Analysis of Synthetic Biology Classic Case Issues
Academician Xie Lixin, an ophthalmology expert from the Chinese Academy of Engineering, led a corneal disease epidemiological survey across 10 provinces, municipalities, and autonomous regions in China. The results showed that the prevalence of corneal disease in China is about 0.32%, which translates to approximately 4.16 million patients. Among them, about 2.99 million people are blind in at least one eye due to corneal disease, with a blindness rate as high as 72%, and around 440,000 are completely blind in both eyes. Additionally, about 200,000 new corneal blindness cases are added each year. However, due to the shortage of donor corneas, only about 10,000 patients receive corneal transplant surgery each year, leaving a large number of blind patients still waiting to regain their sight. Therefore, there is a huge market demand for artificial bio-synthetic corneas.
In 1817, Dr. Weber first implanted a piece of crystal glass into a patient's cornea, pioneering the history of artificial corneal implants. Today, research and development of artificial corneas have spanned over 200 years, with significant advancements in material design, manufacturing processes, surgical techniques, and postoperative care. However, regardless of whether the transplant material is crystal glass or other animal-derived corneas, the limitation of "immune rejection" has not been overcome. In recent years, synthetic corneas produced by biological metabolism have garnered more attention and are expected to surpass the limitations of immune rejection faced by other transplantation methods.
Compared with traditional materials, bio-synthetic corneas offer several potential advantages, including immune inertia, regenerative function, transparency, shelf life, and industrial production. Since the primary component of bio-synthetic corneas is human collagen protein and contains no animal-derived components, they can overcome the immunological defects associated with xenotransplantation or allotransplantation. Additionally, the product provides a tissue engineering scaffold for the migration and growth of the patient’s own corneal epithelial cells and stromal cells, promoting nerve regeneration and the restoration of tactile sensitivity. More importantly, while donor corneas must be transplanted within two weeks, bio-synthetic corneas can have a shelf life of up to three years.
In the field of synthetic biology, Pharmac has a wealth of project cases and strong technical reserves. For instance, at the end of 2022, after several rounds of technical screening, Pharmac successfully undertook a recombinant collagen protein fermentation and purification project in the Suzhou Biomedical Industrial Park. Amid the transition to a new normal after the pandemic, the design team overcame various difficulties and closely communicated with the client, creating favorable conditions for the orderly and rapid delivery of the project. Today, the project has successfully completed commissioning and has entered the pilot production phase.
This project involves yeast cells synthesizing "full-length recombinant human collagen with a stable triple-helix structure" through methanol induction during long fermentation cycles. This bio-synthetic cornea is classified as a Class III medical device and is in the late clinical development stage. The following sections will explain the design challenges and solutions in synthetic biology based on this project.
The cultivation cycle of cells in typical projects usually lasts from a few hours to several days, but in this project, yeast cells require over 10 days of cultivation. During this long cultivation cycle, ensuring the stability of key parameters such as temperature, oxygen levels, and pH, which are crucial for microbial growth, presented a challenge. The design team tailored the design accordingly, and the process parameter curves from pilot production indicated that the design solution operated reliably and stably, meeting production needs.
Image:Biosynthetic Cornea Example
Since yeast cells express the target protein under methanol induction, the addition of methanol became a critical factor determining yield. Unlike regular feeding tanks placed near the fermenter, methanol must be located in an explosion-proof area due to its physical properties. This led to challenges such as long feed pipelines, large storage quantities, and unstable delivery. After analyzing various conditions, the design team employed solutions such as setting up a process buffer tank, feeding scale, servo motor-driven peristaltic pumps, and optimized program control, successfully controlling the entire cycle's hundreds of liters of feed to within ±1g/min precision.
Image:Biological Culture Workshop
Achieving high expression of the target protein upstream means only half the battle is won; the quality of downstream product separation and purification also determines the success of production. Due to the special nature of the end product, traditional stainless steel containers were not allowed at this process point, necessitating the use of more stable borosilicate glass containers. In China, borosilicate glass tanks generally have a capacity of 20 to 50 liters, and few manufacturers can produce containers with a capacity exceeding 50 liters. In contrast, the US and European countries typically set the capacity of glass tanks at this process point at 150 liters. This project was the first to use a large-capacity 300-liter borosilicate glass process tank. After accepting this challenge, the design team integrated domestic and international project cases and supplier resources, overcoming various difficulties to complete system delivery.
Image:300L Borosilicate Glass Process Tank
The production base for this project is located in the Taihu Lake area, where there is no centralized sewage treatment system in the production park. Therefore, all wastewater generated during production must be collected and handed over to third-party companies for treatment, incurring a wastewater treatment fee of nearly 5,000 yuan per ton.
Under general cleaning processes, cleaning a reactor requires approximately 3 to 10 m³/h of water, which represents a significant production cost for the client. Pharmac’s automation team, focused on the client's needs, meticulously refined every step to save water and customized each cleaning process. With the new program control, the estimated annual savings in wastewater treatment fees is about 1.2 million yuan.
From design to implementation, Pharmac offers a one-stop solution for clean fluid process equipment in the pharmaceutical industry.