Project 2–2: Micro- and Nanofluidic Devices for Sorting and Sensing Biowarfare Agents and Engineering Blood Additives

Principal Investigators: Eric Shaqfeh and Eric Darve (Stanford University)

The Push for Platelets

Donated blood is the most common treatment for acute blood loss arising from invasive surgery or traumatic wounding. Donated whole blood can be stored for approximately one month under the proper conditions. Recipient blood types must be cross-matched against available stocks of donor blood, and the threat of spreading infectious diseases such as HIV and hepatitis cannot be eliminated completely. These limitations are exacerbated in field situations, where electricity for refrigeration may be sporadic and a supply of suitable donors is limited. Donor blood can be used more efficiently by separating it into components—including platelets— that are processed for storage and transport. Fresh platelets must be used within five days of donation, and laboratory testing may require as much as one day.

Platelets act as “first responders” at a wound site. Damage to blood vessel walls exposes collagen structural material to direct contact with the bloodstream, activating the platelets and causing them to release granular particles containing tissue growth factors. The growth factors attract fibrin from the blood plasma, which forms a mesh that stops blood loss. Other growth factors stimulate the formation of new tissue cells on the fibrin scaffolding. Platelets can be stored for clinical use by treating them with preserving agents such as glycerol or dimethyl sulfoxide (DMSO) to prevent agglomera- tion, then freeze-drying them (lyophilization). The platelets are thawed and rehydrated at the time of use, which can be up to several months after dona- tion. Reconstituted platelets must be washed and processed to remove the preserving agents, which requires specialized equipment and generates byproducts that must be disposed of properly.

Many platelets are damaged or destroyed during reconstitution. Reconstituted platelets often have a balloon shape that not only affects their ability to circulate in the bloodstream, but makes them unresponsive to biochemical stimulants (agonists, such as thrombin) that would normally activate the clot-forming behavior of the platelets. Reconsti- tuted platelets are less than 35% as responsive to wound-generated agonists as fresh platelets. Wound treatments derived from platelet-enriched concentrates offer the benefits of platelet-generated growth factors and wound sealing properties that stop blood loss. However, the concentrate must be applied to the wound site within a few seconds after the activating agent is added, because hardening is almost instantaneous. The concentrates are often derived from the patient’s own blood, and they must be re-applied daily. This requires repeated blood withdrawal from the patient and on-site processing procedures.

Lyophilized platelet treatments avoid problems associated with platelet concentrates, and thus, are of great interest to Army medical researchers.

Reference: U.S. Patent application 20080213238, James Bennie Gandy and Mackie J. Walker.

Source: AHPCRC Bulletin, Vol. 1 No. 4 (2009)