**Author details**

of fibrin strands can clearly be seen with rounding of the cell bodies with loss of extending processes (**Figure 6**). Cell viability is preserved in cells encapsulated within frPL pellets. The pellets can be degraded and MSCs can be released with dispase treatment. Viability of MSCs within the frPL pellets is preserved for up to 3 days in vitro, as determined with a live/dead assay. The ability of frPL to form dense cell spheroids containing MSCs provides yet another practical application of platelet lysate. The frPL MSC spheroids could serve as an additional

Innovative strategies are needed for enhancing quality of MSCs in patients with CLI while also improving delivery and retention of MSCs for cell‐based therapy. Here we discuss the dual use of human platelet lysate as both a cell culture supplement and a scaffold for cell delivery. When bereft of clotting factors, depleted form of platelet lysate (dPL) supplemented media enables rapid expansion of MSCs without diminishing their angiogenic activity. In contrast, with preservation of clotting factors, frPL forms a rapidly assembling hydrogel with desirable structural properties and biological activity on MSC and ECs. In both soluble and hydrogel form, PL augments the proangiogenic qualities of MSCs and is readily derived from human source materials that have been tested for safe delivery to patients. As a result of these

hydrogels in six well tissue culture dishes with (untethered) and without (tethered) preblocking the plate with 2% albumin solution. MSCs within the frPL formed dense spheroids. Hydrogels were labeled with 5% FITC‐dextran and seeded with CellTracker Red‐labeled MSCs in tethered and untethered culture conditions. Scale bars represent 20 μm

 MSCs/mL were embedded in frPL or fibrin

mechanism of cell delivery, by encapsulating MSCs in a thin fibrin shell.

378 Physiologic and Pathologic Angiogenesis - Signaling Mechanisms and Targeted Therapy

**Figure 6.** MSCs embedded in untethered frPL form cell spheroids. 2×10<sup>5</sup>

**3. Conclusion**

(original figure).

Scott T. Robinson<sup>1</sup> and Luke P. Brewster2, 3\*

\*Address all correspondence to: lbrewst@emory.edu

