Enhancing the robustness of functional biomacromolecules is a critical challenge in biotechnology, which if addressed would enhance their use in pharmaceuticals, chemical processing and biostorage. Here we report a novel method, inspired by natural biomineralization processes, which provides unprecedented protection of biomacromolecules by encapsulating them within a class of porous materials termed metal-organic frameworks. We show that proteins, enzymes and DNA rapidly induce the formation of protective metal-organic framework coatings under physiological conditions by concentrating the framework building blocks and facilitating crystallization around the biomacromolecules. The resulting biocomposite is stable under conditions that would normally decompose many biological macromolecules. For example, urease and horseradish peroxidase protected within a metal-organic framework shell are found to retain bioactivity after being treated at 80 °C and boiled in dimethylformamide (153 °C), respectively. This rapid, low-cost biomimetic mineralization process gives rise to new possibilities for the exploitation of biomacromolecules.

Metal organic frameworks (MOFs) offer the highest surface areas per gram of any known material. As such, they epitomise resource productivity in uses where specific surface area is critical, such as adsorption, storage, filtration and catalysis. However, the ability to control the position of MOFs is also crucial for their use in devices for applications such as sensing, delivery, sequestration, molecular transport, electronics, energy production, optics, bioreactors and catalysis. In this review we present the current technologies that enable the precise positioning of MOFs onto different platforms. Methods for permanent localisation, dynamic localisation, and spatial control of functional materials within MOF crystals are described. Finally, examples of devices in which the control of MOF position and functionalisation will play a major technological role are presented.

Many living organisms are capable of producing inorganic materials of precisely controlled structure and morphology. This ubiquitous process is termed biomineralization and is observed in nature from the macroscale (e.g., formation of exoskeletons) down to the nanoscale (e.g., mineral storage and transportation in proteins). Extensive research efforts have pursued replicating this chemistry with the overarching aims of synthesizing new materials of unprecedented physical properties and understanding the complex mechanisms that occur at the biological-inorganic interface. Recently, we demonstrated that a class of porous materials termed metal-organic frameworks (MOFs) can spontaneously form on protein-based hydrogels via a process analogous to natural matrix-mediated biomineralization. Subsequently, this strategy was extended to functional biomacromolecules, including proteins and DNA, which have been shown to seed and accelerate crystallization of MOFs. Alternative strategies exploit co-precipitating agents such as polymers to induce MOF particle formation thus facilitating protein encapsulation within the porous crystals. In these examples the rigid molecular architecture of the MOF was found to form a protective coating around the biomacromolecule offering improved stability to external environments that would normally lead to its degradation. In this way, the MOF shell mimics the protective function of a biomineralized exoskeleton. Other methodologies have also been explored to encapsulate enzymes within MOF structures, including the fabrication of polycrystalline hollow MOF microcapsules that preserve the original enzyme functionality over several batch reaction cycles. The potential to design MOFs of varied pore size and chemical functionality has underpinned studies describing the postsynthesis infiltration of enzymes into MOF pore networks and bioconjugation strategies for the decoration of the MOF outer surface, respectively. These methods and configurations allow for customized biocomposites. MOF biocomposites have been extended from simple proteins to complex biological systems including viruses, living yeast cells, and bacteria. Indeed, a noteworthy result was that cells encapsulated within a crystalline MOF shell remain viable after exposure to a medium containing lytic enzymes. Furthermore, the cells can adsorb nutrients (glucose) through the MOF shell but cease reproducing until the MOF casing is removed, at which point normal cellular activity is fully restored. The field of MOF biocomposites is expansive and rapidly developing toward different applied research fields including protection and delivery of biopharmaceuticals, biosensing, biocatalysis, biobanking, and cell and virus manipulation. This Account describes the current progress of MOFs toward biotechnological applications highlighting the different strategies for the preparation of biocomposites, the developmental milestones, the challenges, and the potential impact of MOFs to the field.

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