Representative histology of implants after 4 weeks of abdominal implantation. A) Control implant without any factor is essentially constituted of fibroadipose tissue with small areas of bone (arrows). B) Fibrous tissue in control implant is well demonstrated by Masson trichromic staining. C) In contrast, implant with recombinant BMP-2 shows large mature bone trabeculae surrounded by fibrous or mesenchymal tissue. D) This mesenchymal tissue shows numerous cells with PCNA positive immunostaining. E) Similar bone production is observed in implant with BMP-7. F) This implant with BMP7 shows extensive areas of osteoid in section stained with Masson technique (asterisk). G) Even more bone trabeculae are seen in an implant with addition of TGF-1. H) They are mature trabeculae constituted by well calcified bone as show by Von Kossa staining. I) In comparison, fewer bone trabeculae were induced in implant with all the TGF family factors.