Raphael J. Gübeli

Mussel-mimetic tissue adhesive for fetal membrane repair: an ex vivo evaluation.

Iatrogenic preterm prelabor rupture of membranes (iPPROM) remains the main complication after invasive interventions into the intrauterine cavity. Here, the proteolytic stability of mussel-mimetic tissue adhesive (mussel glue) and its sealing behavior on punctured fetal membranes are evaluated. The proteolytic degradation of mussel glue and fibrin glue were compared in vitro. Critical pressures of punctured and sealed fetal membranes were determined under close to physiological conditions using a custom-made inflation device. An inverse finite element procedure was applied to estimate mechanical parameters of mussel glue. Mussel glue was insensitive whereas fibrin glue was sensitive towards proteolytic degradation. Mussel glue sealed 3.7mm fetal membrane defect up to 60mbar (45mmHg) when applied under wet conditions, whereas fibrin glue needed dry membrane surfaces for reliable sealing. The mussel glue can be represented by a neo-Hookean material model with elastic coefficient C(1)=9.63kPa. Ex-vivo-tested mussel glue sealed fetal membranes and resisted pressures achieved during uterine contractions. Together with good stability in proteolytic environments, this makes mussel glue a promising sealing material for future applications.

Pharmacologically triggered hydrogel for scheduling hepatitis B vaccine administration.

The simplification of current vaccine administration regimes is of crucial interest in order to further sustain and expand the high impact of vaccines for public health. Most vaccines including the vaccine against hepatitis B need several doses to achieve protective immunization. In order to reduce the amount of repetitive injections, depot-based approaches represent a promising strategy. We present the application of novobiocin-sensitive biohybrid hydrogels as a depot for the pharmacologically controlled release of a vaccine against hepatitis B. Upon subcutaneous implantation of the vaccine depot into mice, we were able to release the vaccine by the oral administration of the stimulus molecule novobiocin resulting in successful immunization of the mice. This material-based vaccination regime holds high promises to replace classical vaccine injections conducted by medical personnel by the simple oral uptake of the stimulus thereby solving a major obstacle in increasing hepatitis B vaccination coverage.

Synthesis and Characterization of PEG-Based Drug-Responsive Biohybrid Hydrogels

Interactive materials being responsive to a biocompatible stimulus represent a promising approach for future therapeutic applications. In this study, we present a novel biohybrid material synthesized from biocompatible components being stimulus-responsive to the pharmaceutically approved small-molecule novobiocin. The hydrogel design is based on the gyrase B (GyrB) protein, which is covalently grafted to multi-arm polyethylene glycol (PEG) using a Michael-type addition reaction. Upon addition of the GyrB-dimerizing substance coumermycin, stable hydrogels form which can be dissolved in a dose-adjustable manner by the antibiotic novobiocin. The switchable properties of this PEG-based hydrogel are favorable for future applications in tissue engineering and as externally controlled drug depot.

Synthetic biology for mammalian cell technology and materials sciences

The synthetic reconstruction of natural gene networks and the de novo design of artificial genetic circuits provide new insights into the cells regulatory mechanisms and will open new opportunities for drug discovery and intelligent therapeutic schemes. We will present how modular synthetic biology tools like repressors, promoters and enzymes can be assembled into complex systems in order to discover small molecules to shut off antibiotic resistance in tubercle bacteria and to design self-sufficient therapeutic networks. The transfer of these synthetic biological modules to the materials science field enables the construction of novel drug-inducible biohybrid materials for biomedical applications.

Pharmacologically tunable polyethylene-glycol-based cell growth substrate

Biohybrid materials combining synthetic polymers with biological components are highly suited for tissue engineering in order to emulate the behavior of natural materials such as the extracellular matrix (ECM). In order to allow for an optimal cell-material interplay, the physical and biological parameters of the artificial matrix need to be dynamically remodeled during cultivation. Current tissue engineering concepts are mainly based on passive remodeling mechanisms including the degradation of the hydrogel and the release of incorporated biomolecules and therefore do not enable external adjustment of cultivation conditions. We present a novel hydrogel material that is able to serve as a cell growth matrix, whose degradation and presentation of cell-interacting biomolecules can be externally controlled by the addition of a pharmacological substance. The hydrogel is based on branched polyethylene glycol that is covalently decorated with the aminocoumarin-antibiotic switchable gyrase B protein conferring stimulus-responsive degradation. ECM properties were conferred to the hydrogels with cell attachment motifs and a general approach for the incorporation and inducible release of therapeutic biomolecules. This smart biohybrid material has the potential to serve as a next-generation tissue engineering device which allows for dynamic external adjustment of the physical and biological parameters, resulting in optimally controlled tissue formation.

Synthesis and characterization of a stimulus-responsive l-ornithine-degrading hydrogel

Hydrogels provide a highly favorable matrix for immobilizing growth factors, enzymes or cells for biomedical applications like tissue engineering, drug delivery or the treatment of metabolic diseases. In this study we describe the synthesis and characterization of a hydrogel able to degrade L-ornithine, a metabolite that is highly elevated in congenital hyperornithinemia. The hydrogel was synthesized by embedding the L-ornithine-degrading enzymes L-ornithine aminotransferase (OAT) and L-ornithine decarboxylase (ODC) into a polymer network. The network was formed from linear polyacrylamide crosslinked by heterodimers of ODC and ornithine decarboxylase antizyme (OAz). The resulting hydrogel was shown to be stable under physiological conditions and to efficiently degrade L-ornithine. The hydrogel-stabilizing ODC-OAz interactions could subsequently be dissociated by the addition of antizyme inhibitor (AzI) which resulted in the inducible dissolution of the hydrogel. This L-ornithine-degrading hydrogel that can efficiently be eliminated when its functionality is no longer required might represent a first step towards an enzyme substitution approach against hyperornithinemia.

Microfluidic Synthesis of Pharmacologically Responsive Supramolecular Biohybrid Microgels

Biohybrid hydrogels that change their mechanical properties in response to pharmacological cues hold high promises as externally controlled drug depots for biomedical applications. In this study, we devise a generically applicable method for the synthesis of micrometer-scale, injection-ready biohybrid materials. We use droplet-based microfluidics to generate monodisperse pre-microgel fluid droplets, wherein which we react fluorescein-modified 8-arm poly(ethylene glycol) with a thiol-functionalized humanized anti-fluorescein single chain antibody fragment and vinylsulfone-functionalized 8-arm poly(ethylene glycol), resulting in the formation of stable, narrowly dispersed supramolecular microgels (30 and 150 μm diameter). We demonstrate that the addition of free fluorescein to these microgels results in a weakening of their hydrogel structure, eventually leading to its disintegration. This method of formation of pharmacologically responsive biohybrid hydrogels in an injection-ready formulation is a pioneering example of a general approach for the synthesis of biohybrid hydrogel-based drug depots for biomedical applications.