In the last few years, the field of biomaterials has advanced from inert materials to biologically active materials able to interact with the surrounding cells or tissues. The field of engineered living materials (ELM) that combine living cells with a matrix or scaffold has emerged from this vision. ELMs opens up new possibilities for the preparation of advanced functional materials able to adapt and respond to different environmental cues in a programmed manner [1,2]. Engineered materials incorporating living components such as drug-eluting microorganisms are emerging as new concepts for therapeutic treatment of diseases. Previous work from our group has demonstrated the successful encapsulation of drug-eluting bacteria into hydrogel membranes, and their utility for in situ drug production and delivery [3,4]. These bacteria can be further engineered to respond to specific triggers, such as temperature, light or pH, and produce biopharmaceuticals on-demand. The encapsulating matrix must provide a suitable environment for bacteria for the diffusion and exchange of nutrients and drugs, while it retains bacteria and confines them to a closed space.

A particular challenge are living therapeutic materials that can deliver therapeutic proteins, since these are large and diffusion across hydrogels is very slow. In this project, electrospinning technique is used to develop living nanofibrillar meshes with high diffusivity that encapsulate bacteria engineered to produce therapeutic proteins. The electrospinning methodology has been used to entrap bacteria in degradable matrices for the preparation of probiotic products [5]. In this work, a non-degradable network is developed to confine bacteria and facilitate diffusion of nutrients and drugs. Meshes with different fiber diameter, pore size, density and intrafibrillar crosslinking are prepared, and the viability, growth and function of the entrapped bacteria were studied. These materials present a great potential of application for different therapeutic applications such as ocular drug delivery.