**7.2 Collagen purification via filtration**

Ultrafiltration can be applied to remove the non-collagenous material prior to lyophilisation of collagen. Ultrafiltration utilises positive pressure to force a liquid through a semi-permeable membrane to separate species in an aqueous solution by molecular size, shape or charge. Ultrafiltration has the advantages of having a high throughput, cost-effective and large-scale purification is possible without being limited to lab-scale purification by dialysis.

Ultrafiltration enables the removal of solvents and salts of lower molecular weight from a solution (permeate). Thus, this results in the enrichment of the retained molecule (pure collagen). Ultrafiltration membranes can retain molecules in the range of 10 kDa to 1 MDa, thus concentration and purification of collagen (300 kDa) can be successfully achieved through this process.

