Background Pressure therapy improves hypertrophic scar healing, but the mechanisms for this process are not well understood. We sought to investigate the differential expression of matrix metalloproteinases （Mmps） and collagen in post- traumatic hypertrophic scar tissue with mechanical pressure and delineate the molecular mechanisms of pressure therapy for hypertrophic scars. Methods Fibroblast lines of normal skin and scar tissue were established and a mechanical pressure system was devised to simulate pressure therapy. Reverse transcription-polymerase chain reaction （RT-PCR） and Western blotting assays were used to compare differences in the mRNA and protein expression of Mmps and collagen in scar fibroblasts before and after pressure therapy. Results The expression differed between the hypertrophic scar cell line and the normal cell line. RT-PCR assays showed that Collagen I, highly expressed in the hypertrophic scar cell line, decreased significantly after pressure therapy. Mmp2, Mmp9, and Mmp12 expression in the hypertrophic scar tissue increased significantly after pressure therapy （P 〈0.05）. Western blotting assays further revealed that Mmp9 and Mmp12 expression increased significantly in the hypertrophic scar tissue after pressure therapy （P 〈0.05） but not Mmp2 expression （P 〉0.05）. Conclusion Mechanical pressure induces degradation of Collagen I in hypertrophic scar tissue by affecting the expression of Mmp9 and Mmp12.
