Compact Saloplastic Poly(Acrylic Acid)/Poly(Allylamine) Complexes: Kinetic Control Over Composition, Microstructure, and Mechanical Properties

Abstract

Durable compact polyelectrolyte complexes (CoPECs) with controlled porosity and mechanical properties are prepared by ultracentrifugation. Because the starting materials, poly(allylamine hydrochloride) (PAH) and poly(acrylic acid sodium salt) (PAA), are weak acids/bases, both composition and morphology are controlled by solution pH. In addition, the nonequilibrium nature of polyelectrolyte complexation can be exploited to provide a range of compositions and porosities under the influence of polyelectrolyte addition order and speed, and concentration. Confocal microscopy shows these “saloplastic” materials to be highly porous, where pore formation is attributed to a combination of deswelling of the polyelectrolyte matrix and expansion of small inhomogenities by osmotic pressure. The porosity (15–70%) and the pore size (<5 μm to >70 μm) of these materials can be tuned by adjusting the PAA to PAH ratio, the salt concentration, and the pH. The modulus of these CoPECs depends on the ratio of the two polyelectrolytes, with stoichiometric complexes being the stiffest due to optimized charge pairing, which correlates with maximized crosslinking density. Mechanical properties, pore sizes, and pore density of these materials make them well suited to three dimensional supports for tissue engineering applications.

Saloplastics: Processing Compact Polyelectrolyte Complexes

“…The extent of porosity depends on how the CoPECs are prepared. It was found that equimolar polyallylamine(PAH)/polyacrylate (PAA) CoPECs, formed and stored in 2.5 M NaCl, show pores with a typical diameter on the order of 20–40 μm . These are roughly the same size as PEMU microcapsules, which exhibit excess osmotic pressure inside the capsule due to excess polyelectrolyte as is also thought to be the case with strongly swollen, hydrated polylysine/hyaluronic acid multilayers .…”

“…When the centrifugation speed was reduced during CoPEC formation, the size of the large pores increased . Before centrifugation, the solution of polyelectrolyte complexes not only contained large blobs of complexes but also very large voids with typical sizes up to 200 μm.…”

“…Extensive studies on mixing rate and order have been performed on the PAH/PAA system . As seen in Figure , the PAH/PAA ratio in the CoPEC depends on the mixing order and results in a deficit of polyelectrolyte poured into the reaction mixture.…”

Healable and Mechanically Super‐Strong Polymeric Composites Derived from Hydrogen‐Bonded Polymeric Complexes

“…Polymeric complexes can be produced by mixing polymers with complementary noncovalent interactions in bulk solution or sequentially at interface of solid substrates and polymer solutions . Given that various polymers bearing complementary interactions can be employed to prepare polymeric complexes, polymeric composite materials based on polymeric complexes can possess various compositions, controllable cross‐linking density, and well‐tailored mechanical properties . During the formation of polymeric complexes, polymers with self‐assembly ability can generate well‐designed micro‐/nanosized structures, which provide a facile way to further tailor the mechanical properties of the resultant materials .…”

Bioinspired Metal Ion Coordinated Polyelectrolyte Fibrous Nanoreactors

“…To stabilize fibrous hydrogels in aqueous media, thermal or vapor‐phase crosslinking is required which impedes their applications. Polyelectrolyte complexes have been used to improve the stability of fibrous hydrogels in aqueous solutions . A polyelectrolyte complex is formed by mixing oppositely charged polyelectrolytes such as poly(acrylic acid) (PAA) and poly(allyl amine hydrochloric acid) or PAA and chitosan (CS) in solutions with controlled polymer ratio and pH.…”