United States Patent 6,156,331: Scope, Claims, and US Landscape
US Patent 6,156,331 covers a fluid-imbibing active-agent delivery device built around a water-swellable semipermeable plug assembled at an open end or cavity in an impermeable reservoir. Swelling of the semipermeable plug enables displacement of an active agent from the reservoir into a fluid environment of use. The claims also define materials, plug geometry/aspect ratio, and example actives (including biologics and gene therapy agents, plus specific classes like LHRH agonists/antagonists and leuprolide, and blood clotting factors).
What does the invention claim, in plain scope terms?
The independent claim theme is consistent across claims 1 and 4: the system uses a mechanically activated, swelling-driven pumping/dispensing mechanism in contact with water/aqueous media.
Core structural elements (independent claim 1 and claim 4)
- An impermeable reservoir containing an active agent.
- A water-swellable semipermeable material formed as a plug.
- The plug is assembled in sealing relationship with the interior surface at one end of the reservoir (claim 1), or assembled into a cavity in the reservoir (claim 4).
- Swelling causes the plug to expand and commence pumping/displacement of the active agent to the fluid environment of use.
Functional driving principle
- The semipermeable material swells upon water uptake.
- That swelling drives transport by moving/pressurizing/displacing the stored agent toward the environment.
Delivery context
- The device is for delivery of active agent to a fluid environment of use (claims 1 and 4).
- Claim 10 adds that the delivered site can be remote from the device.
What is the claim-by-claim scope and how broad is each limitation?
Claim 1 (independent): plug assembled at an open end with sealing relationship
“A fluid-imbibing device … comprising a water-swellable semipermeable material in the form of a plug … received in sealing relationship with the interior surface of one end of an impermeable reservoir and an active agent … displaced … when the water swellable material swells, wherein the semipermeable material is assembled into an open end of the reservoir.”
Scope takeaways
- Must include: (i) water-swellable semipermeable plug, (ii) impermeable reservoir, (iii) plug at one end assembled into an open end, and (iv) swelling-displaces active agent.
- “Sealing relationship” is a structural constraint. It implies the plug blocks leakage pathways at the assembly interface, making swelling-driven displacement the mechanism.
Design-impacting boundaries
- A device that uses swelling but does not assemble a semipermeable plug into an open end in sealing relationship is outside claim 1.
Claim 2: defined semipermeable material families
“Semipermeable material is selected from … plasticized cellulosic materials, polyurethanes and polyamides.”
Scope takeaways
- Claim 2 is a material-limited dependent claim.
- It narrows claim 1 to three polymer families.
- If an accused device uses a different water-swellable semipermeable polymer system, it may still infringe claim 1 (not claim 2) depending on claim 1’s broader “water-swellable semipermeable material” language.
Claim 3: aspect ratio
“Aspect ratio of the plug is 1:10 to 10:1 length to diameter.”
Scope takeaways
- This is a geometry constraint.
- It covers plugs that are neither extremely thin disks nor extremely long rods relative to diameter.
- Products with plug aspect ratios outside this window would avoid claim 3, but not necessarily claim 1.
Claim 4 (independent): plug assembled into a cavity
“... water-swellable semipermeable material in the form of a plug … received in sealing relationship with … one end … wherein the semipermeable material is assembled into a cavity in said reservoir.”
Scope takeaways
- Claim 4 overlaps with claim 1 but includes a cavity assembly configuration.
- The “cavity” language broadens possible internal geometries while keeping the swelling-driven mechanism.
Claim 5: cavity shapes
“Cavity is … cylindrical, stepped, helical threaded and spaced configuration.”
Scope takeaways
- This claim narrows claim 4 to specified cavity geometries.
- “Spaced configuration” is a functional/structural descriptor with ambiguity: it likely targets reservoirs with spaced features or channels, but the literal terms still tie the structure to the named categories.
Claim 6: active agent categories
“Active agent is selected from … protein, peptide or gene therapy agent.”
Scope takeaways
- Limits the active to biologics and gene therapy categories.
- It covers a broad set of proteins/peptides beyond small-molecule drugs.
Claim 7: LHRH agonist or antagonist
“Active agent is an LHRH agonist or antagonist.”
Scope takeaways
- Narrow to gonadotropin-releasing hormone modulator class.
- This is a further narrowing dependent claim on claim 6.
Claim 8: leuprolide
“Active agent is leuprolide.”
Scope takeaways
- A very narrow dependent claim, likely used to anchor commercial relevance.
Claim 9: Factor VIII or Factor IX
“Active agent is selected from … Factor VIII and Factor IX.”
Scope takeaways
- Another narrow biologic set.
- The presence of both claims 8 and 9 shows the patentee intended to capture multiple therapeutic franchises.
Claim 10: remote delivery site
“Active agent is delivered to a site remote from the device.”
Scope takeaways
- Adds an application/transport constraint.
- It does not specify the transport mechanism (catheter, conduit, fluidic channel), so infringement could be argued for any remote delivery architecture that still uses the swelling-driven plug mechanism.
Claim 11 (independent-like method/product claim): semipermeable plug useful in a system
“A semipermeable plug useful in an active agent delivery system … wherein said system comprises an impermeable reservoir, said plug being water-swellable and expanding linearly in said delivery system to commence pumping of active agent upon insertion … in the fluid environment of use, wherein the semipermeable plug is assembled into an open end of said reservoir.”
Scope takeaways
- Claim 11 is both a plug-level claim and a system-functional claim:
- water-swellable
- expanding linearly
- commence pumping upon insertion into fluid environment
- plug assembled into open end of impermeable reservoir
- “Expanding linearly” can be a key differentiator:
- It implies axial expansion rather than radial “ballooning” behavior.
- This may narrow design-around options that rely on non-linear swelling geometries.
Where is the claim scope strongest for enforcement?
1) Structural mechanism: “water-swellable semipermeable plug” + “impermeable reservoir”
That coupling is the enforcement core. Any design that:
- stores active agent in an impermeable reservoir, and
- uses a semipermeable water-swellable plug assembled to force displacement/pumping of agent,
is close to claim 1 and claim 11.
2) Assembly location: open end sealing/cavity
- Claim 1 requires plug sealing relationship with interior surface at one end and assembly into an open end.
- Claim 4 requires assembly into a cavity (while retaining sealing relationship language).
- Claim 11 requires plug assembled into an open end.
These structural mounting features likely matter in product designs and in infringement claim construction.
3) Plug linear swelling and pumping initiation timing
- Claim 11 ties “expanding linearly” to “commence pumping … upon insertion.”
- If a competitor’s device starts release via diffusion or pressure but lacks linear expansion of a swelling plug, it may be easier to distinguish.
How does claim breadth vary across dependent claims?
Broadest concept in set
- “Water-swellable semipermeable material in the form of a plug” (claim 1/4/11 conceptually), since it is not restricted to specific polymer types there.
Middle narrowing
- Claim 2 (polymer families) and claim 3 (aspect ratio range).
- Claim 5 (cavity shapes) is moderate, because it locks geometry to named forms.
Most narrow and likely easiest to carve out
- Claim 8 (leuprolide) and claim 9 (Factor VIII/IX).
- Claim 7 (LHRH agonist/antagonist) and claim 6 (protein/peptide/gene therapy categories) still cover many therapies, but they are narrower than small-molecule agents.
What does the claim set imply about competitor design-around space?
Key design-around levers created by the claim language:
-
Avoid the “semipermeable plug” mechanism
- Use non-semipermeable swelling elements, purely osmotic tablets without plug architecture, or diffusion-only reservoirs.
-
Avoid plug assembly at open end/cavity as claimed
- Rearrange mounting such that the swelling element is not assembled into an open end with a sealing relationship or into a cavity.
-
Break “expanding linearly” (claim 11)
- Use a swelling element that expands non-linearly or via radial deformation that does not match linear expansion.
-
Material substitution
- Use different water-swellable semipermeable polymers outside claim 2’s listed materials to avoid claim 2, while remaining within claim 1’s broader language if still semipermeable and swellable.
-
Geometry out of aspect ratio window
- Use plugs with aspect ratios outside the 1:10 to 10:1 band to avoid claim 3.
-
Use different active agent class
- If marketing an active that is not protein/peptide/gene therapy, it can avoid claims 6-9, while leaving claim 1/4/11 still potentially implicated.
US patent landscape: what related categories this claim set likely sits near
Because this task requires a landscape with citations, only the provided claim text can be used. No additional document-specific patent citations were included, so a fully evidenced US landscape cannot be constructed from the supplied information alone.
What can be stated from the claim language itself is the technical neighborhood:
- Osmotically driven or imbibition-driven delivery systems that use water uptake to initiate transport.
- Systems featuring semipermeable membranes and impermeable reservoirs with mechanical displacement.
- Biologic delivery contexts where proteins, peptides, and gene therapy agents are compatible with controlled release.
Claim-scope matrix (practical licensing and risk mapping)
| Feature |
Where it appears |
Coverage effect |
| Water-swellable semipermeable plug |
Claims 1, 4, 11 |
Core mechanism; likely hardest to avoid without changing architecture |
| Impermeable reservoir with active agent |
Claims 1, 4, 11 |
Anchors the device architecture |
| Sealing relationship at one end |
Claims 1, 4 |
Limits leakage and assembly configurations |
| Plug assembled into open end |
Claims 1, 11 |
Strong structural requirement |
| Plug assembled into cavity |
Claim 4 |
Alternative structural embodiment |
| Active agent displaced/pumped upon swelling or insertion |
Claims 1, 11 |
Requires swelling-driven initiation; not diffusion-only |
| Aspect ratio 1:10 to 10:1 |
Claim 3 |
Geometric limitation |
| Semipermeable material types |
Claim 2 |
Material-limited narrower coverage |
| Cavity geometry options |
Claim 5 |
Further structural narrowing |
| Active agent categories: protein/peptide/gene therapy |
Claim 6 |
Therapy-class dependent narrowing |
| LHRH agonist/antagonist and leuprolide |
Claims 7, 8 |
Narrow biologic anchoring |
| Factor VIII/IX |
Claim 9 |
Narrow biologic anchoring |
| Remote site delivery |
Claim 10 |
Application scope dependent on transport architecture |
Key Takeaways
- US 6,156,331 is built on a swelling-driven, plug-based architecture: a water-swellable semipermeable plug assembled into an impermeable reservoir displaces/pumps an active agent into a fluid environment.
- Enforcement leverage is structural: the claims repeatedly require plug assembly at the open end (claims 1 and 11) or within a cavity (claim 4), plus swelling initiation.
- Several dependent claims add carve-out handles: polymer class (claim 2), plug aspect ratio (claim 3), cavity shapes (claim 5), “expanding linearly” (claim 11), and specific active agents (claims 6-9).
- Remote delivery is covered (claim 10), but only if the same swelling plug mechanism is used and the active agent is delivered to a site remote from the device.
FAQs
1) Does the patent require an osmotic pump?
The claims describe a fluid-imbibing device where water-swellable semipermeable material swells and thereby displaces/pumps active agent. The claim language is mechanism-based on swelling and semipermeability rather than using the term “osmotic pump.”
2) Is the plug required to be semipermeable and water-swellable?
Yes. Claims 1, 4, and 11 require a water-swellable semipermeable material formed as a plug.
3) Can a competitor avoid infringement by using a different polymer?
Switching away from the exact polymer families listed in claim 2 can avoid claim 2, but not necessarily claims 1/4/11, which are not limited to those polymer families.
4) Are leuprolide and Factor VIII/IX required for coverage?
No. Those are specific dependent claims (leuprolide in claim 8; Factor VIII/IX in claim 9). The independent mechanism claims cover broader active-agent possibilities.
5) Does claim 11 impose a linear-expansion requirement?
Yes. Claim 11 requires the plug to expand linearly in the delivery system to commence pumping upon insertion in the fluid environment of use.
References
- US Patent 6,156,331 (claim text as provided).
