Mechanoresponsive and recyclable biocatalytic sponges from enzyme-polymer surfactant conjugates and nanoparticles.

The development of multifunctional hybrid biomaterials is an important area of focus in tissue engineering, drug delivery, biocatalysis, and biosensing applications. Combining bioconjugation methodology with ice templating technique, we show here the development of a new class of multifunctional and biocatalytic scaffold-like spongy material fabricated from an aqueous solution of enzyme-polymer surfactant (enzyme-PS) core-shell conjugates, and polyethyleneimine (PEI) coated silica/silk nanoparticles. The generality of this process is demonstrated by the fabrication of biocatalytic sponges comprising PEI coated nanoparticles and core-shell conjugates of alkaline phosphatase (ALP-PS), or glucose oxidase (GOx-PS), and horseradish peroxidase (HRP-PS). We show that ALP-PS conjugate driven biocatalytic transformations can be simply achieved by saturating the highly porous, and manoeuvrable sponges with the -nitrophenyl phosphate substrate solution. Subsequently, the compressible and elastic property of the sponge can be utilized for the extrusion of the product, -nitrophenol, by applying controlled and normal mechanical stress. Further, the sponges can be washed and recycled upto ten times, with approximately 67% retention of initial biocatalytic activity. Interestingly, the ALP-PS conjugate based sponges exhibit mechanoresponsive catalytic behaviour; the amount of product obtained over 25 minutes of reaction time can be increased by approx. 8 times by compressing-decompressing the sponge after every 15 seconds. This is attributed to the change in mass transfer and diffusion of the substrate within the porous channels of the sponge. We also highlight the importance of bioconjugation of enzymes for fabricating such sponges; our results show that, whilst the native enzymes either denature or are leached away during the fabrication/biocatalytic usage, their enzyme-PS conjugate counterparts integrate efficiently to form sturdy, robust, highly catalytic, and recyclable sponge material.