A biological fluid filter assembly comprising: a flexible housing having first and second walls; a filtration medium at least partially positioned between the first and second walls of the housing; a post-filter mesh at least partially positioned between the filtration medium and the second wall; and a seal joining the first and second walls of the housing, wherein the first wall includes an inlet port and the second wall includes an outlet port, and the first and second walls are made of a plastic material; a pre-filter is at least partially positioned between the inlet port and the filtration medium; the post-filter mesh is integrally formed with a frame and is made from the plastic material; and an inner seal is formed by integrating a section of the filtration medium at or adjacent to a perimeter of the filtration medium, a section of the pre-filter at or adjacent to a perimeter of the filtration medium, a section of the frame of the mesh element, and a section of the first and second walls at or adjacent to a perimeter of the first and second walls, wherein the inner seal comprises a central section consisting of a layer consisting only of the plastic material of the first wall and having a thickness in the range of approximately 90-250 micrometers, an intermingled layer in which the plastic material of at least the first wall is intermingled with the pre-filter and having a thickness in the range of approximately 170-300 micrometers, and an aggregate in which the plastic material of at least the second wall and the frame are intermingled and having a thickness in the range of approximately 0.84-1.5 millimeters. a flexible housing having first and second walls; a filtration medium at least partially positioned between the first and second walls of the housing; a post-filter mesh at least partially positioned between the filtration medium and the second wall; and a seal joining the first and second walls of the housing, wherein the first wall includes an inlet port and the second wall includes an outlet port, and the first and second walls are made of a plastic material; a pre-filter is at least partially positioned between the inlet port and the filtration medium; the post-filter mesh is integrally formed with a frame and is made from the plastic material; and an inner seal is formed by integrating a section of the filtration medium at or adjacent to a perimeter of the filtration medium, a section of the pre-filter at or adjacent to a perimeter of the filtration medium, a section of the frame of the mesh element, and a section of the first and second walls at or adjacent to a perimeter of the first and second walls, wherein the inner seal comprises a central section consisting of a layer consisting only of the plastic material of the first wall and having a thickness in the range of approximately 90-250 micrometers, an intermingled layer in which the plastic material of at least the first wall is intermingled with the pre-filter and having a thickness in the range of approximately 170-300 micrometers, and an aggregate in which the plastic material of at least the second wall and the frame are intermingled and having a thickness in the range of approximately 0.84-1.5 millimeters. the first wall includes an inlet port and the second wall includes an outlet port, and the first and second walls are made of a plastic material; a pre-filter is at least partially positioned between the inlet port and the filtration medium; the post-filter mesh is integrally formed with a frame and is made from the plastic material; and an inner seal is formed by integrating a section of the filtration medium at or adjacent to a perimeter of the filtration medium, a section of the pre-filter at or adjacent to a perimeter of the filtration medium, a section of the frame of the mesh element, and a section of the first and second walls at or adjacent to a perimeter of the first and second walls, wherein the inner seal comprises a central section consisting of a layer consisting only of the plastic material of the first wall and having a thickness in the range of approximately 90-250 micrometers, an intermingled layer in which the plastic material of at least the first wall is intermingled with the pre-filter and having a thickness in the range of approximately 170-300 micrometers, and an aggregate in which the plastic material of at least the second wall and the frame are intermingled and having a thickness in the range of approximately 0.84-1.5 millimeters. a layer consisting only of the plastic material of the first wall and having a thickness in the range of approximately 90-250 micrometers, an intermingled layer in which the plastic material of at least the first wall is intermingled with the pre-filter and having a thickness in the range of approximately 170-300 micrometers, and an aggregate in which the plastic material of at least the second wall and the frame are intermingled and having a thickness in the range of approximately 0.84-1.5 millimeters.