# How Soft Contact Lenses Were Invented Using Hydrogels

> This patent describes the chemical recipe for soft, water-absorbing plastic materials that form the basis of modern soft contact lenses.

- **Patent:** US 3220960
- **Original title:** Cross-linked hydrophilic polymers and articles made therefrom
- **Owner:** Individual
- **Granted:** 1965
- **Status:** Public domain (expired)
- **Times cited:** 228
- **Field:** biotech, materials, consumer_electronics

## What it does

The patent defines a shaped body made from a hydrogel, which is a material that holds a large amount of water. It uses a base of a water-soluble monoester (like hydroxyethyl methacrylate) mixed with a small amount of a diester to create a cross-linked structure. This cross-linking acts like a microscopic net that holds the water inside the polymer without the material dissolving. By adjusting the ratio of these ingredients, the resulting plastic remains soft and flexible while retaining its shape in an aqueous environment.

## What it does NOT cover

- Does not cover rigid gas-permeable contact lenses made from non-hydrogel materials.
- Does not cover non-cross-linked polymers that would simply dissolve in water.
- Does not cover the specific manufacturing process of spinning or molding the lenses, only the chemical composition of the material itself.

## The clever bit

The inventors realized that by adding just a 'minor amount' of a cross-linking diester to a hydrophilic polymer, they could create a stable, water-swollen solid that wouldn't wash away, effectively trapping water within a plastic matrix.

## Real-world examples

1. Soft contact lenses
2. Hydrogel wound dressings
3. Drug delivery implants

## Why it matters

This invention transformed vision correction by replacing hard, uncomfortable plastic lenses with soft, breathable alternatives. It is the foundational technology for the entire soft contact lens industry, which serves millions of people worldwide.

## Frequently asked questions

### What does How Soft Contact Lenses Were Invented Using Hydrogels cover?

This patent describes the chemical recipe for soft, water-absorbing plastic materials that form the basis of modern soft contact lenses.

### Who owns patent US 3220960?

Individual owns this patent, granted in 1965.

### When does this patent expire?

This patent has expired and is now in the public domain — anyone can use the invention freely.

### What is patent US 3220960 cited by?

This patent has been cited by 228 later patents that build on its ideas.

### What problem does this patent solve?

This invention transformed vision correction by replacing hard, uncomfortable plastic lenses with soft, breathable alternatives. It is the foundational technology for the entire soft contact lens industry, which serves millions of people worldwide.

### What does this patent NOT cover?

Does not cover rigid gas-permeable contact lenses made from non-hydrogel materials.

**Full plain-English explainer:** https://patentbrief.org/patent/us/3220960/soft-contact-lens-hydrogel

**Original patent:** https://patents.google.com/patent/US3220960

---

_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._


## Related patents

Semantically similar inventions in the PatentBrief corpus:

- [How Polystyrene Sulfonate Helps Treat Dry Eye Symptoms](https://patentbrief.org/patent/us/3987163/indomethacin) — A 1975 patent for an eye drop solution that uses a specific polymer to lubricate and cushion the eye, especially for contact lens wearers.
- [Sticky, Tiny Plastic Balls Made from Acrylates](https://patentbrief.org/patent/us/3691140/post-it-repositionable-adhesive) — This 1972 patent describes how to make tiny, sticky, and durable plastic balls (microspheres) using a specific mix of acrylate chemicals and a special water-based process.
- [How Light-Activated Polymers Deliver Skin Care Ingredients](https://patentbrief.org/patent/us/12178901/dragon-xl) — A chemical structure that holds onto skin-care ingredients like fragrances or cooling agents and releases them only when triggered by specific light conditions.
- [How to Make Clear, Waterproof Sunscreen That Doesn't Feel Greasy](https://patentbrief.org/patent/us/4810490/tpa-tissue-plasminogen-activator) — A 1989 patent for a transparent, water-resistant sunscreen formula that uses wood rosin to create a non-sticky, long-lasting protective film on the skin.
- [How Play-Doh Was Invented](https://patentbrief.org/patent/us/3167440/play-doh-modeling-compound) — The original 1965 patent for the soft, non-toxic modeling compound known as Play-Doh, detailing a specific mixture of flour, water, salt, and kerosene.