Recent advances on water-soluble photoinitiators of polymerization

Vat photo-polymerization 3D printing of gradient scaffolds for osteochondral tissue regeneration

In recent decades, osteochondral (OC) tissue regeneration has been one of the major challenges in regenerative medicine. The absence of blood vessels, lymphatic vessels, and nerves in OC tissue prevents self-repair, while the structural complexity and differences between bone and cartilage layers make conventional surgical treatments largely ineffective. To address this issue, tissue engineering has emerged as a promising approach to replacing damaged OC tissue, with a particular focus on innovative strategies such as the design of continuous gradient scaffolds that mimic the complex architecture of native OC tissue. In this review vat photopolymerization (VPP) 3D printing technologies are presented as one of the most effective methods for fabricating gradient scaffolds for OC tissue repair. By leveraging photochemical reactions and light-assisted techniques, such as digital light processing (DLP), stereolithography (SLA) and two-photon polymerization (2-PP), highly precise porous structures made of biocompatible photo-crosslinkable resins have been successfully fabricated, with several relevant examples reported herein. DLP, SLA and 2-PP have proven fundamental in creating compositional, architectural, and mechanical gradients within scaffolds. Moreover, scaffold functionalization with bioactive molecules has demonstrated effectiveness in repairing damaged OC tissue in both in vitro and in vivo conditions. Moreover, the adoption of modeling tools such as the design of experiments (DoE) approach and AI-driven computational methods has proven to be valuable in optimizing the fabrication process and enhancing scaffold designs to more closely replicate the architecture and functionality of osteochondral tissues. STATEMENT OF SIGNIFICANCE: Despite the transformative potential of vat photopolymerization (VPP) techniques, such as stereolithography (SLA) and digital light processing (DLP), for developing high-precision gradient 3D scaffolds for osteochondral (OC) tissue repair, achieving full biomimetic restoration remains a significant challenge. This review offers a comprehensive analysis of advancements in VPP, detailing how these techniques enable precise control over scaffold composition, architecture, and mechanical properties to closely replicate the complex structure of OC tissue. Furthermore, it underscores the critical need for standardized protocols and long-term evaluations in scaffold development. Addressing these gaps is essential to advancing the clinical translation of VPP-based scaffolds, paving the way for more effective treatments for OC tissue damage.

High-Performance Sunlight-Induced Polymerized Hydrogels and Applications in 3D and 4D Printing

Currently, there are only few reports on water-soluble photoinitiating systems. In this study, a highly water-soluble organic dye i.e. sodium (E)-3,3'-((4-(2-(3-methylbenzo[d]thiazol-3-ium-2-yl)vinyl)phenyl)azanediyl)dipropionate iodide, was synthesized and served as a photoinitiator. Notably, this water-soluble initiator, at a low concentration of just 0.01 wt%, demonstrates a high photoinitiation ability, with some hydrogel formulations achieving nearly 100% double bond conversion under sunlight. Photopolymerization kinetics were monitored using Real-Time Fourier Transform Infrared. To explore the complex chemical principles of radical polymerization, UV-visible absorption and fluorescence spectroscopy, steady-state photolysis, fluorescence quenching experiments and cyclic voltammetry were employed to gain a comprehensive understanding of the photochemical mechanism involved. Additionally, several characteristics of the synthesized hydrogels were also investigated i.e. the water content, the water swelling, and the volume swelling. In addition to their excellent photoinitiation capabilities, the hydrogel formulations developed in this study also supported 3D printing. 3D objects with smooth surface and a high spatial resolution could be successfully printed using direct laser writing. The fabricated hydrogels could reversibly change of shape in response to water (adding or removing water), enabling successful 4D printing behavior. Furthermore, the efficient photoinitiation ability of the water-soluble formulations opens new avenues for sunlight-polymerized hydrogels and potential applications in bioprinting.

Exploiting Visible-Light Induced Radical to Cation Transformation Pathway for Reactivity Enhanced Electrophilic Aromatic Substitution Polymerization of Heteroaromatics

A straightforward approach is employed to synthesize methylene-bridged poly(hetero aromatic)s based on furan, pyrrole, thiophene, and thiophene derivatives. The process involves an electrophilic aromatic substitution reaction facilitated by a visible light-initiated system consisting of manganese decacarbonyl and an iodonium salt. The approach mainly relies on the formation of halomethylium cation, the attack of this cation to heteroaromatic, regeneration of methylium cation on the heteroaromatic, and reactivity differences between halomethylium and heteroaromatic methylium cations for successful polymerizations. This innovative synthetic strategy lead to the formation of polymers with relatively high molecular weights as the stoichiometric imbalance between the comonomers increased. Accordingly, these newly obtained polymers exhibit remarkable fluorescence properties, even at excitation wavelengths as low as 330 nm. Moreover, by harnessing the halogens at chain ends of homopolymers, block copolymers are successfully synthesized, offering opportunities for tailored applications in diverse fields.