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3D-Printed Nanocrystals for Oral Administration of the Drugs
Published in Yasser Shahzad, Syed A.A. Rizvi, Abid Mehmood Yousaf, Talib Hussain, Drug Delivery Using Nanomaterials, 2022
Lucía Lopez-Vidal, Daniel Andrés Real, Alejandro J. Paredes, Juan Pablo Real, Santiago Daniel Palma
Developed in 1986, it was the first technique to be used to obtain solid dosage forms (Jain et al., 2018; Wang et al., 2016). In this technique, a UV laser is used to solidify a photopolymerizable polymer solution. The interaction of photoinitiator molecules with ultraviolet light results in the release of free radical molecules that initiate polymerization (Figure 5.11). This technique has the advantage of producing high-resolution objects at room temperature. At the moment, only a few materials can be used with this technique, as is limited to photosensitive polymers only. Due to its biocompatibility and efficient photopolymerization process, the most commonly used polymers are polyethylene glycol diacrylate (PEGDA) and gelatin methacrylate (GELMA) (Zhang et al., 2020). In contrast, many widely used pharmaceutical excipients cannot be printed or must be combined with such polymers, or chemically modified with photosensitive groups. For example, Shen et al. were able to develop a method for printing chitosan by digital light processing (DLP) (Shen et al., 2020). For this, they synthesized a photocurable chitosan derivative by using methacrylic anhydride.
Additive Manufacturing and Its Polymeric Feedstocks
Published in Antonio Paesano, Handbook of Sustainable Polymers for Additive Manufacturing, 2022
The feedstock materials for VP must contain, as mentioned earlier:A reactive, UV-curable monomer or oligomer or a blend of them that crosslink and polymerize into a solid object.A photoinitiator or a blend of them that is degraded when exposed to the light source, and forms radicals, cations, or carbene-like species that activate the process of polymerization (Bartolo 2011). Bagheri and Jin (2019) published a comprehensive and detailed list of photoinitiators with names, chemical structure, wavelength, and references, including among others:For UV light: benzophenone, diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxideFor visible light: camphorquinone, bis(4-methoxybenzoyl)diethylgermanium.
Resin-Based Composites in Dentistry—A Review
Published in S. M. Sapuan, Y. Nukman, N. A. Abu Osman, R. A. Ilyas, Composites in Biomedical Applications, 2020
Z. Radzi, R. A. Diab, N. A. Yahya, M. A. G. Gonzalez
A photoinitiator is a molecule that can absorb light and, as a result, either directly or indirectly, generate reactive radicals that can initiate polymerization (Fouassier, 1995). Hence, the photoinitiator is a compound that can transform the physical energy of light into suitable chemical energy in the form of reactive intermediates (Figure 4.4). Photoinitiators can be classified into Norrish Type I and II initiators. Norrish Type I initiators are typically compounds containing benzoyl groups, which undergo cleavage when exposed to visible light to generate two free radicals where at least one the free radicals reacts with monomers to initiate polymerization. They do not require a co-initiator to produce free radicals. However, Norrish Type II initiators absorb visible light to form excited molecules, which abstract a hydrogen atom from a donor molecule (synergist). The donor then reacts with a monomer to initiate polymerization. Photoinitiators are incorporated in dental RBCs to start the polymerization reaction.
Rapid preparation and performance of degradable ceramic scaffolds based on stereolithography
Published in Journal of Asian Ceramic Societies, 2022
Suocheng Song, Zongqiang Gao, Haiman Xu, Chonggao Bao, Bingheng Lu, Baochao Zheng, Wencai Dong, Haiqiang Ma
Under UV light, the photoinitiator generates free radicals or cations, thereby initiating the polymerization reaction. The additive amount of the photoinitiator has a great impact on the curing efficiency and SLCD. The solid content of the ceramic paste was 55vol.% and the additive amounts of the photoinitiator were 0.3 wt.%, 0.6 wt.% and 0.9 wt.%, respectively. Table 3 presents the SLCD of the ceramic paste under different exposure intensities. The SLCD first increased and then decreased with an increase in the additive amount of the photoinitiator. The optimal additive amount of the photoinitiator was 0.6 wt.%. According to the Beer-Lambert law, taking the lnE as the X-axis, the SLCD as the Y-axis, the software OriginPro was used to fit the data points in Table 3 (see Figure 12). However, the results in Figure 12 and Table 3 were contradictory. The main reason for this might be that when the photoinitiator was added too much, the light-curing speed of the ceramic paste surface was too fast. The cured layer on the surface prevented the UV light from continuing to penetrate the ceramic paste.
Cantilever beam shape control with light activated polymers using hierarchical particle swarm optimizer
Published in Mechanics of Advanced Materials and Structures, 2021
Yu Zhao, Shijie Zheng, Zongjun Li
Light activated polymers (LAPs) have some different forms. Liquid crystal elastomers (LCEs) [13] and [14], whose molecular structure is an elastomeric network consisting of photoisomerizable functionalities, are the earliest researched LAPs systems. Under the irradiation of ultraviolet light, LCEs can be reversibly changed during straight and bending states. Quite different from mechanism of LCEs, a novel series of LAPs coupled polymeric materials have been developed. According to the form of rearranging the polymer network topology via photochemistry, this kind of LAPs can be divided into two categories: light activated shape memory polymers (LASMPs) and photoactivated covalent adaptive network (pCAN) [15]. LASMPs developed by Lendlein et al. [16] and Jiang et al. [17] contains photo-tunable molecular crosslinks (PMC) [18]. Exposed to different wavelengths of ultraviolet light, the crosslinks can be produced (wavelength larger than 260 nm) or cleaved (wavelength less than 260 nm). From a macro perspective, when exposed to ultraviolet light at wavelength larger than 260 nm, the polymer can be deformed into a temporary shape. When the irradiated light at wavelength less than 260 nm, the polymer can recover its original shape. For pCAN developed by Scott et al., [19] its covalently-bonded network is altered due to the bond exchange reaction (BER) mechanism. Irradiation breaks embedded photoinitiator molecules into free radicals, and then these free radicals are rearranged as a result of the interaction of the polymer backbone. This chemical operation is defined as photo-induced network rearrangement (PNR) [18]. Macroscopically, this process leads to photo-induced stress relaxation under irradiation of particular wavelength light. In comparison with the LASMPs (PMC) material, pCAN (PNR) material is strongly dependent on the induced stress/strain and stress relaxation stimulated by irradiation. And for pCAN material, the control of interactions between materials and light becomes more convenient than that for LASMPs.
Digital light processing 3D printing of surface-oxidized Si3N4 coated by silane coupling agent
Published in Journal of Asian Ceramic Societies, 2022
Ping Yang, Zhenfei Sun, Shengwu Huang, Jun Ou, Qiangguo Jiang, Dichen Li, Shanghua Wu
Generally, the printing slurry contains ceramic particle, photosensitive resin and photoinitiator. During printing, ultraviolet light initiates photoinitiator to form free radical, and then the free radical induces photosensitive resin to activate photopolymerization. On the basis of the curing principle of DLP, a white-colored or light-colored ceramic with inborn low light absorption and low refractive index always exhibits good photocuring ability [25]. Consequently, various white-colored or light-colored ceramic parts have been successfully prepared by DLP, such as ZrO2 [20,26], Al2O3 [26], AlN [27], ZTA [28], etc. On the contrary, high light absorption and high refractive index are the innate characteristics of the gray-colored Si3N4 ceramic. As a result, it is difficult to fabricate Si3N4 parts by DLP, as well as has been reported rarely. In our previous research, we found that forming a SiO2 layer on the surface of Si3N4 ceramic via oxidation process can improve their photocuring ability by reducing the light absorption and refractive index of Si3N4 powder [29]. From this, Zou et al. [11] have successfully prepared complicated Si3N4 parts by this oxidation approach. Except for sufficient photocuring ability, the ceramic slurry for obtaining high-quality Si3N4 parts also requires high solid loading and low viscosity [30]. The high solid loading of slurry could provide enough strength for the green body and alleviate the shrink during debinding and sintering process, which is benefit to high-quality product without defects. On the other hand, the suitable viscosity enables the slurry to form a uniform and flat coating for printing, which can promote the homogeneous of Si3N4 ceramics. Nevertheless, there is a trade-off between the high solid loading and the low viscosity. Some approaches have been used to balance this issue. Liu et al. [31–33] found that the modified Si3N4 powder with KH560 can reduce the viscosity and promote stability of slurry because of the epoxy group of KH560 forms an ether covalent bond with the hydroxyl group of photosensitive resin. However, the modification by KH560 cannot enhance the photocuring behavior of the Si3N4 slurry. A desired slurry should simultaneously have abundant photocuring ability, high solid loading and low viscosity. Unfortunately, no one studied the intrinsic relationship of these problems at the same time.