United States Patent 4,957,119: Scope, Claims, and US Landscape for Ethylene/Vinyl Acetate Contraceptive Implants
What does US 4,957,119 cover at the claim level?
US Patent 4,957,119 claims a subcutaneous/local contraceptive implant built from a polymeric core plus a rate-controlling membrane and a polymer “contact layer” that prevents interfacial separation. The core and membrane are both ethylene/vinyl acetate (EVA) copolymer, but with different composition and melt index (MI) and different vinyl acetate (VA) content thresholds, creating a diffusion-controlling structure.
Core technical requirements (independent claim 1 structure)
Claim 1 requires all of the following:
-
Implant type
- Intended for subcutaneous or local administration.
-
Core material composition
- Core includes EVA copolymer with:
- Melt index (MI) > 10 g/10 minutes, and
- VA content ≥ 20 wt%
- The EVA core forms a matrix for at least one contraceptive substance selected from:
- 3-keto-desogestrel
- levonorgestrel
- gestodene
- Contraceptive loading is sufficient for constant release of at least 15–30 μg/day over a predetermined term.
-
Membrane composition
- Membrane encases the core and consists of EVA copolymer with:
- MI < 10 g/10 minutes
- VA content < 20 wt%
- Membrane thickness is 50–250 μm.
-
Contact layer / interfacial compatibility requirement
- The contact layer at the interface of core and membrane:
- forms from core and membrane materials; and
- prevents separation of the core and membrane.
Additional claim set (claims 2–8) refines polymer properties and physical construction
- Claim 2: Core EVA has MI 25–30 g/10 minutes and VA > 25 wt%.
- Claim 3: Membrane EVA has MI ≤ 8 g/10 minutes and VA < 20 wt%.
- Claim 4: Contraceptive substance is specifically 3-keto-desogestrel.
- Claim 5: Device geometry:
- essentially cylindrical
- max external diameter about 2 mm
- length < about 5 cm
- Claim 6: Core composition by weight:
- 50–75% contraceptive
- 25–50% EVA
- Claim 7: Implant ends are covered by an inert polymer.
- Claim 8: Polysiloxane coating on the entire implant.
Independent claim 9 is a parallel restatement with explicit “rate controlling membrane” wording
Claim 9 recites substantially the same architecture as claim 1, with:
- Core: EVA matrix (MI > 10; VA ≥ 20) containing contraceptives (3-keto-desogestrel, levonorgestrel, gestodene, mixtures)
- Release rate: at least 15–30 μg/day over predetermined term
- Membrane: EVA (MI < 10; VA < 20) with 50–250 μm thickness
- Contact layer prevents separation.
Claims 10–15 mirror claims 6–3-type refinements:
- Claim 10: Core contains 50–75% contraceptive and 25–50% EVA.
- Claims 11–13: inert polymer ends and polysiloxane coating.
- Claim 14: core EVA MI 25–30, VA > 25.
- Claim 15: membrane EVA MI ≤ 8, VA < 20.
What is the practical “scope perimeter” in claim language?
The patent’s infringement risk pivots on a few hard thresholds that define whether an accused implant reads on claim 1 (and dependent claims). These thresholds also define the design-around space.
Key “hard” claim thresholds
| Feature |
Claim 1 / 9 requirement |
Dependent narrowing |
| Core EVA melt index |
> 10 g/10 min |
Claim 2: 25–30 |
| Core EVA vinyl acetate |
≥ 20 wt% |
Claim 2: > 25 wt% |
| Membrane EVA melt index |
< 10 g/10 min |
Claim 3: ≤ 8 |
| Membrane EVA vinyl acetate |
< 20 wt% |
Claim 3: < 20 (same threshold) |
| Membrane thickness |
50–250 μm |
None stated |
| Contraceptive identity |
3-keto-desogestrel OR levonorgestrel OR gestodene |
Claim 4 locks to 3-keto-desogestrel |
| Contraceptive release rate |
constant release at least 15–30 μg/day |
None stated |
| Core/EVA vs drug load |
Not fixed in claim 1 |
Claim 6/10: 50–75% drug and 25–50% EVA |
| Contact layer / separation prevention |
Contact layer prevents separation |
Central to claim 1/9 |
| Shape and dimensions |
Not required in claim 1 |
Claim 5: cylinder, ~2 mm dia, <5 cm length |
| End inert polymer + polysiloxane |
Not required in claim 1 |
Claims 7–8 and 11–13 |
“Contact layer” and interfacial separation: the structural centerpiece
Unlike many matrix implants where adhesion is implicit, US 4,957,119 explicitly requires a contact layer at the core/membrane interface that prevents separation. That language can matter for:
- lamination methods,
- co-extrusion,
- graded composition layers,
- adhesive-free interfaces,
- or polymer re-melting during manufacturing.
Even if drug loading and release rate are correct, a design that uses a non-EVA interface strategy without the claimed contact-layer effect may avoid claim 1 and 9.
What is the patent landscape likely to look like in the US?
This patent sits inside a mature niche: hormonal contraceptive implants with polymer-controlled release. The competitive landscape in the US typically includes:
- EVA-based drug reservoir implants,
- other polymer membranes controlling diffusion (silicone, polyurethanes, ethylene-based blends),
- and other drug candidates with similar release-rate targets.
However, the specific combination in US 4,957,119 is narrow enough that the US “true competitors” are usually those that match the claim’s material property split:
- core EVA: higher MI and higher VA
- membrane EVA: lower MI and lower VA
- and an interface contact layer preventing separation.
Practical implication for freedom-to-operate (FTO)
Within this landscape, an implant with:
- different membrane polymer class (not EVA),
- EVA membrane with MI ≥ 10 or VA ≥ 20,
- core EVA with MI ≤ 10 or VA < 20,
- or an interface lacking a separation-preventing contact layer formed from the claimed structure,
is structurally outside the independent claim 1/9 perimeter.
Dependent claims then create further narrowing bands (core MI band 25–30; membrane MI band ≤ 8; drug loading 50–75%; cylindrical geometry; inert ends and polysiloxane).
Claim-by-claim infringement mapping: what matters most?
Claim 1 (and claim 9) elements that usually decide reading-in/out
- Implant architecture: core + EVA membrane + interface contact layer preventing separation.
- Drug identity: must be one or more of the listed hormonal agents.
- EVA material property bifurcation:
- core: MI > 10 and VA ≥ 20
- membrane: MI < 10 and VA < 20
- Membrane thickness: 50–250 μm.
- Release performance: constant release ≥ 15–30 μg/day.
If any of these are missing, claim 1 and 9 are not met.
Dependent claim “tightening” factors
- Claim 2 / 14: makes core EVA property narrower (MI 25–30 and VA > 25).
- Claim 3 / 15: makes membrane property narrower (MI ≤ 8).
- Claims 6 / 10: locks drug:Copol ratio to 50–75% drug by weight.
- Claim 5: locks geometry and approximate size.
- Claims 7–8 and 11–13: add end inert polymer and polysiloxane coating.
In litigation or licensing, dependent claim read depends on whether the product design is fully within those additional limits, not just the independent claim perimeter.
How broad are the claims?
Independent claims 1 and 9 are moderately constrained by material property thresholds (MI and VA split) rather than broad by polymer type. They are not broad enough to capture:
- “any EVA-based implant,” because VA and MI thresholds are specific.
- “any drug-loaded implant,” because drug identity and release rate are tied to listed contraceptives and a quantitative daily release range.
- “any multilayer implant,” because contact-layer formation and separation prevention are explicitly claimed.
At the same time, the independent claims remain broad on drug choice within a closed set and broad on implant form (subcutaneous/local with unspecified overall dimensions unless claim 5 is invoked). The polysiloxane coating and inert end coverings are not required in the independent claims.
Design-around “levers” suggested by the claim language
These levers follow directly from where independent claim 1/9 draws boundaries:
Material-property levers (directly affect claim 1/9)
- Core EVA MI: move to ≤ 10 to exit the “MI > 10” requirement.
- Core EVA VA: move to < 20 wt% to exit “VA ≥ 20” requirement.
- Membrane EVA MI: move to ≥ 10 to exit “MI < 10” requirement.
- Membrane EVA VA: move to ≥ 20 wt% to exit “VA < 20” requirement.
Interface-lever (contact layer / separation prevention)
- Use an interface that does not meet the claimed “contact layer preventing separation” structure/effect tied to the core/membrane materials as recited.
Release/leaching lever
- If actual product release does not meet “constant release at least 15–30 μg/day,” it avoids that functional limitation in claim 1/9.
Geometry and coatings (dependent-claim only levers)
- Cylinder sizing and polysiloxane coatings and inert end covers primarily impact dependent claims, not independent claim 1/9, unless a plaintiff narrows via dependence.
Key takeaways
- US 4,957,119 claims an implant with EVA core + EVA membrane where the core and membrane have intentionally different MI and VA ranges, plus a core/membrane contact layer that prevents separation, achieving constant daily contraceptive release of at least 15–30 μg/day from a matrix containing 3-keto-desogestrel, levonorgestrel, or gestodene.
- The independent claim perimeter is driven by five hard constraints: drug identity, release rate, membrane thickness (50–250 μm), and the core vs membrane MI/VA split (core MI >10 and VA ≥20 vs membrane MI <10 and VA <20) and the contact layer preventing separation.
- Dependent claims add further specificity (core MI band 25–30, membrane MI ≤8, drug loading 50–75%, cylindrical size, inert end polymer, polysiloxane coating). These features narrow scope but do not expand the independent claim.
FAQs
1) Does US 4,957,119 cover all EVA implants for contraception?
No. It requires a specific EVA property split between core and membrane (MI and VA thresholds) and a contact layer preventing separation, plus specified drug identity and release rate.
2) What polymer parameters most directly control infringement risk?
Melt index (MI) and vinyl acetate (VA) wt% for both the core EVA and membrane EVA. The claim draws hard thresholds at 10 g/10 minutes for MI and 20 wt% for VA.
3) Is polysiloxane coating required?
No for independent claims 1/9. Polysiloxane appears in dependent claims (8 and 13 and related).
4) Can the implant be non-cylindrical and still infringe?
Yes for claim 1/9 because shape is only tightened in dependent claim 5. Claim 1/9 require subcutaneous/local administration, not cylinder dimensions.
5) Does claim 1 require a specific contraceptive only?
It is limited to a closed set: 3-keto-desogestrel, levonorgestrel, gestodene, or mixtures of those.
References
[1] US Patent 4,957,119.
