All great questions and everybody(researchers too) are trying to figure out the optimal treatment protocol. One study does not cancel out all prior effective research but hopefully narrows the parameters slightly.
The 0.6 mm is close to the optimal depth found for mice and maybe that's why they used it. I guess they figured human skin is thicker or loss of penetration depth is close to 0.5mm. I would have thought the 0.5 mm was for penetration purposes but minoxidil was not applied that day.
Then the 0.6 mm was applied to barely get blood droplets so their goal WAS wounding and not penetration enhancement.
BUT...and others may know already, IS THE WOUNDING damaging the skin at least for 1 day where the barrier function is impeded so minoxidil applied on day 2 still has better penetration?
Results showed that microneedling in combination with minoxidil was significantly superior to topical minoxidil alone. They also revealed the efficacy of microneedling in males with Androgenetic Alopecia resistant to conventional therapies
in a later study.
The effect of microneedling is applied through the
release of platelet-derived and epidermal growth factors, enabling
skin regeneration through wounds, activation of stem cells in the
bulb, and overexpression of genes related to hair growth.
However, controversy about the best microneedling protocol still remains and
evidence regarding the most effective depth of the microneedle is
insufficient. For example, the most common penetration depth used
in studies applying the roller device is 1.5 mm. However, Fernandes
et al demonstrated that when a roller device with 1 mm needles is
used, the needles only penetrate about 0.75 mm.16 On the other
hand, Ro et al showed that microneedling using a pen device with
a depth of 0.5 mm appears to be more effective than a depth of
0.3 mm.17 Moreover, Kim et al reported that a microneedle depth of
0.5 mm using the roller device was an optimal depth for promoting
hair regrowth in mice.Considering noted results, it is necessary to adjust an optimal
depth for needle penetration. It was hypothesized that microneedling using an electrical pen device with two different depths of
penetration may help to determine the optimal needle depth in
Androgenetic Alopecia treatment. As such, we investigated the effect of microneedle
depths of 0.6 and 1.2 mm on hair regrowth in Androgenetic Alopecia patient
A topical anesthetic cream, mixture of 2.5% lidocaine/ prilocaine
(Xyla-P, Tehran Chemie Pharmaceutical Company, Iran), was applied to the area to be treated, 30-45 minutes prior to microneedling procedure. The area was then washed with saline and
cleansed with betadine. For microneedling procedure, we used an
electrical pen-shaped device (Auto MTS, Korea) with automatic
vertical movements and adjustable depth of penetration from 0.1
to 2 mm. The cartridge we used contained 9 needles, each with
the size of 33 gauge (0.2 mm needle diameter). The device was
moved over the treatment area in linear passes, lifting the device
between each stroke. Pinpoint bleeding from the treated area was
considered the desired endpoint. The scalp was then cleaned with
a gauze moistened in saline, and patients were instructed not to
apply minoxidil on the day of procedure. Each patient received 6
treatments and was questioned about signs and symptoms of infection, prolonged erythema, burning, and itching of the scalp, at
each meeting
pubmed.ncbi.nlm.nih.gov
