In this study, an amino acid microgel from L-Lysine as poly(L-Lysine) (L1) was prepared in a single step for the first time via microemulsion polymerization/crosslinking technique using tetrakis (hydroxymethyl) phosphium chloride (THPC) as crosslinking agent. The spherical L1 microgels with size range of few micrometers revealed by SEM images, were readily modifiable in terms of surface charges upon simple treatment with HCl and NaOH to obtain L2 and L3 forms of the microgel due to protonation of amine groups and deprotonation of carboxylic acid groups to provide tunable surface charge on synthesized L1 microgels. The zeta potential of L1 microgels increased to 29.6 mV with HCl treatment and decreased to -41.8 mV with NaOH treatment from -19.1 mV for L1 microgels. Moreover, the biocompatibility tests of the prepared microgels interestingly showed L3>L2>L1 with over 85% biocompatibility up to 300 mu g/mL particle concentration. Furthermore, the blood compatibility tests revealed that L1 and L3 microgels have high hemocompatibility with 5.12 +/- 0.58% and 0.55 +/- 0.27% hemolysis ratios, and effective hemostatic properties with 96.17 +/- 2.15 and 99.63 +/- 0.17 blood clotting indices, respectively; whereas L2 particles were found to be non-blood compatible due to their highly positively charged nature. Therefore, poly(L-Lysine) microgels possess great potential and may be readily used in vivo for biomedical purposes. (C) 2017 Elsevier Ltd. All rights reserved.