Metastable gels: A novel application of Ogston theory to sickle hemoglobin polymers

Sickle hemoglobin differs from normal adult hemoglobin by its ability to polymerize, which occurs at relatively high concentrations since the solubility for polymerization is typically above 160 mg/ml. We have recently found that the gel formed by polymers is metastable if the gel is not centrifuged or aged for long times in that polymerization ceases before the monomer concentration has decreased from its original value to the solubility. We have proposed that this effect is due to the obstruction of ends by other polymers in the crowded gel. Here we use Ogston's theory describing spaces amid arrays of random rods to provide a framework for describing the failure of the polymers to propagate. We find good agreement between fiber diameter and minimum void spaces. This novel application of a well-established theoretical framework for crowding may apply to other dense gels as well.