprolactone-gelatin (PCG) fibers via alternate soaking process (PCG-HAAS) and other in which hydroxyapatite (HA) powders were blended in electrospinning solution of PCG (PCG-HAB). The microstructure of fibers was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which showed n-HA particles on the surface of the PCG-HAAS scaffold and embedded HA particles in the interior of the PCG-HAB fibers. PCG-HAAS fibers exhibited the better Young's moduli and tensile strength as compared to PCG-HAB fibers. Biological properties such as cell proliferation, cell attachment and alkaline phosphatase activity (ALP) were determined by growing human osteosarcoma cells (MG-63) over the scaffolds. Cell proliferation and confocal results clearly indicated that the presence of hydroxyapatite on the surface of the PCG-HAAS scaffold promoted better cellular adhesion and proliferation as compared to PCG-HAB scaffold. ALP activity was also observed better in alternate soaked PCG scaffold as compared to PCG-HAB scaffold. Mechanical strength and biological properties clearly demonstrate that surface deposited HA scaffold prepared by alternate soaking method may find application in bone tissue engineering.

The influence of nanostructured materials on biointerfacial interactions

Control over biointerfacial interactions in vitro and in vivo is the key to many biomedical applications: from cell culture and diagnostic tools to drug delivery, biomaterials and regenerative medicine. The increasing use of nanostructured materials is placing a greater demand on improving our understanding of how these new materials influence biointerfacial interactions, including protein adsorption and subsequent cellular responses. A range of nanoscale material properties influence these interactions, and material toxicity. The ability to manipulate both material nanochemistry and nanotopography remains challenging in its own right, however, a more in-depth knowledge of the subsequent biological responses to these new materials must occur simultaneously if they are ever to be affective in the clinic. We highlight some of the key technologies used for fabrication of nanostructured materials, examine how nanostructured materials influence the behavior of proteins and cells at surfaces and provide details of important analytical techniques used in this context.

Overview of micro- and nano-technology tools for stem cell applications: micropatterned and microelectronic devices

In the past few decades the scientific community has been recognizing the paramount role of the cell microenvironment in determining cell behavior. In parallel, the study of human stem cells for their potential therapeutic applications has been progressing constantly. The use of advanced technologies, enabling one to mimic the in vivo stem cell microenviroment and to study stem cell physiology and physio-pathology, in settings that better predict human cell biology, is becoming the object of much research effort. In this review we will detail the most relevant and recent advances in the field of biosensors and micro- and nano-technologies in general, highlighting advantages and disadvantages. Particular attention will be devoted to those applications employing stem cells as a sensing element.

Interplay between grain structure and protein adsorption on functional response of osteoblasts: ultrafine-grained versus coarse-grained substrates

The rapid adsorption of proteins is the starting and primary biological response that occurs when a biomedical device is implanted in the physiological system. The biological response, however, depends on the surface characteristics of the device. Considering the significant interest in nano-/ultrafine surfaces and nanostructured coatings, we describe here, the interplay between grain structure and protein adsorption (bovine serum albumin: BSA) on osteoblasts functions by comparing nanograined/ultrafine-grained (NG/UFG) and coarse-grained (CG: grain size in the micrometer range) substrates by investigating cell-substrate interactions. The protein adsorption on NG/UFG surface was beneficial in favorably modulating biological functions including cell attachment, proliferation, and viability, whereas the effect was less pronounced on protein adsorbed CG surface. Additionally, immunofluorescence studies demonstrated stronger vinculin signals associated with actin stress fibers in the outer regions of the cells and cellular extensions on protein adsorbed NG/UFG surface. The functional response followed the sequence: NG/UFG(BSA) > NG/UFG > CG(BSA) > CG. The differences in the cellular response on bare and protein adsorbed NG/UFG and CG surfaces are attributed to cumulative contribution of grain structure and degree of hydrophilicity. The study underscores the potential advantages of protein adsorption on artificial biomedical devices to enhance the bioactivity and regulate biological functions.

Fibronectin layers by matrix-assisted pulsed laser evaporation from saline buffer-based cryogenic targets

The deposition of fibronectin (FN) from saline buffer-based cryogenic targets by matrix-assisted pulsed laser evaporation (MAPLE) onto silicon substrates is reported. A uniform distribution of FN was revealed by Ponceau staining after control experiments on nitrocellulose paper. Well-organized particulates with heights from hundreds of nanometers up to more than 1 μm packed in homogeneous layers were evidenced by optical microscopy and profilometry on Si substrates. Atomic force microscopy images showed regions composed of buffer and FN aggregates forming a compact film. Comparison of infrared spectra of drop-cast and MAPLE-deposited FN confirmed the preservation of composition and showed no degradation of the protein. The protein deposition on Si was confirmed by antibody staining. Small aggregates and fluorescent fibrils were visualized by fluorescence microscopy. Superior attachment of human osteoprogenitor cells cultivated for 3 h proved the presence of stable and intact FN molecules after transfer.