"About one quarter of all of the protein in your body is collagen. Collagen is a major structural protein, forming molecular cables that strengthen the tendons and vast, resilient sheets that support the skin and internal organs."
--http://www.rcsb.org/pdb/101/motm.do?momID=4

Each STL file contains one of the three strands that makes collagen. Model based on the Protein Data Bank entry 1CAG:
--http://www.pdb.org/pdb/explore/explore.do?pdbId=1cag

Model created using VMD:
http://www.ks.uiuc.edu/Research/vmd/

Successfully printed in PLA on a Makerbot Replicator2 using MakerBot Desktop beta 3.4.1.48, standard resolution with 3 shells and 15% infill. Use rafts and supports.

Each of the three models is colored in the images as follows:
1CAG-A_fixed: Red
1CAG-B_fixed: Green
1CAG-C_fixed: Blue

The 5th (multicolor) image is by David Goodsell:
http://www.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/bio.html
and is used under the CC-BY-3.0 license:
http://creativecommons.org/licenses/by/3.0/us/