For example, to evaluate the suitability of a hydrogel for its end-use as a cartilage substitute, what sort of in-vitro mechanical experiments can provide a reliable data?
Rheological studies like dynamic frequency test (G* vales - stiffness; G and G'' values - storage and loss modulus); stress relaxation experimnets; shear state measurements etc.
-Rheological testing such as with rheometer
-Surface hydrophilicity such as contact angle to compare with collagen values
-If you are looking at spine, consider some compressive testing over many cycles (1M)
-If you are looking at articular cartilage, consider some compressive testing or indentation testing
-In vitro cell culture on samples, then take histology
AFM (atomic force microscopy) is the most accurate way to measure the modulus (stiffness) of hydrated hydrogels, but be sure to use the correct model. The Hertz model is the most widely used but is inappropriate for hydrogels, since it fails to take deformation of the substrate into account. The Oliver & Pharr model overcomes this limitation but requires significant data processing, and the technique itself is very time-consuming. Other important considerations include the cantilever spring constant and tip/microbead size.
The most pertinent properties you want to consider are those that are important for cartilage, a material that provides cushioning, support and a frictionless surface in the bodies joints.
Mechanical analysis of the materials properties in compression is therefore a very important properties to investigate, consider the fracture stress and compressive modulus. Cartilage also has to be very tough and therefore you might want to extend your compressive mechanical analysis with an examination of the materials toughness.
The dynamic and periodic nature of locomotion, for example the cyclic loading and unloading of knee cartilage during walking/running indicates that it might be worthwhile to also examine the dynamic mechanical properties as Manithar suggested earlier - this could be done with a rheometer or a uniaxial dynamic mechanical analyser.
The resistance to wear and lubricity is another important aspect of cartilage properties and the analysis of this is referred to as tribology which can also be performed with a rheometer assuming you have correct accessories to do it with.
- Regarding mechanical performance of hydrogels, from my point of view, the basic mechanical properties, such as strength, stiffness, and toughness, should be considered. In this case, you should carry out tensile test, compressive test, cyclic test, rheology test, as well as fracture or tearing test to obtain the data of tensile strength, compressive strength, stiffness, fracture energy, and so on.
- Of course, the hydrophilicity, the friction or lubricity of the samples' surface, and the biocompatibility evaluated by cell culture experiments on hydrogels' surface are also important.
- Looking forward to hearing your good experimental results.
Depending on your specific experiments or next research steps, nanoindentation could also be of good value to your experiment. Nanoindentation enables you to capture local variations in your hydrogels, as well as cell-material interactions once you seed cells on top of, or inside, the hydrogel. This also enables you to study local variation of your scaffolds over time, and include, for example, degeneration or substitution effects in cell-laden scaffolds.
Also you can measure the hydrogel inside the same petridish you keep it in for further experiments, and no further sample prep is required. Nanoindentation also allows for non-destructive testing, often not possible in other types of mechanical testing.
Whenever considering nanoindentation of biomaterials, have a look at our Piuma Nanoindenter. As this instrument is specifically designed for this purpose, it includes all necessary elements for evaluating the elasticity of soft materials, such as spherical tips, high load-displacement S/N on very soft samples (even
- Badges
- Science topic
- Similar topics
- Chemistry
- Pharmacology
- Pharmaceuticals
- Drugs