Orthogonally Spin-Coated Bilayer Films for Photochemical Immobilization and Patterning of Sub-10-Nanometer Polymer Monolayers

Versatile and spatiotemporally controlled methods for decorating surfaces with monolayers of attached polymers are broadly impactful to many technological applications. However, current materials are usually designed for very specific polymer/surface chemistries and, as a consequence, are not very broadly applicable and/or do not rapidly respond to high-resolution stimuli such as light. We describe here the use of a polymeric adhesion layer, poly(styrene sulfonyl azide-alt-maleic anhydride) (PSSMA), which is capable of immobilizing a 1-7 nm thick monolayer of preformed, inert polymers via photochemical grafting reactions. Solubility of PSSMA in very polar solvents enables processing alongside hydrophobic polymers or solutions and by extension orthogonal spin-coating deposition strategies. Therefore, these materials and processes are fully compatible with photolithographic tools and can take advantage of the immense manufacturing scalability they afford. For example, the thicknesses of covalently grafted poly(styrene) obtained after seconds of exposure are quantitatively equivalent to those obtained by physical adsorption after hours of thermal equilibration. Sequential polymer grafting steps using photomasks were used to pattern different regions of surface energy on the same substrate. These patterns spatially controlled the self-assembled domain orientation of a block copolymer possessing 21 nm half-periodicity, demonstrating hierarchical synergy with leading-edge nanopatterning approaches.

Synthesis and Application of New Photocrosslinkers for Poly(ethylene glycol)

Photocrosslinking of polyethylene glycol (PEG) using exogenous agents is a convenient way to produce branched PEG from commercial sources thus avoiding the tricky synthesis of new reactive and functional polymers. In this study, we synthesized two series of new photocrosslinkers, i.e. bis-fluorophenyl azide and bis-trifluoromethyl diazirine, which under soft UV-irradiation produce reactive species (i.e. nitrene and carbene respectively) that insert into the C–H bond of the polymer backbone, building new bridges between macromolecular chains. These photocrosslinkers are different in terms of behaviour under irradiation and affinity for the target substrate (i.e. PEG). Thus, practical conditions for photocrosslinking of a 10-kDa PEG were studied and followed by NMR and size-exclusion chromatography. In particular, we investigated irradiation in bulk or in solvent, at different irradiation times, with several concentrations of PEG and photolinkers. Finally, we were able to design a procedure to obtain soluble crosslinked PEGs of 300 kDa.

Light-Induced Functionalization of Amphiphilic Block Copolymers: Application to Nanoparticles for Drug Targeting

Photografting of bifunctional photolinker on biocompatible amphiphilic copolymers, such as PCL-b-PEGs and PLGA-b-PEGs, has been developed as a practical and versatile strategy for the materials functionalisation. Depending on the copolymer nature (block length, % of crystallinity) and the experimental conditions we could selectively direct the grafting on the hydrophilic PEG segments. The resulting copolymers were further derivatized with molecules of interest (RGD-peptides, LDV-peptides, “home-made”peptidomimetics, mannose derivatives,…) by substitution of the O-succinimidyl ester of the photolinker. The derivatization rates were controlled by radiolabelling, colorimetric assay and XPS spectroscopy. The functionalized copolymers were used in the formulation of nanoparticles displaying the ligands on their outer-shell. This nanoparticulate system was successfully employed for the oral vectorisation of antigen and for the targeted delivery of an anticancer drug.

Photografting of albumin onto dimethyldichlorosilane-coated glass

4-Azido-2-nitrophenyl albumin (ANP-albumin) was prepared by displacing the fluoro group of 4-fluoro-3-nitrophenyl azide (FNPA) by an amino group of albumin. Photolysis of phenyl azides of ANP-albumin was studied by Fourier-transform infrared (FTIR) spectroscopy. The band of phenyl azide disappeared completely after a 12-min exposure to long wave UV light (366 nm), and the photolysis was first-order. Albumin was grafted onto dimethyldichlorosilane-coated glass (DDS-glass) by photolysis of the azido groups of ANP-albumin without any premodification of the surface. The albumin-grafted DDS-glass was characterized by determining the relative amount of nitrogen resulting from the grafted albumin on the surface using electron spectroscopy for chemical analysis (ESCA). The amount of nitrogen increased when the concentration of ANP-albumin in the adsorption solution increased up to 0.1 mg/ml. As the solution concentration increased above this value, the amount of nitrogen decreased. The platelet resistance of the albumin-grafted surfaces was evaluated by measuring the number of adherent platelets and the extent of activation that was quantitated by the area of platelets spread on the surfaces. The maximum platelet-resistant effect was observed when the ANP-albumin was adsorbed for more than 50 min at the solution concentration ranging from 0.05 to 10 mg/ml.

Synthesis of photoreactive poly(ethylene glycol) and its application to the prevention of surface-induced platelet activation

Photoreactive poly(ethylene glycol) (PEG) was synthesized by reacting 4-fluoro-3-nitrophenyl azide (FNPA) with sodium salt of PEG. The synthesized 4-azido-2-nitrophenyl PEG (ANP-PEG) was characterized by 1H-NMR, IR, and UV spectroscopy. ANP-PEG was grafted to dimethyldichlorosilane-coated glass (DDS-glass) by photolysis without any premodification of the surface. The effects of various grafting factors, such as the polymer adsorption time, concentration of ANP-PEG, and UV irradiation time, on the PEG grafting efficiency were examined. The PEG-grafted DDS-glass was characterized by measuring surface free energies, surface-induced platelet activation, and the relative amount of PEG grafted on the surface using electron spectroscopy for chemical analysis (ESCA). Platelet adhesion and activation was analyzed by measuring the number and spread area of adherent platelets. The results showed that ANP-PEG had to be adsorbed onto DDS-glass for at least 12 h before photolysis for the maximum grafting efficiency. No platelets could adhere to the PEG-grafted DDS-glass, if the bulk concentration of ANP-PEG in the adsorption solution was between 1 mg/mL and 10 mg/mL. Above 10 mg/mL, platelet activation gradually increased and reached the maximum at 30 mg/mL. Our data indicate that the grafting of ANP-PEG requires careful control of the grafting conditions and that the grafted PEG can prevent surface-induced platelet activation.