If you have already collected a tendons, then you need to define what lenghtscale you want to work on. If you want to work at the molecular scale, then you could simply disolve part of the tendon in acetic acid. The collagen should disolve failry rapidly and the solution obtained would be collagen rich, with the molecules still intact. If you wish to work on fibrillar collagen, then i would advise to cut about 5mm long piece of the tendon and use sharp tweezers to open the fasicles for examples. However, in the long run the best option is to work on cryo-section of the tendon as you would conserve the fibrillar alignement too.