Popular Regenerative Materials in Aesthetic Medicine: CaHA, PLLA, PDLLA, PCL

Physicochemical Properties and Experimental Measured Data of Four Materials

1. CaHA (Calcium Hydroxylapatite)

CaHA is an inorganic mineral material with the molecular formulaCa10(PO4)6(OH)2. Its chemical composition is homologous to the inorganic mineral components of human bone. The purity of medical‑grade raw material is ≥98%.

• Crystallinity ＞95%; no melting point; microspheres are fabricated via high‑temperature sintering. The particle‑size range for commercial aesthetic‑grade microspheres is 25‑45 μm (particles smaller than 10 μm are prone to macrophage phagocytosis, while particles larger than 45 μm raise the risk of foreign‑body reaction). Scanning electron microscopy confirms the spherical morphology and excellent sphericity of CaHA particles.

• Young’s modulus: 10‑30 GPa, far higher than polyester polymers, delivering outstanding rigid supporting performance.

• No hydrolysis occurs in‑vivo; CaHA is gradually metabolized via macrophage‑mediated processes, with an in‑vivo retention period of 12‑18 months.

• Histological analysis of 6‑month subcutaneous implantation in animal models: dermal collagen density increases by approximately 210 % relative to blank control groups, dominated by type‑I collagen. In‑vitro cellular experiments verify that CaHA up‑regulates the expression of COL1A1 collagen gene with an up‑regulation magnitude of 36.5 % ± 3.7.

2. PLLA (Poly‑L‑Lactic Acid)

A semi‑crystalline aliphatic polyester synthesized by ring‑opening polymerization of L‑lactide. Medical‑grade PLLA has a weight‑average molecular weight (Mw) of 120 000‑180 000 and an intrinsic viscosity (IV) of 1.0‑1.5 dL/g.

• Crystallinity: 35‑42 %; melting point (Tm): 150‑160 ℃; glass‑transition temperature (Tg) ≈ 60 ℃; Young’s modulus: 2.7‑4.0 GPa; tensile strength: 50‑70 MPa with relatively notable brittleness.

• Common particle‑size range for aesthetic‑grade solid microspheres: 20‑50 μm / 40‑60 μm. Degradation mechanism: surface hydrolysis. Dense crystalline structures hinder water penetration into particle interiors, yielding a complete in‑vivo degradation cycle of 18‑30 months.

• Gamma‑ray sterilization test: gamma irradiation reduces PLLA molecular weight by 40‑60 %, which directly shortens degradation duration. This is a critical process variable that must be evaluated in formulation development.

• Histological findings from animal implantation: type‑I collagen begins to form around microspheres at 4‑month implantation, accompanied by peripheral type‑III collagen; collagen accumulates continuously at 6 months; a fibrous capsule predominantly composed of type‑I collagen forms at 9 months.

• Particle morphology mostly presents as irregular flaky or spherical solid particles.

3. PDLLA (Poly‑DL‑Lactic Acid)

Random copolymer of L‑lactic acid and D‑lactic acid; amorphous structure with crystallinity ≈0 % and no distinct melting point.

• Medical‑grade weight‑average molecular weight (Mw): 80 000‑140 000; Tg ≈ 55‑60 ℃; Young’s modulus: 1.9‑2.4 GPa. PDLLA possesses superior toughness compared with PLLA yet reduced rigid supporting capacity.

• Compared with solid particles, porous PDLLA microspheres exhibit a 2‑3‑fold increase in specific surface area and markedly improved hydrophilicity. In‑vitro reconstitution experiments show complete reconstitution of porous PDLLA microspheres within 7 min, considerably faster than solid PLLA microspheres. Typical microsphere particle‑size range: 20‑45 μm.

• Degradation mechanism: bulk homogeneous hydrolysis. Water molecules can permeate the entire microsphere matrix, yielding an in‑vivo degradation cycle of 12‑18 months.

• Experiments in aged‑mouse models: PDLLA down‑regulates the oxidative‑stress biomarker 4‑HNE (to 0.71‑fold) and up‑regulates TGF‑β expression. Under identical implantation conditions, local oxidative‑stress levels are lower in the PDLLA group than in PLLA and CaHA groups, indicating a milder inflammatory response. Split‑face controlled clinical observations demonstrate measurable improvement scores as early as week 4 for PDLLA, with an earlier onset profile than conventional solid PLLA.

4. PCL (Polycaprolactone)

Semi‑crystalline aliphatic polyester obtained by ring‑opening polymerization of ε‑caprolactone. It features the slowest hydrolysis rate among the four polymeric biomaterials.

• Crystallinity: 20‑33 %; melting point (Tm): 58‑61 ℃; Tg ≈ −60 ℃; Young’s modulus: merely 0.34‑0.43 GPa; elongation at break ＞700 %, demonstrating exceptional material flexibility.

• Aesthetic‑grade microsphere particle‑size range: 20‑50 μm with high‑sphericity smooth microspheres. Degrades slowly via bulk hydrolysis in‑vivo; full degradation cycle spans 24‑48 months.

• Representative industrial formulation: 30 % PCL microspheres compounded with 70 % CMC gel carrier. The carrier delivers immediate volumization, while PCL microspheres stimulate long‑term collagen remodeling. 24‑month clinical follow‑up data report sustained volumetric gain of 50‑150 % among subjects, with inter‑individual variation.

• Comparative studies in aged‑rat models: PCL achieves prominent elevation of dermal collagen density with a prolonged collagen‑remodeling window.

Key‑Parameter Comparison of Four Regenerative Materials

Note: All in‑vivo duration and collagen‑related data originate from animal experiments and public pre‑clinical literature. Actual performance may fluctuate due to sterilization processes, carrier systems and individual physiological differences.

Formulation Development and Application Analysis Based on Experimental Data

CaHA

A high Young’s modulus of 10‑30 GPa endows CaHA with powerful osseous supporting capacity. The 25‑45 μm microsphere size range avoids macrophage phagocytosis risks. Key formulation considerations: As rigid particles, CaHA requires high‑strength gel carriers to suppress particle agglomeration and mitigate displacement risks. Collagen induction is realized via physical scaffolding effects. CaHA is not hydrolyzed and dissolves; it is metabolized gradually through cellular activity. Suitable for R&D of consumables for deep‑layer contour restoration.

PLLA

The 35‑42 % crystalline structure brings surface‑hydrolysis behavior with degradation cycles extending up to 30 months, positioning PLLA for long‑term biostimulation. Experiment‑identified risk notes: Gamma irradiation causes substantial molecular‑weight attenuation; sterilization workflows must be validated in R&D. Solid particles show poor hydrophilicity; lyophilized semi‑finished products require sufficient soaking for reconstitution. Irregular micro‑particle morphology may elevate nodule risks if dispersion processes are inadequately controlled. Suited for formulations targeting long‑term regenerative effects.

PDLLA

Amorphous structure combined with porous‑microsphere technology yields two major experimental advantages: fast reconstitution, uniform hydrolysis, together with superior oxidative‑stress and inflammatory profiles relative to PLLA control groups. Limitation: Young’s modulus of merely 1.9‑2.4 GPa results in insufficient osseous support; PDLLA is not recommended for severe contour augmentation. It is more applicable to dermal mid‑to‑superficial soft‑tissue improvement scenarios.

PCL

With elongation at break ＞700 %, PCL exhibits the highest flexibility among the four materials and the longest degradation cycle (24‑48 months). The mainstream formulation combines PCL microspheres with CMC gel, achieving dual effects: immediate volumization from the carrier plus long‑term collagen remodeling by microspheres. Limitation: poor mechanical support, unsuitable for demanding osseous‑contour sites. Formulation developers mainly adjust molecular weight to precisely modulate degradation rates.

Raw‑material Selection and OEM Development Guidance

Microsphere raw‑materials are available for all four biomaterials. As demonstrated by experimental data, material selection should not rely merely on material nomenclature. Core quantifiable indicators include: weight‑average molecular weight, intrinsic viscosity, microsphere D50/D90 particle size, sphericity, porosity and crystallinity. These parameters directly govern degradation rate, injectability, in‑vivo inflammatory response and collagen‑inducing performance.

Important Compliance Reminder: Injectable finished products fall under Class III medical devices in China. Raw materials and semi‑finished products shall not be directly injected into human bodies. During product development, full safety assessments including cytotoxicity, in‑vivo implantation‑degradation testing and biocompatibility evaluation must be completed. Market access is permitted only after successful medical‑device registration.

Conclusion

There is no absolute superior‑inferior ranking among CaHA, PLLA, PDLLA and PCL. Physicochemical and animal‑experimental data define their respective positioning:

1. CaHA delivers osseous physical support dominated by high modulus and triggers scaffold‑mediated collagen regeneration.

2. PLLA leverages its semi‑crystalline structure to achieve extended degradation cycles and long‑term stimulation of type‑I and type‑III collagen synthesis.

3. PDLLA features amorphous porous architecture, enabling rapid reconstitution, uniform hydrolysis and relatively mild inflammatory responses.

4. PCL demonstrates optimal flexibility and the longest degradation cycle, balancing immediate carrier‑based volumization and long‑term tissue remodeling.

For formulation R&D and OEM sourcing, developers shall select raw‑materials with matched physicochemical parameters according to target injection depth, expected duration of action and product positioning. Appropriate carrier systems should be adopted, and comprehensive safety assessments shall be implemented to guarantee product stability and regulatory compliance.

References

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