A method for preparing a collagen particle comprising: subjecting an animal skin having a thickness of about 0.1-1 mm to a decellularization process; subjecting the decellularized animal skin of step to the treatment of an aqueous solution comprising a non-ionic surfactant; subjecting the aqueous solution treated animal skin of the step to the treatment of a protease; subjecting the protease treated animal skin of step to the treatment of a nuclease; subjecting the nuclease treated animal skin of step to a de-ionization process; subjecting the de-ionized animal skin of step to a chemical removal process so as to produce a collagen matrix; and subjecting the collagen matrix of step to a granulation process so as to produce the collagen particle having a size of about 10-250 μm, wherein in the step, the animal skin having a thickness of about 0.1-1 mm is subject to the treatment of a supercritical fluid under a pressure of about 10 - 50 MPa (100 - 500 bar) at a temperature between 30-50°C for about 20 min to 5 days and the SCF is a supercritical carbon dioxide (scCO 2) or a supercritical nitrous oxide (scN 2 O); wherein the non-ionic surfactant of the aqueous solution of step is selected from the group consisting of octylphenol ethoxylates, sorbitan monostearate, polysorbate, poloxomer, nonoxynols, cetyl alcohol, and alkylpolyglucoside; wherein the protease of the step is any of pepsin, trypsin, chymotrypsin, papain, chymopapain, bromelain, actinidain, proteinase A, proteinase K, peptidase, ficin, calpain, caspase, or a combination thereof; wherein the nuclease of the step is a DNA nuclease or a RNA nuclease; wherein the de-ionization process of step comprises treating the nuclease treated animal skin of the step with a hydrogen peroxide solution for an hour; wherein in the step, the de-ionized animal skin of step is subject to the treatment of a supercritical fluid under a pressure of about 10-50 MPa (100 - 500 bar) at a temperature between 30-50°C for about 20 min to 5 days to remove residual chemicals therefrom and the SCF is a supercritical carbon dioxide (scCO 2) or a supercritical nitrous oxide (scN 2 O) and the SCF is applied to the de-ionized animal skin of step along with a co-solvent which is ethanol, wherein "about" means within 10% of a given range. subjecting an animal skin having a thickness of about 0.1-1 mm to a decellularization process; subjecting the decellularized animal skin of step to the treatment of an aqueous solution comprising a non-ionic surfactant; subjecting the aqueous solution treated animal skin of the step to the treatment of a protease; subjecting the protease treated animal skin of step to the treatment of a nuclease; subjecting the nuclease treated animal skin of step to a de-ionization process; subjecting the de-ionized animal skin of step to a chemical removal process so as to produce a collagen matrix; and subjecting the collagen matrix of step to a granulation process so as to produce the collagen particle having a size of about 10-250 μm, wherein in the step, the animal skin having a thickness of about 0.1-1 mm is subject to the treatment of a supercritical fluid under a pressure of about 10 - 50 MPa (100 - 500 bar) at a temperature between 30-50°C for about 20 min to 5 days and the SCF is a supercritical carbon dioxide (scCO 2) or a supercritical nitrous oxide (scN 2 O); wherein the non-ionic surfactant of the aqueous solution of step is selected from the group consisting of octylphenol ethoxylates, sorbitan monostearate, polysorbate, poloxomer, nonoxynols, cetyl alcohol, and alkylpolyglucoside; wherein the protease of the step is any of pepsin, trypsin, chymotrypsin, papain, chymopapain, bromelain, actinidain, proteinase A, proteinase K, peptidase, ficin, calpain, caspase, or a combination thereof; wherein the nuclease of the step is a DNA nuclease or a RNA nuclease; wherein the de-ionization process of step comprises treating the nuclease treated animal skin of the step with a hydrogen peroxide solution for an hour; wherein in the step, the de-ionized animal skin of step is subject to the treatment of a supercritical fluid under a pressure of about 10-50 MPa (100 - 500 bar) at a temperature between 30-50°C for about 20 min to 5 days to remove residual chemicals therefrom and the SCF is a supercritical carbon dioxide (scCO 2) or a supercritical nitrous oxide (scN 2 O) and the SCF is applied to the de-ionized animal skin of step along with a co-solvent which is ethanol, wherein "about" means within 10% of a given range.