# Lab-on-Chip Culturing System for Fungi--Towards Nanosatellite Missions
## 2 Materials and Methods
### Loc--Construction and Technology  
In each microfluidic project, selection of the proper construction material, technology flow, and lab-on-chip geometry is a key factor. Cell culturing LOCs are typically equipped with microchamber(s)--area for cells growth and microchannel(s), passing through the microchamber(s) and delivering the culturing media for cells feeding. Depending on the technology employed for the lab-on-chip fabrication, some limitations in LOC construction may appear, which can simply modify the ultimate microchamber and microchannel geometry. Other issue is the fact that every microscopic object, e.g., fungi species _Fusarium culmorum_, has its own characteristics, that may simply determine the most appropriate chip design. The literature on the subject is rich in examples of cell culturing LOCs fabricated out of polymers (e.g., PDMS, COC, PMMA), glass (borosilicate, FOTURAN), as well as utilizing 3D printing method; nevertheless, as mentioned earlier, the papers only to a small extent mention about the LOCs dedicated to fungi cultivation. Moreover, these LOCs are made of PDMS majorly [18; 19; 23; 24; 51], which based on recent literature reports [52; 53; 54] and investigation provided by the authors [55], may face some problems with biocompatibility. For instance, leaching of uncured oligomers from the polymer network to the culture medium may badly affect the cells, making cell culture unreliable. For this reason, in this paper the authors decided to employ all-glass technology for the chip fabrication. Borosilicate glass chosen as a construction material for LOC is characterised by high mechanical and chemical resistance, as well as excellent light transmission in the ultraviolet (UV) to near-infrared (IR) range [56]. Borosilicate glass is also a biocompatible material that does not interact with the tested biological samples [57]. As mentioned earlier, an important factor in LOC design is the construction of the microchannels/microchambers to ensure optimal conditions for cell growth. In addition to providing the necessary nutrients, the proper gas atmosphere is essential for many types of cultured cells and must be guaranteed. In the subject literature, we can find example constructions of microbiological incubation chambers connected with a gas cavity. This closed volume of gas must meet the demand of the microorganisms for gas exchange during culture [58]. However, in this solution, the microorganisms can only use the gas in the cavity, which reduces the culture time. Another example of structures providing an appropriate gas atmosphere for cell cultivation is the use of PDMS membranes [59; 60]. Thin membranes made of this material are permeable for gases, which can ensure proper aeration of the culture medium. Apart from the substantial experience of the group covering development of many structures dedicated to culturing of radically different bio-objects (e.g., freshwater microorganisms, animal oocytes, human cancer and normal cells) [3; 54; 55; 57], the preliminary research on LOC design for microscopic fungi was recently done and presented in the paper [55]. However, the aforementioned research did not include microflow culture--only stationary culture conditions were applied. On that basis, other research had to be undertaken to propose to best LOC design for _F. culmorum_ fungi species, assuming powdered fungi form obtainment (necessary to ensure delayed experimentation on fungi, e.g., due to long waiting for the rocket launch), and autonomous media delivery system. Therefore, in this paper, we have designed a lab-on-chip with a view to efficient delivery of the needful medium, while also providing the appropriate gas atmosphere which is necessary for the proper growth of the fungi culture. As assumed earlier in this work, all-glass technology has been employed for the fabrication of the lab-on-chip. We propose the lab-on-chip (Figure 1) consisting of two glass substrates, hereinafter referred to in the text as the lower and upper substrate.