Synthesis and Properties of Bombyx Mori Chitosan Nanoascorbate Complexes Based on Oligochitosan and High-molecular-weight Chitosan

In the quiet world of sericulture, where farmers raise silkworms to produce silk, a persistent challenge remains: keeping the delicate larvae healthy and productive. These insects are vulnerable to disease, and their growth can be stunted by environmental stress, leading to fewer and lighter cocoons. Scientists have long looked to nature for solutions, particularly to chitosan, a natural material derived from the shells of crustaceans or, in this case, the pupae of the mulberry silkworm itself. Chitosan is known for being safe, biodegradable, and capable of fighting off harmful microbes. However, in its raw form, it does not dissolve easily in water, which limits how it can be used. To make it useful, researchers often mix it with other substances, such as ascorbic acid, which is simply vitamin C. When these two materials interact, they can form tiny, water-soluble structures that might protect the silkworms better than the ingredients alone. The question for scientists is not just whether these mixtures work, but how to build them most effectively and whether the size or structure of these tiny particles changes how well they help the silkworms survive and thrive.

A researcher at the Institute of Polymer Chemistry and Physics in Uzbekistan set out to answer these questions by creating and testing new versions of these chitosan-vitamin C mixtures. They focused on two different ways to make the material. The first method involved taking high-quality chitosan from silkworm pupae and breaking it down into smaller pieces, known as oligochitosan, before mixing it with vitamin C. The second method used the larger, original chitosan molecules and combined them with vitamin C using a special cross-linking agent to hold the structure together. The goal was to see which method produced the most effective particles and to measure exactly how big these particles were and how they behaved in water.

The researcher found that the method used to create the mixture significantly changed the size of the resulting particles. When they used the smaller, broken-down chitosan without any extra stabilizing agents, the resulting particles were quite small, with an average size of about 117 nanometers. In contrast, when they used the larger, original chitosan and added a stabilizer to help the particles form, the resulting structures were much bigger, ranging between 360 and 380 nanometers. By looking at the particles under a powerful microscope called an atomic force microscope, the researcher could see the physical shape of these structures. The smaller particles appeared as tiny, flat objects on the surface, some less than 50 nanometers wide, while the larger particles formed more complex, aggregated shapes. These observations confirmed that the researcher had successfully created two distinct types of nanostructures, each with its own physical footprint.

Beyond just measuring size, the researcher wanted to know if these new materials actually worked better than the original ingredients. They tested the ability of these mixtures to stop the growth of a common fungus, Fusarium oxysporum, which can harm plants and animals. The results showed that the mixture made from the smaller chitosan pieces was the most powerful. When this specific mixture was tested, it created a zone where the fungus could not grow that was 34 millimeters wide. This was significantly larger than the zones created by the original chitosan, the original vitamin C, or the larger particles made with the stabilizer. This suggests that breaking the chitosan down into smaller pieces before mixing it with vitamin C creates a more potent antimicrobial shield.

The most practical test, however, took place in the real world of the silkworm farm. The researcher applied these new mixtures to the mulberry leaves that the silkworms eat. They raised two groups of silkworms: one group ate leaves treated with the new nano-mixture, and the control group ate leaves treated only with water. The results were clear. The silkworms fed the treated leaves were healthier and more resilient. In the group eating the nano-mixture, the rate of disease dropped significantly, with only about 4.5 percent of the larvae showing signs of illness, compared to nearly 9 percent in the control group. Furthermore, the treated silkworms produced more cocoons, and those cocoons were slightly heavier. The average weight of a single cocoon from the treated group increased by more than 5 percent compared to the untreated group.

This study demonstrates that by carefully engineering the size and structure of chitosan-based materials, scientists can create a simple, natural treatment that improves the health and productivity of silkworms. The work highlights that smaller, specifically structured particles made from broken-down chitosan and vitamin C are more effective at fighting disease and boosting growth than larger, more complex structures. For the sericulture industry, this offers a promising, environmentally friendly tool to protect crops and increase yields without relying on harsh chemicals. The findings suggest that the way these natural materials are assembled is just as important as the materials themselves, opening a path for more effective biological solutions in agriculture.