Experimental optimization of an in situ forming hydrogel for hemorrhage control

The fabrication of a novel in situ forming hydrogel composed of a multifunctional poly(ethylene glycol) (PEG) N-hydroxysuccinimide ester (NHS) and poly(allylamine hydrochloride) (PAA) was investigated. FTIR confirmed that PAA formed the hydrogel matrix (i.e., the formation of a PAA-like hydrogel). A factorial experiment was conducted to identify the key parameters that controlled gelation time, gel content, and swelling properties. The type of PEG (e.g., 4- and 6-arm) appeared to play a major role in determining all three performance parameters, with the greatest effect on gelation time. Other influencing factors include (a) the PEG concentration, which contributes to the gelation time and gel content; (b) pH of the buffer used for dissolving each polymer, which can affect the gelation time; and (c) PAA molecular weights, which contribute to the gel content and swelling. The concentration of PAA solution had no significant effects on hydrogel formation and properties within the investigated range, presumably due to negligible changes in the crosslinking density of the hydrogels. The PAA buffer pH influenced the gel content as well. Finally, thromboelastography was used to examine the effects of each polymer and their in situ gelation on blood coagulation in vitro. All individual polymers tested reduced clot strength, while the gelation of the polymers enhanced overall procoagulant effects. These results suggest that the biomaterial can be optimized to provide a combination of rapid gelation and swelling properties suitable for hemorrhage control and thus warrant further studies in animal bleeding models.