https://radiopaedia.org/articles/chiba-needle

Introduction

The 22G Chiba needle that can be flexibly manipulated by clinical doctors is backed by an extremely complex and sophisticated modern manufacturing system. With an outer diameter of 0.7mm, an inner diameter of approximately 0.5mm, and a wall thickness of only about 0.1mm - at this microscopic scale of a few millimeters, achieving high strength, high precision, defect-free, and sterile mass production is an extreme challenge for materials science, precision processing, and quality control. A qualified 22G Chiba needle can be regarded as an industrial masterpiece of micro-metric precision manufacturing. This article will start from each step of the manufacturing process, deeply analyze its core techniques, and reveal the nearly stringent quality control system that runs through it.

I. From Raw Materials to Pipe: The Starting Point of Precise Forming

The manufacturing process begins with the purest raw materials. Medical-grade stainless steel 316L or nickel-titanium wire/filament, which must undergo strict chemical composition and biocompatibility certifications.

• Multi-pass cold drawing forming: This is the core process for creating ultra-fine hollow tubes. The raw pipe material is subjected to plastic deformation under the action of external force through a series of diamond or hard alloy molds with gradually decreasing diameters. The outer diameter and wall thickness are gradually reduced to the target size (such as 22G). This process requires precise control of the reduction rate per pass, drawing speed, lubrication, and annealing procedures. Any unevenness will result in inconsistent wall thickness, rough inner walls, or even fractures.
• Inner surface treatment: The inner walls of the drawn tubes may have microscopic scratches. Through inner diameter polishing or fluid grinding, the inner cavity is ensured to reach a mirror-like surface finish, which is crucial for reducing suction resistance, preventing sample adhesion, and ensuring smooth injection.

II. Needle Tip Forming: The Soul of Piercing Performance

The needle tip is the key factor determining the puncture feel, tissue damage, and success rate. The manufacturing of the 22G needle tip is particularly meticulous.

• Precision Grinding: On a dedicated CNC grinding machine, a grinding wheel with a specific angle and grit size is used to perform oblique grinding on the end of the tube, creating a classic single inclined plane of approximately 20-30 degrees. This angle has been proven to be the gold standard through decades of clinical trials: it ensures sufficient sharpness to easily penetrate while also allowing for a "sliding" effect rather than puncturing when piercing elastic tubes (such as the bile duct). The grinding must ensure a smooth inclined plane without burrs or frays.
• Side Hole Processing: On the back side of the needle tip's inclined plane, using laser drilling or micro-electrical discharge machining technology, a side hole with a diameter of approximately 0.3mm is machined. Laser processing has a small heat-affected zone and smooth hole edges; electrical discharge machining has extremely high precision. The smooth hole edges prevent cutting of tissue strips, ensuring the acquisition of complete cell samples.

III. Surface Finishing and Treatment: Ensuring Smoothness

• Electrolytic polishing: This is a crucial step for improving the surface quality. By immersing the needle body in the electrolyte as the anode, through electrochemical reactions, the microscopic protrusions on the surface are selectively dissolved, resulting in a uniform, shiny, and stress-free surface. This not only significantly reduces the friction resistance of the tissue during puncture but also removes any possible microscopic cracks on the surface, thereby greatly enhancing the fatigue strength and corrosion resistance of the needle body.
• Cleaning and passivation: For stainless steel needles, acid washing and passivation treatment is required. A dense chromium oxide passivation film is formed on the surface, which is the final barrier for its excellent corrosion resistance.

IV. Quality Control

Quality control is not the final step; rather, it is integrated into every second from raw materials to the final product.

• Dimensions and geometric accuracy: Use a laser diameter measuring instrument (with an accuracy of 0.1 μm) to fully inspect the outer diameter; use an optical projector or visual measurement system to detect the tip angle, slope length, and side hole position; use an air displacement meter to test the internal diameter's smoothness.
• Surface integrity: Conduct random inspections of the tip and side hole edges under a scanning electron microscope to ensure there are no burrs, cracks, etc. defects. Use a surface roughness meter to measure the Ra value (typically required <0.2 μm).

Functional performance testing:

Piercing force test: Test the piercing force using simulated skin tissue to ensure uniform sharpness.

Flowability and flow rate test: Test the flow rate using standard viscosity liquids to ensure compliance with requirements.

Connection strength test: Test the connection strength between the needle holder and the needle tube.

• Biological performance and sterility assurance: Conduct biocompatibility tests such as cytotoxicity, sensitization, and irritation according to ISO 10993. The final product is sterilized by ethylene oxide or gamma radiation and undergoes sterility testing and bacterial endotoxin detection.
• Full traceability throughout the process: From the batch number of raw materials to the production parameters of each process, operators, and environmental data, all are electronically recorded. Each needle has a unique batch number and production information associated with it.

Conclusion

The manufacturing of 22G Chiba needles is a systematic engineering process that transforms macroscopic clinical needs into microscopic physical implementations. Its value lies not in the preciousness of the materials, but in the relentless pursuit of precision, performance, and reliability at the extreme fine scale. Every qualified 22G Chiba needle is the best interpretation of the integration of "craftsmanship" and "technology." It is precisely this meticulousness, almost obsessive, in the slightest details that gives clinical doctors the confidence and assurance to handle complex surgeries with such fine needles. For manufacturers, mastering the manufacturing process of 22G Chiba needles is the ultimate manifestation of their technical strength and quality management system.