UC San Diego

In recent years, Polydopamine (PDA) materials have garnered substantial attention inthe fields of chemistry and materials science due to their adaptable properties, which encompass metal-ion chelation, facile functionalization, strong adhesion, and the capacity for scavenging free radicals. Created through the autoxidation of dopamine precursor, polydopamine emerges as a nanomaterial suspendable in colloidal form. Initially conceived as a versatile biomimetic coating akin to the adhesive foot protein found in mussels, PDA later evolved into nanoparticles suitable for scavenging free radicals and serving as contrast agents in biomedical applications, with its uses continuously expanding. At present, PDA nanoparticles offer flexibility in their size, ranging from ten to several hundred nanometers. Size tunability is used as a means to add to the already considerable control over PDA structure-function and enhancing its immense potential across diverse fields. In chapter 2, the controlled synthesis of amorphous, organic, bio-inspired polydopamine (PDA) nanoparticles in varying atmospheric conditions was investigated. Specifically, we examine the role of oxygen (O2) partial pressure on PDA particles' distribution during the synthesis process. Our systematic exploration reveals that precise control of O2 content significantly impacts the quality, speed, and reliability of PDA nanoparticle production. Results indicate that 40% or higher O2 compositions lead to superior outcomes, including reduced polydispersity index (PDI) values and enhanced reproducibility. Notably, introducing an 80% O2 composition significantly accelerates the reaction, reducing the synthesis time from the typical 24 h under ambient conditions to just over 30 min. This breakthrough suggests the potential for large-scale or continuous reaction schemes, offering substantial time and resource savings for applications involving PDA nanoparticles and similar materials. In chapter 3, a multifaceted exploration of PDA is presented, starting with the synthesis of a diverse spectrum of PDA nanoparticle sizes ranging from dPDA = 29 to 731 nm, followed by the determination of average particle mass. Establishing a correlation between particle mass and volume led to a linear fit represented by the equation ? = 1.5 × 10^(-21)x with R^(2) value of 0.981. Subsequently, the chapter detailed the fabrication process of PDA-chitosan thin films, assessing their purity, optical quality, and the potential influence of bubbles and aggregate formations on the overall spectra. With a consistent film homogeneity between 99.8% and 98.3% with increased PDA concentration, fundamental trends observed in the spectra were consistent throughout. The study further explored the impact of composite materials in fundamental studies and potential applications of PDA-chitosan films for radiation protection across the UV to NIR spectrum. It was revealed that PDA was most effective at shorter wavelengths with higher energies, while chitosan and water exhibited greater influence at longer wavelengths with lower energies, rendering the composite material effective across a broad range of wavelengths. Moreover, the chapter highlighted the advantageous attributes of chitosan, including its antimicrobial properties, flexibility, and rehydration capabilities, positioning PDA-chitosan films as strong contenders for applications in wound healing. Lastly, the investigation showcased the versatility of PDA and its adaptability to various polymer matrices with different polarities. The successful introduction of PDA into resin, followed by 3D printing and polishing, resulted in the creation of transparent materials with designer structures. The chapter proposes expanding this project to create a more extensive collection of composite materials, aiming to deepen the understanding of PDA and increase their accessibility in our daily lives.