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Project titleNear-infrared 3D photopolymerization assisted with upconversion nanoparticles: towards subsurface and in situ rapid prototyping applications

Research area 09 - ENGINEERING SCIENCES, 09-205 - Development of new structural materials and coatings

KeywordsPolymerization, NIR light, upconversion, 3D structure, nanoparticle, microstructure, prototyping

Annotation
Today the process of photopolymerization is widely used in various fields of science, industry and technology, namely: 3D laser drawing, microprocessing, holography, micro- and optoelectronics, formation of optical elements, recording and storage of data, etc. Typically, the photopolymerization process involves the conversion of a liquid mixture of a photopolymerizable monomer or a crosslinkable polymer containing photoinitiator (called a photocurable composition-PC) into a solid material upon irradiation. Most photopolymerizable materials are sensitive to ultraviolet radiation. However, the use of ultraviolet radiation imposes limitations on a number of applications. So, for example, in biomedical applications, ultraviolet (UV) light can not penetrate deeply into the biotissue and, if the threshold dose of irradiation is exceeded, leads to damage to the biomaterial. Optical information is recorded, UV light can shorten the life of the medium at optical information reordering. In addition, single-photon UV polymerization is limited to the production of 2D structures due to the exponential absorption of light into the PC and requires the development of special systems to overcome this limitation. Compared with ultraviolet light, near infrared (IR) light is better suited for biomedical applications, the formation of three-dimensional (3D) structures and recording and storage of information. IR light causes less photodamage and is able to penetrate deeper into biotissues and polymeric materials. The discovery of a method of launching photoreactions using IR light, due to two-photon absorption, provided a qualitative leap in the development of technology. The development of two-photon photopolymerization technology allows growing 3D structures according to a given program directly in the PC volume with an unprecedented high spatial resolution. However, expensive instruments (femtosecond lasers), high laser intensities and the raster nature of 3D structures formation hamper the wide use of this technology. Recently, in several pioneering works, including the authors of the project, a new effective approach was demonstrated, based on the use of upconversion materials for the initiation of photoreactions by IR light. The unique optical properties of the upconverting materials are the result of the consecutive absorption of photons and energy transfer processes within the matrix of an inorganic crystal, codoped with lanthanide ions. As one of the most effective nanomaterials with the effect of upconversion, nanoparticles NaYF4, which are codoped with Yb3 +, and Er3 + or Tm3 + are considered. These nanoparticles have narrow photoluminescence lines in the UV and visible spectral ranges with high quantum efficiency at moderate intensity of the exciting IR radiation. Nanoparticles are capable to resonantly transferring excitation energy to photoinitiators and triggering the reactions by IR light. The authors of the project aim to study the process of photopolymerization activated by near-IR light to for fast 3D prototyping applications. We will solve the following tasks: 1. Synthesis of upconverting nanoparticles possessing the necessary set of photophysical and chemical characteristics, which will be measured with the help of specially developed unique equipment. Nanoparticles will be developed to provide an unprecedentedly high conversion efficiency of IR radiation at moderate intensity (up to 5 W / cm2) in the UV photoluminescence lines. The unique luminescent properties of synthesized nanomaterials will allow us to demonstrate the process of IR induced polymerization both on macro- and micro scales using commercially available photocompositions. 2. Molecular design of the nanoparticles surface that will provide colloidal stability of nanoparticles in the PC and creation of supramolecular complexes based on nanoparticles, in which the Forster resonance transfer of nanoparticles photoexcitation energy to photoinitiator molecules is realized. It is expected that such structures due to nonradiative resonance energy transfer will reduce the dose of IR radiation to initiate the photopolymerization reaction. 3. Investigation of the polymerization process in the vicinity of the upconversion nanoparticles. It is expected that new data on the photophysics of upconversion nanoparticles will be obtained, the maximum resolution of 3D-printing technology will be determined and "self-assembling" nanostructures will be created, the polymer shell can be filled, for example, with drugs and bioactive molecules. 4. Formation of 3D structures in the depth of weakly absorbing near-IR light materials, including biotissues. It is expected that in the final stage of the project we will demonstrate the cross-linking of biocompatible polymers under a phantom mimicking the biotissue properties. Thus, it can be concluded that combining the possibilities of converting near-IR light into UV photons by upconversion nanomaterials and photopolymerization of photosensitive compounds opens a new direction in the development of a cost-effective innovative 3D printing technology.

Expected results
Within the framework of the project, the 3D prototyping technology of photocurable compositions activated by near-IR light, containing upconverting nanoparticles and creating "self-assembling" nanostructures will be investigated and developed. The following most significant scientific results will be obtained: 1) Nanoparticles will be synthesized providing an unprecedentedly high conversion efficiency of exciting IR radiation of moderate intensity (up to 5 W/cm2) in the UV photoluminescence line. The unique luminescent properties of synthesized nanomaterials will allow us to demonstrate the process of IR induced polymerization both on macro- and micro scales using commercially available photocompositions. 2) A molecular design of the nanoparticle surface will be developed to ensure the colloidal stability of nanoparticles in the PC. Supramolecular complexes based on upconversion nanoparticles will be obtained, in which the Forster resonance transfer of nanoparticles photoexcitation energy to photoinitiator molecules is realized. It is expected that such structures due to nonradiative resonance energy transfer will reduce the dose of IR radiation to initiate the photopolymerization reaction. 3) The process of photopolymerization in the vicinity of individual upconversion nanoparticles will be investigated. It is expected that new data on the photophysics of upconversion nanoparticles will be obtained, since the polymerization process will allow to "fix" the distribution of PL intensity in the near field. The maximum resolution of 3D printing technology, the required concentrations of nanoparticles in the PC, the formation of the voxel when focusing the IR light in a medium with inclusions of a nonlinear optical material, the dose of laser radiation, etc. will be studied. "Self-assembling" nanostructures will be obtained, the polymer shell of which can be filled, for example, drugs and bioactive molecules. 4) For a given program 3D structures will be formed in the depth of materials with a low IR extinction coefficient, including biotissues. It is expected that the final stage of the project we will demonstrate the cross-linking of biocompatible polymers under a phantom mimicking the biotissue properties.

Annotation of the results obtained in 2020
During the reporting period, the following scientific results were achieved: 1) Nanoparticles with an active core / inert shell structure were synthesized, providing a high conversion efficiency of exciting IR radiation of moderate intensity into a UV photoluminescence line. On the platform of synthesized nanoparticles, nanocomplexes of the form of an upconverting nanoparticle-photoinitiator were created, where Irgacure 369 and LAP (lithium phenyl-2,4,6-trimethylbenzoylphosphinate) were used as photoinitiators. Complexes based on upconverting nanoparticles were obtained, in which the Förster resonance transfer of the photoexcitation energy of nanoparticles to photoinitiator molecules is realized. It was shown that in nanocomplexes the transfer of IR photoexcitation energy from upconverting nanoparticles to photoinitiator molecules occurs, followed by the formation of radicals initiating the polymerization process. 2) The process of photopolymerisation of oligocarbonate methacrylate was investigated with the introduction of upconverting nanoparticles below the percolation threshold. Under the action of light with a wavelength of 975 nm, polymer structures were formed directly in the volume of the photocomposition. It was shown that two types of ordered objects from upconverting nanoparticles are formed in the structures: microspheres and superlattices in the form of sheets. A qualitative explanation of these processes is given. The possibility of forming coupled structures under such conditions with a tendency to a decrease in the resolution of the method is shown. 2) The process of photocrosslinking of biocompatible polymers, namely polyethylene glycol diacrylate and methacrylated hyaluronic acid, has been investigated. In biopolymers using two types of photoinitiators, the dependence of the voxel volume (the minimum polymerized volume) on the radiation power density at a wavelength of 975 nm and the concentration of nanoparticles in the photocomposition was studied. It has been shown that to obtain an increased spatial resolution, it is preferable to use a nanoconstruction with Irgacure 369, and for better filling of the volume, it is better to use upconverting nanoparticles with the inclusion of LAP. 3) The survival and growth of cells (immortalized human fibroblasts BJ-5ta) in the photopolymerized construct was assessed for several days. Evaluation of cell morphology was performed using light / fluorescence microscopy, and a colorimetric test for cell viability was carried out, which made it possible to measure the dynamics of cell viability in the construct. It was shown that by the 7th day of cultivation, the cells fill almost the entire surface of the formed structures available for growth, while the resulting constructs retained their shape in the culture medium during the entire study period. Obtaining constructs with such characteristics means the possibility of moving from in vitro studies to in vivo experiments in order to study the possibility of in situ polymerization. 4) A system for laser 3D photocrosslinking of biocompatible polymers under a layer of biological tissue has been created. The process of structure formation under the influence of IR radiation is demonstrated. To obtain an increased spatial resolution, an optical clearing agent, glycerin, was used. It is shown that, in spite of the deterioration of the resolution, it is possible to reproduce the shape of the object under in situ conditions.

Publications

1. Demina P.A. , Sholina N.V., Akasov R.A., Khochenkov D.A., Arkharova N.A., Nechaev A.V., Khaydukov E.V., Generalova A.N. A versatile platform for bioimaging based on colominic acid-decorated upconversion nanoparticles BIOMATERIALS SCIENCE, Том: 8 Выпуск: 16 Стр.: 4570-4580 (year - 2020) https://doi.org/10.1039/D0BM00876A

2. Sajti L., Karimov D.N., Rocheva V.V. , Arkharova N.A. , Khaydukov K.V. ,Lebedev O.I. , Voloshin A.E., Generalova A.N. , Chichkov B.N., Khaydukov E.V. Pulsed laser reshaping and fragmentation of upconversionnanoparticles – from hexagonal prisms to 1D nanorods through“Medusa”-like structures Nano Research, - (year - 2020) https://doi.org/10.1007/s12274-020-3163-4

3. Demina P.A. , Sholina N.V., Nechaev A.V., Asharchuk I.M. , Grigoriev Y.V., Khaydukov E.V., Generalova A.N. Поверхностная модификация наночастиц с антистоксовой люминесценцией в процессе полимеризации, фотоиндуцируемой ИК-светом,для создания тераностических нанокомплексов Перспективные направления физико-химической биологии и биотехнологии Сборник тезисов XXXI зимней молодежной научной школы, С. 144 (year - 2020)

4. Demina P.A., Khaydukov К.V., Sochilina A.V., Savelyev A.G., Rocheva V.V., Archarova N.A., Nechaev A.V., Khaydukov E.V., Generalova A.N. Получение биосовместимых наноконструкций с использованием нанокристаллов с антистоксовой флуоресценцией для инициирования реакции фотополимеризации Перспективные направления физико-химической биологии и биотехнологии Сборник тезисов XXXII зимней молодежной научной школы, C. 156 (year - 2020)

Annotation of the results obtained in 2018
In this year, the following main results have been obtained: 1) Nanoparticles with the active core / inert shell and active core / active shell structures were synthesized, providing high conversion efficiency of the exciting IR radiation of moderate intensity into the UV photoluminescence lines. It was shown that nanoparticles possess an enhanced quantum yield (~ 8%) under excitation intensity of 10 W / cm2. The presence of an active shell in nanoparticles will allow us in future to investigate qualitatively two different mechanisms for initiating a polymerization reaction: the case of nonradiative energy transfer from nanoparticles to photoinitiator molecules and the case of radiative energy transfer in such systems. 2) The system was created for 3D laser prototyping in order to demonstrate the formation of a 3D polymer structure in the volume of a photocomposition (PC) containing upconverting nanoparticles. The system is equipped with a semiconductor laser with a wavelength of 975 nm and galvanoscanner to deflect the laser beam in the X-Y plane. The movement of the voxel along the z-coordinate was realized using a motorized micrometric movement. A program code was developed to produce structures with the desired geometry and to manage the parameters of the experiment. 3) A molecular design of the surface of nanoparticles has been developed, providing their colloidal stability in FC. Complexes based on upconverting nanoparticles, in which the Förster resonance photoexcitation energy transfer from nanoparticles to photoinitiator molecules is realized, have been obtained. 4) The unique luminescent properties of the synthesized nanomaterials allowed us to demonstrate the process of IR-induced polymerization both at the macro and micro scales using commercially available photocompositions. Under the action of light at 975 nm wavelength, polymeric 3D structures were formed directly in the volume of the photocomposition. 5) To understand deeply the process of formation of structures in a photopolymer initiated by up-conversion of nanoparticles, a voxel formation process in a medium with uniformly distributed nanoparticles was theoretically considered. The percolation theory explaining the concentration threshold for the formation of 3D structures during IR-induced polymerization was investigated.

Publications

1. Sochilina A.V., Savelyev A.G., Demina P.A., Sizova S.V., Zubov V.P., Khaydukov E.V. Generalova A.N. Quantitative detection of double bonds in hyaluronic acid derivative via permanganate ions reduction Measurement Science and Technology, MST-108220.R1 (year - 2019) https://doi.org/10.1088/1361-6501/ab0fb4

2. Sochilina A.V., Savelyev A.G., Sholina N.V., Karimov D.N., Nechaev A.V., Khaydukov E.V., Generalova A.N. Nanohybrid scaffolds with luminescent remote control EPJ Web of Conferences, V. 190, Article Number 04022 (year - 2018) https://doi.org/10.1051/epjconf/201819004022

Annotation of the results obtained in 2019
Upconversion nanoparticles with an active core and inert shell structures were synthesized with intense photoluminescence lines in the visible and ultraviolet spectral ranges when excited by radiation with a wavelength of 975 nm. Due to core / shell technology and sequential monitoring of the synthesis parameters, it was possible to achieve an integral conversion coefficient of 1-2% at an excitation intensity of ~ 5 W / cm2. The unique luminescent properties of the synthesized nanomaterials allowed us to lower the dose of infrared radiation to initiate the radical photopolymerization reaction and to demonstrate the formation of structures under a phantom simulating the scattering and absorption coefficients of biological tissue. The system for 3D laser prototyping with near-infrared light has been improved. An optical microscope was integrated into the system, which allows visual inspection during the formation of structures in photocurable compositions. Using this system, 3D printing resolution was studied, optimal concentrations of up-converting nanoparticles in various photocompositions were found, voxels were studied, shapes and volume of minimal objects depending on the dose of laser radiation were studied, etc. The system is controlled by program code, which is necessary to create structures with the desired geometry and control experiment parameters. During the reporting period, two key technologies of the proposed method were demonstrated, namely, the formation of structures in the volume of the photocomposition and polymerization in the vicinity of single nanoparticles. The method of surface modification of upconverting nanoparticles (ANCs) by PEG molecules was demonstrated. The possibility of the formation of supramolecular structures based on UCNPs by self-assembly in emulsion droplets was demonstrated. Low radiation intensity, short irradiation time and the ability to adapt the technique are the advantages that are able to provide a one-stage assembly of nanoconstructions with desired characteristics for specific tasks. 3D microstructures obtained in the volume of photocompositions during polymerization induced by near-IR light were demonstrated. Photopolymerization were performed in an initially homogeneous reaction mixture containing up-converting nanoparticles above and below the percolation threshold. It was shown that the resolution of the method substantially depends on the concentration of nanoparticles in the photocomposition. An explanation was given for this mechanism. The cross-linking process of hydrogels based on methacrylated hyaluronic acid containing up-conversion nanoparticles was studied under the influence of IR radiation, as a promising material for the formation of structures directly in a living organism. Cellular structures were formed, and cytotoxicity assays were performed.

Publications

1. Ivan V. Krylov, Roman A. Akasov, Vasilina V. Rocheva, Natalya V. Sholina, Dmitry A. Khochenkov, Andrey V. Nechaev, Nataliya V. Melnikova, Alexey A. Dmitriev, Andrey V. Ivanov, Alla N. Generalova and Evgeny V. Khaydukov Local overheating of biotissue labeled with upconversion nanoparticles under Yb3+ resonance excitation Frontiers in Chemistry, Front. Chem. 8:295 (2020). doi: 10.3389/fchem.2020.00295 (year - 2020) https://doi.org/10.3389/fchem.2020.00295

2. Polina Demina, Natalya Arkharova, Ilya Asharchuk, Kirill Khaydukov, Denis Karimov, Vasilina Rocheva, Andrey Nechaev, Yuriy Grigoriev, Alla Generalova, Evgeny Khaydukov Polymerization Assisted by Upconversion Nanoparticles under NIR Light MOLECULES, Том: 24, Выпуск: 13, Номер статьи: 2476 (year - 2019) https://doi.org/10.3390/molecules24132476

3. Kirill V. Khaydukov, Alexander G. Savelyev, Andrey V. Nechaev, Alla N. Generalova, Denis N. Karimov, Evgeny V. Khaydukov Upconversion nanoparticles for IR-induced laser photopolymerization of 3D structures Single-Molecule Sensors and NanoSystems International Conference, April 3-5, 2019, Book of abstracts, стр. 135 (year - 2019)

4. Polina A. Demina, Natalia V. Sholina, Ilya M. Asharchuk, Yuriy V. Grigoriev, Denis N. Karimov , Natalya A. Arkharova, Dmitry A. Khochenkov, Roman A. Akasov, Andrey V. Nechaev, Alla N. Generalova, Evgeny V. Khaydukov Upconversion nanoparticles as biocompatible visualizing nanosystems Single-Molecule Sensors and NanoSystems International Conference, April 3-5, 2019, Book of abstracts, Стр. 6 (year - 2019)