Engineering temperature‐sensitive poly(N‐isopropylacrylamide) polymers as carriers of therapeutic proteins

Abstract

This study was carried out to engineer N-isopropylacrylamide (NiPAM) polymers that contain protein-reactive N-acryloxysuccinimide (NASI) and hydrophobic alkylmethacrylates (AMAs). These thermoreversible, protein-conjugating polymers hold potential for retention of therapeutic proteins at an application site where tissue regeneration is desired. The lower critical solution temperatures (LCST) of the polymers were effectively controlled by the AMA mole content. The AMAs with longer side-chains were more effective in lowering the LCST. Polymers without NASI exhibited a stable LCST in phosphate buffer and in serum over a 10-day study period. The LCST of polymers containing NASI was found to increase over time in phosphate buffer, but not in serum-containing medium. The LCST increase in phosphate buffer was proportional to the AMA content. The feasibility of localizing a therapeutic protein, recombinant human bone morphogenetic protein-2 (rhBMP-2), to a site of application was explored in a rat intramuscular injection model. The results indicated that polymers capable of conjugating to rhBMP-2 were most effective in localizing the protein irrespective of the LCST (13-25 degrees C). For polymers with no NASI groups, a lower LCST resulted in a better rhBMP-2 localization. We conclude that thermosensitive polymers can be engineered for delivery of therapeutic proteins to improve their therapeutic efficacy.

Type‐specific separation of animal cells in aqueous two‐phase systems using antibody conjugates with temperature‐sensitive polymers

“…The shift in the cloud-point of poly(NIPAM) is based on the balance between the hydrophilic and hydrophobic groups on the polymer backbone. Similar changes in cloud-points were shown by other works introducing hydrophilic or hydrophobic moieties in the poly(NIPAM) backbone (Takei et al, 1993;Brazel and Peppas, 1995;Kumar et al, 1998;Homan, 2000;Uludag et al, 2001). If the NIPAM monomer is copolymerized with more hydrophilic monomers such as acrylamide, the LCST increases and may even disappear.…”

Hydrogels of Thermoreversible Comb‐Polymers Exhibit Increased Resistance for Dissolution

“…A close relationship between the physicochemical properties of the polymers and the protein retention was established. Lowering the LCST of NiPAM polymers (from $27 o C for the homopolymer to <20 o C) by incorporating hydrophobic monomers resulted in better entrapment of proteins with increased protein localization at an injection site [13]. Incorporating protein-reactive NASI groups into the polymers resulted in protein conjugation to polymers, which increased the retention of proteins and reduced their burst release [12,13].…”

“…Previous studies from this group have focused on the use of NiPAM-based thermoreversible polymers to localize morphogenetic proteins at a desired anatomical site [12,13]. The morphogenetic proteins are de novo tissue inducers whose activity depends on the local retention of the proteins.…”

“…The thermoreversible character of the polymer allows one to process the polymers in aqueous conditions by keeping the temperature below the LCST, but also enables one to create a gelled phase by simply raising the temperature above the LCST. The fact that gel formation occurs under gentle conditions (in aqueous buffers without the need for exogenous agents) makes the polymers attractive for biomedical applications, such as tissue engineering scaffolds for cell culture and transplantation [6][7][8][9] and controlled delivery of therapeutic proteins [10][11][12][13].…”

The Effect of Partial Dissolution-Precipitation Treatment on Calcium Phosphate Ceramics in the Release of BMP-2 and Osteoinduction

“…An optimized delivery system might improve the osteoinduction of the device, while reducing the loading amount of BMP as much as possible, which offers double advantages of being safer as well as less expensive 3) . Several reports indicated that too rapid release of BMP-2 decreased osteoinduction while high retention of BMP-2 elicited more bone formation 4,5) . It is likely that an extremely low dose of BMP-2 is enough to enhance osteoinduction if BMP-2 is appropriately delivered to the site of action 6) .…”