Surface Engineering

Porous Silicon - Polymer Composites

We are working on several different pSi-polymer composite for applications in drug delivery, cell culture and tissue engineering.

1) PLLA/pSi Composites: In this work, we prepare a composite material comprised of biodegradable inorganic/organic materials by grafting poly(L-lactide) (PLLA) from pSi films and microparticles by means of ring opening polymerisation.

 

Figure 5. Preparation of pSi-PLLA Composites: Left - Atomic Force Microscopy (AFM) image showing short nanobrushes of PLLA "grafted from" the surface of pSi. Central - Schematic of the chemistry used to create the silane linkage between the pSi and the PLLA. Right - Degradation curves of oxidized pSi and oxidized pSi protected with PLLA nanobrushes (pSi-PLLA).

 

2) DNA/pSi and peptide/pSi Composites: The conventional production of short oligonucleotides and peptides involves stepwise coupling of the constituent bases/amino acids onto a solid support. With this work we attempt to prepare volatilisable solid supports that dissolve upon incubation in bodily fluids resulting in the release of active tailor-made biomolecules. These supports are based on pSi, which is susceptible to hydrolytic degradation in vivo and in vitro and should completely dissolve allowing 100% of the payload to be delivered.

 Figure 6. Schematic for the production of DNA/pSi composites: Stage 1 - pSi is shattered via sonication to create microparticles approximately 20 - 50 microns in size. Stage 2 - The pSi microparticles are functionalized with various linkers depending on the application. Stage 3 - DNA is grown from the pSi surface on a DNA synthesizer in a similar manner to that performed on conventional CPG resins. Stage 4 - The pSi is dissolved in NH4OH (quick) or bodily fluid (slow) and free DNA strands are released.

 

3) pSi/PNIPAM Composites: Research in our lab is being conducted towards the fabrication and characterisation of porous silicon polymer composite materials. We have grafted the thermoresponsive polymer poly(N-isopropylacrylamide) from pSi substrates using surface-initiated polymerisation and have studied the application of the hybrid for the controlled release of model drugs. Additionally, the hybrid is also currently being investigated for application as a substrate for cell culture and cell sheet engineering.

 

Figure 7. A) Schematic depicting the change in surface chemistry of the BiBB-APTES functionalised pSi template upon polymerization with NIPAM;
B) Illustration of the LCST behaviour of surface grafted PNIPAM chains within the pores of the pSi template.