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Prolonged Release of Bioactive Model Proteins from Anionic Microgels Fabricated with a New Microemulsion Approach



Therapeutic proteins have become an integral part of health care. However, their controlled delivery remains a challenge. Protein function depends on a delicate three dimensional structure, which can be damaged during the fabrication of controlled release systems. This study presents a microgel-based controlled release system capable of high loading efficiencies, prolonged release and retention of protein function.


A new DMSO/Pluronic microemulsion served as a reaction template for the crosslinking of poly(acrylic acid) and oligo (ethylene glycol) to form microgels. Poly(acylic acid) molecular weights and microgel crosslinking densities were altered to make a series of microgels. Microgel capacity to capture and retain proteins of different sizes and isoelectric points, to control their release rate (over ~30 days) and to maintain the biofunctionality of the released proteins were evaluated.


Microgels of different sizes and morphologies were synthesized. Loading efficiencies of 100% were achieved with lysozyme in all formulations. The loading efficiency of all other proteins was formulation dependent. Release of lysozyme was achieved for up to 30 days and the released lysozyme retained over 90% of its activity.


High loading efficiencies and prolonged release of different proteins was achieved. Furthermore, lysozyme’s functionality remained uncompromised after encapsulation and release. This work begins to lay the foundation for a broad platform for the delivery of therapeutic proteins.

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Acrylic acid


4,4’-azobis(4-cyanopentanoic acid)


4-cyanopentanoic acid dithiobenzoate


4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride


Gel permeation chromatography




Oligo(ethylene glycol)


Poly(acrylic acid)


Phosphate buffered saline


Isoelectric point


Reversible addition-fragmentation chain transfer


Scanning electron microscopy


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We would like to gratefully acknowledge the Coleman Foundation and the NSF Graduate Research Fellowship for their support (J.L.R.). The authors would like to acknowledge Dr. Lindsey Crawford for her assistance with cell culture and MTT assay. This work made use of Cornell Center for Materials Research facilities funded through NSF MRSEC DMR-1120296 and the Cornell University NMR Chemistry facility.

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Correspondence to David Putnam.

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Rios, J.L., Lu, G., Seo, N.E. et al. Prolonged Release of Bioactive Model Proteins from Anionic Microgels Fabricated with a New Microemulsion Approach. Pharm Res 33, 879–892 (2016).

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  • bioactive proteins
  • microemulsion
  • microgels
  • prolonged release