Abstract: A method of fabricating composite filaments is provided. An initial composite filament including a core and a cladding (such as a Pt-group metal) is cut into smaller pieces (or is first mechanically reduced and then cut into smaller pieces). The smaller pieces of the filaments are inserted into a metal matrix, and the entire structure is then further reduced mechanically in a series of reduction steps. The process can be repeated until the desired cross sectional dimension of the filaments is achieved. The matrix can then be chemically removed to isolate the final composite filaments with the cladding thickness down to the nanometer range. The process allows the organization and integration of filaments of different sizes, compositions, and functionalities into arrays suitable for various applications.