Purpose: Natural proteins are very attractive candidates in medical application because of their inherent biocompatibility and potential for degradation into non-cytotoxic natural amino acids. However, their raw chemical structures are typically difficult to utilize in a means precise for embolization. Here, we report two types of protein hydrogel microspheres (PHMS) synthesized from methacrylated whey protein (WP-MA) and from methacrylated soy protein (SP-MA) reinforced with poly(ethylene glycol) diacrylate (PEGDA) and their drug loading and releasing potential. This approach demonstrated the possibility of using affordable proteins as the main component of embolization agents in a more controlled manner.
Material and Methods: WP-MA and SP-MA were modified from food grade whey protein concentrate and soy protein isolate. The PHMS were synthesized by crosslinking pre-gel solution (WP-MA or SP-MA with PEGDA) droplets formed in a stirred oil phase, via photo initiated reaction in the presence of lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) under 405 nm LED light. After 10 minutes of exposure, the PHMS were collected by settling and washed to remove oil and unreacted residues. Drug loading and releasing was investigated by immersing beads in a solution of Bevacizumab (Avastin, Roche), or immersing loaded beads in a PBS solution, and sampling periodically to monitor drug concentration.
Results: Gelation of WP-MA and SP-MA in the presence of LAP under 405 nm LED light suggested sufficient methacrylate groups had been added to the proteins, whereas no gels were formed using the control (unmodified protein) solutions under the same circumstance. The bulk hydrogels contain more than 80 wt% water with Young’s modulus in the range of 10 kPa (similar to the Young’s modulus of human skin and muscle). Microspheres consisting of WP-MA or SP-MA/PEGDA were successfully synthesized. These PHMS were generally clear spherical with a smooth, uniform surface that sized 100-600 µm. The ability to load and release bevacizumab drug was demonstrated for both PHMS's, loading up to 70µg Bevacizumab per mg of wet weight microspheres and releasing approximately 90% of the loaded drug after four hours.
Conclusions: The feasibility of utilizing chemically modified natural proteins was demonstrated. PHMS made from both WP-MA and SP-MA/PEGDA were drug loadable and releasable. This is encouraging for the use of chemically modified proteins as components in the development of improved embolic materials.