Carbon 3D Prints Resorbable Bioelastomer That Shows Biocompatibility in the Body

A resorbable bioelastomer is a crosslinked polymer network designed to break down inside the body and leave through normal metabolic routes. The elastic part matters: the network has to stretch and recover, not crack, when a surgeon sutures it or when tissue moves against it. The material pairs that elasticity with controlled degradation, so the implant holds shape for a defined window and then loses strength.

Degradation is driven by hydrolysis of the backbone, which means water access sets the rate. A dense, closed surface resorbs slowly; a porous lattice with open struts resorbs much faster. That is one reason printing matters. Pore size, strut diameter, and total surface area are all design variables, not chemistry variables. Two parts from the same resin batch can degrade on completely different timelines if the geometry differs.

Strength loss and mass loss are not the same curve. Mechanical integrity usually drops first, before the implant loses significant weight. Design the load-bearing window around the strength curve, not the mass curve. If a mesh only needs to hold tissue for six weeks, the specification should say six weeks of retained strength, with a test method attached.

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  Elastic recoveryNeeded for sutured meshes and tissue that flexes.
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  Hydrolytic breakdownRate set by water access and surface area.
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  Two curvesStrength falls before mass does.

Photopolymerization builds a part by curing liquid resin layer by layer with controlled light. For a bioelastomer the cure has to be complete enough to avoid unreacted monomer, yet gentle enough not to embrittle the network. Print parameters such as light dose, layer thickness, and build orientation feed directly into the mechanical result.

The process prints features that machining cannot reach. Open-pore lattices, thin struts, and internal channels are native to additive manufacturing. A machined block of the same polymer would be solid, or would need drilled holes that are straight, round, and limited in aspect ratio.

Resolution is not the whole story. Surface finish inside a printed lattice is rough compared with a machined face, and that roughness changes cell attachment and fluid flow. If a design calls for a smooth sealing surface alongside a porous body, the two features are usually made as separate parts and joined.

Post-processing decides whether the part is usable. Excess resin has to be cleared from internal channels, and the cleaning step is where thin struts break. Design clearance into the lattice so solvent can reach every strut, and avoid blind pockets that trap uncured material.

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  Light doseSets crosslink density and elastic behavior.
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  Build orientationChanges anisotropy and strut strength.
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  Cleaning accessOpen paths for resin removal, no blind pockets.

An in-vivo study asks a narrow question: does the body tolerate this material in this form, at this site, for this duration? A result showing all samples non-toxic and no adverse tissue response supports that specific configuration. It does not automatically transfer to a different pore size, a thicker section, or a longer implant period.

The usual readouts are local tissue response, inflammatory cell presence, and capsule formation around the implant. Toxicology screens cover leachables and residual monomers. If a printed part is under-cured, residual monomer can dominate the response, which is why cure validation belongs in the process specification, not only in the material datasheet.

Adjustable duration is the commercially interesting part. If resorption time can be tuned by geometry and crosslink density rather than by switching resins, one material platform covers several indications. That shortens qualification work, because the leachables profile stays largely the same.

Sterilization is an open item. Terminal sterilization methods differ in how they affect a hydrolytically sensitive network. Gamma, ethylene oxide, and electron beam each interact differently with the polymer. Validate the sterilized state, not just the as-printed state.

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  Form-specificResults apply to the tested geometry and site.
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  Cure validationResidual monomer drives tissue response.
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  SterilizationTest the final sterilized device.

Skip it when the part carries structural load beyond the resorption window. Once strength drops, the implant is no longer a frame. If the indication needs permanent fixation, use titanium or stainless instead and treat the printed part as a soft tissue interface only.

Skip it when the tolerance stack is tight. Printed lattices cannot hold ±0.005 mm, and asking for it drives cost without improving function. Put the precision features on a machined component and let the printed part locate loosely against it.

Skip it when the part must be steam sterilized at high temperature. Hydrolytically sensitive networks do not enjoy moisture plus heat. Check the sterilization route before the design freeze, not after.

There is also a supply question. Resorbable photopolymer resins come from a small number of suppliers, and changing resin grade can trigger fresh biocompatibility work. Lock the resin specification early and keep a documented second source plan.

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  Load past resorptionUse permanent metal instead.
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  Tight tolerancesMove those features to a machined part.
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  Steam sterilizationCheck compatibility before freeze.

Most resorbable implants are hybrids. The printed lattice handles the soft tissue interface, while a machined component handles fixation, alignment, or a rigid frame. That gives a design team two specification sets to manage, and they should be written separately.

For the metal side we work in titanium TA1, TA2, and TC4 (Ti-6Al-4V), plus 316L and 17-4PH stainless for instruments and fixtures. Tolerances to ±0.005 mm, finishes from Ra 1.6–3.2 μm as-machined down to Ra 0.2–0.8 μm when a sealing face needs it. Five-axis work covers undercuts and angled holes that a three-axis setup would need multiple fixtures for.

Small features matter here. A fixation hole, a suture slot, or a locating boss on a 6 mm frame is normal work. We run 127 CNC machines across three plants, 16 of them simultaneous 5-axis centers, so a fixture plate and a set of implant blanks can move through the same week.

For early-stage work, no minimum order quantity applies. One prototype or a 10,000-part run both go through the same inspection route: raw material check, in-process monitoring, and 100% inspection before shipment, with reports on request.

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  TitaniumTA1, TA2, TC4 (Ti-6Al-4V).
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  Stainless316L, 17-4PH (SUS630), 420, 440C.
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  CertificationsISO 9001:2015, ISO 13485:2016, IATF 16949:2016.