Aminated dendritic surfaces characterization: a rapid and versatile colorimetric assay for estimating the amine density and coating stability

Everything You Always Wanted to Know about Poly-l-lysine Dendrigrafts (But Were Afraid to Ask)

Less than a decade ago, dendrigrafts of poly-l-lysine (DGLs) joined the family of polycationic dendritic macromolecules. Resulting from the iterative polycondensation of an N-carboxyanhydride in water, four generations of the dendrigraft can be obtained on a multigram scale and without chromatographic purification. DGLs share features with both dendrimers and hyperbranched polymers, but turned out to have unique biophysical and bioactive properties. The macromolecules-in their native form or functionalized-have been extensively characterized by various analytical and computational methods, and have already found numerous applications in the biomedical field, such as drug and gene delivery, biomaterials, tissue engineering, bioimaging, and biosensing. Despite a growing interest for DGLs, there is still plenty of room for further exciting developments that could result from a better exposure of these macromolecules, which is the ambition of this short review.

Direct silanization of zirconia for increased biointegration

High-performance bioinert ceramics such as zirconia have been used for biomedical devices since the early seventies. In order to promote osseointegration, the historical solution has been to increase the specific surface of the implant through roughness. Nevertheless these treatments on ceramics may create defects at the surface, exposing the material to higher chances of early failure. In zirconia, such treatments may also affect the stability of the surface. More recently, the interest of improving osseointegration of implants has moved the research focus towards the actual chemistry of the surface. Inspired by this, we have adapted the current knowledge and techniques of silica functionalization and applied it to successfully introduce 3-aminopropyldimethylethoxy silane (APDMES) directly on the surface of zirconia (3Y-TZP). We used plasma of oxygen to clean the surface and promote hydroxylation of the surface to increase silane density. The samples were extensively characterized by means of X-ray photoelectron spectroscopy (XPS) and contact angle, mechanically tested and its cytotoxicity was evaluated through cell adhesion and proliferation tests. Additionally, aging was studied to discard negative effects of the treatment on the stability of the tetragonal phase. No adverse effect was found on the mechanical response of treated samples. In addition, plasma-treated samples exhibited an unexpectedly higher resistance to aging. Finally, silane density was 35% lower than the one reported in literature for silica. However cells displayed a qualitatively higher spreading in opposition to the rounder appearance of cells on untreated zirconia. These results lay the foundations for the next generation of zirconia implants with biologically friendlier surfaces.

STATEMENT OF SIGNIFICANCE

The use of zirconia-based ceramics in biomedical devices is broad and well accepted, especially in dental implants. However, they do not bond naturally to bone, therefore to ensure fixation surgeons typically rely on roughness at different scales, or on cements. Alternatively in this work we present a new perspective of surface modification through chemistry to enhance the interaction between surface and biological environment, without the downsides of roughness. This surface treatment is proposed for zirconia, which allowed a direct silanization of its surface and a higher cell attachment. The results of this research may open the possibility for the next generation of bioinert ceramic implants with more advanced tailored surfaces for increased osseointegration.

Grafting of poly-L-lysine dendrigrafts onto polypropylene surface using plasma activation for ATP immobilization - Nanomaterial for potential applications in biotechnology

The present work describes a new environmental friendly strategy for the development of surfaces with high amine density via the grafting of native or modified poly-L-lysine dendrigraft (DGL G3) onto plasma activated polypropylene (PP), polystyrene (PS), polyimide, and polytetrafluoroethylene (PTFE) surface. Modified DGL G3 was prepared by replacement of few peripheral amines by various functionalities. Grafting efficiency was determined by wettability measurements, IRTF, XPS, AFM, and by colorimetry using optimized Coomassie Brilliant Blue method tailored for surface analysis. It was shown that a 4-7nm DGL G3 monolayer with 4×10(14)aminecm(-)(2) was covalently grafted onto various surfaces. Immobilization of adenosine triphosphate on the DGL-g-PP material from dilute solution was studied by bioluminescence and proved the ability of the material to interact with polyanionic biological compounds: 1 ATP complex with 5 amine groups. So, this material has a potential use in diagnostic and more widely for biotechnology due to its high capacity for biomolecule immobilization.

Characterization of three amino-functionalized surfaces and evaluation of antibody immobilization for the multiplex detection of tumor markers involved in colorectal cancer

Antibody microarrays are powerful and high-throughput tools for screening and identifying tumor markers from small sample volumes of only a few microliters. Optimization of surface chemistry and spotting conditions are crucial parameters to enhance antibodies' immobilization efficiency and to maintain their biological activity. Here, we report the implementation of an antibody microarray for the detection of tumor markers involved in colorectal cancer. Three-dimensional microstructured glass slides were functionalized with three different aminated molecules ((3-aminopropyl)dimethylethoxysilane (APDMES), Jeffamine, and chitosan) varying in their chain length, their amine density, and their hydrophilic/hydrophobic balance. The physicochemical properties of the resulting surfaces were characterized. Antibody immobilization efficiency through physical interaction was studied as a function of surface properties as well as a function of the immobilization conditions. The results show that surface energy, steric hindrance, and pH of spotting buffer have great effects on protein immobilization. Under optimal conditions, biological activities of four immobilized antitumor marker antibodies were evaluated in multiplex immunoassay for the detection of the corresponding tumor markers. Results indicated that the chitosan functionalized surface displayed the highest binding capacity and allowed to retain maximal biological activity of the four tested antibody/antigen systems. Thus, we successfully demonstrated the application of amino-based surface modification for antibody microarrays to efficiently detect tumor markers.

Preparation and full characterization of a micro-immunoaffinity monolithic column and its in-line coupling with capillary zone electrophoresis with Ochratoxin A as model solute

A micro-immunoaffinity monolithic column (μIAC) was developed and in-line coupled with capillary zone electrophoresis in a fully automated way with Ochratoxin A as test solute. The in-line micro-immunoaffinity columns based on monolithic methacrylate polymers (EDMA-GMA) were prepared in situ at the inlet end of a PTFE coated fused silica capillary by UV initiated polymerization and subsequently grafted with antibodies. These μIACs were thoroughly characterized. The synthesis of the polymeric support was first demonstrated to be reproducible in terms of permeability, surface properties and efficiency. The antibodies immobilization was then studied by a new original hydrodynamic method (ADECA) allowing the in situ quantitative determination (at a miniaturized scale) of the total amount of immobilized antibodies. The combination of this measurement with the binding capacity of the μIAC allowed, for the first time, the in situ determination of immobilized antibody activity. A total of 260 ± 15 ng (1.6 ± 0.1 pmol) of IgG antibodies/cm in 75 μm i.d. monolithic column (i.e. 18 μgmg(-1)) was obtained with (anti-Ochratoxin A/Ochratoxin A) as antibody/antigen model. 40% of the immobilized antibodies remain active corresponding to a binding capacity of 1.2 ± 0.2 pmol antigen/cm (i.e. 600 pg/cm of our test solute OTA), a very high capacity when dealing with trace analysis and with regard to the detection limits (30 pg and 0.5 pg with UV and LIF detection, respectively). The recovery yields were quantitative with negligible non-specific adsorption and allow analysis of diluted samples (1 ngmL(-1)) for a percolated volume of 10 μL. It was also demonstrated that despite the progressive denaturation of antibodies consecutive to the elution step, the binding capacity of the μIAC remained high enough to implement at least 15 consecutive analyses with the same column and in a fully automated way.

Quantification of primary amine groups available for subsequent biofunctionalization of polymer surfaces

Biocompatible polymers are commonly functionalized with specific moieties such as amino groups to modify their surface properties and/or to attach bioactive compounds. A reliable method is usually required to characterize amino group surface densities. In this study, aminated polyethylene terephthalate (PET) films were generated via an aminolysis reaction involving either ethylenediamine molecules (EtDA), in order to vary easily the amino group density on PET surfaces, or 25 kDa polyvinylamine (PVAm) as an alternative reagent preventing bulk damages resulting from the aminolysis reaction. Among commonly used dyes for amino group quantification, Orange II and Coomassie Brillant Blue (CBB) were selected to quantify the extent of amine grafting resulting from these derivatization procedures. Rapid and convenient colorimetric assays were compared to surface atomic compositions obtained from X-ray photoelectron spectroscopy (XPS) measurements. Orange II was found to be the most appropriate dye for quantifying primary amine groups in a reliable and specific way. Due to its unique negative charge and low steric hindrance compared to CBB, the Orange II dye was very sensitive and provided reliable quantification over a wide range of amino group surface densities (ca. 5 to at least 200 pmol/mm(2)). In order to further validate the use of the Orange II dye for amino group quantification, a heterobifunctional linker reacting with amino groups was then grafted on modified PET surfaces. Interestingly, the good correlation between the densities of adsorbed Orange II and covalently grafted linkers suggests that the Orange II method is a relevant, reliable, easy, and inexpensive method to predict the amount of amino groups available for subsequent functionalization of polymer surfaces.