Figure 4: Shows the tissue reactions to the Collprotect® membrane (CP). A and B show that a thin layer of mononuclear cells (black arrow heads in A) and smallsized vessels (read arrows in A) were located at the surface of the membrane (CP) at day 3 after implantation. The membrane (CP=double arrow in B) was detectable within the subcutaneous connective tissue (CT) and shows no signs of tissue ingrowth (CT=connective tissue) (H&E-stain; A: 400x magnification, scale bar=10 μm; B: 100x magnification, scale bar=100 μm). C and D show the tissue reaction to the Collprotect® membrane (CP= double arrow) at day 10 after implantation. The surface of the membrane was still covered by a thin wall of mononuclear cells (black arrow heads in C); while few cells invaded the body of the membrane at this time point (green arrow heads in C). The membrane (CP= double arrow in D) was still detectable with the connective tissue (CT) without any change in its integrity (C: MovatPentachrome-stain, 400x magnification, scale bar=10 μm; D: Sirius-stain, 100x magnification, scale bar= 100 μm). E and F show the tissue reaction to the Collprotect® membrane (CP= double arrow) at day 15 after implantation. The membrane surfaces were covered by mono- and multinuclear cells (black/red arrow heads in E), while the membrane (CP=double arrow in F) was still observable within the connective tissue (CT) without loss of its volume stability. At this time point more cells have started to penetrate the membrane in its superficial regions (green arrow heads in E) (E: Movat Pentachrome-stain, 400x magnification, scale bar=10 μm; F: H&E-stain, 100x magnification, scale bar=100 μm). G and H show the tissue reaction to the Collprotect® (CP=double arrow) at day 30 after implantation. Complex tissue threads with mono- and multinucleated cells (black / red arrow heads in G), cells penetrating the membrane (green arrow heads in G), as well as vessels (red arrows in G) have started to invade its superficial and deeper regions, while the membrane (CP=double arrows in H) maintained its integrity (CT=Connective Tissue) (G: Azan-stain, 400x magnification, scale bar=10 μm; H: Sirius-stain, 100x magnification, scale bar=100 μm).