New approach to measuring oxygen diffusion and consumption in encapsulated living cells, based on electron spin resonance microscopy.

Cell microencapsulation within biocompatible polymers is an established technology for immobilizing living cells that secrete therapeutic products.  These can be transplanted into a desired site in the body for the controlled and continuous delivery of the therapeutic molecules.  One of the most important properties of the material that makes up the microcapsule is its oxygen penetrability, which is critical for the cells' survival.  Oxygen reaches the cells inside the microcapsules via a diffusion process.  The diffusion coefficient for the microcapsules' gel material is commonly measured using bulk techniques, where the gel in a chamber is first flushed with nitrogen and the subsequent rate of oxygen diffusion back into it is measured by an oxygen electrode placed in the chamber.  This technique does not address possible heterogeneities between microcapsules, and also cannot reveal O2 heterogeneity inside the microcapsule resulting from the living cells' activity.  Here we develop and demonstrate a proof of principle for a new approach to measuring and imaging the partial pressure of oxygen (pO2) inside a single microcapsule by means of high-resolution and high-sensitivity electron spin resonance (ESR).  The proposed methodology makes use of biocompatible paramagnetic microparticulates intercalated inside the microcapsule during its preparation.  The new ESR approach was used to measure the O2 diffusion properties of two types of gel materials (alginate and extracellular matrix - ECM), as well as to map a 3D image of the oxygen inside single microcapsules with living cells. STATEMENT OF SIGNIFICANCE: The technology of cell microencapsulation offers major advantages in the sustained delivery of therapeutic agents used for the treatment of various diseases ranging from diabetes to cancer. Despite the great advances made in this field, it still faces substantial challenges, preventing it from reaching the clinical practice. One of the primary challenges in developing cell microencapsulation systems is providing the cells with adequate supply of oxygen in the long term. Nevertheless, there is still no methodology good enough for measuring O2 distribution inside the microcapsule with sufficient accuracy and spatial resolution without affecting the microcapsule and/or the cells' activity in it. In the present work, we introduce a novel magnetic resonance technique to address O2 availability within cell-entrapping microcapsules. For the first time O2 distribution can be accurately measured and imaged within a single microcapsule. This new technique may be an efficient tool in the development of more optimal microencapsulation systems in the future, thus bringing this promising field closer to clinical application.

Innovative encapsulation platform based on pancreatic extracellular matrix achieve substantial insulin delivery.

Cell-based therapies for the treatment of diabetes, generally aim to provide long-term glucose regulated-insulin delivery using insulin producing cells. The delivery platform is crucial for the therapeutic outcome as well as for immunoisolation of the entrapped cells. We have developed a novel artificial pancreas encapsulation platform for the treatment of diabetes that is based on solubilized whole porcine pancreatic extracellular matrix (ECM). These unique capsules were used to entrap human liver cells and mesenchymal stem cells that were induced to differentiate into glucose-regulated insulin-producing cells. We demonstrate that the ECM-microcapsule platform provides a natural fibrous 3D niche, supporting cell viability and differentiation, while significantly improving insulin delivery. In vivo, ECM-encapsulated cells were shown to be non-immunogenic, and most importantly, to significantly improve the glycemic control in diabetic mouse preclinical model, thus establishing a proof-of-concept for this new cell-based insulin delivery platform.