Buffer uptake and mass loss characteristics of freeze-dried cellulosic and alginate devices

The buffer uptake and mass loss characteristics of freeze dried unitary devices prepared from aqueous solutions of Sodium Carboxymethylcellulose (CMC), cross-linked Sodium Alginate (ALG) and Methylcellulose (MC) were evaluated. Some of the devices also contained 50% (by weight) Poly (d,l Lactide-co-Glycolide) (PLGA) microspheres. Devices prepared from cross-linked ALG solutions imbibed the highest amounts of isotonic Phosphate Buffered Saline, followed by those from prepared from CMC solutions, and lastly, MC. In all cases, the presence of microspheres within the devices significantly decreased buffer uptake. Uptake was determined to be approximately proportional to the weight percent of the hydrophilic matrix polymer. Highest levels of overall mass loss were observed with devices prepared from cross-linked ALG solutions (approximately 80% in 60 days), followed by those prepared from CMC solutions (approximately 45 to 65%) and MC (approximately 35 to 60%). A majority of the unitary devices retained their shape and integrity, however, over the two month test period, indicating possible use as long term delivery systems for incorporated bone growth factors.