United States Patent 4,968,507: Scope, Claims, and US Patent Landscape
United States Patent 4,968,507 claims an osmotic pump structure where controlled release is driven by an osmotic pressure gradient across a rate-controlling, water-insoluble, microporous wall with tightly defined permeability and “low reflection coefficient” characteristics, and where the wall includes a pH-insensitive pore-forming additive dispersed through a water-permeable, solute-impermeable polymer matrix.
What is the claimed invention in US 4,968,507?
The patent is directed to an “osmotic pump, for the controlled release of a pharmaceutically active agent to an environment of use,” with the core and the rate-controlling wall defined by functional and compositional limitations.
Claim-1 “pump” architecture (the core scope)
The pump consists essentially of:
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Core (A) that includes:
- An active agent soluble in external fluid; or
- A mixture of:
- An active agent of limited solubility in the external fluid and
- An osmotically effective solute soluble in the fluid
- The core exhibits an osmotic pressure gradient across the wall against the external fluid.
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Rate-controlling wall (B) that is:
- Water insoluble
- Rate controlling
- Fluid permeability: 6.96×10−18 to 6.96×10−14 cm³ sec/g
- Reflection coefficient: < 0.5
- Wall is prepared from:
- (i) a polymer permeable to water but impermeable to solute, and
- (ii) 0.1 to 60 wt% of at least one pH insensitive pore forming additive, dispersed throughout the wall.
This combination defines both the “driving force” (osmotic core) and the “hydraulic gate” (wall permeability and reflection coefficient), while the pore-forming additive is positioned as the structural lever that sets the wall transport properties.
What do the dependent claims narrow?
Claim 2 through claim 17 add percentage ranges, polymer and additive selections, wall thickness and pore geometry, and specific active-agent exemplars.
Rate-controlling wall composition (Claims 2, 4, 14, 15)
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Pore forming additive loading (Claim 2)
- Solid additive: 0.1 to 50 wt%
- Liquid additive: 0.1 to 40 wt%
- Total pore-forming additive: not to exceed 60 wt%
-
Plasticizer/flux regulating and surfactant optional additives (Claim 4)
- Plasticizer and flux regulating additives: 0 to 50 parts per 100 parts of (i)+(ii)
- Surfactant additive: 0 to 40 parts per 100 parts of (i)+(ii)
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Pore forming additive range (Claim 14)
- 0.1 to 50 wt% (distinct from Claim 2’s “not to exceed 60 wt%” total)
-
pH-insensitive pore-forming additive exemplars (Claim 15)
- Polyethylene glycol, sorbitol, glucose, and mixtures
Reflection coefficient refinement (Claim 3)
- Reflection coefficient: < 0.1 (narrower than Claim 1’s < 0.5)
Wall microstructure and pore size (Claims 5 and 6)
Active-agent quantity (Claims 7 and 8)
- At least 0.05 ng active agent (Claim 7)
- At least 1 microgram active agent (Claim 8)
Polymer family selection (Claims 9–12)
Claim 9 sets a broad polymer “selected from” list; dependent claims segment by polymer class.
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Polymers (Claim 9)
- Cellulose esters
- Acylated polysaccharides
- Polyurethane
- Polymers of acrylic and methacrylic acid and esters thereof
- Poly(ortho ester)s
- Polyacetals
- Mixtures
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Cellulose esters and acylated polysaccharides (Claim 10)
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Polyurethanes and acrylic/methacrylic polymers (Claim 11)
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Poly(ortho ester)s and polyacetals (Claim 12)
Pore-forming additive selection (Claims 13 and 15)
Active-agent exemplars (Claims 16 and 17)
How strong is the claim “scope,” based on claim language?
Claim 1 drives coverage; dependent claims define carve-outs and “preferred embodiments”
- The core infringement risk is structured around Claim 1’s wall transport parameters:
- permeability window: 6.96×10−18 to 6.96×10−14 cm³ sec/g
- reflection coefficient: < 0.5
- The structural material limiter is wall composition:
- polymer permeable to water but impermeable to solute + 0.1–60 wt% pH insensitive pore-forming additive dispersed throughout the wall.
“Consists essentially of” narrows additions but does not kill broad operation
Claim 1 says the pump “consisting essentially of” (A) and (B) components. That permits additional non-material changes, but bars additional components that would materially alter the basic and novel characteristics: (i) osmotic gradient generation and (ii) rate-controlled water/solute transport via microporous, low-reflection, water-insoluble wall.
The pore former is a transport-design parameter, not only a filler
The claims repeatedly tie the pore-forming additive to “pH insensitive” behavior and to the resulting wall structure (pore size distribution), permeability, and reflection coefficient. This is important because many competing osmotic pump technologies rely on different mechanisms (e.g., specific membranes, different pore formers, or solubility-controlled release) rather than low reflection coefficient plus this particular permeability band.
US patent landscape: where this claim fits
Practical claim “neighbors” in the osmotic pump space
The landscape for US osmotic pumps commonly clusters around:
- Elementary osmotic pumps with semipermeable membranes (water-permeable, solute-rejecting) and a solute/osmogen core.
- “Rate-controlling membrane” evolution: modifications to membrane microstructure, including pore-forming strategies, to tune water flux.
- Pore-former controlled microporosity (including leachable pore formers and phase-separated domains).
- Membrane performance metrics: permeability and reflection coefficient thresholds to quantify solute rejection and water transport.
US 4,968,507 sits at the intersection of (2) and (3) with (4) expressly quantified in Claim 1, and it narrows the wall “recipe” via (i) polymer type and (ii) pH-insensitive pore formers and loading ranges.
Clearance mapping: what to design around
If you are assessing freedom-to-operate for an osmotic pump product in the US, the most actionable “design-around vectors” from the claims are:
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Escape the transport parameter window
- avoid wall fluid permeability in 6.96×10−18 to 6.96×10−14 cm³ sec/g
- avoid wall reflection coefficient < 0.5 (or < 0.1 for tighter embodiments)
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Escape the “pH insensitive pore forming additive” dispersion
- use a pore-forming approach that does not meet “pH insensitive pore forming additive” definition, or does not have the required wt% dispersion into (i)+(ii) wall formulation
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Escape pore-former loading
- avoid 0.1–60 wt% (or 0.1–50 wt% embodiments)
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Escape wall microstructure windows
- avoid the claimed pore diameter ranges and distributions if you rely on Claim 5/6
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Polymer class alternatives
- Claim 9 is broad, but narrowing to other membrane classes or chemistries may exit the “selected from” lists (depending on how strictly a court construes “selected from” and whether equivalents apply)
Claim scope versus “active ingredient” scope
Active ingredient is mostly non-limiting in Claim 1, because Claim 1 only requires “pharmaceutically active agent soluble in external fluid or limited solubility plus osmotically effective solute.” Claims 16 and 17 list exemplars and active classes, but those are not required for Claim 1 coverage unless asserted as limiting.
Operationally, that means the patent can remain relevant even if the active ingredient differs from the exemplars.
Claim chart style deconstruction (infringement elements)
| Element |
Claim language hook |
Key numeric gates |
| Osmotic gradient core |
Active agent (soluble or limited solubility) + osmotically effective solute |
None stated in claim text beyond functional solubility/osmogen concept |
| Rate-controlling wall type |
Water insoluble; rate controlling; “surrounded by” core |
Water insoluble is structural/functional |
| Wall permeability |
“fluid permeability” range |
6.96×10−18 to 6.96×10−14 cm³ sec/g |
| Solute rejection / selectivity proxy |
“reflection coefficient” |
< 0.5 (or < 0.1 in Claim 3) |
| Membrane recipe |
(i) water-permeable, solute-impermeable polymer |
Polymer must be permeable to water but impermeable to solute |
| Pore-former and amount |
pH-insensitive pore forming additive dispersed in wall |
0.1–60 wt% in Claim 1; 0.1–50 wt% in Claim 14 |
| Pore microstructure (where asserted) |
pores diameter distribution |
Claim 5: 1–1,000 microns thickness; 5–95% pores 10 Å to 100 microns; Claim 6: 20–500 microns thickness; pores 10 Å to 25 microns |
| Optional excipients |
plasticizer/flux regulating additives and surfactant |
Plasticizer/flux: 0–50 parts/100; surfactant: 0–40 parts/100 |
Business implications for R&D and licensing
Where this patent is strongest
- A competitor that uses an osmotic pump with:
- a water-insoluble microporous wall,
- a defined permeability band and low reflection coefficient,
- and a pH-insensitive pore former dispersed within a water-permeable/solute-impermeable polymer
faces direct claim 1 exposure.
Where the patent is weakest
- Products that move away from:
- measured permeability and reflection coefficient targets,
- or that eliminate the pH-insensitive pore-former architecture (or shift wt% out of the claim window),
are less likely to remain within Claim 1’s tight technical gates.
Key Takeaways
- US 4,968,507 Claim 1 is a structured combination of an osmotic core and a rate-controlling, water-insoluble wall with quantified transport metrics: permeability 6.96×10−18 to 6.96×10−14 cm³ sec/g and reflection coefficient < 0.5.
- The claimed wall requires a polymer permeable to water but impermeable to solute plus 0.1–60 wt% pH-insensitive pore-forming additive dispersed throughout the wall.
- Dependent claims narrow the pore former to specific loading rules, pore-former exemplars (PEG, sorbitol, glucose), polymers (cellulose esters, acylated polysaccharides, polyurethanes, acrylic/methacrylic polymers, poly(ortho ester)s, polyacetals), and wall pore geometry (10 Å to 100 microns, with thickness windows).
- For freedom-to-operate and design-around, the most actionable vectors are: miss the permeability window, miss the reflection coefficient threshold, and miss the pH-insensitive pore-former dispersion/loading architecture.
FAQs
1) Does Claim 1 require a specific drug?
No. Claim 1 requires a pharmaceutically active agent that is soluble in external fluid, or a mixture with a limited-solubility agent plus an osmotically effective solute. Specific actives appear only in dependent claims (Claims 16 and 17).
2) What parameters most directly determine infringement risk?
Measured fluid permeability and reflection coefficient of the water-insoluble rate-controlling wall are the tightest numerical gates in Claim 1.
3) Can a design use a different polymer and avoid the patent?
Claim 9 lists polymer options “selected from the group consisting of,” so using polymers outside those classes can be a design-around route, but equivalents can still matter. The claim 1 language also requires a polymer that is permeable to water but impermeable to solute.
4) What is the pore-former doing legally?
It is structurally embedded: the wall is prepared from (i) the specified functional polymer and (ii) pH-insensitive pore forming additive dispersed through the wall at defined wt% ranges.
5) Which dependent claims are most useful for narrowing scope?
Claims 3 (reflection coefficient <0.1), 5 and 6 (pore size distribution and thickness), and 15 (specific pore-former exemplars) are the most technically constraining dependent claims.
References
[1] US Patent 4,968,507, “Osmotic Pump,” claims 1-17 (as provided in the prompt).
