Preservation of Blood Vessels with an Oxygen Generating Composite.

Damage caused by oxygen deficiency (hypoxia) is one of the major factors limiting tissue and organ preservation time. Cooling tissues slows down metabolic rate of cells thereby prolonging tissue and organ survival sufficiently to allow transport and transplantation within a few hours. Although metabolism is slowed, cells and some enzymes continue to consume oxygen that can render cold stored tissues hypoxic. Here, an oxygen-generating composite (OGC) with sustained oxygen release is reported for ex vivo blood vessel preservation. Aorta segments are cultured under hypothermia for 25 days in vascular preservation media. The presence of OGC increases cell viability from 9 ± 6% to 96 ± 3% and retains 65 ± 8% of original KCl stimulated contractile force after 25 days compared with 25 ± 4% in controls. Culture for 7 days in nitrogen demonstrates proof-of-concept for normothermic blood vessel preservation, OGC increases the cell viability from 45 ± 15% to 78 ± 2%, and KCl stimulates contractile force from 49 ± 7% to 95 ± 8%, respectively. Oxygen release materials then may have a role in augmenting current preservation techniques.

Mimicking oxygen delivery and waste removal functions of blood.

In addition to immunological and wound healing cell and platelet delivery, ion stasis and nutrient supply, blood delivers oxygen to cells and tissues and removes metabolic wastes. For decades researchers have been trying to develop approaches that mimic these two immediately vital functions of blood. Oxygen is crucial for the long-term survival of tissues and cells in vertebrates. Hypoxia (oxygen deficiency) and even at times anoxia (absence of oxygen) can occur during organ preservation, organ and cell transplantation, wound healing, in tumors and engineering of tissues. Different approaches have been developed to deliver oxygen to tissues and cells, including hyperbaric oxygen therapy (HBOT), normobaric hyperoxia therapy (NBOT), using biochemical reactions and electrolysis, employing liquids with high oxygen solubility, administering hemoglobin, myoglobin and red blood cells (RBCs), introducing oxygen-generating agents, using oxygen-carrying microparticles, persufflation, and peritoneal oxygenation. Metabolic waste accumulation is another issue in biological systems when blood flow is insufficient. Metabolic wastes change the microenvironment of cells and tissues, influence the metabolic activities of cells, and ultimately cause cell death. This review examines advances in blood mimicking systems in the field of biomedical engineering in terms of oxygen delivery and metabolic waste removal.

Cellular internalization of rod-like nano hydroxyapatite particles and their size and dose-dependent effects on pre-osteoblasts.

Nano hydroxyapatite particles (n-HA) have been reported to promote osteogenic activities of bone-related cells, while inhibiting tumor cell growth, and the biological effects of n-HA are related with the particle size, dose, culture time and cell type. In this work, we prepared n-HA with a strictly controlled rod-like shape and adjustable sizes without any surface chemical contaminations. Using the prepared n-HA, we investigated the size and dose effect of the nano particles on pre-osteoblasts for up to 7 days. We probed cell proliferation and gene expression in the presence of n-HA, the cellular uptake pathways of n-HA particles, as well as the extracellular and intracellular [Ca2+] ([Ca2+]i) changes caused by the particles, in order to get a better understanding of the biological effects of n-HA of various sizes. The n-HA exhibited size- and dose-dependent impacts on MC3T3-E1 proliferation, intracellular reactive oxygen species (ROS) generation, mitochondrial membrane potential, and osteogenic gene expression. 40 nm n-HA caused the slowest MC3T3-E1 growth, the highest intracellular ROS concentration, the largest mitochondrial membrane potential loss and the lowest level of osteogenic gene expression among the samples. The cytotoxicity of 40 nm n-HA increased with the dose and culture time. 70 nm n-HA showed beneficial effects on MC3T3-E1 growth, but the positive effect disappeared at the highest concentration on day 7. 100 nm n-HA promoted cell growth and the promoting effect increased with the dose. Cells cultured with 100 nm n-HA expressed the highest level of osteogenic gene expression among the experimental groups. We discovered that the presence of n-HA increased [Ca2+]i but did not elevate extracellular [Ca2+]. The [Ca2+]i increased as the n-HA size decreased. We also found that n-HA may enter cells through two pathways and that the amount of engulfed particles depended on the particle size. The internalized n-HA particles located in the cytosol, endosomes, lysosomes and nuclei. The particles dissolved in lysosomes and raised [Ca2+]i, which correlated with the cell death and osteogenic gene expression. In conclusion, the particle size, dose, and culture time influenced the biological effects of n-HA on ME3T3-E1 cells, probably by changing the [Ca2+]i in the cells instead of the extracellular [Ca2+].