Highly Robust Interfacially Polymerized PA Layer on Thermally Responsive Semi-IPN Hydrogel: Toward On-Demand Tuning of Porosity and Surface Charge

Abstract

Hydrogel composites with skin layer that allows fast and selective rejection of molecules possess high potential for numerous applications, including sample preconcentration for point-of-use detection and analysis. The stimuli-responsive hydrogels are particularly promising due to facile regenerability. However, poor adhesion of the skin layer due to swelling-degree difference during continuous swelling/deswelling of the hydrogel hinders its further development. In this work, a polyamide skin layer with strong adhesion was fabricated via gel−liquid interfacial polymerization (GLIP) of branched polyethyleneimine (PEI) with trimesoyl chloride (TMC) on a cross-linked N-isopropyl acrylamide hydrogel network containing dispersed poly sodium acrylate (PSA), while the traditional m-phenylenediamine (MPD)-TMC polyamide layer readily delaminates. We investigated the mechanistic design principle, which not only resulted in strong anchoring of the polyamide layer to the hydrogel surface but also enabled manipulation of the surface morphology, porosity, and surface charge by tailoring interfacial reaction conditions. The polyamide/hydrogel composite was able to withstand 100 cycles of swelling/deswelling without any delamination or a significant decrease in its rejection performance of the model dye, i.e., methylene blue. Regeneration can be done by deswelling the swollen beads at 60 °C, which also releases any loosely bound molecules together with absorbed water. This work provides insights into the development of a physically and chemically robust skin layer on various types of hydrogels for applications such as preconcentration, antifouling-coating, selective compound extraction, etc.

Toward highly effective loading of DNA in hydrogels for high-density and long-term information storage

“…3D . The above result is also supported by earlier work ( 38 ) where high rejection was observed for the PA layer formed by low–molecular weight PEI. Because high loading density of DNA was desired, we only focused on using the HPEI-25k TRFG hydrogel for further study.…”

“…In this study, HPEI is used as a cationic polyelectrolyte, with augmented positive charge density and abundant reactive functional groups (primary amine groups), because of its ability to condense DNA ( 27 , 29 , 38 ). Once the PNIPAM/PSA semi-IPN hydrogels are obtained, the fully swollen hydrogel beads are then immersed in an aqueous solution containing HPEI with different molecular weights, i.e., 2 and 25 kDa at 2 wt % for 30 min.…”

“…The high charge density of HPEI provides enough reaction sites for the formation of a PA layer while interacting with the PSA dispersed within the hydrogel. The noncovalent interaction of branched PEI with PSA is known to enhance the PA layer stability on the hydrogel surface ( 38 ). Both the PA layer on the hydrogel surface and the HPEI loading in the hydrogel will critically affect the DNA loading density and hence will be discussed further.…”

“…Upon examination of the TRFG hydrogels with the fluorescent-labeled DNA via laser scanning confocal microscopy (LSCM), through nine swelling/deswelling cycles, it was clear that the HPEI-2k and HPEI-25k TRFG hydrogels with different HPEI molecular weights (2 kDa/25 kDa) demonstrated markedly different DNA uptake. A previous study (38) on the PNIPAM/PSA semi-IPN hydrogel with a PA layer has shown that both pH and molecular weight of PEI will affect the morphology of the surface crosslinked PA layer formed. In the case of HPEI-2k, the DNA was absorbed mostly on the surface of the hydrogels, as shown in Fig.…”

“…Because the size and porosity of PNIPAM hydrogels can be easily controlled by temperature, they are commonly used in controlled drug delivery applications. Moreover, it can be easily chemically modified through copolymerization as well as by forming a semi-interpenetrating network (semi-IPN) and an interpenetrating network (IPN) to improve functionality and to provide versatile properties (38,39). Besides, they are considered good DNA carriers because of their excellent biocompatibility (40)(41)(42)(43)(44)(45) and blend easily with DNA protectants (25,46).…”