Manipulating the mechanical stiffness and biological stability of collagen hydrogels

  • Laura Beattie

Student thesis: Doctoral Thesis

Abstract

Collagen is the most abundant protein in the human body. It is biocompatible, biodegradable and weakly antigenic, making it an ideal biomaterial for cell scaffolds and as the basis for many biomimetic materials. In vitro and in vivo, collagen scaffolds are in a constant state of flux, as new collagen is synthesised and existing collagen is degraded by collagenases (matrix metalloproteinases; MMP) from cellspresent in the scaffold. The main aim of this work was to improve the mechanical strength and biological stability of Type I collagen hydrogels. Three approaches were investigated. Firstly, collagen hydrogels produced from collagen isolated from different species and by different isolation methods were compared to validate the method of mechanical testing. Enzymatic solubilisation was found to produce collagen hydrogels which were mechanically weaker than their acid solubilised comparators. However, enzymatic solubilisation did not affect the contraction of free-floating fibroblast populated collagen lattices. Secondly, ACE inhibitors: captopril, enalapril and lisinopril, were added to collagen hydrogels. ACE inhibitors have long been used in the treatment of hypertension. Literature suggested ACE inhibitors may also inhibit the action of MMPs, so adding them to cell-seeded collagen hydrogels may slow degradation, thus maintaining the mechanical stiffness of the hydrogel. The effect of ACE inhibitors on hydrogels was tested over 9 days, but evidence of any change in bulk stiffness was inconclusive. Neither enalapril nor lisinopril affected cell numbers; however captopril had a cytostatic effect. This result was reflected in contraction of free-floating hydrogels with no significant contraction of captopril hydrogels. Further testing would be required to measure mechanical properties at the cellular level but was beyond the scope of this study. The third, and most successful approach was dehydration of hydrogels. A method of dehydrating cell-seeded hydrogels was developed, based on the plastic compression method designed by Robert Brown and colleagues (2005). A novel super-absorber, sodium polyacrylate, was used in the dehydration process, which proved extremely effective in increasing the mechanical strength of hydrogels. Gel weight decreased by 98% in 10 minutes maintaining viable fibroblast cells within the hydrogel, at a fraction of the cost of commercially available systems and without the need for any specialist equipment. After 4 weeks in culture, there was no significant difference in cell numbers in the hydrogel between hydrated and dehydrated gels, while de novo collagen synthesis was increased in dehydrated gels. Further, supplementing dehydrated hydrogels with ascorbic acid and hyaluronic acid promoted cell viability and collagen synthesis. This dehydration system has great potential to be further developed to 3D tissue models, and could prove invaluable to the tissue engineering community, as well as widening access to simple 3D cell culture systems.
Date of Award15 Apr 2021
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorMary Grant (Supervisor) & Phil Riches (Supervisor)

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