Chapter 1: The Unlikely Pairing of Silk and Diamonds

Silk, an age-old natural fiber, is proving to be remarkably versatile in the field of medicine, especially when paired with diamonds.

Asma Khalid, who enjoys the elegance of silk dresses and appreciates the allure of diamonds, never anticipated that these materials would become pivotal in her work as a physicist. However, they have indeed opened avenues for advanced imaging techniques and drug delivery systems. While pursuing her PhD at the University of Melbourne, Khalid explored the potential of nano-diamonds—tiny particles of carbon structured in a crystal formation, measuring less than a millimeter. Their inert nature and remarkable light-emitting qualities make them promising candidates for applications in biology, particularly in diagnostic imaging and sensing.

"We discovered that nano-diamonds exhibit fluorescence, glowing vividly when exposed to laser light. However, their rough surfaces often cause them to clump together, leading to inconsistent fluorescence," explained Khalid, now a postdoctoral researcher at RMIT University and an associate investigator at the Centre for Nanoscale BioPhotonics (CNBP). "To enhance their surface and optical characteristics, we experimented with coating them in a biocompatible material—silk."

Section 1.1: The Historical Significance of Silk

Silk's origins trace back over 12,000 years to the Yangshao culture near China's Yellow River. The most recognized variety is derived from the cocoons of the mulberry silkworm, which is farmed under controlled conditions. The fiber's lustrous quality is attributed to its prism-like structure, which refracts light in various angles, producing a spectrum of colors. Khalid noted that silk is non-toxic and compatible with living tissues, as it consists entirely of proteins and amino acids. "Silk significantly enhances the brightness of nano-diamonds. When we implanted a silk-coated hybrid in mice, we observed that the silk dissolved naturally without inducing inflammation."

Her findings, published in Biomedical Optics Express, garnered considerable interest, leading to a scholarship at Professor Fiorenzo Omenetto's Silk Lab at Tufts University in Boston. This lab has been at the forefront of incorporating silk into photonics and biotechnology. "I learned how to extract silk from cocoons and convert the liquid silk into various structures, such as implantable films and 3D printed frameworks for biomedical applications," she recounted.

Chapter 2: Exploring New Frontiers with Silk

In the first video, "One more technique on how to Paint Silk without Resist (Gutta) ORNAMENT - YouTube," viewers can learn how to manipulate silk fabric in creative ways, illustrating the material's versatility beyond medicine.

Khalid established her own lab at the CNBP's RMIT node, focusing on the production of liquid silk nanoparticles from cocoons. This included creating fiber coatings and electrospun membranes—sheets of interlinked pores suitable for health monitoring applications.

At the same time, Dr. Jiawen Li, a biomedical engineer from the University of Adelaide’s CNBP node, was experimenting with new ultra-thin fibers capable of taking measurements deep within living organisms, rather than relying on excised samples.

"The goal is to determine the nature of a tumor deep in the lung by measuring pH, oxygen, carbon dioxide, or other specific molecules without needing a biopsy," she described. "Instead of drawing blood to analyze calcium or glucose levels, we aim to insert extremely thin optical fibers, smaller than a human hair, to take localized measurements in real-time without waiting for lab results."

The fibers required protective sheathing to prevent chemical interactions with living tissues. Li was initially exploring synthetic polymers but faced challenges due to the harsh chemicals often needed for measurement accuracy. "These chemicals could interfere with the data we were trying to collect," he noted.

Khalid proposed using silk for coating Li's optical fibers, leading to successful tests for biosensing and bioimaging in mice. "It was surprisingly simple," Li remarked. "Silk is completely biocompatible and is not recognized as a foreign body. The process of adding sensors to the fiber can be done at room temperature by merely dipping the fiber into a solution for 30 seconds."

The next hurdle involved ensuring that biomarkers remained attached to the silk during incorporation. Organic chemists Aimee Horsfall and Patrick Capon from the CNBP's biosensors group joined the initiative. "We needed to assess the durability of the system," Horsfall explained. "If we insert the fiber into a body to reach an organ or tumor, will the biomarkers stay attached and function correctly?"

After attempting various methods, they shifted their focus to finding a bonding peptide to secure the sensors to the silk. After immersing the fiber in a silk and sensor mixture, followed by a brief exposure to methanol, they significantly improved bonding. "This process alters the silk structure, making it more crystalline and enhancing adhesion to the fiber," Capon explained.

With proven sensor attachment, the team is expanding their work beyond pH sensors to include hydrogen peroxide sensors for assessing sperm cell health and metal ion sensors for fertility applications. Silk is clearly emerging as an essential component in optical fiber sensor technology.

"We have much work ahead, but we're thrilled about the possibilities," Horsfall stated. Capon added, "Every time we discuss our findings, we come up with new ideas. How many sensors can we integrate into a fiber? What needs exist that biologists or clinical staff are looking to address?"

Meanwhile, Khalid is broadening her research into silk-coated fluorescent nanoparticles for cancer imaging in partnership with CNBP's Macquarie University node in Sydney. She is also developing silk-coated magnetic particles for brain imaging and collaborating with the University of Melbourne to create metal oxide-silk nanoparticles for cellular imaging.

Khalid is also working on innovative hybrid silk materials aimed at overcoming current challenges in wound and burn care technologies. "I always thought of silk as merely a fabric," she reflected. "However, my research revealed its long-standing use in medicine, particularly in sutures. While silk and diamond may seem luxurious, they offer remarkable optical characteristics and significant advantages in healthcare."

In the second video, "Learning About Fabrics 3: Identifying Silk Fabrics - YouTube," viewers can deepen their understanding of silk fabrics, highlighting their significance in both fashion and technology.

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