Regenerative injectable fillers are widely used in soft tissue restoration and anti‑aging for aesthetic applications. Calcium hydroxylapatite (CaHA‑CMC) and poly‑L‑lactic acid (PLLA) are two clinically prevalent biostimulant fillers. Both can stimulate endogenous collagen regeneration in human tissue, yet they differ in in vivo tissue responses and working mechanisms. A morphological comparative study published in Skin Research and Technology in 2024 adopted light microscopy and scanning electron microscopy to analyze differences between the two materials at the microparticle level, providing experimental evidence for understanding their biological behaviors.
Microscopic Observation of Particles from Two Types of Biostimulant Fillers
The study systematically tested particle samples of CaHA‑CMC and PLLA. Key evaluation indicators included particle shape, particle size, roundness, circularity and aspect ratio. The proportion of fine particles phagocytosable by macrophages was also quantified.
Microscopic results revealed distinct morphological features between the two materials. CaHA‑CMC particles exhibited a smooth, homogeneous spherical structure with particle diameters mainly ranging from 20 to 45 μm. They achieved higher values for circularity and roundness with well‑defined, nearly perfect spherical geometry. Only 8.20% of the particles were phagocytosable by macrophages (particle size ＜ 20 μm).
In contrast, PLLA particles showed high morphological variability and appeared as irregular micro‑flakes. Their major axis spanned from 2 to 150 μm with uneven outlines. Statistical data indicated markedly lower circularity and roundness as well as a higher aspect ratio compared with CaHA‑CMC. Most particles were elongated or irregularly shaped, and the proportion of phagocytosable fine particles reached 46.32%.
How Particle Morphology Modulates Host Tissue Responses
Existing biomaterial research confirms that particle geometry, surface smoothness and particle size distribution directly regulate immune cell responses. Smooth, uniformly spherical particles tend to trigger a relatively mild inflammatory reaction, while irregular, fragmented particles are more likely to activate macrophages and induce a stronger local inflammatory response.
The study hypothesized that the uniform spherical CaHA‑CMC particles recruit fewer inflammatory cells and predominantly activate fibroblasts for collagen regeneration via mechanical signal transduction. By comparison, irregular PLLA particles and abundant phagocytosable micro‑fragments readily initiate macrophage‑mediated inflammation, which serves as a major pathway driving neo‑collagenesis.
Study Limitations and Objective Notes
The authors noted that this work was an in vitro particle morphological observation. The actual performance of these materials within the complex human tissue environment requires further validation through additional in vitro models and clinical investigations.
Reference
McCarthy AD, Hartmann C, Durkin A, Shahriar S, Khalifian S, Xie J. A morphological analysis of calcium hydroxylapatite and poly‑L‑lactic acid biostimulator particles. Skin Research and Technology. 2024; 30:e13764. DOI：10.1111/srt.13764 原文链接：https://onlinelibrary.wiley.com/doi/10.1111/srt.13764
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