Pore Structure Tuning of Poly-EGDMA Biomedical Material by Varying the O-Quinone Photoinitiator

Abstract

Porous polymer monoliths with thicknesses of 2 and 4 mm were obtained via polymerization of ethylene glycol dimethacrylate (EGDMA) under the influence visible-light irradiation in the presence of a 70 wt% 1-butanol porogenic agent and o-quinone photoinitiators. The o-quinones used were: 3,5-di-tret-butyl-benzoquinone-1,2 (35Q), 3,6-di-tret-butyl-benzoquinone-1,2 (36Q), camphorquinone (CQ), and 9,10-phenanthrenequinone (PQ). Porous monoliths were also synthesized from the same mixture but using 2,2'-azo-bis(iso-butyronitrile) (AIBN) at 100 °C instead o-quinones. According to the results of scanning electron microscopy, all the resulting samples were conglomerates of spherical, polymeric particles with pores between them. Use of mercury porometry showed that the interconnected pore systems of all the polymers were open. The average pore size, D_mod, in such polymers strongly depended on both the nature of the initiator and the method of initiation of polymerization. For polymers obtained in the presence of AIBN, the D_mod value was as low as 0.8 μm. For polymers obtained via photoinitiation in the presence of 36Q, 35Q, CQ, and PQ, the D_mod values were significantly greater, i.e., 9.9, 6.4, 3.6, and 3.7 μm, respectively. The compressive strength and Young's modulus of the porous monoliths increased symbatically in the series PQ < CQ < 36Q < 35Q < AIBN with decreasing proportions of large pores (over 12 μm) in their polymer structures. The photopolymerization rate of the EGDMA and 1-butanol, 30:70 wt% mixture was maximal for PQ and minimal for 35Q. All polymers tested were non-cytotoxic. Based on the data from MTT testing, it can be noted that the polymers obtained via photoinitiation were characterized by their positive effect on the proliferative activity of human dermal fibroblasts. This makes them promising osteoplastic materials for clinical trials.

Keywords: camphorquinone; cytotoxicity; ethylene glycol dimethacrylate; o-benzoquinone; phenanthrenequinone; photoinitiator; porosity; scanning electron microscopy; strength properties; visible radiation.

Scheme 1

The structure of dimethacrylate and components of the photoinitiating system (quinones and amines).

Figure 1

Porograms of the porous polymers obtained via polymerization of EGDMA and 1-butanol mixture, 30:70 wt% in the presence of photoinitiators (a–e), T = 25 °C and AIBN, T = 100 °C (f). Photoinitiators: (a) 36Q-amine1; (b) 35Q-amine1; (c) CQ-amine2; (d) PQ; and (e) PQ [quinone] = 0.1 wt%; and (f) [AIBN] = 0.1 wt%. Irradiation with Philips UHP halogen lamp (400–750 nm, 190 W), (a–d) I = 50 kLx and (e) I = 10 kLx.

Figure 2

SEM images of porous polymer surfaces obtained via polymerization of an EGDMA and 1-butanol mixture, 30:70 wt%: (a,b) 35Q, (c) 36Q, (d) PQ, (e) CQ, and (f) AIBN.

Figure 3

Young’s modulus (E) and compressive breaking stress (σ) values of the porous polymer monoliths obtained via polymerization of the EGDMA and 1-butanol 30:70 wt% composition in the presence of o-quinone photoinitiators (Philips UHP halogen lamp (400–750 nm, 190 W), I = 50 kLx, T = 25 °C) and AIBN (T = 100 °C).

Figure 4

Dependence of Young’s modulus (E) and compressive breaking stress (σ) of the investigated porous polymer monoliths on φ_12-100.

Scheme 2

The mechanism of radical photopolymerization initiation in the presence of o-quinones.

Figure 5

Kinetic curves for the photopolymerization of EGDMA mixed with 1-butanol, 30:70 wt% in the presence of different photoinitiators: PQ (orange curve); CQ-amine2 (blue curve); 35Q-amine1 (red curve); and 36Q-amine1 (green curve). I = 50 kLx.

Figure 6

Optical density of extracts of PQ polymer samples after one day (a) and seven days (b) of extraction (MTT assay).