Interfacial process engineering group

Calcification is the process of depositing calcium phosphate salts in tissues. This process is responsible for the high mineralisation and strength of bone tissue. However, pathological calcification can also occur in the human body, which can limit the service life of biological heart valve prostheses. At the IMP, an in-vitro test facility is available to investigate the calcification tendency of biological prostheses. This method produces a pulsatile flow that imitates the physiological environment of prostheses in the cardiovascular field. Studying calcification in vitro allows for shorter test durations and lower costs compared to animal experiments.

The in-vitro test system is suitable for conducting endurance tests on structures with pulsatile flow. Additionally, the particle image velocimetry method can be used to visualize the flow field near these structures. This method can also be used to analyze the effects of material changes on flow conditions.

Both genetic defects and concomitant symptoms of e.g. myocarditis can lead to degradation of heart valves or insufficiency due to calcification, which can sometimes be life-threatening. In addition to a biological heart valve prosthesis or reconstruction of the remaining valve, they can also be replaced by a mechanical heart valve. However, as these involve constant medication, attempts are also being made to develop a degradable solution with the help of electrospun heart valves. Based on suitable imaging, the geometric conditions are recorded and the scaffolds are produced specifically for the patient. The heart valve scaffolds produced in this way will then be colonised in vitro with the patient's own adult stem cells. The resulting tissue thus requires medication only for the period during which the scaffold structure remains in place.

In biomedical applications, component surfaces often encounter a flowing suspension of cells and large molecules. These react to flow influences, especially shear stress, which can cause activation or damage. Therefore, the flow shape significantly affects the processes at the interface. The working group focuses on investigating blood flows.

• Visualisation and analysis of flow fields in natural and artificial heart valves
• Vascular prostheses and dynamic in vitro test systems for blood compatibility
• Design, construction and production of test circuits for flow visualisation using particle image velocimetry (PIV)
• Stressing cell cultures with shear stresses in a cone-plate bioreactor

Synthetic prostheses have the advantage of being produced in standardised quantities and are therefore available at any time. However, they have the disadvantage of being a foreign body for the human body during the entire implantation period, which requires patients to take medication such as anticoagulants. An alternative in this context is the production of prostheses from the patient's own blood. Here, the patient's own material is processed to create an implant that is not recognized as a foreign body by the body. This implant can also be populated with the body's own cells using tissue engineering. After implantation, the body continuously breaks down the implant, leaving a completely autologous tissue replacement.

Due to the complex nature of human whole blood, fluid mechanics analyses can be challenging. Therefore, single-phase substitute fluids are often used for flow analysis. However, these can only represent physiological haemodynamics in a simplified manner.

Currently, the IMP is researching the establishment of a multiphase blood substitute fluid to more accurately depict the physiological fluid mechanical behaviour of blood in investigations. Experimental and numerical methods are used to analyse blood flows in vascular implants, particularly near the wall. Particle image velocimetry (PIV) is used for experimental investigations.

Microparticles are widely used in biological, chemical, and technical applications, such as cell cultivation and material analysis. Precise control of particle volume and coalescence behaviour enables analysis and characterization of chemical reactions on a micro-scale. The Institute for Multiphase Processes uses droplet-based microfluidics methods to synthesize these particles. A variety of hydrogel and polymer mixtures can be utilised for particle synthesis. In collaboration with various partners, diverse processes are employed to fabricate microfluidic systems, allowing for the adaptation of microchannel design to the specific problem at hand.

In recent years, microfluidic systems have become increasingly popular in biomedical engineering for material synthesis, as well as biological and chemical analysis. The available manufacturing methods can cover many questions due to the variety of channel structures and liquid and particle mixtures.
However, the physical understanding of the flow within the microchannels is still limited. The Institute for Multiphase Processes analyzes flows within microfluidic systems using droplet-based microfluidics. The focus is on characterizing the influence of particle polymerization on channel and particle microflows.