LORs for BME grad school

<p>Hi everyone,</p>

<p>I'm applying to Ph D programs and am concerned about my LOR's. My only significant research experience is working in the lab I'm currently in, and I should be able to get a strong letter from my PI, who is well-known in the field I want to go into (orthopaedic biomechanics). However, I don't know what to do for my other 1-2 recommendations. I'm not the most outgoing person, so most of my professors could only write something along the lines of "nice kid, got an A in my class." I have a strong personal relationship with a non-BME professor, but again, he couldn't say much about me as a potential researcher. For my design project next semester, I will be working with an MD who could write me a letter, but he doesn't know me well at all right now. Would having one strong letter and 1-2 mediocre ones be a major blow to my application? If so, would it be worth waiting a year to apply so I can build a relationship with the MD and then maybe do an internship over the summer to get a third LOR?</p>