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OPINION Reactions ShareShare onFacebookTwitterWechatLinked InRedditEmail C&EN, 2021, 99 (20), p 5May 31, 2021Cite this:C&EN 99, 20, 5(Credit: Andy Brunning)Figure1of1Letters to the editorHyaluronic acidI enjoyed reading Craig Bettenhausen’s article “Hyaluronic Acid, the Everywhere Biopolymer” (C&EN, May 3, 2021, page 26). It has much personal relevance for me. Within a few days of retirement in January 2019 from my position as a research chemist with the US Food and Drug Administration, I started feeling extreme pain in my right knee. X-rays revealed I had developed a moderate case of osteoarthritis in the knee just as I was starting my wonderful new life of retirement. Cortisone shots and physical therapy did nothing to ease the pain. In May of 2019, I received a course of three gel shots—hyaluronic acid—from my orthopedic specialist. The pain was reduced almost immediately after the first injection. After the third injection, the arthritic knee pain was gone. It is now almost 2 years later, and the right knee still feels very good, just an occasional twinge if I overexert it. I now take two capsules of a supplement containing hyaluronic acid, 100 mg total, every day. For me, hyaluronic acid is a miracle drug. Sincere thanks from me to the chemists, medical researchers, and doctors who have developed this treatment.Joseph E. JablonskiTwinsburg, Ohio. CorrectionsApril 26, 2021, page 20: The feature story on using the mass-balance concept to make chemicals should have described a Neste plant as a refinery, not a cracker. Neste’s brand of renewable naphtha is Neste RE, not Naphtha RE. And Neste’s oil is made from 100% renewable raw materials and thus does not have to be independently mass-balance audited.May 17, 2021, page 18: The feature story about a global plastics treaty implies that Inger Andersen suggested that the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal is a strong contender for an existing environmental treaty that could be modified to include plastics. She did not. Also, she said that the UN Environment Assembly could recommend the new accord be an extension of an existing treaty, not that the UNEA is likely to do so.May 24, 2021, page 24: The Periodic Graphics on bicycle materials mistakenly omits an oxygen in the structure of the example polyester (polyethylene terephthalate). The correct structure is shown here.