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Ionically cross-linked poly(allylamine) as a stimulus-responsive underwater adhesive: ionic strength and pH effects
Patrick G Lawrence1, Yakov Lapitsky
1Department of Chemical and Environmental Engineering and ‡School of Green Chemistry and Engineering, University of Toledo , Toledo, Ohio 43606, United States.
Langmuir : the ACS Journal of Surfaces and Colloids
|January 9, 2015
Summary
New underwater adhesives made from poly(allylamine) (PAH) and phosphates offer tunable adhesion. Their strength and dissolution are controlled by pH and ionic strength, enabling applications like injectable hydrogels.
Area of Science:
- Materials Science
- Polymer Chemistry
- Biomaterials Engineering
Background:
- Underwater adhesives are crucial for biomedical and industrial applications.
- Poly(allylamine) (PAH) complexed with pyrophosphate (PPi) or tripolyphosphate (TPP) forms gel-like coacervates with adhesive properties.
- The stimulus-responsive nature of these adhesives, particularly their pH-dependent dissolution, requires further investigation.
Purpose of the Study:
- To investigate the effects of pH and ionic strength on the formation, rheology, and adhesion of PAH/PPi and PAH/TPP complexes.
- To understand how environmental factors influence the stability and performance of these underwater adhesives.
- To explore the potential of these tunable adhesives for applications like injectable delivery systems.
Main Methods:
- Preparation of poly(allylamine) (PAH) coacervates cross-linked with pyrophosphate (PPi) and tripolyphosphate (TPP).
- Systematic variation of pH and ionic strength (NaCl concentration) during complex formation and testing.
- Rheological measurements and tensile adhesion tests to quantify adhesive properties and cross-link stability.
- Evaluation of adhesive performance under varying ionic conditions to assess injectable design potential.
Main Results:
- Adhesive formation required lower cross-linker concentrations at higher pH and ionic strength, ceasing above pH 8.5.
- Optimal ionic cross-link stability and adhesion strength were observed near neutral to slightly alkaline pH (6.5-9) and low ionic strengths.
- Elevated NaCl concentrations (150-300 mM) and non-optimal pH reduced adhesion strength and longevity, but short-term adhesion often exceeded 10^5 Pa.
- Injectable adhesive formulations were successfully demonstrated by triggering spontaneous formation upon injecting PAH/TPP dispersions into buffer solutions.
Conclusions:
- The pH and ionic strength sensitivity of PAH/PPi and PAH/TPP complexes allows for controlled formation, dissolution, and adhesion.
- These tunable properties enable novel functionalities, including minimally invasive injectable delivery systems.
- The study highlights the potential of ionically cross-linked PAH networks as versatile underwater adhesives with on-demand bonding capabilities.
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