Polymer Science: BioFlex®, PTFE, and Biocompatible Materials for Body Jewelry

Polymers have transformed body jewelry from a purely metallic discipline into a materials science field. The key advantage of polymers over metals is their ability to flex with tissue movement rather than resisting it, this reduces mechanical stress at the piercing site, lowers the risk of migration and rejection, and allows for jewelry designs that would be impossible in rigid materials. However, not all polymers are equal: biocompatibility varies dramatically between polymer families, and the wrong choice can lead to chemical leaching, bacterial colonisation, or mechanical failure.

BioFlex® (PP-R): The Original Flexible Polymer for Body Jewelry

BioFlex® body jewelry is made from an advanced random copolymer in the PP-R class, a resin grade selected for body jewelry after a 14-month material search. Unlike standard polypropylene homopolymer, random copolymerisation with ethylene gives a material with better impact resistance, flexibility and long-term dimensional stability. BioFlex® is medical grade: it is certified as passing the ISO 10993 biological tests and is made from a USP Class VI resin [1]. The values below are typical of PP-R grades, not a BioFlex® data sheet.

• »Chemical structure: -(CH₂-CHCH₃)ₙ- with random ethylene co-monomer insertion (~2–5%)
• »Crystallinity: 40–55% (semi-crystalline), provides balance of strength and flexibility
• »Glass transition temperature (Tg): ~0°C, material is above Tg at body temperature, providing flexibility
• »Melting point (Tm): 145–155°C, well above autoclave temperatures, ensuring dimensional stability during sterilisation
• »Density: 0.90 g/cm³, significantly lighter than titanium (4.5 g/cm³) or steel (8.0 g/cm³)
• »Water absorption: <0.03% after 24h immersion, negligible swelling in tissue fluid
• »Metal content: BioFlex® contains no metal, so there is no nickel, chromium, cobalt or cadmium to release

Why PP-R Outperforms Standard Polypropylene

Standard polypropylene homopolymer becomes brittle at low temperatures and has poor impact resistance. The random copolymer structure of PP-R introduces ethylene units that disrupt crystallinity, creating a tougher, more flexible material without sacrificing the chemical inertness that makes polypropylene biocompatible. This is critical for body jewelry applications where the material must withstand repeated flexural loading without fatigue cracking.

PTFE (Teflon): Maximum Chemical Inertness

Polytetrafluoroethylene is the most chemically inert polymer available for body jewelry. Its fully fluorinated carbon backbone creates an extremely low surface energy (18–20 mN/m), making it highly resistant to biofilm adhesion. PTFE is widely used for initial piercings in nickel-sensitised patients and for jewelry components that contact mucosal tissue. However, its mechanical properties differ significantly from PP-R: PTFE exhibits cold flow (creep) under sustained load, meaning threaded connections can loosen over time.

• »Chemical structure: -(CF₂-CF₂)ₙ-, fully fluorinated, no hydrogen atoms available for oxidative degradation
• »Coefficient of friction: 0.05–0.10, lowest of any solid material, reducing insertion trauma
• »Service temperature: -200°C to +260°C, far exceeds any sterilisation requirement
• »Limitation: PTFE withstands autoclave temperatures but creeps (cold-flows) under sustained load, and heat makes it worse; tightly fitted or threaded PTFE parts can loosen, so check the fit after sterilisation
• »Available in USP Class VI grades; check the grade on the certificate rather than assuming it
• »Surface energy: 18 mN/m, hydrophobic surface resists protein adsorption and biofilm formation

Medical-Grade Silicone: Flexibility Without Compromise

Medical-grade silicone elastomers (polydimethylsiloxane, PDMS) offer the highest flexibility of any body jewelry material. With elongation at break typically exceeding 300%, silicone can conform to anatomical contours that rigid materials cannot match. However, silicone's low tear strength means it is unsuitable for threaded designs, it is typically used for plugs, tunnels, and o-rings where compressive rather than tensile forces dominate.

• »Shore hardness: Typically Shore A 30–70 for body jewelry applications
• »Tensile strength: 7–10 MPa, significantly lower than PP-R (30–40 MPa)
• »Elongation at break: 300–700%, highest of any body jewelry polymer
• »Tear strength: 25–45 kN/m, the limiting factor; avoid sharp edges and threaded designs
• »Autoclavable: Can withstand repeated 134°C steam cycles without degradation
• »Peroxide-cured vs platinum-cured: Platinum-cured is preferred for implant applications, no peroxide byproducts

Emerging Biopolymers: PHA and PLA

Polyhydroxyalkanoates (PHA) and polylactic acid (PLA) represent the next generation of body jewelry materials. PHA is produced by bacterial fermentation and is fully biodegradable, a potential advantage for temporary implant applications where a second removal procedure is undesirable. PLA is already used in absorbable surgical sutures and orthopedic fixation devices. However, both materials face significant hurdles for body jewelry: their degradation rates are difficult to control, degradation byproducts can cause local pH changes, and long-term ISO 10993 data for dermal contact is still being accumulated.

• »PHA: Flexural modulus 1,000–3,500 MPa depending on co-monomer, tunable stiffness
• »PLA: degrades by hydrolysis to lactic acid, a substance the body metabolises
• »Degradation time: PHA 6–24 months · PLA 12–36 months, depends on molecular weight and crystallinity
• »Current limitation: No long-term (>5 year) implantation data for dermal applications
• »Status: designed to degrade, so not suited to permanent wear in a piercing

Sterilisation Compatibility Matrix

Polymer selection must account for the sterilisation method used in the studio. Some polymers degrade under autoclave conditions, while others require specific cycle types. The table below summarises compatibility.

1. 1BioFlex® (PP-R): ✅ Autoclave 134°C · ✅ Ethylene oxide · ✅ Chemical sterilisation · ❌ Gamma (polypropylene embrittles) [7]
2. 2PTFE: ⚠️ Autoclave (creeps under load; check the fit) · ✅ EtO · ✅ Gas plasma · ❌ Gamma (chain scission) [7]
3. 3Medical Silicone: ✅ Autoclave 134°C · ✅ EtO · ✅ Gas plasma · ⚠️ Gamma (crosslinking increases)
4. 4PHA: ⚠️ Autoclave (may deform) · ✅ EtO · ✅ Gas plasma · ❌ Gamma
5. 5PLA: ❌ Autoclave (hydrolyses) · ✅ EtO · ✅ Gas plasma · ❌ Gamma

Where Polymer Jewelry Actually Fails

Polymer failures in body jewelry are rarely failures of the polymer class. They are almost always a mismatch between the grade, the sterilisation method, the site, or the supply chain. These are the patterns worth recognising before they cost a client a piercing.

• ⚠️Counterfeit material sold under a real brand name — cheap uncertified copolymer and TPU are sold as "bioflex" and "bioplast". The adverse-event reports attached to those names describe the counterfeit, not the certified PP-R, and no certificate accompanies them. Ask for the ISO 10993 documentation and the resin grade before you put it through skin.
• ⚠️Autoclaving tight PTFE assemblies — PTFE cold-flows under sustained load, and heat makes it worse, so a threaded PTFE assembly that goes through a 134°C cycle can come out dimensionally changed and loosen in wear. Check the fit afterwards, or use EtO or gas plasma for tight PTFE assemblies.
• ⚠️Gamma-sterilised polyolefins — gamma irradiation drives chain scission in polypropylene and PTFE, which embrittles the part without changing its appearance. A piece that arrives gamma-sterilised from a supplier cannot be assumed to have the mechanical properties on the data sheet.
• ⚠️Threaded designs in silicone — silicone tear strength of 25 to 45 kN/m is the limiting property, not its tensile strength. Threads and sharp internal corners concentrate the tear, which is why silicone belongs in plugs, tunnels and o-rings rather than in bars and closures.
• ⚠️Treating PTFE and PP-R as interchangeable — PTFE is supplied as extruded rod that must be cut and machined, so any decorative end is a separate threaded part that rotates freely in wear. For plain bars that does not matter. For a directional or asymmetric ornament it does: BioFlex® is made in one piece, with no joints or glued parts, even with a jewel, so the ornament keeps its orientation.
• ⚠️Assuming a biopolymer is a substitute — PHA and PLA are designed to degrade, and neither has long-term data for permanent wear in a piercing. Using them because they are "biocompatible plastics" confuses a resorbable material with a permanent one.
• ⚠️Plasticiser-bearing look-alikes — a flexible polymer that owes its flexibility to added plasticiser rather than to its own copolymer structure can carry restricted phthalates. REACH Annex XVII entry 51 caps DEHP, DBP, BBP and DIBP at 0.1% by weight of the plasticised material in essentially all articles since 7 July 2020 [14]. PP-R needs no plasticiser at all, which is why the question does not arise for it.
• ⚠️Buying on colour and price instead of on grade — polymer body jewelry is sold by appearance, and two visually identical bars can be different resins with different melting points, different sterilisation windows and different leachables profiles. The grade is the product; the colour is not.

How Polymer Body Jewelry Is Regulated

Polymer body jewelry sits in an awkward regulatory position. It is not a medical device, so device law does not apply to it by default, but it is an article in prolonged contact with broken skin, so chemicals law does. The practical consequence is that biocompatibility for body jewelry is evidenced voluntarily, against device standards, while the legally binding obligations come from chemicals legislation.