Modulation of osteosarcoma cell growth and differentiation by silane-modified surfaces

Study of Protective Layers Based on Crosslinked Glutaraldehyde/3-aminopropyltriethoxysilane

In this paper, we report the synthesis and characterization of novel coatings based on (3-aminopropyl)-triethoxysilane (AP) mixed with different amounts of glutaraldehyde (GA). The synthesized coatings have been layered on a glass substrate and characterized by optical microscopy and roughness measurements, thermogravimetric analyses and differential scanning calorimetry, contact angle analysis, rheological measurement, and an adhesion test. It was observed that the higher the GA content (up to AP:GA ratio of 0.3), the sooner the crosslinking reaction starts, leading to a coating with increased hydrophobic and adhesion features without compromising the final AP cross-linked network. Hence, the obtained results show the effectiveness of AP modification with GA from the perspective of an application as protective coatings.

Functionalization and Surface Modifications of Bioactive Glasses (BGs): Tailoring of the Biological Response Working on the Outermost Surface Layer

Bioactive glasses (BGs) are routinely being used as potent materials for hard and soft tissue engineering applications; however, improving their biological activities through surface functionalization and modification has been underestimated so far. The surface characteristics of BGs are key factors in determining the success of any implanted BG-based material in vivo since they regulate the affinity and binding of different biological macromolecules and thereby the interactions between cells and the implant. Therefore, a number of strategies using chemical agents (e.g., glutaraldehyde, silanes) and physical methods (e.g., laser treatment) have been evaluated and applied to design properly, tailor, and improve the surface properties of BGs. All these approaches aim at enhancing the biological activities of BGs, including the induction of cell proliferation and subsequent osteogenesis, as well as the inhibition of bacterial growth and adhesion, thereby reducing infection. In this study, we present an overview of the currently used approaches of surface functionalization and modifications of BGs, along with discussing the biological outputs induced by these changes.

Natural Diatom Biosilica as Microshuttles in Drug Delivery Systems

Unicellular diatom microalgae are a promising natural resource of porous biosilica. These microorganisms produce around their membrane a highly porous and extremely structured silica shell called frustule. Once harvested from living algae or from fossil sediments of diatomaceous earth, this biocompatible and non-toxic material offers an exceptional potential in the field of micro/nano-devices, drug delivery, theranostics, and other medical applications. The present review focused on the use of diatoms in the field of drug delivery systems, with the aim of presenting the different strategies implemented to improve the biophysical properties of this biosilica in terms of drug loading and release efficiency, targeted delivery, or site-specific binding capacity by surface functionalization. The development of composite materials involving diatoms for drug delivery applications is also described.

Lubricant-Infused Surfaces with Built-In Functional Biomolecules Exhibit Simultaneous Repellency and Tunable Cell Adhesion

Lubricant-infused omniphobic surfaces have exhibited outstanding effectiveness in inhibiting nonspecific adhesion and attenuating superimposed clot formation compared with other coated surfaces. However, such surfaces blindly thwart adhesion, which is troublesome for applications that rely on targeted adhesion. Here we introduce a new class of lubricant-infused surfaces that offer tunable bioactivity together with omniphobic properties by integrating biofunctional domains into the lubricant-infused layer. These novel surfaces promote targeted binding of desired species while simultaneously preventing nonspecific adhesion. To develop these surfaces, mixed self-assembled monolayers (SAMs) of aminosilanes and fluorosilanes were generated. Aminosilanes were utilized as coupling molecules for immobilizing capture ligands, and nonspecific adhesion of cells and proteins was prevented by infiltrating the fluorosilane molecules with a thin layer of a biocompatible fluorocarbon-based lubricant, thus generating biofunctional lubricant-infused surfaces. This method yields surfaces that (a) exhibit highly tunable binding of anti-CD34 and anti-CD144 antibodies and adhesion of endothelial cells, while repelling nonspecific adhesion of undesirable proteins and cells not only in buffer but also in human plasma or human whole blood, and (b) attenuate blood clot formation. Therefore, this straightforward and simple method creates biofunctional, nonsticky surfaces that can be used to optimize the performance of devices such as biomedical implants, extracorporeal circuits, and biosensors.

Feasibility Study Exploring the Potential of Novel Battacin Lipopeptides as Antimicrobial Coatings

Colonization of medical implant surfaces by pathogenic microorganisms causes implant failure and undermines their clinical applicability. Alarming increase in multidrug-resistant bacteria poses serious concerns with the use of medical implants. Antimicrobial peptides (AMPs) that form part of the innate immune system in all forms of life are attractive alternatives to conventional antibiotics to treat multidrug-resistant bacterial biofilms. The aim of this study was to assess the in vitro antibacterial potency of our recently discovered lipopeptides from the battacin family upon immobilization to various surfaces. To achieve this, glass, silicon, and titanium surfaces were functionalized through silanization followed by addition of the heterobifunctional cross-linker, succinimidyl-[N-maleimidopropionamido]-poly(ethylene glycol) ester to generate maleimide-functionalized surfaces. The lipopeptide, GZ3.27, with an added N-terminal cysteine was covalently coupled to the surfaces via a thioether bond through a Michael-type addition between the cysteine sulfhydryl group and the maleimide moiety. Success of surface immobilization and antimicrobial activity of the coated surfaces was assessed using water contact angle measurements, X-ray photoelectron spectroscopy, ellipsometry, scanning electron microscopy, colony forming unit assays and biofilm analysis. The lipopeptide-coated surfaces caused significant damage to the cellular envelop of Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli) upon contact and prevented surface colonization by P. aeruginosa and E. coli biofilms. The lipopeptides investigated in this study were not hemolytic to mouse blood cells in solution. Findings from this study indicate that these lipopeptides have the potential to be developed as promising antimicrobial coatings on medical implants.

Biosilica from Living Diatoms: Investigations on Biocompatibility of Bare and Chemically Modified Thalassiosira weissflogii Silica Shells

In the past decade, mesoporous silica nanoparticles (MSNs) with a large surface area and pore volume have attracted considerable attention for their application in drug delivery and biomedicine. Here we propose biosilica from diatoms as an alternative source of mesoporous materials in the field of multifunctional supports for cell growth: the biosilica surfaces were chemically modified by traditional silanization methods resulting in diatom silica microparticles functionalized with 3-mercaptopropyl-trimethoxysilane (MPTMS) and 3-aminopropyl-triethoxysilane (APTES). Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses revealed that the -SH or -NH₂ were successfully grafted onto the biosilica surface. The relationship among the type of functional groups and the cell viability was established as well as the interaction of the cells with the nanoporosity of frustules. These results show that diatom microparticles are promising natural biomaterials suitable for cell growth, and that the surfaces, owing to the mercapto groups, exhibit good biocompatibility.

Effects of different functional groups on metastatic behavior of SPC-A-1/human lung cancer cells in self-assembled monolayers

Self-assembled monolayers terminated with different functional groups were used to explore their effects on the metastatic behaviors of human lung cancer cells (SPC-A-1) in vitro. The addition of –SH group has potential applications for lung cancer metastasis therapy.

Rapid cell sheet detachment using spin-coated pNIPAAm films retained on surfaces by an aminopropyltriethoxysilane network

The ability to harvest cell sheets grown on thermoresponsive polymers, such as poly(N-isopropylacrylamide) (pNIPAAm), has been widely studied for use in tissue engineering applications. pNIPAAm is of special interest because of the phase change that it undergoes in a physiologically relevant temperature range. Two primary approaches have been adopted to graft pNIPAAm chains covalently onto tissue culture polystyrene dishes: electron beam irradiation and plasma polymerization. These approaches often involve non-easily accessible (e.g. e-beam) facilities and complicated procedures that have hindered most tissue culture laboratories in adopting this technology for their specific applications. In this study, we developed a simple and cost-effective approach to create thermoresponsive surfaces using commercially available pNIPAAm. Using a simple spin-coating technique, thermoresponsive thin films were deposited on glass slides or silicon wafers using pNIPAAm blended with a small amount of 3-aminopropyltriethoxysilane (APTES), which enhances the retention of pNIPAAm on the surface. We found that the thermoresponsive films created using our method support cell attachment and proliferation without additional adhesive proteins as well as cell sheet detachment within minutes.

Functional polymer brushes via surface-initiated atom transfer radical graft polymerization for combating marine biofouling

Dense and uniform polymer brush coatings were developed to combat marine biofouling. Nonionic hydrophilic, nonionic hydrophobic, cationic, anionic and zwitterionic polymer brush coatings were synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-hydroxyethyl methacrylate, 2,3,4,5,6-pentafluorostyrene, 2-(methacryloyloxy)ethyl trimethylammonium chloride, 4-styrenesulfonic acid sodium and N,N'-dimethyl-(methylmethacryloyl ethyl) ammonium propanesulfonate, respectively. The functionalized surfaces had different efficacies in preventing adsorption of bovine serum albumin (BSA), adhesion of the Gram-negative bacterium Pseudomonas sp. NCIMB 2021 and the Gram-positive Staphylococcus aureus, and settlement of cyprids of the barnacle Amphibalanus amphitrite (=Balanus amphitrite). The nonionic hydrophilic, anionic and zwitterionic polymer brushes resisted BSA adsorption during a 2 h exposure period. The nonionic hydrophilic, cationic and zwitterionic brushes exhibited resistance to bacterial fouling (24 h exposure) and cyprid settlement (24 and 48 h incubation). The hydrophobic brushes moderately reduced protein adsorption, and bacteria and cyprid settlement. The anionic brushes were least effective in preventing attachment of bacteria and barnacle cyprids. Thus, the best approach to combat biofouling involves a combination of nonionic hydrophilic and zwitterionic polymer brush coatings on material surfaces.

Starch and its Derived Products: Biotechnological and Biomedical Applications

Starches are one of the most abundant renewable natural resources available to us, however their potential as a biomass feedstock for the production of a vast range of commercially viable chemicals/components for application in many areas of industrial, food and biomedical sciences is currently under-exploited. This review begins by presenting an overview of starch sources, composition and structure, and physicochemical characteristics. Specific topics discussed include amylose and amylopectin structure, their location in the amorphous and crystalline regions of starch granules, granule morphology, gelatinisation and pasting characteristics. The remainder of the review then focuses upon the biotechnological production of starch hydrolysis products, such as maltodextrins, glucose and fructose syrups, and cyclodextrins, and the chemical modification of starch, namely, oxidation, stabilisation (esterification and etherification), and cross-linking. Finally some specific examples of the development of starch-derived biomaterials for application in areas such as orthopaedics, bone cements, tissue engineering, and hydrogels are presented.

Chemical vapor deposition of three aminosilanes on silicon dioxide: surface characterization, stability, effects of silane concentration, and cyanine dye adsorption

Covalently bonded monolayers of two monofunctional aminosilanes (3-aminopropyldimethylethoxysilane, APDMES, and 3-aminopropyldiisopropylethoxysilane, APDIPES) and one trifunctional aminosilane (3-aminopropyltriethoxysilane, APTES) have been deposited on dehydrated silicon substrates by chemical vapor deposition (CVD) at 150 °C and low pressure (a few Torr) using reproducible equipment. Standard surface analytical techniques such as x-ray photoelectron spectroscopy (XPS), contact angle goniometry, spectroscopic ellipsometry, atomic force microscopy, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) have been employed to characterize the resulting films. These methods indicate that essentially constant surface coverages are obtained over a wide range of gas phase concentrations of the aminosilanes. XPS data further indicate that the N1s/Si2p ratio is higher after CVD with the trifunctional silane (APTES) compared to the monofunctional ones, with a higher N1s/Si2p ratio for APDMES compared to that for APDIPES. AFM images show an average surface roughness of 0.12- 0.15 nm among all three aminosilane films. Stability tests indicate that APDIPES films retain most of their integrity at pH 10 for several hours and are more stable than APTES or APDMES layers. The films also showed good stability against storage in the laboratory. ToF-SIMS of these samples showed expected peaks, such as CN(-), as well as CNO(-), which may arise from an interaction between monolayer amine groups and silanols. Optical absorption measurements on adsorbed cyanine dye at the surface of the aminosilane films show the formation of dimer aggregates on the surface. This is further supported by ellipsometry measurements. The concentration of dye on each surface appears to be consistent with the density of the amines.

The fabrication of nano-hydroxyapatite on PLGA and PLGA/collagen nanofibrous composite scaffolds and their effects in osteoblastic behavior for bone tissue engineering

Bone is a nanocomposite consisting of two main components, nano-hydroxyapatite (n-HA) and Type I collagen (Col). The aim is to exploit the nano-scale functional and material characteristics of natural bone in order to modulate cellular functions for optimal bone repair in bone graft systems. Here, we present an effective and novel technique in obtaining n-HA in cognate with native apatite on electrospun nanofibers within minutes without any pre-treatment. Using an alternate calcium and phosphate (Ca-P) solution dipping method, n-HA was formed on poly(lactide-co-glycolide) acid (PLGA) and blended PLGA/Col nanofibers. The presence of the functional groups of collagen significantly hastened n-HA deposition closed to nine-fold. The quantity of n-HA impinged upon the specific surface area, whereby mineralized PLGA/Col had a greater surface area than non-mineralized PLGA/Col, whereas n-HA did not significantly improve the specific surface area of mineralized PLGA compared to pure PLGA. The novelty of the process was that n-HA on PLGA had a positive modulation on early osteoblast capture (within minutes) compared to pure PLGA. Contrary, cell capture on mineralized PLGA/Col was comparable to pure PLGA/Col. Interestingly, although n-HA impeded proliferation during the culture period (days 1, 4 and 7), the cell functionality such as alkaline phosphatase (ALP) and protein expressions were ameliorated on mineralized nanofibers. The amount of n-HA appeared to have a greater effect on the early stages of osteoblast behavior (cell attachment and proliferation) rather than the immediate/late stages (proliferation and differentiation).

Synthesis of bone formation deriving biosilanes

Six silane coupling agents having amide group (biosilanes) were synthesized with the aim to construct the material surface that allows cells to be compatible with it without their destruction. These agents were expected to make a soft landing to cytoplasm through the hydrogen bonding between their amide groups and cells. Evaluations of cell affinity using glass substrates modified with the synthesized biosilanes revealed that many cells remain on the modified glass plate. In addition, the implantation into the body of immunodeficient mouse of a composite material composed of porous hydroxyapatite and osteoblast showed the formation of a bone-like structure.

Novel biodegradable poly(1,8-octanediol malate) for annulus fibrosus regeneration

A novel elastic scaffold that simulates the deformability of annulus fibrosus (AF) and has good biocompatibility was developed. The scaffold was formed of a malic acid-based polyester poly(1,8-octanediol malate) (POM), which was synthesized by direct polycondensation. The tensile strength of POM gradually increased with the extension of the polymerization time, while the degradation rate decreased. Rat AF cells proliferated on the POM films and maintained their phenotype. The 3D scaffold also supported the growth of the AF cells, as confirmed by Safranin-O and type II collagen staining. POM also demonstrated a good biocompatibility in an in vivo foreign body response assay, an important prerequisite for tissue engineering applications. This study suggests that elastic POM scaffold may be an ideal candidate for AF tissue engineering.

Proliferation of osteoblasts and fibroblasts on model surfaces of varying roughness and surface chemistry

Physical and chemical properties of the surfaces of implants are of considerable interest for dental and orthopedic applications. We used self-assembled monolayers (SAMs) terminated by various functional chemical groups to study the effect of surface chemistry on cell behavior. Cell morphology and proliferation on silicon wafers of various roughnesses and topographies created by chemical etching in caustic solution and by corundum sandblasting were analyzed as well. Water contact angle data indicated that oxidized wafer surfaces displayed high hydrophilicity, modification with poly(ethylene glycol) (PEG) created a hydrophilic surface, and an amino group (NH2) led to a moderately wettable surface. A hydrophobic surface was formed by hydrocarbon chains terminated by CH3, but this hydrophobicity was even further increased by a fluorocarbon (CF3) group. Cell proliferation on these surfaces was different depending primarily on the chemistry of the terminating groups rather than on wettability. Cell proliferation on CH3 was as high as on NH2 and hydrophilic oxidized surfaces, but significantly lower on CF3. Precoating of silicon wafers with cell culture serum had no significant influence on cell proliferation. Scanning electron microscopy indicated a very weak initial cell-surface contact on CF3. The cell number of osteoblasts was significantly lower on sandblasted surfaces compared with other rough surfaces but no differences were detected with 3T3 mouse fibroblasts. The different surface roughnesses and topographies were recognized by MG-63 osteoblasts. The cells spread well on smooth surfaces but appeared smaller on a rough and unique pyramid-shaped surface and on a rough sandblasted surface.

Optimization of silica silanization by 3-aminopropyltriethoxysilane

Thin films of 3-aminopropyltriethoxysilane (APTES) are commonly used to promote adhesion between silica substrates and organic or metallic materials with applications ranging from advanced composites to biomolecular lab-on-a-chip. Unfortunately, there is confusion as to which reaction conditions will result in consistently aminated surfaces. A wide range of conflicting experimental methods are used with researchers often assuming the creation of smooth self-assembled monolayers. A range of film morphologies based on the film deposition conditions are presented here to establish an optimized method of APTES film formation. The effect of reaction temperature, solution concentration, and reaction time on the structure and morphology was studied for the system of APTES on silica. Three basic morphologies were observed: smooth thin film, smooth thick film, and roughened thick film.

Controlling the phenotype and function of mesenchymal stem cells in vitro by adhesion to silane-modified clean glass surfaces

The behaviour of human mesenchymal stem cells (hMSC) when cultured in contact with a range of silane-modified surfaces was examined to determine if changing the surface chemistry affected the early differentiation potential of mesenchymal stem cells in vitro over a 7-day period. Cells were cultured for 1 and 7 days in direct contact with glass which had been functionalized by surface treatment to provide a range of different surfaces: -CH(3), -NH(2), -SH, -OH, and -COOH modified surfaces and a clean glass reference (TAAB). Viable cell adhesion was quantified by Lactate Dehydrogenase assay, and morphology and viability was qualitatively evaluated using calcein AM, ethidium homodimer, cytoskeletal (F Actin), extra-cellular matrix (fibronectin and vitronectin) and Hoechst staining (nucleus). The expression of selected differentiation markers, Collagen II (chondrocytes), CBFA1 (bone transcription factor), Collagen I (MSC marker) and TGF-beta3 (extra-cellular matrix production) was determined using real time polymerase chain reaction. The expression of ornithine decarboxylase was evaluated as a marker of proliferation. Surfaces of the -NH(2) group demonstrated the greatest level of cell adhesion by the 7-day period, and mRNA expression profiles indicated osteogenic differentiation, increased CBFA1 and decreased Collagen II expression. Cells cultured in contact with the -COOH surfaces displayed different cell morphologies, fibronectin and vitronectin spatial distributions compared with the cells in contact with the -NH(2) surfaces, in addition to an increase in Collagen II expression, indicative of chondrogenic differentiation. The modifications to the surface chemistry of glass did affect cell behaviour, both in terms of viable cell adhesion, morphology and profiles of mRNA expression, providing the means to alter the differentiation potential of the MSCs.

Surface modification of surface sol–gel derived titanium oxide films by self-assembled monolayers (SAMs) and non-specific protein adsorption studies

Biological events occurring at the implant-host interface, including protein adsorption are mainly influenced by surface properties of the implant. Titanium alloys, one of the most widely used implants, has shown good biocompatibility primarily through its surface oxide. In this study, a surface sol-gel process based on the surface reaction of metal alkoxides with a hydroxylated surface was used to prepare ultrathin titanium oxide (TiOx) coatings on silicon wafers. The oxide deposited on the surface was then modified by self-assembled monolayers (SAMs) of silanes with different functional groups. Interesting surface morphology trends and protein adhesion properties of the modified titanium oxide surfaces were observed as studied by non-specific protein binding of serum albumin. The surface properties were investigated systematically using water contact angle, ellipsometry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) measurements. Results showed that the surface sol-gel process predominantly formed homogeneous, but rough and porous titanium oxide layers. The protein adsorption was dependent primarily on the silane chemistry, packing of the alkyl chains (extent of van der Waals interaction), morphology (porosity and roughness), and wettability of the sol-gel oxide. Comparison was made with a thermally evaporated TiOx-Ti/Si-wafer substrate (control). This method further extends the functionalization of surface sol-gel derived TiOx layers for possible titanium alloy bioimplant surface modification.

Effects of controlled fibronectin surface orientation on subsequentStaphylococcus epidermidis adhesion

Several bacterial species, including Staphylococcus aureus and Staphylococcus epidermidis (SE) are known to express cell receptors that bind specifically to surface immobilized or extracellular matrix ligands, such as the protein fibronectin (FN). Yet, few existing studies have examined the effect of protein surface orientation on bacterial adhesion. We report here a substratum modification protocol that allows for the specific orientation of FN molecules on a surface at known levels of surface coverage. Monoclonal antibodies (Mabs), specific to either the COOH-terminus or NH3-terminus of FN, are conjugated to biotin, then immobilized to streptavidin-coated glass substrata. Specific orientation of the bound FN molecules is verified using the same Mabs in an ELISA. Bacterial adhesion of Staphylococcus epidermidis (SE) to FN bound by either its C-terminus or its NH3-terminus was quantified in batch static adhesion assays. Results indicate an increase in SE adhesion to FN-coated surfaces when the FN is bound by its C-terminus (NH3-terminus free), indicating SE receptor-specific adhesion to the FN NH3-terminus. These studies demonstrate that antifibronectin monoclonal antibodies can be used to specifically bind and orient fibronectin on a surface. In addition, adhesion of SE to these model substrata can be controlled by the orientation of the protein.

Self-assembled monolayers with different terminating groups as model substrates for cell adhesion studies

Cell shapes induced by cell-substratum interactions are linked with proliferation, differentiation or apoptosis of cells. To clarify the relevance of specific surface characteristics, we applied self-assembled monolayers (SAM) of alkyl silanes exhibiting a variety of terminating functional groups. We first characterised the SAMs on glass or silicon wafers by measuring wettability, layer thickness and roughness. Water contact angle data revealed that methyl (CH(3)), bromine (Br), and vinyl (CH=CH(2)) groups lead to hydrophobic surfaces, while amine (NH(2)) and carboxyl (COOH) functions lead to moderately wettable surfaces, and polyethylene glycol (PEG) and hydroxyl (OH) groups created wettable substrata. The surfaces were found to be molecular smooth except for one type of NH(2) surface. The SDS-PAGE analysis of proteins adsorbed from bovine serum to the SAMs showed less protein adsorption to PEG and OH than to CH(3), NH(2) and COOH. Immunoblotting revealed that a key component of adsorbed proteins is vitronectin while fibronectin was not detectable. The interaction of human fibroblasts with CH(3), PEG and OH terminated SAMs was similarly weak while strong attachment, spreading, fibronectin matrix formation and growth were observed on COOH and NH(2). The strong interaction of fibroblasts with the latter SAMs was linked to an enhanced activity of integrins as observed after antibody-tagging of living cells.