Control of collagen gel mechanical properties through manipulation of gelation conditions near the sol–gel transition

Abstract

The ability to control the mechanical properties of cell culture environments is known to influence cell morphology, motility, invasion and differentiation. The present work shows that it is possible to control the mechanical properties of collagen gels by manipulating gelation conditions near the sol gel transition. This manipulation is accomplished by performing gelation in two stages at different temperatures. The mechanical properties of the gel are found to be strongly dependent on the duration and temperature of the first stage. In the second stage the system is quickly depleted of free collagen which self assembles into a highly branched network characteristic of gelation at the higher temperature (37 °C). An important aspect of the present work is the use of advanced rheometric techniques to assess the transition point between viscoelastic liquid and viscoelastic solid behaviour which occurs upon establishment of a sample spanning network at the gel point. The gel time at the stage I temperature is found to indicate the minimum time that the gelling collagen sample must spend under stage I conditions before the two stage gelation procedure generates an enhancement of mechanical properties. Further, the Fractional Maxwell Model is found to provide an excellent description of the time-dependent mechanical properties of the mature collagen gels.

Roles of the molecular weight of n‐ethylene glycol diacrylates and UV irradiance on the mechanical properties at the gel point of acrylic acid based hydrogels

“…D f s increased when the UV irradiance levels were varied. This was contrary to the reported photocrosslinking–gelation between acrylic acid and methylene bisacrylamide, where isoconversion gelation was observed with respect to variations in the UV irradiance . The results of our study show that the rate at which the networks clusters were branching increased with greater UV irradiance.…”

“…As Table shows, I t could have also been affected the UV irradiance dose and dose rate used during the reaction. The greater the UV irradiance was, the greater the amount of radical species that were generated was; this led to a faster formation of network clusters …”

“…In addition, a lack of any effect of the MWs of the EGDAs on the rate of conversion of the reactant materials could be expected because the pH of the reaction media was largely the same and constant at an approximate pH of 2.5. If the pH had changed because of the variation in the series of the crosslinkable EGDAs, it would have been possible to considerably affect the dissociation and reactivity of the monomeric acrylate …”

“…Figure shows how the gel point was reached more rapidly with a higher UV intensity. With more irradiation, after photocleavage of the photoinitiator molecules at the start of the reactions, there was a greater concentration of reactive radical active centers in comparison to when lower UV intensities were used . This scenario led to greater monomer–crosslinker reactive species being generated and thereby sped up the rate of the reaction(s) and consequently produced quicker gelation.…”

Microengineered three-dimensional collagen fiber landscapes with independently tunable anisotropy and directionality

“…Cells can be introduced to the system in two common ways: first by pre-mixing them into the ECM solution before injection [37] , or second, through the use of peripheral access channels that are separated from the main channel with small constrictions [35] . Including cells in the gel precursor solution limits the extent to which we can further modify fiber properties because changing solution pH, ionic strength, composition, and polymerization temperature can cause cell damage [38][39][40] . To overcome these limitations, we demonstrate two methods of accessing the microengineered collagen landscape.…”