Novel Hydrogel Actuator Based on Biomimetic Chemistry
- PDF / 2,705,888 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 1 Downloads / 221 Views
Novel Hydrogel Actuator Based on Biomimetic Chemistry Bruce P. Lee,1,* Yuan Liu,1 and Shari Konst2 1 Department of Biomedical Engineering, 2 Department of Chemistry, Michigan Technological University, Houghton, MI 49931, U. S. A. ABSTRACT Hydrogel actuators were prepared by combining ionoprinting technique with reversible metal ion coordination chemistry found in mussel adhesive proteins. Hydrogels were formulated with biomimetic dopamine moiety, which contains a catechol side chain that is capable of forming mono-, bis-, and tris-complexes with ferric (Fe3+) ions with increasing pH. CatecholFe3+ complexation increased local crosslinking density, which induced hydrogel bending at the site of Fe3+ ionoprinting. The effect of pH on the dynamic response of hydrogel actuation was tracked by following the radius of curvature at the ionoprinting site. Both the rate of change and the maximum radius of curvature increased when the pH with increasing pH (2.5-9.5), indicating that pH can be used to modulate hydrogel actuation. Additionally, hydrogels containing Fe3+ demonstrated higher extent of deswelling when equilibrated at a basic pH. Similarly, dynamic mechanical analysis in the compression mode revealed that both the storage and loss modulus values for Fe3+-containing hydrogels increased with increasing pH. These results indicated that bis- and tris-complexes formed at an elevated pH level contributed to a faster rate of actuation and a more condensed network architecture. Hydrogel actuation and deswelling were also observed at pH of 3.5 although to a lesser degree, potentially due to a stronger affinity between network-bound catechol and Fe3+ ions as compared to complexes formed in a dilute solution. INTRODUCTION Hydrogels are three-dimensional polymer networks with high water contents. These materials are widely used in a variety of biomedical applications ranging from tissue engineering, drug delivery, to tissue adhesives [1]. Hydrogels that can change their shape and physical properties in response to various environmental stimuli (e.g., temperature, pH, humidity) are being explored in applications such as soft robotic components, biosensors, and controlled drug delivery [2-4]. Recently, we combined ionoprinting techniques pioneered by Palleau et. al.[3] with reversible metal coordination chemistry found in mussel adhesive proteins (MAPs) to create a pH responsive hydrogel actuator [5]. Hydrogels were prepared with networkbound catechol through photopolymerization of dopamine methacrylamide (DMA). DMA mimics the adhesive moiety, 3,4-dihydroxyphenylalanine (DOPA), which is responsible for strong interfacial binding in MAPs and wear resistant properties of mussel byssus thread coatings [6]. Catechol is capable of forming strong complexes with metal ions (e.g., ferric ion (Fe3+)) with log stability constants greater than 40 (45 for Fe3+) [7]. Depending on the pH, catechol forms mono-, bis-, and tris-complexes with Fe3+ ions (Figure 1) [8, 9]. DMA-containing hydrogels were locally imprinted with Fe3+ through electrochem
Data Loading...
