The ability of substances to enter the bloodstream and successfully travel to their intended location via a transdermal delivery system (such as a patch) depends on the amount of substance(s) and the time periods at which they are released. Studies conducted using porcine skin (a model human skin) and hairless mouse skin attests to the ability of specifically tailored transdermal patches to transmit non-essential and essential amino acids.
Amongst the various amino acids tested for penetration across the dermal layers and into the bloodstream, study A shows BCAAs valine, cysteine, isoleucine and leucine formulations yielded the highest rates of penetration. Study A also notes the general success of the above stated amino acids in penetrating the skin: "...utilizing L-α-amino acids for enhancing the rate of penetration through the skin of both topical medicaments and of drugs employed for systemic administration."
Overall, with a controlled dosage and time-release delivery system, it is feasible for amino acids (including BCAAs) to enter the bloodstream. For further information on the subject, click here to learn more from the study.