Engineering Insight

As much as necessary, as little as possible—that has been the prime directive of minimally invasive surgery (MIS) since its introduction. Instead of the large incisions in the stomach, rib cage or joints that are an unavoidable part of conventional open-surgery methods, MIS requires only very small incisions. The actual operation is conducted inside the body with the aid of inserted video cameras, light sources and endoscopic instruments. This surgical method, also known as keyhole surgery, accelerates patient recovery and reduces the risk of scar hernias, deformations or other postsurgical complications.

However, MIS requires sophisticated technology. Instruments such as endoscopic video cameras and powerful light sources are necessary for the surgeon to be able to see the surgical area.

Gently creating space for the operation

The older version of the insufflator block made of milled aluminium, partially equipped with specially manufactured valves.

In laparascopic examinations (also known as endoscopy), technical aids are required to create the space needed to perform the surgery. Insufflators gently pump CO_² into the body to enlarge the surgical area and enable insertion of the required medical instruments.

A core element of this device is the insufflator block, which controls the pumping and removal of gases. The newest generation of insufflators from Berlin-based World of Medicine (WOM, Ludwigsstadt, Germany), a supplier of MIS instruments, uses an insufflator block developed in cooperation with fluid technology specialist Bürkert (Ingelfingen, Germany).

The valve unit consists of two Type 6013 DN 6 direct-acting 2/2-way mini solenoid valves, a Type 2873 DN 2 frictionless 2/2-way solenoid control valve and a low-pressure safety switch from WOM, all mounted on an injection-moulded plastic block. The Type 2833 valve first regulates the input pressure down to a few millibars (0-40 mbar), since the human stomach can withstand only very low pressure. A Type 6013 valve serves as a direct output valve for pumping gas into the body. The second valve of the same type functions purely as a safety valve that can be switched immediately, if necessary, to release pressure into the environment. The similarly integrated low-pressure safety switch is a fully mechanical unit that opens automatically if a configured maximum pressure is exceeded.

Smaller, lighter and less expensive
The new insufflator block is a further development of the valve unit that was used in previous generations of WOM insufflators.The goal was to reduce the manufacturing cost, size and weight of the block, while maintaining the same level of performance and safety. The specialists at Bürkert modifed the design and replaced a specially manufactured solenoid control valve without a valve body with a Type 2873 valve equipped with a standard body. In the previous version of the insufflator block, three valves were screwed onto a milled aluminium block that was flange-mounted on a second block from WOM. Two low-pressure safety switches and the control board also were mounted on the second block.

A prototype of the new, compact insufflator block with two Type 6013 valves and one Type 2833 solenoid control valve on an injection-moulded plastic block.

The basis of the new system is an injection-moulded block made of polycarbonate, a material that achieves UL approval for flammability, as required by WOM. The new design made it possible to eliminate the use of a second pressure stage directly upstream from the solenoid control valve and to reduce the size of the valve unit by 29%. Replacing the milled aluminium block with a plastic block and using a solenoid control valve in a standard valve body enabled an even more significant weight reduction: the new insufflator block weighs 64% less than the previous version and resulted in a 30% saving in production costs.

Comprehensive simulations in the development phase
During the development phase, Bürkert conducted extensive tests and simulations in order to optimise the block design. This included flow optimisation by means of a computational fluid dynamics test to determine whether the flow rate required by WOM would actually be achieved in the insufflator block. “Based on the results of the simulation, we enlarged the so-called kidney around the seat of the output valve on the plastic block to optimise the flow rate,” Product Engineer Julia Adelmann of Global Marketing at Bürkert explains.

The new insufflator from World of Medicine AG.

The injection moulding process of the new block also was examined closely by Bürkert during development. A computer-aided MoldFlow analysis, which simulates filling of the injection mould with liquid plastic, determined that the geometry of the kidney on the output valve also needed to be modified. “The valve seats are especially critical in moulded parts,” says Adelmann. “To determine that the valve seat is always filled correctly during injection moulding, it was necessary [to design] a contour that rises at an angle to the valve seat.”

The new insufflator block has been certified for medical use and has been installed in the WOM insufflator. The device is now being used in medical facilities in Germany and the United States.