Noninvasive Absolute Electron Paramagnetic Resonance Oxygen Imaging for the Assessment of Tissue Graft Oxygenation

Abstract

Oxygen is the single most important molecule for sustaining life and, therefore, an important variable in tissue engineering and regenerative medicine. It has been shown that the change in oxygen concentration in an artificial or tissue-engineered graft affects cell survival, differentiation, and tissue growth in profound ways. However, at present, there are no reliable methods to map partial oxygen pressure (pO) in growing artificial tissues. Here, we adapt and test the suitability of electron paramagnetic resonance oxygen imaging (EPROI) in assessing tissue graft oxygenation in vitro. EPROI is an established method to assess absolute pO and has been widely applied to study tumor hypoxia in small animals. In this study, we demonstrate the feasibility of EPROI in evaluating oxygen dynamics in tissue grafts. We measured oxygen concentration in mesenchymal stem cell (MSC)-seeded polylactic-co-glycolic acid (PLGA) scaffolds with variable porosity. The pO maps of these scaffolds showed that the mean pO inside the scaffolds was smaller than the ambient air pO (21% oxygen, 160 torr) and was gradually increased with increasing pore size. We assessed the local oxygen dynamics of the MSC-seeded osteogenic scaffold made from collagen-chitosan hydrogels in a partially sealed Eppendorf tube. The change in pO values as a function of time inside the graft showed that the cells had used available oxygen within first 2 h of the experiment and then went to a dormant low oxygen consumption state until the oxygen supply was reestablished. Collectively, these data suggest that EPROI could be successfully used for mapping pO in tissue-engineered grafts. The knowledge of tissue graft oxygenation may be used to improve scaffold design and to assess the tissue viability and growth.

An inverse-breathing encapsulation system for cell delivery

“…S20). These measurements were acquired using pulse electron paramagnetic resonance (EPR) O 2 imaging ( 42 – 44 ) via a 25-mT preclinical O 2 imager, the JIVA-25 instrument (O2M Technologies LLC, Chicago, IL) ( Fig. 5, A and B).…”

A bioinspired scaffold for rapid oxygenation of cell encapsulation systems

“…O 2 distribution mapping was performed on an electron paramagnetic resonance (EPR) 44 , 45 O 2 imager to characterize O 2 transport through the SONIC scaffold (Fig. 3 ).…”

Amniotic growth factors enhanced human pre‐adipocyte cell viability and differentiation under hypoxia

“…Briefly, EPROI manipulates unpaired electron spins with the help of magnetic field and magnetic field gradients to generate images of spin magnetization. If the relaxation of the spin probe is oxygen‐dependent, then EPROI can provide a map of local oxygen pressure at the site of inquiry 24 . The oxygen sensing molecule of choice is Trityl OX071 (also known as OX063‐D24) since its relaxation time is strongly influenced by pO 2 , its non‐toxic, and small nonpolar O 2 molecules can efficiently reach each radical.…”

“…If the relaxation of the spin probe is oxygen-dependent, then EPROI can provide a map of local oxygen pressure at the site of inquiry. 24 The oxygen sensing molecule of choice is Trityl OX071 (also known as OX063-D24) since its relaxation time is strongly influenced by pO 2 , its non-toxic, and small nonpolar O 2 molecules can efficiently reach each radical. Briefly, 10 mm sample tube and rubber stopper were sterilized using Sporklenz for 40 min.…”