Biomimetic hydrogels gate transport of calcium ions across cell culture inserts
- 450 Downloads
Control of the in vitro spatiotemporal availability of calcium ions is one means by which the microenvironments of hematopoietic stem cells grown in culture may be reproduced. The effects of cross-linking density on the diffusivity of calcium ions through cell culture compatible poly(2-hydroxyethyl methacrylate) [poly(HEMA)]-based bioactive hydrogels possessing 1.0 mol% 2-methacryloyloxyethyl phosphorylcholine (MPC), 5 mol% N,N-(dimethylamino)ethylmethacrylate (DMAEMA) and ca. 17 mol% n-butyl acrylate (n-BA) have been investigated to determine if varying cross-link density is a viable approach to controlling transport of calcium across hydrogel membranes. Cross-linking density was varied by changing the composition of cross-linker, tetraethyleneglycol diacrylate (TEGDA). The hydrogel membranes were formed by sandwich casting onto the external surface of track-etched polycarbonate membranes (T = 10 μm, φ = 0.4 μm pores) of cell culture inserts, polymerized in place by UV light irradiation and immersed in buffered (0.025 HEPES, pH 7.4) 0.10 M calcium chloride solution. The transport of calcium ions across the hydrogel membrane was monitored using a calcium ion selective electrode set within the insert. Degree of hydration (21.6 ± 1.0%) and void fraction were found to be constant across all cross-linking densities. Diffusion coefficients, determined using time-lag analysis, were shown to be strongly dependent on and to exponentially decrease with increasing cross-linking density. Compared to that found in buffer (2.0–2.5 × 10−6 cm2/s), diffusion coefficients ranged from 1.40 × 10−6 cm2/s to 1.80 × 10−7 cm2/s and tortuosity values ranged from 1.7 to 10.0 for the 1 and 12 mol% TEGDA cross-linked hydrogels respectively. Changes in tortuosity arising from variations in cross-link density were found to be the primary modality for controlling diffusivity through novel n-BA containing poly(HEMA)-based bioactive hydrogels.
KeywordsPoly(HEMA) Biomimetic Hydrogels Co-networks Modulus Cross-linking density
The authors acknowledge support from the US Department of Defense (DoDPRMRP) grant PR023081/DAMD17-03-1-0172 and the Consortium of the Clemson University Center for Bioelectronics, Biosensors and Biochips (C3B). A.M. Wilson acknowledges support from the Department of Chemistry, University of the West Indies, St. Augustine and ABTECH Scientific, Inc.
- T. Alfrey Jr., E.F. Gurnee, W.G. Lloyd, J. Polym. Sci. Part C 12, 249 (1966)Google Scholar
- M.J. Berridge, M.D. Bootman, H.L. Roderick, Calcium signalling: dynamics, homeostasis and remodelling. Nature Reviews 4, 517–529 (2003)Google Scholar
- C. Capuccini, P. Torricelli, F. Sima, E. Boanini, C. Ristoscu, B. Bracci, G. Socol, M. Fini, I.N. Mihailescu, A. Bigi, Strontium-substituted hydroxyapatite coatings synthesized by pulsed-laser deposition: in vitro osteoblast and osteoclast response. Acta Biomater 4, 1885 (2008)CrossRefGoogle Scholar
- J. Crank, The Mathematics of Diffusion, 2nd edn. (Clarendon, Oxford, Eng, 1975)Google Scholar
- M.A. Khan, M. Masudul Hassan, L.T. Drzal, Effect of 2-hydroxyethyl methacrylate (HEMA) on the mechanical and thermal properties of jute-polycarbonate composite. Composites Part A: Applied Science and Manufacturing 36(1), 71–81 (2005)Google Scholar
- E. Mack, T. Okano, S. Kim, N. Peppas, Hydrogels in Medicine and Pharmacy (CRC Press, Boca Raton, 1988). Polymers Vol IIGoogle Scholar
- S. Nakamura, T. Matsumoto, J.-I. Sasaki, H. Egusa, K.Y. Lee, T. Nakano, T. Sohmura, A. Nakahira, Effect of calcium ion concentrations on osteogenic differentiation and hematopoietic stem cell niche-related protein expression in osteoblasts. Tissue Engineering Part A 16(8), 2467–2473 (2010)CrossRefGoogle Scholar
- M. Naraghi, E. Neher, Linearized buffered Ca2+ diffusion in microdomains and its implications for calculation of [Ca2+] at the mouth of a calcium channel. J. Neurosci. 17(18), 6961–6973 (1997)Google Scholar
- R.M. Ottenbrite, K. Park, T. Okano (eds.), Biomedical Applications of Hydrogels Handbook, 1st edn. (Springer, New York, 2010)Google Scholar