First Steps

This section guides you to your first project with MoBi® and familiarizes yourself with the software's user interface. First, the window structure of MoBi®and the basic steps for setting up a new MoBi® project are described and second how to set up and carry out a simulation. Additionally, the import of a PK-Sim® simulation is explained. However, more sophisticated applications can be performed in MoBi®, and you are referred to the following chapters for a more detailed description.

To create your first MoBi® project, simply follow the steps described in the sections below.

Start the Program‌

After successful installation, MoBi® can be found under Programs in program group Open Systems Pharmacology in the Windows® Start menu. Start the program by clicking on this menu entry and an empty workspace will appear.

MoBi® - Window Overview‌

In this section, we give a brief overview of the MoBi® window architecture and introduce some nomenclature.

A typical MoBi® window looks like screenshot below. The window contains different subviews; although some of them are visible only after creating a project, we describe them right here in a comprehensive way.

  • The tabs File, Modeling & Simulation, Import/Export etc. with a Ribbon Bar specific for the selected tab in the upper part of the window provide shortcuts to functions on the currently selected building block or simulation,

  • the Building Block Explorer on the left, which gives access to all building blocks of the project,

  • the Simulation Explorer on the left,

  • the History Manager at the bottom that shows the history of model development,

  • the Building Block Editor with a building block specific layout. Generally, it consists of a List, Tree or Diagram Area of all elements of the building block and a Properties Editor where you can edit the properties of the selected Element.

You can rearrange the window by different actions:

In the following we describe some details of the different subviews.

The Modeling & Simulation ribbon bar is separated into the History group, Create Building Blocks group, the Simulation group, options for specific Workflows and the Project functionality that helps to manage and display the units of parameters. Views contains the selection of the basic windows in MoBi®, the building block explorer window, the simulation explorer, and the history manager window.

The Building Block Explorer consists of the different building blocks for Molecules, Reactions, Spatial Structures, Passive Transports, Observers, Events, Simulation Settings and the Start Values defined for Molecules and Parameters. Additionally, you may find imported observed data in the building block window. More elaborate information on the concept of building blocks with an explicit explanation of all building blocks of the MoBi® concept can be found in The Building Block Concept.

A detailed introduction on how to use the building block concept to develop a project in MoBi® is given in Model Building and Model Components. An in-depth explanation on how to use the Create simulations ribbon to define specific simulations from the different building blocks can be found in Setting up a Simulation.

Once you have defined the simulations in the current project, the Simulations Explorer lists all of them. For details, see Simulation Results.

The History Manager lists all modeling steps and gives the opportunity to look at earlier versions and thus at the modeling history of the project. For details, see History Manager and History Reporting‌.

Create a Project‌

The first step to start working with MoBi® is to create a new project. To do this, click on the New Project command in the File menu. You can either work with amount or concentration based reaction networks which needs to be specified when creating a new project. Empty building blocks are automatically created shortly after in the Building Block Explorer: Molecules, Reactions, Spatial Structures, Passive Transports, Observers, and Events. Some of these building blocks need to be filled with data, which is successively done in the next sections.

Enter Molecules‌

You now need to create molecules which are later used as reaction partners. Do this by the following steps:

  1. Enter "A" as name and press the Enter key, or click OK. The molecule "A" appears in the left part of the Molecules tab, and a tab on the right shows the properties of the molecule.

  2. Enter "100" into the input box named Value, which represents molecule A's start amount in µmol.

The window should now look like this:

Enter a Reaction‌

  1. Double-click the newly visible building block name "Reaction" in the Building Block Explorer. A new tab with an empty space will open.

  2. Mark both molecules "A" and "B" by clicking on them with the mouse while simultaneously keeping the Shift key pressed. Then release the Shift key and click the OK button. Green circular symbols will appear on the Diagram Area for each molecule.

  3. Enter "R" into the Name input box.

  4. You can now move the reaction triangle or either molecule within the Diagram Area by clicking on them, holding the left mouse button and moving the mouse into the desired direction. To move a reaction, its grey center needs to be clicked on. To move a molecule, it needs to be clicked on in its darker green center.

Practice this procedure before advancing to the next step!

  1. Now you are going to connect molecules to a reaction to use them as educt and product. Some preparations are needed:

  • First, move the reaction triangle and the molecules into a position where "A" is on the left of the reaction triangle, and "B" on the right. Educts of a reaction are by default connected to the blue circle at the left triangle corner of a reaction, and products to the right green circle on the right triangle.

  • Connections can be drawn by either "grabbing" (keeping the left mouse key pressed) the outer light green rim of a molecule and pulling it to the corresponding place of a reaction triangle, or by "grabbing" the corresponding reaction port (i.e., the colored circle) and pulling it to the desired molecule.

Try it first without making a connection by just hovering with the mouse over a reaction or molecule symbol!

  • A line will be extended from the reaction or the molecule symbol. If it does not connect, the line will disappear as soon as you release the mouse key.

  • If you want to delete a connection (or if you produced a connection by mistake), click on the connection (which will then be highlighted by green squares) and then press the Delete key on your keyboard.

  1. To complete the reaction where "A" reacts to "B", click onto the blue circle in the reaction triangle (educt port), keep the left mouse key pressed, and pull the line to molecule "A". Release the mouse key, and a connection line will be displayed between molecule "A" and the left corner of the triangle.

  2. Move the mouse pointer to the green reaction triangle circle (product port) on the left, click it, hold the left mouse key, and pull a connection to molecule "B".

Below the Diagram Area you find a window with the three tabs Properties, Stoichiometry, and Parameters. Click the tab Stoichiometry. If the previous steps went well, you should see the molecule "A" listed in the "Educts" part with a stoichiometric coefficient of 1, and molecule "B" listed in the "Products" part, also with a stoichiometric coefficient of 1.

Now start to create a kinetic equation; in this example assuming an irreversible first order kinetic of molecule "A" reacting to "B". To proceed, define a first order rate constant as a reaction parameter.

  1. Click the Parameters tab, and then the Add Parameter button. A new window titled "New Parameter" will open.

  2. Input "k1" into the Name input box.

  3. Select Inversed Time as Dimension in the combobox, and enter 0.001 as Value. Then press Enter or click OK. The new parameter "k1" should be visible in the parameters list. Like for the molecule values, you can always change the entered values in the right part of the edit tab in case you pressed Enter prematurely.

  4. Click the Properties tab in the window. In the lower right of the window, there is a list called "Possible Referenced Objects". Click on the + sign in front of reaction name "R", and the reaction parameter "k1" that was just created will appear. Drag and drop the parameter "k1" into the left part of the window, to the blank space below the list with the molecules "A" and "B" and their corresponding paths and dimensions. "k1" will appear just below both molecules.

Create Start Values for the Simulation‌

Now, you need to create the Molecules and Parameters Start Values. In our example, these are the initial amounts for the two molecules.

  1. Enter the name "1" (or any other name you prefer) and click the OK button. A window showing the start values for the molecules "A" and "B", 100 and 0 µmol, opens in the edit window of the screen. The values could be edited if other values than the defaults are required for the simulation.

Create and Run a Simulation‌

Now you are ready to create a simulation using all the generated building blocks of the previous sections.

  1. Click the ribbon tab Modeling & Simulation.

  2. Click the now activated Finish button in the bottom of the window. After a few seconds, a tabbed simulation window should appear in the edit window.

  3. In case any warnings appear on the screen, you can ignore them at this point and click OK again.

Finally, after the computation is now done, we want to visualize the simulated results. In the simulation window, click the Results tab. On the right, a vertical Chart Editor bar is visible. Clicking it or hovering over it with the mouse pointer will bring up the possible selections for displaying the result curves.

  1. Repeat the previous step for molecule "B". Two curves should be visible.

The above description refers to an Editor Layout set to "Standard View". This should be the case in a fresh installation.

In other layouts, if you do not see any molecules, subsequently click on the + symbols in front of compartments, like "Organ" until you will see the checkboxes for the molecules "A" and "B" .

In the Chart Options section, the chart editor allows you to select grid lines and scales. You may want to try this option as well. You can look at the kinetics curves by clicking into the chart section and making the Chart Editor disappear.

Congratulations, you have done your first simulation using MoBi®!

Running a PK-Sim® Simulation‌

If you want to run a simulation in MoBi® that you have already created in PK- Sim®, proceed with the following steps:

  1. Save your project as PK-Sim® simulation to a .pkml (see Export To MoBi®.

  2. Select the Results tab.

  3. Click the vertical Chart Editor bar on the right edge of the window (see the previous section).

Exit MoBi®‌

After a successful simulation session, MoBi® can be closed by selecting File -> Exit from the menu bar; alternatively, press Alt+F4. Before the program is closed you are asked to save the current project. If you answer "Yes", all data belonging to the project are saved using the filename and folder you choose. You can reopen this project in a later session and continue your work at exactly the point where you left it.

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