Currently CNF is sold at a cost of $90-100/kg.28 This high cost is due to the high cost of TEMPO and to the cost of processing the spent hypochlorite dilute solution containing the genotoxic TEMPO catalyst (as well as corrosive NaBr).29 Separating nitroxyl radicals in solution is a multi-step, expensive process,30 whereas TEMPO concentration in any material suitable for biomedical use, must be lower than the threshold of toxicological concern (i.e., 4 ppm).31