Development of functional nanoparticles for in situ tissue engineering

Mesenchymal stem/stromal cells (MSCs) are of significant clinical interest in regenerative medicine because of their trilineage potential to differentiate into cells integral for tissues such as bone and cartilage. Current therapies for tissue damage often require surgical intervention, which has drawbacks including invasiveness and susceptibility to infection. Stem cell-based therapies likely offer a more natural alternative to repair damaged tissue. Nanoparticles are a promising tool for biomedical applications, especially as a vehicle for biomolecule delivery when coated with temperature-responsive polymers to entrap and release biomolecules, such as proteins, in a triggered manner. Superparamagnetic iron oxide nanoparticles (SPIONs) can undergo a phenomenon termed magnetic heating in the presence of an alternating magnetic field. SPIONs surface-functionalised with temperature-responsive polymers present a potential combination for protein delivery and release.
In this study, I report the development of SPIONs coated with temperature-sensitive polymer poly(N-isopropylacrylamide) (PNIPAM). PNIPAM-coated SPIONs showed temperature-sensitive properties above the lower critical solution temperature (LCST) of PNIPAM (32oC) when heated with or without magnetic heating. I could characterise the protein encapsulation and release of test protein apotransferrin from PNIPAM-coated nanoparticles in both a pH- and temperature-sensitive manner. Magnetic heating, though a constant or pulsed application, was sufficient to trigger the release of encapsulated apotransferrin from PNIPAM-coated nanoparticles, where switching off the magnetic field halted further protein release. Magnetically-triggered Wnt3a release from PNIPAM-coated nanoparticles elicited cellular activation through the enhanced green fluorescent protein (eGFP) response of an MSC Wnt reporter line, as well as increased proliferation of both immortalised and primary MSCs. I also developed temperature-responsive polymer, poly(N-isopropylmethacrylamide) (PNIPMAM), which exhibited a higher LCST than PNIPAM (42oC) and could release apotransferrin above physiological temperature with/without magnetic heating.
The developed temperature and magnetically-responsive SPIONs could be a potential tool to promote MSC-driven tissue regeneration through biomolecule delivery and temperature-sensitive release.