Self-assembled photoadditives in polyester films allow stop and go chemical release.
Near-infrared (NIR) triggered chemical delivery allows on-demand release with the advantage of external tissue stimulation. Bioresorbable polyester poly-l-lactic acid (PLLA) was compounded with photoadditives of neat zinc oxide (ZnO) nanoparticles and 980→365nm LiYF4:Tm3+, Yb3+upconverting nanoparticles (UCNP). Subsequently, neat ZnO and UCNP blended PLLA films of sub-50μm thickness were knife casted with a hydrophobic small molecule drug mimic, fluorescein diacetate. The PLLA films displayed a 500 times increase in fluorescein diacetate release from the 50mW NIR irradiated PLLA/photoadditive film compared to non-irradiated PLLA control films. Larger ratios of UCNP/neat ZnO increased photocatalysis efficiency at low NIR duty cycles. The synergistic increase results from the self-assembled photoadditives of neat zinc oxide and upconverting nanoparticles (UCNPs), as seen in transmission electron microscopy. Colloidal ZnO, which does not self-assemble with UCNPs, had less than half the release kinetics of the self-assembled PLLA films under similar conditions, advocating Förster resonance energy transfer as the mechanism responsible for the synergistic increase. Alternative to intensity modulation, pulse width modulation (duty cycles from 0.1 to 1) of the low intensity 50mW NIR laser diode allowed tailorable release rates from 0.01 to 1.4% per day. With the low intensity NIR activation, tailorable release rates, and favorable biocompatibility of the constituents, implanted PLLA photoadditive thin films could allow feedback mediated chemical delivery.



Upconverting nanoparticles and zinc oxide nanorods were found to spontaneously self-assemble into submicron particles in organic solvents. Exposure of the submicron particles to near-infrared light allows stop and go chemical release from biocompatible polymers. Sample preparation of thin films is done with ease through physical mixing of the photoadditives followed by air-dried knife casting. A colloidal ZnO variant that does not self-assemble with upconverting nanoparticles had slower chemical release, suggesting that synergistic chemical release is brought upon by highly efficient energy transfer mechanisms when the nanoparticles are less than 10nm apart. Never before seen composite particles of UCNP/ZnO are displayed, which shows the close interaction of the photoadditives within the polymer matrix.
School of Materials Science & Engineering, College of Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
Ting
T
Cheng
School of Materials Science & Engineering, College of Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
Richard
R
O'Rorke
School of Materials Science & Engineering, College of Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
Raphael Francois
RF
Ortiz
School of Materials Science & Engineering, College of Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore; Facility for Analysis, Characterization, Testing and Simulation, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
Tay Yee
TY
Yan
Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Université du Québec, 1650 Lionel-Boulet, Varennes, QC J3X 1S2, Canada.
Eva
E
Hemmer
Institut National de la Recherche Scientifique - Énergie, Matériaux et Télécommunications, Université du Québec, 1650 Lionel-Boulet, Varennes, QC J3X 1S2, Canada; Centre for Self-Assembled Chemical Structures, McGill University, Montreal, QC H3A 2K6, Canada.
Fiorenzo
F
Vetrone
School of Materials Science & Engineering, College of Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore; Department of Biotechnology Engineering, Faculty of Engineering Sciences, Ben Gurion University of the Negev, P.O. Box 653, Beer Sheva 84105, Israel.
Robert S
RS
Marks
School of Materials Science & Engineering, College of Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. Electronic address: wjsteele@ntu.edu.sg.
Terry W J
TWJ
Steele
D003102:Colloids; D008567:Membranes, Artificial; D053758:Nanoparticles / Q000737:chemistry*; D055668:Photochemical Processes; D011091:Polyesters / Q000737:chemistry*; D015034:Zinc Oxide / Q000737:chemistry*
D003102:Colloids; D008567:Membranes, Artificial; D011091:Polyesters; C033616:poly(lactide); D015034:Zinc Oxide
Chemical delivery; Controlled release; FRET; PLLA; Photocatalysis; Upconversion emission