Effect of concentration and degree of saturation on co-precipitation of catechin and poly(l-lactide) by the RESOLV process

Rapid expansion of subcritical solutions into liquid solvents (RESOLV) was able to consistently produce catechin (CTC)-loaded poly(l-lactide) (PLLA) nanoparticles. The effects of CTC concentration and processing conditions – pre-expansion temperature and pressure, and degree of saturation – on the size and morphology of CTC-loaded PLLA nanoparticles were investigated, as well as the loading capacity (LC), entrapment efficiency (EE), and release of CTC. RESOLV experiments were carried out with 0.1 wt% CTC + 0.2 wt% PLLA and 0.2 wt% CTC + 0.2 wt% PLLA solutions in mixtures of EtOH and CO2 (3:2, wt/wt) with pre-expansion temperature and pressure of 60–100 °C and 265–325 bar, respectively. The obtained CTC-loaded PLLA nanoparticles were spherical, with average sizes, LC, and EE ranges of ∼30–40 nm, 2.4–7.3%, and 4.7–22.0%, respectively. CTC concentration, pre-expansion temperature, and degree of saturation had significant effects on LC and EE of CTC, without affecting the size of composite nanoparticles. The LC and EE of CTC increased with increasing pre-expansion temperature and degree of saturation, and with decreasing CTC concentration. The release profiles of CTC from the nanoparticles exhibited an initial stage of burst release (first 8 h) followed by a sustained release (∼1–9 days). Furthermore, the fraction of CTC being released from the nanoparticles decreased with increasing the degree of saturation of subcritical solutions prior to rapid expansion and with increasing the LC of CTC.