The present invention relates to an irregularly shaped grain for providing ingrowth and growth of connective tissue as well as growth of other cell types leading to cluster of cells, tissues and parts of organs. Said grain includes multiple pores that are continuous through said grain, and openings of said multiple pores and ducts or passages interconnecting at least a portion of said multiple pores have a width of greater than about 10 .mu.m. Said grain is preferably a metal or metal alloy. The invention also relates to different applications of the grains.