I used the following protocol to prepare Gelatin-MA:

1.  2g of Gelatin is mixed with 20 ml of Dulbecco’s phosphate buffered saline (DPBS: GIBCO) at 50 °C and stirred until fully dissolved.

2.  3 ml Methacrylic Anhydride is added to the above solution at 50 °C under vigorous stirring, and this mixture is left in a dark space for 2 hours (While still being stirred on a Magnetic stirrer).

4. 165 ml DPBS at 40 °C is added to the solution.

5. The mixture is dialyzed against distilled water using 12-14 kDa cutoff dialysis tubing for 1 week at 40 °C to remove salts and MA.

6. The solution is freeze-dried for 1 week to generate a white porous foam and stored at ~80°C until further use.

I have completed steps 1-4 around 12 hours ago, and the mixture is currently being dialyzed. One thing that I observed inside the dialysis tubing a few hours ago, was the presence of white particulate matter. This is also found at the bottom of the beaker that we used to prepare the initial mixture (I have attached some pictures). Is this to be expected? Should I perhaps filter the solution? Is my protocol a valid one for preparing Gel-MA?