# Building Otto: An open-source Franz diffusion cell autosampler for automating in vitro skin permeation studies

## TL;DR

Otto is an affordable, open-source automation system for skin permeation studies that reduces manual labor and improves consistency.

## Contribution

The novel contribution is Otto, a customizable and retrofittable open-source autosampler for Franz diffusion cells.

## Key findings

- Otto can handle 100 samples per run, enabling high-throughput skin permeation studies.
- Otto integrates with existing Franz diffusion cells without requiring modifications.
- OttoMate software simplifies programming with a graphical user interface.

## Abstract

The Franz diffusion cell (FDC), widely used for measuring drug absorption across the skin, is usually operated manually. However, manual operation is not only labour-intensive and time-consuming, but inevitably introduces human errors and inter-operator variability. The requirement to perform regular sampling around the clock also presents a significant logistical challenge for researchers. Commercial FDC automation solutions are costly and require proprietary/bespoke FDC designs. To overcome these challenges, we have developed Otto as a customisable and affordable, aftermarket FDC automation solution, to be retrofitted to existing FDCs of generic specifications. Otto uses a modified cartesian 3D-printer as a gantry and adds liquid-handling capabilities using 3D-printed components and common, inexpensive laboratory consumables. Liquid samples are collected into standard autosampler vials. Capable of handling 100 samples per run, Otto supports a high throughput and integrates well with downstream analytical equipment, without modifying the FDC or the analytical equipment. Its programming is facilitated by OttoMate, a companion software application with a graphical user interface designed to generate human-readable code for Otto. Here, we describe the design, construction, operation and characterisation of Otto. To our knowledge, this is the first open-source, retrofittable FDC autosampler with such throughput.