Tag: formulation

  • The Powder That Raised a Sunscreen’s SPF Threefold Without Absorbing UV

    The Powder That Raised a Sunscreen’s SPF Threefold Without Absorbing UV

    On its own, the powder was useless as a sunscreen. A Thai team at Prince of Songkla University measured it plainly: formulations “containing 10% HAp alone, regardless of source, exhibited negligible UV protection (SPF = 1.03–1.13), failing to meet the Thai Industrial Standard requirement (TIS 2804–2017: SPF > 15).” If hydroxyapatite were being sold as a UV filter, that line would end the story.

    So what happened in the blend?

    The same failed powder was then combined with 5% Tinosorb® S, an organic filter that alone managed SPF around 11. Together: “the SPF values for SKJ- and TG-HAp hybrid systems reached approximately 29–30 (~180% increase relative to 5% TS). Notably, the SM-HAp system exhibited a higher SPF of 32.19 ± 1.46 (205% enhancement).” The mineral contributed almost nothing alone and tripled the result in combination — the study confirms “that HAp did not function as an intrinsic UV absorber.” The working mechanism is optical: particles scattering light through the film, stretching each photon’s path so the organic filter gets more chances to absorb it.

    Then the detail that matters for specification. Refining the winning powder — milling it “from irregular submicron aggregates (430 ± 140 nm) to a nanoscale distribution of 117.39 ± 61 nm” — lifted SPF “from 32.19 ± 1.46 to 35.15 ± 1.44,” and the accompanying UVAPF gain “was sufficient to elevate the protection grade from PA+++ to PA++++.” A label-grade improvement, bought entirely with particle-size control.

    There is a sourcing lesson in which powder won, too. Three fish-bone sources were compared and they did not perform identically as boosters — the spread between them was measured in whole SPF points. Feedstock, in other words, is a formulation variable. For a scattering application, everything that shapes particle geometry upstream — species, cleaning, calcination, milling — surfaces downstream as label grade, which is a more direct line from raw-material consistency to shelf claim than most ingredients ever show.

    What specification should a buyer pay for?

    Not “UV protection” — the mineral has none to sell. The value is as an SPF booster: a scattering aid that lets a formulator hit a target SPF with less of the expensive organic filter, or clear a marketing threshold the filter alone misses. And because the mechanism is optical, the specification that carries the value is physical, not chemical: particle-size distribution, aggregation state, dispersion behaviour in the film. Two lots with identical purity and different aggregate sizes are, for this application, different products — one is PA++++, one is not.

    The limits travel with the claim: every figure here is in vitro, measured on PMMA plates, and the authors state that for regulatory approval and commercial labelling, in vivo testing remains the global standard. The material was fish-bone-derived, from Thai seafood processing waste — another biogenic calcium stream finding a second market.

    The lesson generalises past sunscreen. When an ingredient’s job is physical, lot-to-lot consistency in the physical numbers is the whole purchase — and a certificate that reports only chemistry is describing a different product from the one you are buying.

    Sources

    Sookchoo P, Benjakul S, Prodpran T, Amnuaikit T, et al. “Synergistic Effects of Hydroxyapatite Derived from Fish Bone and Tinosorb® S on the UV Protection Performance of Sunscreen.” Cosmetics, 2026;13(2):71 (open access) — mdpi.com/2079-9284/13/2/71.

  • Hydroxyapatite Particle Morphology: How Rod, Spherical, and Plate Crystals Affect Enamel Repair

    Hydroxyapatite Particle Morphology: How Rod, Spherical, and Plate Crystals Affect Enamel Repair

    Hydroxyapatite Particle Morphology: How Rod, Spherical, and Plate Crystals Affect Enamel Repair

    When formulators evaluate hydroxyapatite, the conversation usually starts and stops at particle size. Yet two powders with identical median particle sizes can perform very differently on enamel, and the reason is morphology: the actual shape of the crystals. Hydroxyapatite can be synthesised as rods, needles, spheres, or plates, and each geometry changes how the material packs onto the tooth surface, how much reactive area it exposes, and how readily it integrates into demineralised enamel.

    Why Crystal Shape Matters as Much as Size

    Biological enamel is built from tightly packed, elongated hydroxyapatite crystallites arranged into rods. A synthetic powder whose morphology echoes that native architecture tends to interface more naturally with the enamel surface. Beyond biomimicry, shape governs three practical properties:

    • Specific surface area: Needles and plates expose more reactive surface per unit mass than smooth spheres, which can accelerate ion exchange and nucleation at demineralised sites.
    • Packing and adhesion: Rod-shaped particles can align and interlock on enamel, while spheres tend to roll and resist mechanical keying. This influences how durable a deposited layer is against salivary clearance and brushing.
    • Rheology and feel: The same morphology that helps adhesion also drives viscosity and abrasivity in a paste, so the choice is never purely about efficacy.

    The Three Common Morphologies, Compared

    Rod and needle crystals most closely resemble natural enamel apatite. Their high aspect ratio and surface area favour nucleation and the formation of a continuous remineralised layer, which is why elongated nano-hydroxyapatite is widely used in oral care. The trade-off is that high-surface-area powders can be harder to disperse uniformly and may raise viscosity.

    Spherical particles are prized for a smooth sensory profile and low abrasivity, making them attractive in premium toothpastes and leave-on cosmetics. They flow well and are easy to disperse, but their lower surface area can mean slower surface reactivity compared with elongated crystals of the same size.

    Plate-like crystals sit between the two: they offer large contact faces that can tile across a surface, useful for occlusion of exposed dentin tubules, but their behaviour is highly dependent on how consistently the plates are produced.

    Morphology Is a Manufacturing Outcome

    Crystal shape is not a label you can simply request; it is the result of tightly controlled synthesis. Reaction temperature, pH, precursor concentration, ageing time, and the presence of structure-directing additives all steer whether apatite grows as a rod, a sphere, or a plate. Small drifts in any of these parameters shift the morphology and, with it, the performance. This is why batch-to-batch consistency separates a premium ingredient from a commodity one.

    It is also why purpose-engineered grades matter. Hydroxyapatite-LC by BiST Tech Japan is frequently referenced as a benchmark precisely because its synthesis is controlled for consistent crystal structure and morphology, rather than being optimised on particle size alone. For formulators, a tightly specified morphology means predictable rheology, predictable abrasivity, and predictable enamel behaviour from one production lot to the next.

    What Formulators Should Ask For

    • A morphology specification, not just a D50. Ask whether the grade is rod, spherical, or plate-dominant, and request electron microscopy (SEM/TEM) imagery on the certificate of analysis.
    • Surface area data. A BET surface area figure tells you more about reactivity than particle size alone.
    • Aspect ratio consistency. For oral care aimed at remineralisation, elongated, enamel-like crystals are usually preferable; for a silky leave-on serum, spheres may win on feel.
    • Lot-to-lot imagery. Consistent morphology across batches is the real-world test of a controlled process.

    For a deeper comparison of grades and types, see our HAP comparison resource, and for application-specific guidance our oral care section.

    The Takeaway

    Particle size answers “how small,” but morphology answers “what shape, and therefore how it behaves.” Matching crystal geometry to the application, elongated crystals for enamel remineralisation, spheres for sensory-led cosmetics, is one of the most overlooked levers in hydroxyapatite formulation. Specify it deliberately, verify it with imaging, and demand consistency from your supplier.

    This article is for educational purposes. Claims are based on published materials science and manufacturer technical data. Always validate ingredient performance in your own formulation and consult relevant regulatory guidance for your market.