Additive manufacturing of a paper medical diagnostic device

In recent years, rapid diagnostic devices – particularly point-of-care and lateral flow tests – have proven their crucial role in the fight against epidemics. However, their manufacturing process raises environmental concerns due to the use of petrochemical-based materials and heavy industrial processes.

This project aims to develop a more sustainable alternative by designing a cellulose-based device using additive manufacturing techniques. The objective is to replace the nitrocellulose membranes and plastic cartridges typically used in conventional lateral flow devices. This new system is primarily designed for serological and molecular testing. The development strategy is built on three main components: (i) the development of a porous cellulose composite to serve as a microfluidic membrane, replacing nitrocellulose; (ii) the design of a cellulose-based encapsulation to contain fluids within the membrane, substituting plastic cassettes; (iii) and the integration of printed heating elements to meet the thermal requirements of serological and molecular tests.

To ensure full integration of the device, an all-in-one manufacturing process compatible with a 6-axis robotic arm has been implemented. The porous composite is made from cellulose microfibrils acting as a binder, combined with microcrystalline cellulose and silica particles to structure the internal porosity. This material exhibits capillary flow dynamics comparable to nitrocellulose and enables the migration of gold nanoparticles for protein detection. Encapsulation is achieved using cellulose microfibrils rendered hydrophobic through treatment with alkyl ketene dimer (AKD), applied via spray coating. The encapsulation layer is structured and openings are created by laser etching to allow fluid deposition. This layer confines the fluid within the composite while remaining semi-transparent to allow result reading and protein observation. However, this encapsulation reduces the flow migration, limiting nanoparticle mobility.

Finally, the heating function relies on printed electrical resistors that use the Joule effect. These resistors are printed onto a wet cellulosic film and dried after encapsulation. They can maintain stable temperatures or perform thermal cycling, depending on the needs of serological and molecular tests.

Looking ahead, the project aims to fully integrate all these functionalities, including the immobilization and detection of various proteins and DNA samples.