Needle Clogging in Biostimulator Injection: Rheological Context and Clinical Experience

We read with great interest the recent article in the Journal of Cosmetic Dermatology entitled “Electron Microscopy–Based Study of Cannulas for Suspension-Based Dermal Filler and Biostimulator Application.” Radke et al. [1] compared 22-gauge blunt cannulas from two brands using electron microscopy, focusing on exit opening geometry and inner lumen surface features relevant to the risk of clogging during administration of suspension-based injectables. We offer the following comments in the spirit of complementing the authors' important findings with additional rheological and clinical context. In the article, biostimulators are described as generally behaving as Newtonian fluids [1]. However, from a rheological standpoint, they should not be classified as Newtonian. Rather, they represent non-Newtonian particulate suspensions whose flow behavior is governed by microparticle–microparticle interactions, the properties of the suspending medium, and geometric confinement within needles or cannulas [2]. With respect to needle clogging, our clinical experience differs from the implication that clogging is common when using 22-gauge cannulas. Numerous biostimulators are currently approved for clinical use in China, and clogging is seldom encountered when using 27- or 25-gauge cannulas and is only very rarely observed with 23- or 22-gauge cannulas. Most instances of clogging occur with lyophilized, carboxymethylcellulose-based biostimulators, particularly Sculptra. When reconstitution is performed thoroughly and uniformly, the occurrence of clogging can be largely eliminated [3, 4]. Needle clogging is a multifactorial phenomenon. Prior research has shown that smaller needle inner diameter (ID), higher vehicle viscosity, and larger particle size significantly increase obstruction risk—findings consistent with our experience. Additional contributing factors are summarized in Table 1 [5]. Although Radke et al. cite a microparticle size range of 2–150 μm [1], most published reports indicate that the majority of commercially available biostimulators contain microparticles predominantly within the 20–80 μm range [6], which remains smaller than the ID of a 32-gauge needle (Table 2). In practice, clogging may occur through two principal mechanisms. First, microparticle aggregation may arise, particularly in products containing carboxymethylcellulose that require reconstitution before injection. When reconstitution is incomplete, some microparticles may form clumps; if the size of such a clump exceeds the needle ID, mechanical obstruction results. Second, microparticle jamming may occur in small-bore needles even when individual microparticles are smaller than the lumen. Near the needle orifice or within the lumen, interactions between multiple microparticles—mediated by wall-to-microparticle and microparticle-to-microparticle friction—may create transient or persistent packing structures that impede flow [3, 4]. More recently, biostimulators have also been introduced for intradermal injection to improve skin texture. This technique commonly employs automated multi-needle injectors with very small-bore needles (e.g., 32-gauge), under which conditions clogging is observed more frequently than in deeper injection planes [4]. Several measures may help mitigate this problem, including thorough and uniform reconstitution to eliminate microparticle clumps, use of lower-concentration suspensions to reduce viscosity, and application of a mesotherapy injector control device (MICD; Hertz Bio., Shenzhen, China) to reduce the likelihood of microparticle jamming. The MICD continuously monitors subtle changes in extrusion resistance, injection speed, and negative pressure at the skin–probe interface and temporarily interrupts injection to relieve microparticle packing before resuming delivery. With appropriate reconstitution, optimization of suspension concentration, and MICD assistance, needle clogging during intradermal injection becomes uncommon. In conclusion, needle clogging is a multifactorial event. Although needle geometry contributes to risk, key determinants include needle ID, particle size, and suspension concentration. While clogging is uncommon in routine practice, it may occur when reconstitution is incomplete or when intradermal delivery is performed through very small-bore multi-needle devices. Attention to reconstitution technique, viscosity optimization, and supportive delivery technologies may help reduce obstruction risk and improve procedural safety. The authors used ChatGPT-5.2 for final proofreading purposes. The authors declare no conflicts of interest. This article is linked to https://doi.org/10.1111/jocd.70572. The authors have nothing to report.