Near-infrared photopolymerization assisted by upconversion nanophosphors for biomedical applications

We present the concept and the experimental demonstration of near-infrared photopolymerization assisted by specially designed upconversion nanophosphors. The principle of this technique is based on conversion of 980 nm laser irradiation to ultraviolet photons subsequently absorbed by photoinitiator. The nonlinearity of upconversion allows for activation of the process locally in the laser beam waist. This approach enables precise fabrication of 3D constructs directly in the volume of photocurable composition. Furthermore, the presented technique is suitable for polymerization of a wide range of photocurable resins as well as gelation of hydrogels for biomedical applications

Near-infrared photopolymerization assisted by upconversion nanophosphors for biomedical applications

We present the concept and the experimental demonstration of near-infrared photopolymerization assisted by specially designed upconversion nanophosphors. The principle of this technique is based on conversion of 980 nm laser irradiation to ultraviolet photons subsequently absorbed by photoinitiator. The nonlinearity of upconversion allows for activation of the process locally in the laser beam waist. This approach enables precise fabrication of 3D constructs directly in the volume of photocurable composition. Furthermore, the presented technique is suitable for polymerization of a wide range of photocurable resins as well as gelation of hydrogels for biomedical applications

Role of energy transfer in a nanoinitiator complex for upconversion-driven polymerization

Upconversion nanoparticle (UCNP)-driven polymerization attracts great attention due to the ability of near-infrared light to penetrate deeper into biological media and synthetic materials than ultraviolet or visible light. Despite significant progress, the limitation of near-infrared light-triggered polymerization is associated with a key element of the photocurable composition, a UCNP/photoinitiator complex or a nanoinitiator. To determine the impact of resonance energy transfer from UCNPs to photoinitiator (PI) and its effect on polymerization, we developed two different photocurable compositions consisting of the polyethylene glycol diacrylate (PEG-DA), ultraviolet- and blue-emitting NaYF4: Yb3+, Tm3+ UCNPs with hydrophobic surface combined with water-soluble or insoluble PI. We found that transfer energy in these nanoinitiators proceeds differently: in UCNP/water-soluble PI (lithium phenyl-2,4,6-trimethylbenzoylphosphinate or LAP), it occurs through the photon-mediated transfer while in UCNP/water-insoluble PI (2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone or Irgacure 369), it takes place via the non-radiative resonant energy transfer. The impact of these processes in homolytic decomposition of initiator is extremely important in terms of the precisely controlled fabrication of polymer structures. PEG-DA facilitates the affinity between hydrophilic and hydrophobic components of the photocurable composition, which provides UCNP-driven cross-linking of biopolymers such as methacrylated hyaluronic acid and gelatin. 3D structures were prototyped to demonstrate the one-step rapid procedure of nanoinitiator preparation and emphasize the control of the energy transfer in UCNP/PI complexes for further development of UCNP-driven polymerization

High-resolution 3D photopolymerization assisted by upconversion nanoparticles for rapid prototyping applications

Abstract Three-dimensional (3D) rapid prototyping technology based on near-infrared light-induced polymerization of photocurable compositions containing upconversion nanomaterials has been explored. For this aim, the rationally-designed core/shell upconversion nanoparticles NaYF4:Yb3+,Tm3+/NaYF4, with the distinct ultraviolet-emitting lines and unprecedentedly high near-infrared to ultraviolet conversion efficiency of $${\eta }_{{\bf{UC}}}^{({\bf{UV}})}=2{\boldsymbol{ \% }}$$ ηUC(UV)=2% have been used. The upconverted ultraviolet photons were capable to efficiently activate photoinitiators contained in light-sensitive resins under moderate intensities of NIR excitation below 10 W cm−2 and induce generation of radicals and photopolymerization in situ. Near infrared-activated polymerization process, both at the millimeter and sub-micron scales, was investigated. Polymeric macro- and microstructures were fabricated by means of near infrared laser scanning photolithography in the volume of liquid photocurable compositions with focused laser light at 975 nm wavelength. Examination of the polymerization process in the vicinity of the nanoparticles shows strong differences in the rate of polymer shell growth on flat and edge nanoparticle sides. This phenomenon mainly defines the resolution of the demonstrated near infrared - ultraviolet 3D printing technology at the micrometer scale level

Upconversion Nanoparticles Intercalated in Large Polymer Micelles for Tumor Imaging and Chemo/Photothermal Therapy

Frontiers in theranostics are driving the demand for multifunctional nanoagents. Upconversion nanoparticle (UCNP)-based systems activated by near-infrared (NIR) light deeply penetrating biotissue are a powerful tool for the simultaneous diagnosis and therapy of cancer. The intercalation into large polymer micelles of poly(maleic anhydride-alt-1-octadecene) provided the creation of biocompatible UCNPs. The intrinsic properties of UCNPs (core@shell structure NaYF4:Yb3+/Tm3+@NaYF4) embedded in micelles delivered NIR-to-NIR visualization, photothermal therapy, and high drug capacity. Further surface modification of micelles with a thermosensitive polymer (poly-N-vinylcaprolactam) exhibiting a conformation transition provided gradual drug (doxorubicin) release. In addition, the decoration of UCNP micelles with Ag nanoparticles (Ag NPs) synthesized in situ by silver ion reduction enhanced the cytotoxicity of micelles at cell growth temperature. Cell viability assessment on Sk-Br-3, MDA-MB-231, and WI-26 cell lines confirmed this effect. The efficiency of the prepared UCNP complex was evaluated in vivo by Sk-Br-3 xenograft regression in mice for 25 days after peritumoral injection and photoactivation of the lesions with NIR light. The designed polymer micelles hold promise as a photoactivated theranostic agent with quattro-functionalities (NIR absorption, photothermal effect, Ag NP cytotoxicity, and Dox loading) that provides imaging along with chemo- and photothermal therapy enhanced with Ag NPs