Introduction: Hydrogels are extensively used for tissue engineering and regenerative medicine. Their mechanical properties determine not only their function but also cell response (i.e. proliferation and differentiation of stem cells) and their degradation kinetics is particularly important to predict scaffold resorption, new tissue formation and integration after implantation. Non-destructive methods are needed to screen and follow long-term evolution of rheological properties. In this work, we demonstrate the potential of a new non-destructive instrument, ElastoSensTM Bio2 (Rheolution Inc., Montréal, QC), that measures in real-time and without contact the evolution of rheological properties of chitosan hydrogels during network formation and degradation during exposure to human lysozyme.
Materials and Methods: Validated[1] and patented[2] ElastoSensTM Bio2 technology is based on acoustic vibration. Response is measured using a laser and converted into elasticity. 1) Measuring viscoelastic properties of hydrogels: several chitosan thermogels (2% w/v; Mw 250kDa; DDA 94%) were prepared by mixing chitosan solution with a combination of phosphate buffer (PB) or beta-glycerophosphate (BGP) and sodium hydrogen carbonate (SHC) as gelling agents. Viscoelastic properties were measured after 1 and 24 hours of gelation at 37°C and compared with conventional rheometry (Physica MCR301) and compression tests (Bose Electroforce). 2) Following degradation: Chitosan thermogels with high (HDDA) or low degree of deacetylation (LDDA) were prepared. After 24h of gelation, a solution of lysozyme (1mg/mL) was added in the sample holder and kinetics of lysozyme-induced degradation was monitored once a day.
Results and Discussion: ElastoSensTM Bio2 data confirmed that viscoelastic properties of chitosan thermogels are highly dependent on formulation. The results correlated with Young’s secant modulus obtained by compression tests (Figure 1), while conventional rheometry showed higher shear modulus for two formulations. Lysozyme is known to cleave the linkages between acetylated groups and lower DDA is expected to increase the degradation rate. Preliminary results showed that changing DDA of chitosan can impact the kinetics of degradation (Figure 2). In contrast to conventional in vitro degradation studies which follow the evolution of polymer mass with time, these results give rapid and direct insight on the degradation of mechanical properties and their possible adjustment by varying hydrogel composition.
Conclusions: This study presents a new non-destructive approach to characterize viscoelastic properties of biomaterials in real-time during long periods. This new tool would allow fine-tuning the biomaterial formulations in terms of mechanical properties and degradation kinetics for targeted applications. It could also be used in presence of encapsulated cells for tissue engineering applications.
Funding by Natural Sciences and Engineering Research Council of Canada (Engage grant). Caroline Ceccaldi acknowledges FRQ-S scholarship.
References:
[1] Ceccaldi, C., Nguyen, L.-C., Assaad, E., Hadj Henni, A., Schmitt, C., Lerouge, S., New Instrument for Real-Time Monitoring of Viscoelasticity of Soft Biomaterials and Engineered Tissues, Society for Biomaterials Annual Meeting 2014, abstract
[2] Hadj Henni, A.R., Schmitt, C.R., System and method for the measurements of visoelastic parameters in soft materials, WO 2015027336 A1