Poly(ethylene glycol) Gradient for Biochip Development

Abstract

A novel method of producing a poly(ethylene glycol) (PEG)-based gradient matrix that varies gradually in thickness from 0 to 500 A over a distance of 5-20 mm is presented. The gradient matrix is graft copolymerized from a mixture of PEG methacrylates onto organic thin films providing free radical polymerization sites initiated by UV irradiation at 254 nm. The films used as grafting platforms consist of either a spin-coated cycloolefin polymer or a self-assembled monolayer on planar gold. The thickness/irradiation gradient is realized by means of a moving shutter that slowly uncovers the modified gold substrate. The structural and functional characteristics of the gradient matrix are investigated with respect to thickness profile, degree of carboxylation, and subsequent immobilization of two model proteins of different sizes and shapes. These characteristics are studied with ellipsometry and infrared reflection-absorption microscopy using a grazing angle objective. It is revealed that the relatively small carboxylation agent used offers homogeneous activation throughout the gradient, even in the thick areas, whereas the diffusion/interpenetration and subsequent immobilization of large proteins is partially hindered. This is crucial information in biosensor design that can be easily obtained from a gradient experiment on a single sample. Moreover, the partially hindered protein interpenetration, the marginal swelling upon hydration, and the unspecific nature of the graft polymerization suggest a matrix growth mechanism that favors the formation of a bushlike polymer structure with a certain degree of cross linking.

Patterned Hydrogels for Controlled Platelet Adhesion from Whole Blood and Plasma

“…In order to determine the minimum thickness required, the patterning technique was combined with a method that enables fabrication of hydrogel thickness gradients. This approach has been used previously to investigate protein immobilization and biomolecular interactions within related hydrogels 29, 32. The patterned hydrogel was prepared on a PS film spin‐coated on a silanized silicon wafer to simulate the use of a plastic substrate yet enabling reliable thickness measurements with ellipsometry.…”

“…The immobilized proteins appear to have retained their biological activity and were clearly accessible for cellular interactions. In previous works, we have noted that the poly(PEG 10 MA‐ co ‐HEMA) hydrogel constitutes a significant barrier to protein diffusion, particularly for larger proteins 29, 32. This may be a disadvantage if the intended use for the hydrogel is as a 3D matrix for the study of protein–protein interactions.…”

“…The method used to prepare the gradient surfaces is a further development of the grafting procedure, and has been described in detail previously 32, 42. A custom‐built motorized shutter traversed the substrate, exposing gradually more and more of the surface to the light from the UV lamp.…”

The mechanism for the motion of nanoscale water droplet induced by wetting gradient: A molecular dynamic study

“…Recent years have witnessed explosive growth of interest in motion and transportation of liquid droplet on solid surface for its significant application in micro/nano-fluidic devices [1][2][3][4][5][6], condensation heat transfer [7], cell motility [8][9][10] and biochips [11][12][13][14][15]. Therefore, in order to manipulate the motion of liquid droplet in these application fields, many approaches have been proposed such as applying electric field [16,17], external force [18] or implementing a gradient [19][20][21][22] (e.g., wetting gradient and thermal gradient [23]).…”

Functional Hydrogel Density Patterns Fabricated by Dip‐Pen Nanolithography and Photografting

“…Previous studies have shown that PEGMA:HEMA polymer brushes can be grafted on air plasma‐treated cycloolefin‐polymer‐coated substrates using SIPGP 18. For example, Larsson et al also prepared PEG hydrogel micropatterns and gradients on different thiol and silane self‐assembled monolayers (SAMs) 10, 19. So far the smallest features made by illuminating the sample and monomer solution through a photomask are 5 μm‐wide lines 10…”