How far has PCL thread research in humans progressed? The distance from animal studies

There are studies examining PCL (polycaprolactone) thread on human faces, but most are observational studies from actual clinical practice without a control group, and we did not find direct comparative trials with PDO thread in this literature review[1][2]. The central basis for "PCL produces collagen longer than PDO" is primarily from experiments in rats and mice[3][4]. Based on the literature, the realistic expectation for humans is "temporary improvement lasting approximately six months to one year"[5].

What kind of research has been verified in humans?

Clinical studies documenting improvements immediately after the procedure are representative. In a study examining PLCL (a copolymer of PCL and lactic acid) barbed thread in Indian patients, improvements were observed in approximately 96% immediately after treatment, and approximately 71% showed further improvement on follow-up, with significant improvement reported compared to immediately post-treatment.[1]. Adverse reactions were reported to be at the same level as in previous PLCL thread studies[1].

However, this study did not include comparisons with other threads or no treatment.[1]. A systematic review examining all dissolvable thread lifts in the literature from October 2018 to December 2022 concluded that previous studies have not demonstrated long-term efficacy data[2].

What did animal studies show?

PCL showed the greatest increase in collagen. In a study dividing 30 UV-aged rats into 6 groups, PDO, PLLA, and PCL threads all brought dermal collagen density closer to that of young animals, with PCL showing particularly high activity.[3]. In a mouse study presented in the same paper, PCL thread increased Type III collagen more, while PDO thread increased Type I collagen more[3].

Another study in mice comparing a new PCL thread with commercially available threads also stated that PCL produces collagen over a longer period than PDO or PLLA.[4]. In a 6-month experiment in 5 pigs using a copolymer of PCL and lactic acid thread, the hyaluronic acid-coated thread outperformed on more tissue markers[6].

Can animal results be directly applied to humans?

There is distance in direct application. The authors of the rat study themselves wrote that further research is needed on the long-term effects from thread absorption through tissue remodeling.[3]. The authors of the pig study also stated that confirmation in humans remains to be done[6].

An increase in collagen is also not the same as the face appearing lifted. For facial lifting, a compilation of 111,948 cases states that approximately 6–12 months is the benchmark for effect duration depending on material and treatment site.[5].

Are there human trials directly comparing PCL with PDO?

We did not find any in this literature review. A prospective study of 3D-barbed PDO thread did not include comparison groups with PLCL or polypropylene thread, and stated that larger randomized trials are needed to confirm comparative efficacy and duration.[7]. Large-scale compilations also do not include satisfaction or objective outcome measures[5].

A previous systematic review concluded there is no scientific evidence that thread lift effects last long, and cited recommendations that objective photographic assessments should be performed at defined intervals in a double-blind manner.[8]. Research addressing this recommendation has not yet been published for PCL thread.

How does the complication data look?

Complications patterns are common regardless of thread material. A meta-analysis of complications from facial thread lifts identifies five types: short-term symptoms such as bruising and swelling, skin dimpling and contour irregularities, sensory changes such as numbness, infection and thread exposure, and nerve or parotid gland injury.[9].

PCL-specific large-scale data was not found, but there are clues. In China, when PCL and lactic acid thread was approved in 2018, a relatively high complication rate was observed due to insufficient physician experience and technique.[10]. The review also notes that dissolvable thread and younger age were associated with lower complication risk[11].

How to set realistic expectations and what to confirm at consultation

The Japanese Association for Aesthetic Surgery guideline positions thread lift as offering temporary improvement that is not large in effect and has short duration, assigning it recommendation level 2 (weakly recommended).[12]. PCL thread should currently be considered within this evaluation.

At your consultation, ask whether the basis for the expected duration with this thread comes from human research or animal studies, and discuss with your physician how many months to plan for based on your degree of Sagging (skin laxity). For areas where research lags, decisions will need to be made as you observe the progression.