FDA testing of Hydrogels

We were able to use our expertise and resources at Applied Molecules to run photorheology cure testing on hydrogels to aid in the material’s FDA approval for a customer. For many

radiation-cured polymer applications, especially those that need FDA approval, knowing

the correlation between applied light energy or dose and crosslink density is critical.

Partially cured polymers can lead to properties that can change or uncrosslinked

components that can leach out over time.

A rheometer measures the way a fluid flows in response to an applied force. By varying

the amplitude and frequency of this applied force, rheological properties such as

storage modulus, loss modulus, and viscosity can be measured. By modifying the

temperature, the thermal effect of these measurements can be determined as well. If we

attach a light source to the rheometer, photoactive liquids can be radiated during these

measurements allowing us to view the time dependency of the photorheological

properties during crosslinking.

This photorheology technique, along with a spectrometer and light meter, give us the

ability to measure storage modulus, loss modulus, and viscosity based on a given light

dose at known wavelengths. To connect this data with a degree of conversion of

functional groups, we combine this technique in sequence with a Fourier Transform

Infrared (FTIR) Spectrometer. This instrument allows us to get an infrared spectrum of

the absorption of a material giving an indication of the relative quantity of different types

of bonds. We can take our samples directly off the photorheometer and immediately

scan them with the FTIR. When compared to a baseline of a scan of the uncrosslinked

neat liquid, we can see the decrease in the number of functional bonds allowing us to

back out the conversion.

The photorheometer and the FTIR in sequence give us the ability to accurately

determine the required light dose to obtain a fully crosslinked material while

simultaneously seeing how the material physically responds as well. For example, we

can see at what degree of conversion the material reaches its maximum storage

modulus or if a material never exceeds a certain conversion threshold. These

instruments, along with other resources at Applied Molecules, allow us to not only be

material formulation experts, but also give us the capability to combine that expertise

with advanced analytical data.