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. 2009 Dec;30(35):6702-7.
doi: 10.1016/j.biomaterials.2009.08.055. Epub 2009 Sep 23.

Photoinitiated polymerization of PEG-diacrylate with lithium phenyl-2,4,6-trimethylbenzoylphosphinate: polymerization rate and cytocompatibility

Benjamin D Fairbanks  1 , Michael P Schwartz, Christopher N Bowman, Kristi S Anseth
Affiliations

Photoinitiated polymerization of PEG-diacrylate with lithium phenyl-2,4,6-trimethylbenzoylphosphinate: polymerization rate and cytocompatibility

Benjamin D Fairbanks et al. Biomaterials. 2009 Dec.

Abstract

Due to mild reaction conditions and temporal and spatial control over material formation, photopolymerization has become a valuable technique for the encapsulation of living cells in three dimensional, hydrated, biomimetic materials. For such applications, 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone (I2959) is the most commonly used photoinitiator (by virtue of its moderate water solubility), yet this initiator has an absorption spectrum that is poorly matched with wavelengths of light generally regarded as benign to living cells, limiting the rate at which it may initiate polymerization in their presence. In contrast, acylphosphine oxide photoinitiators, generally exhibit absorption spectra at wavelengths suitable for cell encapsulation, yet commercially available initiators of this class have low water solubility. Here, a water soluble lithium acylphosphinate salt is evaluated for its ability to polymerize diacrylated poly(ethylene glycol) (PEGDA) monomers rapidly into hydrogels, while maintaining high viability during direct encapsulation of cells. Through rheometric measurements, the time to reach gelation of a PEGDA solution with the phosphinate initiator is one tenth the time for that using I2959 at similar concentrations, when exposed to 365 nm light. Further, polymerization with the phosphinate initiator at 405 nm visible light exposure is achieved with low initiator concentrations and light intensities, precluded in polymerizations initiated with I2959 by its absorbance profile. When examined 24h after encapsulation, survival rates of human neonatal fibroblasts encapsulated in hydrogels polymerized with the phosphinate initiator exceed 95%, demonstrating the cytocompatibility of this initiating system.

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Figures

Figure 1
Figure 1
Chemical structures of the photoinitiator 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propanone(I2959) (1) and lithium phenyl-2,4,6-trimethylbenzoylphosphinate(LAP) (2).
Figure 2
Figure 2
(a) Cleavage of I2959 and LAP into substituent radicals following photon absorption. (b) Molar absorptivities of the I2959 (solid line)and cleavage products (dashed line). (c) Molar absorptivities of LAP (solid line) and cleavage products (dashed line).
Figure 3
Figure 3
Comparison of the solution polymerization of PEG-diacrylate initiated by either I2959 or LAP. Storage/loss moduli crossover, as a measure of the time required to achieve gelation, is plotted against the initiator concentration (a) and light absorbed by initiator (b). Squares represent samples prepared with I2959 and circles represent samples prepared with LAP polymerized at 5mW/cm2 365 nm filtered light at ambient temperature. Triangles represent samples polymerized with LAP at 10mW/cm2 405 nm filtered light. Solid lines provided for clarity only.
Figure 4
Figure 4
Normalized light intensity, I/Io (a) and Initiator concentration (b) as a function of sample depth for 10 seconds (solid black line) 60s (dashed line) 150s (dotted line) and 300s (dash-dot) of exposure to 365 nm light. Plots are generated with a presumption of an initial initiator concentration of 2.2mM, a light intensity of 10mW/cm2 and assuming a quantum yield of 1.
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