Patent: 4,846,835

Summary for Patent: 4,846,835

Title:	Technique for healing lesions in cartilage
Abstract:	A grafting technique entailing the transplantation of chondrocytes for promoting the healing of lesions in articular cartilage, use being made for this purpose of in vitro autologous cultured chondrocytes prior to transplantation. The chondrocytes are preferably seeded in a three-dimensional collagen matrix which serves as the graft material. In order to internally fix the graft during the healing process, use is made of a periosteal flap which is sutured to the cartilage after the graft material is implanted therein.
Inventor(s):	Grande; Daniel A. (Glen Cove, NY)
Application Number:	07/061,952
Patent Claims:	see list of patent claims

United States Patent 4,846,835: Claim-by-Claim Validity Check and U.S. Patent Landscape

What does US 4,846,835 actually claim?

US 4,846,835 claims a four-step, autologous cell-based cartilage repair method with a specific fixation construct. The independent claim (claim 1) is the core combination:

1. In vitro autologous cultured chondrocyte preparation prior to grafting
2. Seeding an ex vivo collagen matrix with the cultured chondrocytes to provide an “activated matrix”
3. Implanting the activated collagen matrix into an articular cartilage lesion
4. Mechanically fixing the graft using a periosteal flap sutured to the cartilage so the graft remains in place during healing

Dependent claims specify collagen matrix formats:

• Claim 2: matrix is a collagen gel
• Claim 3: matrix is a collagen sponge
• Claim 4: collagen matrix is a collagen gel where chondrocytes are dispersed prior to polymerization

Claim text elements that control claim scope

Element in claim 1	Legal scope effect	Critical technical scope questions
“producing in vitro autologous cultured chondrocytes prior to grafting”	Requires autologous cultured chondrocytes, not fresh cells	Any prior art with “autologous chondrocytes” plus culture will overlap
“seeding a collagen matrix… to provide an activated matrix”	Requires an ex vivo cell-seeding step into collagen scaffold	Prior art that implants cells mixed with collagen in situ may avoid some literal reading, but likely not the “seeding” step
“implanting… in the lesion”	Standard implantation into cartilage defect	Most art falls here, narrowing novelty to scaffold + fixation
“mechanically fixing… by a periosteal flap sutured to the cartilage”	Narrowest and likely most distinctive limitation	Prior art that uses fibrin glue, membrane cover, or sutures without periosteal flap can avoid literal “periosteal flap”

Where are the novelty and obviousness pressure points?

The claim is a combination of three known modules plus one more specific fixation approach. The validity risk concentrates where prior art can map each limitation in one reference, or combine multiple references without teaching away.

1) Cultured autologous chondrocytes + collagen scaffold

Cell-based cartilage repair using autologous cultured chondrocytes and implantation into articular cartilage lesions was a mature pathway well before 4,846,835. The novelty in claim 1 then shifts to how the cells are presented to the lesion:

• Ex vivo seeding into a collagen matrix (“activated matrix”)
• Matrix categories are later narrowed in dependent claims: gel, sponge, and polymerized gel with dispersed cells

From a patentability standpoint, this creates two predictable prior-art patterns:

• Direct overlap pattern: earlier patents describing cultured chondrocytes seeded onto collagen scaffolds and implanted
• Motivation to combine pattern: earlier chondrocyte culture methods plus earlier collagen scaffold methods

If earlier disclosures already teach “cultured autologous chondrocytes” plus “collagen matrix” implantation, claim 1 can face obviousness even if the exact phrase “activated matrix” is absent, because claim construction often treats such labels as a process outcome rather than a new structural distinction.

2) Periosteal flap sutured to cartilage (the likely differentiator)

Claim 1 becomes strongest where the prior art departs:

• Many cartilage repair systems used membranes, periosteum, sutures, or fixation methods, but not always in the same “periosteal flap sutured to the cartilage to keep graft in place” framing.
• If earlier publications used periosteal tissue as a cover but did not use it as the specified flap sutured to cartilage for graft retention, claim 1 can retain a practical novelty hook.

In practice, this limitation can be a double-edged sword:

• It narrows literal scope and can avoid some references.
• It also creates infringement sensitivity to fixation method differences (fibrin glue only, collagen patch only, different flap design, membrane instead of periosteum, different anchoring geometry).

3) Dependent claims convert scaffold type into narrower subject matter

• Claim 2 (collagen gel) and claim 3 (collagen sponge) reduce claim scope.
• Claim 4 (collagen gel where cells are dispersed prior to polymerization) introduces a process condition that can matter for both validity and infringement:
  • Prior art that seeds cells after polymerization can avoid literal “dispersed… prior to polymerization.”
  • Prior art that mixes cells into monomer/collagen solution before polymerization can hit directly.

How does the claim read against typical cartilage repair prior art?

Below is a critical mapping of claim limitations to common prior art buckets that existed before the mid/late-1990s. This is not a substitute for citation-level search, but it shows the exact places where earlier documents likely overlap or diverge.

A. Prior art bucket: “autologous cultured chondrocytes” (the baseline)

If a reference teaches:

• harvest chondrocytes,
• expand culture in vitro,
• implant into cartilage lesion,

then limitation A is likely met. That pushes novelty evaluation to B, C, and especially D.

B. Prior art bucket: “collagen scaffold + cells”

If a reference teaches:

• collagen scaffold,
• cell seeding (or mixing prior to polymerization),
• implantation into defect,

then limitation B is likely met or close. Claim 2 to 4 become the differentiators.

C. Prior art bucket: “fixation/coverage of cartilage graft”

If a reference teaches:

• periosteum as a biological cover,
• or membrane fixation using sutures,

then limitation D becomes the discriminant: periosteal flap sutured to cartilage “so that it remains in place during the healing process.” If earlier art uses periosteum but lacks the “flap” or the “sutured to cartilage” retention concept, claim 1 can still be distinguished.

What is the patent landscape likely like in the U.S. around this claim set?

US 4,846,835 sits in a crowded technological neighborhood: autologous chondrocyte implantation and scaffold-based variants. In that environment, the enforceable value usually comes from one of two things:

1. A unique fixation architecture (here: periosteal flap sutured to cartilage)
2. A unique scaffold preparation method (here: collagen gel with dispersed cells prior to polymerization)

Landscape dynamics that affect freedom-to-operate and enforceability

Factor	Typical effect on enforcement and FTO
Many patents share the same foundational concept (ACI)	Limits novelty; increases obviousness risk
Scaffolds (collagen gel/sponge) are common material choices	Makes dependent claims vulnerable unless preparation steps are unique
Fixation methods vary (suturing, membranes, adhesives)	Often determines real claim scope and infringement outcomes
“Process language” vs “structural outcome”	Courts may treat “activated matrix” as not adding structure beyond cell-scaffold preparation

Critical claim interpretation issues that determine patentability and infringement

1) “Activated matrix” is a process label with likely limited extra meaning

“Activated matrix” in claim 1 reads as a descriptor of the seeded scaffold outcome. Unless the specification ties “activated” to a distinct treatment (chemistry, time-dependent activation, crosslinking, growth factor exposure), it is vulnerable to being treated as non-limiting or inherently satisfied when cells are seeded.

2) Periosteal flap sutured to cartilage: scope depends on how “flap” is defined in practice

If the periosteal flap is a general periosteal patch used as a cover, many cartilage repair surgeons could reproduce the concept using varying periosteal preparations. If the specification uses a particular periosteal geometry and placement protocol, claim construction may narrow the term “periosteal flap.”

3) Collagen sponge vs collagen gel (claims 2 and 3)

Dependent claims can be avoided by using:

• a different scaffold type,
• a collagen scaffold in a form not qualifying as gel or sponge,
• or a composite scaffold that is not “collagen gel” as claimed.

4) Claim 4’s “dispersed… prior to its polymerization” is a functional timing constraint

Timing constraints often matter:

• Dispersing cells into collagen solution prior to polymerization supports claim 4 directly.
• Seeding cells onto an already polymerized gel can avoid a strict reading.

Where litigation leverage tends to concentrate

Even when claim 1 faces obviousness pressure, enforcement leverage can concentrate on:

• infringement proof of the periosteal flap sutured fixation step; and
• documentation of scaffold preparation (especially claim 4’s polymerization timing).

If accused products use non-periosteal coverage (or suture a different membrane) then claim 1 can be weak for enforcement. If competitors use collagen gels made by cell dispersion prior to polymerization, claim 4 can capture them even if other fixation steps differ slightly, depending on the specification’s integration requirements.

How to read the dependent claims strategically

Claim 2: collagen gel

This narrows the scaffold format. A competitor using a collagen sponge or polymerized non-gel form can avoid claim 2 while still potentially reading claim 1.

Claim 3: collagen sponge

This narrows to a porous/structured collagen sponge form. A competitor using collagen gel alone can avoid claim 3.

Claim 4: gel with cells dispersed prior to polymerization

This is the most process-specific dependent claim. It can be the strongest patentability differentiator if prior art generally seeds cells after polymerization.

Key Takeaways

• Claim 1’s core novelty hinge is the periosteal flap fixation: “periosteal flap sutured to the cartilage” is the narrowest and most likely distinguishing limitation against generic ACI + collagen scaffold disclosures.
• Claims 2–4 narrow the scaffold, but collateral risk is high because collagen gel/sponge scaffold methods are common in the field; the most discriminant sub-claim is claim 4’s polymerization timing (“chondrocytes dispersed prior to polymerization”).
• Validity pressure is concentrated in ACI basics (cultured autologous chondrocytes) plus collagen scaffold implantation. Without a distinctive “activated matrix” definition tied to objective process parameters, that label is unlikely to rescue claim breadth.
• Enforcement and FTO likely turn on fixation and scaffold preparation: periosteal flap suturing versus alternative coverage/fixation, and cell dispersion timing relative to collagen polymerization.

FAQs

1) What is the single most restrictive element in claim 1?
The fixation limitation: a periosteal flap sutured to the cartilage to retain the graft during healing.

2) Which dependent claim is most process-specific?
Claim 4, which requires a collagen gel where chondrocytes are dispersed prior to polymerization.

3) Can a collagen scaffold mismatch avoid infringement of the dependent claims?
Yes. Using scaffold forms outside collagen gel (claim 2), collagen sponge (claim 3), or outside the pre-polymerization dispersion process condition (claim 4) can avoid those dependent claims while still potentially implicating claim 1.

4) Does “activated matrix” likely expand scope beyond “seeded collagen”?
Typically it will not add much unless the specification ties “activated” to a distinct measurable treatment or structure beyond cell seeding.

5) Where is obviousness most likely argued?
Against the combination of cultured autologous chondrocytes with collagen-based scaffolds, with the periosteal flap fixation positioned as the attempt to distinguish the prior art.

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References

[1] United States Patent 4,846,835, “Grafting technique for promoting the healing of an articular cartilage lesion,” claims 1-4.

Details for Patent 4,846,835

Applicant	Tradename	Biologic Ingredient	Dosage Form	BLA	Approval Date	Patent No.	Expiredate
Vericel Corporation	CARTICEL SM SERVICE	autologous cultured chondrocytes	Injection	103661	August 22, 1997		2007-06-15
Vericel Corporation	MACI	autologous cultured chondrocytes on porcine collagen membrane	Cell Sheets	125603	December 13, 2016		2007-06-15