Ureteroscope Clamps Made Of Titanium Alloy Lost-wax Casting

o Commonly used titanium alloys for ureteroscopic clips include Ti-6Al-4V. Aluminum (Al) enhances the strength and thermal stability of titanium alloys, maintaining good mechanical properties under varying surgical temperatures. Vanadium (V) improves machinability, facilitating casting.

o Other elements, such as iron (Fe) and oxygen (O), can be added in small amounts to meet specific performance requirements. Appropriate amounts of iron further increase alloy strength, while a certain amount of oxygen improves hardness; however, the amount added must be strictly controlled to avoid affecting toughness and biocompatibility.

o The purity of raw materials is crucial. Impurity content in titanium alloy raw materials must be strictly controlled. Heavy metal impurities such as lead (Pb) and mercury (Hg) must be kept at extremely low levels to ensure biocompatibility.

o Strict inspection of purchased titanium alloy raw materials is essential, including chemical composition analysis and mechanical property testing. Chemical composition analysis can employ methods such as spectral analysis to ensure that the content of each element meets design requirements. Mechanical property tests, such as tensile tests and hardness tests, ensure that the material possesses appropriate strength, toughness, and hardness.

o Design and Modeling: First, based on the design drawings of the ureteroscope clamp, a 3D model is created using computer-aided design (CAD) software. Considering the functional requirements of the clamp, such as clamping force and opening angle, the shape, size, and structure of the clamp are precisely designed. For example, the clamp head needs to be designed with a suitable shape to ensure accurate grasping of tissue or foreign objects, while ensuring uniform distribution of clamping force.

o Wax Model Forming: Using precision injection molding, wax is injected into a mold to create a wax model identical in shape to the ureteroscope clamp. Choosing a suitable wax is crucial; the wax should have good flowability and formability to accurately replicate the details of the mold. During injection molding, parameters such as temperature, pressure, and injection speed must be carefully controlled to avoid defects such as bubbles and cracks in the wax model.

o Wax Model Assembly: Individual wax models are connected by wax rods to form a wax model assembly for subsequent casting operations. The diameter and length of the wax rods must be appropriately selected based on the size and weight of the clamp to ensure that the wax model assembly can be stably suspended in the mold shell during the casting process.

o Refractory Material Coating: Immerse the wax model assembly in a coating containing refractory materials (such as silica sol, zircon sand, etc.), ensuring a uniform coating layer on the surface. Then sprinkle a layer of zircon sand, allowing it to adhere to the coating surface, forming the first shell layer. Repeat the coating and sand-sprinkling process multiple times, gradually increasing the shell thickness, generally requiring 4-6 layers. The drying time for each shell layer must be controlled according to the properties of the coating and environmental conditions to ensure the shell is fully dried and free of cracks.

o Dewaxing: Place the coated wax model assembly in a dewaxing furnace, heating it to melt the wax and allow it to flow out of the shell. The dewaxing temperature and time must be adjusted according to the melting point of the wax and the thermal stability of the shell, generally holding at 150-200℃ for a certain time to ensure complete wax removal.

o Shell Firing: Place the dewaxed shell in a high-temperature firing furnace for firing to improve its strength and refractoriness. The firing temperature is generally between 900 and 1100℃, and the firing time depends on the thickness and material of the mold shell. During firing, the heating and cooling rates must be carefully controlled to prevent the mold shell from cracking due to thermal stress.

o Titanium Alloy Melting: The titanium alloy raw materials are heated and melted using a vacuum induction melting furnace. During the melting process, the vacuum level inside the furnace must be maintained to prevent the titanium alloy from reacting with oxygen, nitrogen, and other gases in the air, which would affect the alloy's properties. Precise control of the melting temperature and time ensures that the titanium alloy is fully melted and has a uniform composition.

o Casting: When the titanium alloy reaches the appropriate casting temperature (generally 1600-1700℃), it is quickly poured into the preheated mold shell. The casting speed should be moderate; too fast a speed may cause the mold shell to crack, while too slow a speed may cause the alloy liquid to cool and solidify during casting, affecting the quality of the casting. At the same time, attention should be paid to the design of the gating system to ensure that the alloy liquid can smoothly fill the mold shell.

o. Shell Removal and Cutting: After the casting cools, the shell is removed mechanically. The casting is then cut from the gating system, removing excess gating and risers. Care must be taken to avoid damaging the clamp body during cutting; appropriate cutting tools and processes, such as abrasive wheel cutting or wire cutting, should be used.

o. Heat Treatment: The cut casting undergoes heat treatment to improve its mechanical properties. Common heat treatment processes include solution treatment and aging treatment. Solution treatment allows the elements in the alloy to fully dissolve, forming a homogeneous solid solution, improving the alloy's strength and toughness. Aging treatment involves holding the casting at a specific temperature for a period of time to allow the precipitated phases in the alloy to precipitate uniformly, further improving the alloy's hardness and strength.

o. Surface Treatment: The heat-treated clamp undergoes surface treatment to improve its corrosion resistance and smoothness. Chemical polishing and electrochemical polishing methods can be used to polish the clamp surface, making it smooth and reducing the possibility of bacterial adhesion. Passivation treatment can also be performed to form a dense oxide film on the clamp surface, improving its corrosion resistance.

* Precision measuring equipment such as a coordinate measuring machine (CMM) is used to inspect the dimensions of the ureteroscope clamps. Key dimensions of the clamps, such as length, width, thickness, and bore diameter, are inspected to ensure they meet the tolerance requirements of the design drawings. For example, the dimensional tolerance of the clamp head may be within ±0.05mm to ensure its clamping accuracy.

* The shape accuracy of the clamps, such as the clamp opening angle and bending degree, also needs to be accurately inspected. Dedicated angle measuring instruments and shape measuring instruments can be used to ensure that the shape of the clamps meets the design requirements and can perform its function properly.

* Visually inspect the clamp surface for defects such as cracks, pinholes, and pores. For some minor surface defects, a microscope can be used for observation and analysis.

* Inspect the surface roughness of the clamps using a roughness meter. Generally, the surface roughness of the clamps should reach Ra0.4 - Ra0.8μm to ensure a smooth surface and reduce damage to tissues.

* Conduct tensile tests to measure the tensile strength, yield strength, and elongation of the clamps. Tensile tests can be performed using a universal testing machine. The clamp sample is clamped and stretched according to standard requirements, and the test data is recorded.

* Conduct hardness tests using a Rockwell hardness tester or Vickers hardness tester to measure the hardness of different parts of the clamps. Ensure the clamps have appropriate hardness to withstand certain external forces during use without deformation or damage.

* Conduct cytotoxicity tests according to relevant standards. The clamp sample is co-cultured with cells, and cell growth and activity are observed. If cell growth is normal and there is no obvious toxic reaction, the clamps have good cytocompatibility.

* Conduct hemolysis tests to detect the hemolysis rate of the clamp material to blood. The hemolysis rate should be controlled at a low level, generally less than 5%, to ensure that it will not cause a hemolytic reaction upon contact with blood.

* Design appropriate packaging materials and forms based on the size and shape of the ureteroscope clamps. The packaging materials should have good sealing and protective properties to prevent damage from collisions, contamination, etc., during transportation and storage.

* The packaging should clearly label the clamp's model, specifications, production date, expiration date, etc., for easy management and use. It must also comply with relevant standards and regulations for medical device packaging.

* Sterilize the packaged ureteroscope clamps using appropriate sterilization methods. Commonly used sterilization methods include ethylene oxide sterilization and irradiation sterilization. Ethylene oxide sterilization has advantages such as good sterilization effect and minimal damage to the instrument, but strict control of sterilization conditions, such as temperature, humidity, ethylene oxide concentration, and sterilization time, is required. Irradiation sterilization has advantages such as fast sterilization speed and no residue, but care must be taken to control the irradiation dose to avoid affecting the clamp's performance.

After sterilization, the clamps should be tested for sterilization effectiveness, using methods such as biological indicators, to ensure the clamps meet aseptic requirements.

* Provide professional training to personnel involved in the lost-wax casting production of ureteroscope clamps, including casting process knowledge, quality control requirements, and operational skills. For example, wax mold makers should be trained to understand the characteristics of wax and methods for controlling injection molding process parameters; smelting operators should be trained to control key parameters such as temperature and vacuum degree in titanium alloy smelting.

* Regularly organize skills assessments and knowledge update training for personnel to improve their professional skills and quality awareness.

* Maintain the cleanliness and hygiene of the production workshop, and conduct regular cleaning and disinfection. The temperature and humidity of the production workshop should be controlled within a suitable range, such as temperature between 20-25℃ and humidity between 40%-60%, to ensure the stability of processes such as wax mold making and shell making.

* Regularly maintain and service production equipment to ensure its normal operation. For example, the heating and vacuum systems of the melting furnace should be inspected regularly to ensure the stability and reliability of the melting process.

* Establish a comprehensive production documentation system, recording key parameters, raw material information, and quality inspection results for each production stage. For example, record the injection temperature and pressure during wax mold making, and the coating formula, firing temperature, and time during shell molding.

* Achieve product traceability. Through product numbers and other methods, information such as the source of raw materials, production process, and quality inspection can be traced. Once product quality issues are discovered, they can be traced and addressed promptly, with appropriate corrective measures taken.