COMMUNICATION 1804717 (1 of 6) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.small-journal.com Optoregulated Drug Release from an Engineered Living Material: Self-Replenishing Drug Depots for Long-Term, Light-Regulated Delivery Shrikrishnan Sankaran,* Judith Becker, Christoph Wittmann, and Aránzazu del Campo* Dr. S. Sankaran, Prof. A. del Campo INM – Leibniz Institute for New Materials Campus D2 2, 66123 Saarbrücken, Germany E-mail: shrikrishnan.sankaran@leibniz-inm.de; aranzazu.delcampo@ leibniz-inm.de Dr. J. Becker, Prof. C. Wittmann Institute of Systems Biotechnology Saarland University 66123 Saarbrücken, Germany Prof. A. del Campo Chemistry Department Saarland University 66123 Saarbrücken, Germany The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.201804717. DOI: 10.1002/smll.201804717 production. [1,3] These challenges have trig- gered new design concepts, outside the box, to move therapeutic administration into a new era. [4–6] From a bioengineering perspective, the idea of “living therapeu- tics,” i.e., the use of metabolic engineered therapeutic bacteria to deliver the drug in vivo seems particularly attractive. [5,6] The ability to synthesize the drug at the appli- cation site (i.e., in the body) is appealing as it avoids previous drug manufacture and encapsulation steps, overcomes drug stability issues, and could facilitate long- term therapeutic treatments. However, issues like infection or immune response associated with freely circulating microor- ganisms in the body make clinical trans- lation of such approaches complicated. [5] From a biomaterial perspective, a prac- tical solution could be to encapsulate the drug-producing microorganisms within hydrogels to form living therapeutic mate- rials. The hydrogel provides a supportive environment for the sustenance of a bacterial population and could potentially mini- mize safety concerns of bacteria freely released into the body. Bacteria have been successfully entrapped in a viable and func- tional manner within various hydrogel matrices. Alginate [7] agarose, [8] polyacrylamide (PAAM), [8] and Pluronic F127, [9] among others, have been employed for biocatalysis, [8] probi- otic food processing, [7] biosensing, [9] and other applications. [10] Toward therapeutic applications, penicillin-producing fungi have been encapsulated in an agar-based hydrogel and sand- wiched between an elastomer and a porous membrane to con- struct a living material capable of releasing the antibiotic for several days and killing gram-positive bacteria in vitro. [11] Very recently, hydrogels supporting bacterial growth have also been used for cell cultures and delivery of proteins [12] to eukaryotic cells, or growth factors to induce differentiation. [13] Apart from programing metabolic synthesis of drugs, bacteria can also be engineered to sense and respond to external triggers such as small-molecule inducers, [9] temperature, [14] and light. [15] Of particular relevance are optogenetic modules which allow bacteria to produce proteins in response to light irradiation. [16] Such modules have been developed to activate gene expression in Escherichia coli in response to ultraviolet (382 nm), [17] blue (470 nm), [16] green (532 nm), [18] red (650 nm), [18] and near- infrared (760 nm) [19] light. Irradiation is a particularly attractive trigger for controlled drug release since light is readily available On-demand and long-term delivery of drugs are common requirements in many therapeutic applications, not easy to be solved with available smart polymers for drug encapsulation. This work presents a fundamentally different concept to address such scenarios using a self-replenishing and optogenetically controlled living material. It consists of a hydrogel containing an active endotoxin-free Escherichia coli strain. The bacteria are metabolically and optogenetically engineered to secrete the antimicrobial and antitumoral drug deoxyviolacein in a light-regulated manner. The permeable hydrogel matrix sustains a viable and functional bacterial population and permits diffusion and delivery of the synthesized drug to the surrounding medium at quantities regulated by light dose. Using a focused light beam, the site for synthesis and delivery of the drug can be freely defined. The living material is shown to maintain considerable levels of drug production and release for at least 42 days. These results prove the potential and flexibility that living materials containing engineered bacteria can offer for advanced therapeutic applications. Optically Active Materials Improved understanding of pharmacokinetic profiles, biolog- ical barriers, and physiological responses for numerous drugs has spawned an era of personalized medicine in which drug delivery systems need to be adaptable to individual patients. [1,2] Smart synthetic materials, typically drug-loaded microcar- riers made of responsive materials, are tailored to meet drug-, tissue-, and eventually patient-specific requirements. How- ever, their increased complexity reduces their drug-loading capacity, complicates industrial scale-up, and increases cost of Small 2018, 1804717