Periodic Reporting for period 1 - HOLOCELL (Holographic Assembler for 3D Cell Cultures)
Reporting period: 2023-03-01 to 2024-08-31
Reducing, refining and replacing animal models (3R principle) requires new technologies to create tissue models in vitro, which physiologically resemble organ-specific tissues at the same level (or better). Much work has been devoted to conventional biofabrication techniques, such as 3D-printing. Bioassembly methods could add another approach to the bioengineer’s toolbox by gently manipulating and stimulating cells at a distance. Ultrasound is especially promising due to its limited side effects, high transmission through tissue and low required intensities. Latest achievements in the scientific community are not readily translated to be used in a regular biolab. The aim of this project is to develop a fully operational, stand-alone benchtop bioassembler that uses ultrasound and holography to instantly aggregate biological cells, spheroids, particles or hydrogel capsules into defined 3D structures. The goal is that the device can be operated in biolaboratory environments and under typical process conditions, e. g. it can withstand sterilization using ethanol and ultraviolet light and operate at 37°C. Another planned feature is that the user interface is semi-automatic, designed to minimize user interaction and to help enforce a reproducible protocol for 3D cell culture using bioassembly. New algorithms have to be developed to compute optimal holographic plates for user-defined assemblies. Overall, the project will lead to a fast, programmable assembler where cells in suspension can be assembled with ultrasound into compact shapes directly from suspension – thereby maximizing cell density and minimizing any stress on cells.
We carefully planned the system and system requirements. We then contracted the company Achilles (Belgium) to undertake the industrial design work for the benchtop bioassembler according to our specifications. Throughout the project we met virtually every second week for a progress update and feedback. The prototype consists of two parts, the controller unit and the assembly unit. Both are connected via electrical cables for power and control. A simple user interface allows setting of process parameters such as exposure time, curing time, sound intensity. The water bath on top of the assembly unit can be heated to a set-point by a PID controller. At the end of the project, three units of the bioassembler have been built and shipped to Heidelberg. We rewrote our optimization software to use the Pytorch library for automatic differentiation and using GPU-acceleration. This accelerates the hologram optimization about 10-fold. We developed new way to insert and change holograms quickly and user-friendly with a turn-and-lock mechanism.We designed and fabricated custom high-power ultrasound transducers specifically suited for holography and our needs (5W power, 4.7MHz center frequency, 40mm diameter).
The prototypes are ready to be evaluated for their use with biological cells. More experiments are needed to assess ultrasound-based bioassembly for specific tissues, such as vascularization. However, this work can now be performed as part of scientific studies with partner laboratories.