On the toughness of photopolymerizable (meth)acrylate networks for biomedical applications

Abstract

Photopolymerizable networks are being explored for a variety of biomedical applications because they can be formed in situ, rendering them useful in minimally invasive procedures. The purpose of this study was to establish fundamental relationships between toughness, network chemical structure, and testing temperature of photopolymerizable (meth)acrylate networks deformed in air and under hydrated conditions. Networks were formed by combining at least one monofunctional (meth)acrylate with a difunctional methacrylate, and weight ratios were adjusted to vary the degree of crosslinking, elastic modulus, and glass transition temperature (T g ). Stress-strain behavior and toughness were determined by performing tensile strain to failure tests at temperatures spanning the glassy and rubbery regimes of each network both in air and phosphate-buffered saline. In air, all of the networks demonstrated a peak in toughness below the network's T g . At an ''equivalent'' test temperature relative to T g , crosslinking concentration and monomer chemistry influenced the toughness of each network. Apparent toughness is significantly altered in an aqueous environment, an effect driven by water absorption into the network causing the T g to decrease. The results from this study provide the fundamental knowledge required to guide the development of tougher photopolymerizable networks for mechanically strenuous biomedical applications.

High‐Strain Shape‐Memory Polymers

“…[3] Other applications require enhanced toughness. [4][5][6][7] Yet other SMP applications in the biomedical device field require high strains to enable large on-demand shape changes. [8][9][10][11][12] Enabling large-strain applications of SMPs are of particular interest in this study.…”

The effect of the glass transition temperature on the toughness of photopolymerizable (meth)acrylate networks under physiological conditions

“…[5, 6] Based off of this trend from a brittle to ductile to rubbery state, maximal toughness typically occurs at a testing temperature slightly below or at the polymer's T g where the chains are becoming more mobile allowing the network to sustain larger strains without losing much strength. [7] Because of this relationship between toughness and temperature, the mechanical properties at body temperature rather than room temperature must be considered for implantation into the body.…”

Mechanical Testing of Hydrogels in Cartilage Tissue Engineering: Beyond the Compressive Modulus

“…Smith et al 12 studied the toughness of hydrogels in phosphate-buffered saline at different temperatures, conducting failure tests and comparing the elastic modulus and toughness of the specimens. In the test, dog-bone specimens (laser-cut according to dimensions specified in ASTM D 638-03 Type IV or V) were loaded on a universal testing machine (MTS Systems, Insight 2) using a 2 kN load cell with a 1 mm/min strain rate.…”

“…2 Some studies only consider ultimate compressive stress or strain, which may suffer from issues with reproducibility. 10,12 In traditional fracture mechanics, fracture toughness is defined as the quantitative expression of the ability of a brittle material to resist fracture in the presence of an existing sharp crack. The material property of fracture toughness is defined for a given material by measurement using a minimum specimen size that will guarantee dominance of plane strain conditions, therefore allowing for consistent fracture toughness values for the given material.…”