This section introduces the experimental equipment, the material used, a description of fiber morphology analysing and preparation of in vitro testing.
5.1 Experimental equipment
Manipulator. The manipulator we used for the mechanical drawing of fibers is based on the “Uarm swift pro” robotic arm (Fig. 8 A). It is an affordable, open-source robotic manipulator with four degrees of freedom and a maximum payload of half a kilogram. The manipulator enables the drawing of fibers by the movement of its arm between two arbitrarily selected points in 3D space. The polymer solution is extruded automatically from a micropipette at the tip of the robotic arm at the beginning of each drawing movement (Fig. 8 B). The fiber is created between the delivered droplet on the substrate and the polymer solution that remains on the pipette orifice. The robotic arm leads its fiber end to a substrate point determined by the control software. This process can be performed consistently over a great number of repetitions.
The idea of using a robotic arm for this application comes from an open-source project called OpenLH (an open Liquid-Handling System for creative experimentation with biology) from miLAB research laboratory . The project has undergone deep alterations and improvements in both its mechanical and software aspects.
Extruder. A special effector for the robotic arm was designed for polymer extrusion (Fig. 8 B). It is based on the so-called positive displacement pipette (PDP) Microman from the company Gilson. The Microman pipette does not need an air cushion, as opposed to air displacement pipettes . This technology offers a reduction of solvent evaporation and prevents cross contamination, since there is no direct contact between the substrate and the pipette. For operation with a robotic manipulator, we designed a custom-made construction and combined it with the original components. All necessary parts for connections and the installation of the manipulator were made using additive manufacturing technology based on the HP Jet Fusion 3D printer. The pipette tip could be updated with a special 3D printed ceramic  heater which was specially developed by us for this extruder (Fig. 8 C). As a result, our device can now use heat to change the rheological properties of polymeric melts and solutions. We conducted a series of experiments with PCL polymer by melting it instead of dissolving it in solvents and got promising results.
Fig. 8 General view of the manipulator and work surface (A). Effector of manipulator. Dosing pipette (B). Heater element for PDP tip (C).
User interface. We developed user-friendly software to allow every user to program this system to his or her needs, e.g., to change and combine algorithms and to use the manipulator for different, previously mentioned applications. The graphical user interface (GUI) is based on the uArm Python Software Development Kit (SDK) supplied by Ufactory, producer of the uArm.
Applications. The manipulator enables the fibers made from different polymer solutions. Such structures could also be used in nanoelectronics  or be applied as optical sensors . Furthermore, the manipulator can be used in the fields of nanomaterials and biology for routine laboratory pipetting operations thanks to its highly accurate liquid dosing mechanism. The manipulator can also be used to good effect in the field of dip-coating, which is a popular way of creating thin film coated materials. Dip-coating involves the immersion of a substrate into a tank containing coating material, removing the piece from the tank, and allowing it to drain. The coated piece can then be dried by force-drying or baking. All these operations can be carried out by the robotic arm of the manipulator .
5.2 Polymer solution
Polymer solutions PCL (Mw 80,000, Sigma) and PLCL (PLC7015, Corbion), prepared with a concentration of 12% (w/w) in chloroform (Penta), were used to produce drawing fibers.
5.3 Fiber characterization
Fiber morphology was analyzed using pictures taken by a scanning electron microscope (SEM). Samples were sputter coated with gold (10nm) and then observed by SEM (Tescan, Vega 3 SB easy probe). Fiber diameter was measured using ImageJ software and then evaluated from a total of 100 measurements and shown in the form of a box plot.
5.4 Differential scanning calorimetry analysis
Processing - in our case mechanical fiber drawing – can have an impact on the initial crystallinity of PCL. The first heating cycle assesses the properties of the material in its post-production state, i.e., just after mechanical drawing of fibers. Heating the sample above its melt transition and the following cooling erases information about the fiber’s technological history and imparts a normalized thermal profile upon the sample. The second heating cycle evaluates the inherent properties of the material . Moreover, the degree of crystallinity affects the rate of biodegradation of polymeric materials. Therefore, it is important to study the relationship between the degree of crystallinity on one side and the material and technological parameters on another.
The crystallinity measurement was performed using a Mettler Toledo DSC1 calorimeter from -20°C to 100°C for PCL fibers and from -40°C to 130°C for PLCL fibers with a heating rate of 10°C/min. All experiments were conducted in a nitrogen atmosphere. The degree of crystallinity was evaluated from equation (1) using melting enthalpy.
where is the enthalpy of melting measured during the first heating cycle (Fig. 5 A black) and is the melting enthalpy of a pure PCL crystal (139.5 J.g-1) (Fig. 5 A red) .
5.5 In vitro tests
Samples for in vitro testing were prepared as set of 1000 individual fibers fixed with a supporting ring designed to fit the cavities of a 24-well culture plate . Prior to cell seeding, samples were sterilized in 70% ethanol for 30 minutes, then washed several times in PBS (phosphate buffer saline, pH 7.4) and given a final wash in a DMEM medium (Biosera). 3T3 mice fibroblasts (3T3 Swiss Albino, ATCC) were seeded at a concentration of 1.105 cells per well in 24-well plates. The cells were maintained in Dulbecco's modified eagle medium (DMEM, Biosera) and supplemented with fetal bovine serum (FBS, Biosera), glutamine (Biosera), and antibiotics Pen/Strep Amphotericin B (Lonza). The cells were cultured in an incubator at 37° C and 5% CO2, the medium was changed three times a week and the sixth passage were used for the in vitro experiments.
The samples were analyzed for cell behavior using florescence microscopy and scanning electron microscopy (SEM) on days 1, 3 and 7 after cell seeding. The samples processed for microscopy were fixed with 2.5% glutaraldehyde for 15 minutes. After the fixation of cells, the samples for fluorescent microscopy were rinsed in PBS and then permeabilised for 10 minutes in a solution of 0.1% BSA (Merck) and 0.1% Triton in PBS. Next, the cells were stained with DAPI (Merck) and phalloidin-FITC (Merck). After permeabilisation, the samples were washed with PBS and stained with phalloidin-FITC (1µg/ml) in for 30 minutes at room temperature. Then the samples were washed with PBS and stained with 0,1% DAPI for 10 minutes at room temperature. The samples were then analyzed with a fluorescence microscope (Nikon Eclipse Ti-e). Samples intended for SEM were rinsed in PBS and then dried with in an increasing concentration of ethanol (60%, 70%, 80%, 90%, 96% and 100%). After drying, the samples were fixed on targets, sputter-coated with a 10nm-thick layer of gold and analyzed by a scanning electron microscope (Tescan, Vega 3 SB easy probe).