I have not seen studies showing micro-needling by itself to be effective in the treatment of alopecia areata. Anything you apply to the skin at the time of micro-needling needs to be sterile and safe for "injection" into the skin. Micro-needling creates invisible micro-perforations in the upper layers of the skin which enhances penetration of topical serums and medications, dramatically increasing their effectiveness. Up to 80% of product can penetrate the skin compared to 7 to 10% with normal topical application.
Recent studies have shown that applying a serum derived from human stem cells containing growth factors that are specific for hair growth can have a significant impact on restoring hair. When combined with micro-needling, the results can be quite impressive for regrowing hair, possibly even in cases of alopecia areata.