Substrate-mediated delivery from self-assembled monolayers: Effect of surface ionization, hydrophilicity, and patterning

Abstract

Gene transfer has many potential applications in basic and applied sciences. In vitro, DNA delivery can be enhanced by increasing the concentration of DNA in the cellular microenvironment through immobilization of DNA to a substrate that supports cell adhesion. Substrate-mediated delivery describes the immobilization of DNA, complexed with cationic lipids or polymers, to a biomaterial or substrate. As surface properties are critical to the efficiency of the surface delivery approach, selfassembled monolayers (SAMs) of alkanethiols on gold were used to correlate surface chemistry of the substrate to binding, release, and transfection of non-specifically immobilized complexes. Surface hydrophobicity and ionization were found to mediate both DNA complex immobilization and transfection, but had no effect on complex release. Additionally, SAMs were used in conjunction with soft lithographic techniques to imprint substrates with specific patterns, resulting in patterned DNA complex deposition and transfection, with transfection efficiencies in the patterns nearing 40%. Controlling the interactions between complexes and substrates, with the potential for patterned delivery, can be used to locally enhance or regulate gene transfer, with applications to tissue engineering scaffolds and transfected cell arrays.

Surface polyethylene glycol enhances substrate-mediated gene delivery by nonspecifically immobilized complexes

“…2b). These amounts are similar to, or much greater than, previous reports of lipoplexes binding to SAMs [15,22], but are consistent with binding densities for PEI-DNA complexes on hydrophilic, serum-coated polystyrene substrates [13].…”

“…Previous studies suggest that nonspecific DNA complex adsorption is mediated by at least two mechanisms: electrostatic and hydrophobic interactions [15]. Increasing the density of charged functional groups (COO − ) in a background of uncharged groups (OH) increased complex immobilization, suggesting that electrostatic interactions play a major role in binding [15].…”

“…Poly(L-lysine) (PLL) and polyethylenimine (PEI), modified with biotin residues, were complexed with DNA and bound to a neutravidin substrate [7,8], resulting in 100-fold increased transgene expression from the immobilized complexes relative to bolus delivery of complexes [7]. Plasmid DNA or DNA complexed with cationic polymers or lipids can also interact with substrates through nonspecific mechanisms [10][11][12][13][14][15][16][17][18]. Polyplexes and lipoplexes nonspecifically immobilized to substrates enhanced the extent of transgene expression in both cell lines and primary human-derived cells, along with an increased cellular viability [13].…”

“…Self-assembled monolayers (SAMs) of alkanethiols on gold were used to provide a flexible system for regulating surface chemistry [19][20][21] to examine complex-substrate interactions. DNA, complexed with cationic lipids, was immobilized through nonspecific mechanisms to SAMs presenting combinations of hydrophilic and charged (COO − ), hydrophilic and uncharged (OH), and hydrophobic terminal functional groups (CH 3 ) [15]. Surface hydrophilicity and ionization were found to mediate both DNA complex immobilization and transfection, but had no effect on complex release.…”

“…The greatest amounts of binding and transfection were observed on surfaces presenting charged, hydrophilic groups, suggesting that electrostatic interactions allow for reversible interactions between the substrate and complexes and result in efficient gene delivery [22]. Hydrophobic substrates bound similar quantities of DNA as the hydrophilic surfaces, yet transfection was significantly reduced, suggesting the conformation of the DNA complexes may be altered upon binding to hydrophobic surfaces and result in low transfection levels [13,15].…”