Does anyone know that it is always required to frost scaffolds before starting the freeze drying process? If so, does this pre-frosting step give any harm to the scaffold's internal structure? Or can we put the scaffolds directly into freeze dryer without frosting them? Could you please share your ideas? Thanks in advance!
If your gel is going to be highly porous which I suspect, then its very likely It'll collapse following freeze drying. For that reason, I strongly recommend critical point drying (CPD) to preserve internal gel structure.
My experiences are such that before freeze drying use a pre-freezing.
Try it different conventional cryoprotectants.
If you can add DMSO to your gel, it will help avoiding cristal formation. If this is your problem.
If the freeze drier reach very fast 4degree celsius the probability that 3D is maintained during the freezing and drying stages of frost samples is big. You are in a more safe situation if your samples are frozen.Again even for frozen samples case if it take too long to reach 4-0 celssius your sample may collapse and loose its 3D dimensions.Therefore you have to check the performance of your freeze drying equipment before you make decisions!
If you dont freeze the material, it will collapse when you start to do vaccum. There is many of reports in the literature that describe the control of pores size and orientation by using the combination of different freezing stages. However the final struture of the scaffold also depends of the materials that compose the gel and their interations with the solvent.
If you freeze the gels first the water will be removed by sublimation and the structure will remain in tact; as opposed to collapsing of the structure when the liquid water is evaporated.
Dear Professors thank you for your all valuable answers which helped too much. I have one more question. Do you think there would be any differences if I frosted my gels into a normal freezer (-18C) before freeze drying process? Can I use normal freezer to frost my gels instead of leaving them in liquid nitrogen (-196C)? Thank you for your cooperation!
I used to freeze my gels at -18, but to be in a safe situation i poured liquid nitrogen to cover the samples to ensure they will not collapse .you do not have to freeze them in liquid nitrogen only in case you want to determine if the sample freezing rate effect is significant on the physical properties of the dried gels
Dear Ory Ramon, thank you for your answers. I left them at -18C untill they get completely frozen. I think it worked! They dried very well without any collapse. Thank you for your support and help.
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