3D printed polypyrrole scaffolds for pH-dependent drug delivery for bone regeneration

The "gold standard” of treatment for areas of significant bone loss involves using autologous bone grafts harvested directly from patients. However, these grafts have a complication rate of 10 to 40% during harvest and can only be harvested in limited quantities; this drives the research for alternative bone scaffold materials, such as polymers. Polypyrrole (PPy) is a biocompatible polymer with useful electrical properties that can be harnessed for bone healing. PPy has been shown to hold and release charged drug molecules according to changes in localized pH. A natural change in pH around areas of bone regeneration can act as a trigger for this polymer. Resins comprised of poly(ethylene) glycol (PEG) and PPy nanoparticles (NP’s) with entrapped fluoresceine (FL) were 3D printed using stereolithography techniques. This novel resin formulation was able to achieve a repeatable minimum XY feature resolution of 200 μm with a 25 μm layer thickness. Drug release testing showed a linear trend favouring larger FL release in more alkaline environments with an average release of 46.0 ± 6.0 μg FL release per gram of PPy NP’s incorporated into the resin at pH 8 over a 14-day period (n = 3). These tests show success of a biocompatible PPy/PEG polymer blend capable of being 3D printed for potential use in patient customized bone scaffolds. The pH sensitive drug release from PPy validates that it can be successful in areas of natural bone regrowth to release molecules that help promote healing.