A bioerodible endoprosthesis includes a composite including a matrix comprising a bioerodible magnesium alloy and a plurality of ceramic nanoparticles within the matrix. The bioerodible magnesium alloy has a microstructure including equiaxed Mg-rich solid solution-phase grains having an average grain diameter of less than or equal to 5 microns. The microstructure can be produced by one or more equal-channel high-strain processes.
