The present invention provides methods and compositions for augmenting organ functions using small-scale matrix implants generated by seeding tissue-specific or undifferentiated cells onto a matrix materials (e.g., a wafer, sponge, or hydrogel). The seeded matrix composition can then be implanted and will develop into an organ-supplementing structure in vivo. Continued growth and differentiation of the seeded cells on the implanted matrix results in the formation of a primitive vascular system in the tissue. The primitive vascular system can then develop into a mature vascular system, and can also support the growth and development of additional cultured cell populations. The seeded matrix system can be used to introduce a variety of different cells and tissues in vivo.
