Extrusion Behavior, Osmolality and pH of a Reconstituted Conditioned-Medium Cosmetic Product: A Pilot Physicochemical Comparison of Two Reconstitution Vehicles

Lyophilized cosmetic biologics are supplied as an active powder and a base solution, but the physicochemical properties of the reconstituted preparation are seldom reported. In this preliminary study one production lot of a commercial human stem cell conditioned medium extract was reconstituted either with the supplied base solution or with 0.9% sodium chloride, at the same active concentration, and compared in a standardized extrusion test (26 G orifice, 50 g load, 0.2 mL, 25 °C). Replicates were repeated measurements on one preparation of each fluid rather than on independent preparations, so the data are summarized descriptively. The saline-reconstituted preparation gave a median extrusion time of 3.05 s (range 2.52–3.58) and the manufacturer-directed preparation 39.63 s (20.85–107.97), a 13-fold difference; the latter could not be aspirated into a freezing-point-depression osmometer. The base solution alone did not extrude within 60 s at 50 g, but did at 100 g, with medians of 8.03, 5.98 and 6.48 s in three independently opened vials. Doubling the load changed the observed extrusion time of the reference saline by a factor of 2.5 and that of the base solution by at least nine, which suggests a dependence of flow on the applied stress that a Newtonian fluid would not show, although the two loads were measured in separate sessions. The saline-reconstituted preparation measured 374 mOsm/kg against 286 mOsm/kg for its diluent; both preparations had a pH of 5.0 and both diluents 5.5, so the diluent did not determine the final pH. These preliminary observations require confirmation with independently prepared replicates and indicate that such properties are worth measuring on the final reconstituted fluid rather than inferred from the ingredient declaration.