results have been found in small animals. joint repair osteoarthritis is the main cause of joint pain both in animals and humans. horses and dogs are most frequently affected by arthritis. natural cartilage regeneration is very limited. different types of mesenchymal stem cells and other additives are still being researched to find the best type of cell and method for long-term treatment. adipose-derived mesenchymal cells are currently the most often used for stem cell treatment of osteoarthritis because of the non-invasive harvesting. this is a recently developed, non-invasive technique developed for easier clinical use. dogs receiving this treatment showed greater flexibility in their joints and less pain. muscle repairs stem cells have successfully been used to ameliorate healing in the heart after myocardial infarction in dogs. adipose and bone marrow derived stem cells were removed and induced to a cardiac cell fate before being injected into the heart. the heart was found to have improved contractility and a reduction in the damaged area four weeks after the stem cells were applied. a different trial is underway for a patch made of a porous substance onto which the stem cells are "seeded" in order to induce tissue regeneration in heart defects. tissue was regenerated and the patch was well incorporated into the heart tissue. this is thought to be due, in part, to improved angiogenesis and reduction of inflammation. although cardiomyocytes were produced from the mesenchymal stem cells, they did not appear to be contractile. other treatments that induced a cardiac fate in the cells before transplanting had greater success at creating contractile heart tissue. recent research, such as the european ntrack research project, aims to demonstrate that multimodal nanoparticles can structurally and functionally track stem cell in muscle regeneration therapy. the idea is to label stem cells with gold nano-particles that are fully characterised for uptake, functionality, and safety. the labelled stem cells will be injected into an injured muscle and tracked using imaging systems. however, the system still needs to be demonstrated at lab scale. nervous system repairs spinal cord injuries are one of the most common traumas brought into veterinary hospitals. spinal injuries occur in two ways after the trauma: the primary mechanical damage, and in secondary processes, like inflammation and scar formation, in the days following the trauma. these cells involved in the secondary damage response secrete factors that promote scar formation and inhibit cellular regeneration. mesenchymal stem cells that are induced to a neural cell fate are loaded onto a porous scaffold and are then implanted at the site of injury. the cells and scaffold secrete factors that counteract those secreted by scar forming cells and promote neural regeneration. eight weeks later, dogs treated with stem cells showed immense improvement over those treated with conventional therapies. dogs treated with stem cells were able to occasionally support their own weight, which has not been seen in dogs undergoing conventional therapies. in a study to evaluate the treatment of experimentally induced ms in dogs using laser activated non-expanded adipose derived stem cells. the results showed amelioration of the clinical signs over time confirmed by the resolution of the previous lesions on mri. positive migration of the injected cells to the site of lesion, increased remyelination detected by myelin basic proteins, positive differentiation into olig2 positive oligodendrocytes, prevented the glial scar formation and restored axonal architecture. treatments are also in clinical trials to repair and regenerate peripheral nerves. peripheral nerves are more likely to be damaged, but the effects of the damage are not as widespread as seen in injuries to the spinal cord. treatments are currently in clinical trials to repair severed nerves, with early success. stem cells induced to a neural fate injected in to a severed nerve. within four weeks, regeneration of previously damaged stem cells and completely formed nerve bundles were observed. stem cells are also in clinical phases for treatment in ophthalmology. hematopoietic stem cells have been used to treat corneal ulcers of different origin of several horses. these ulcers were resistant to conventional treatments available, but quickly responded positively to the stem cell treatment. stem cells were also able to restore sight in one eye of a horse with retinal detachment, allowing the horse to return to daily activities. society and culture marketing and costs in the late 1990s and early 2000s, there was an initial wave of companies and clinics offering stem cell therapy, while not substantiating health claims or having regulatory approval. by 2012, a second wave of companies and clinics had emerged, usually located in developing countries where medicine is less regulated and offering stem cell therapies on a medical tourism model. like the first wave companies and clinics, they made similar strong, but unsubstantiated, claims, mainly by clinics in the united states, mexico, thailand, india, and south africa. by 2016, research indicated that there were more than 550 stem cell clinics in the us alone selling generally unproven therapies for a wide array of medical conditions in almost every state in the country, altering the dynamic of stem cell tourism. in 2018, the fda sent a warning letter to stemgenex biologic laboratories in san diego, which marketed a service in which it took body fat from people, processed it into mixtures it said contained various forms of stem cells, and administered it back to the person by inhalation, intravenously, or infusion into their spinal cords; the company said the treatment was useful for many chronic and life-threatening conditions. costs of stem cell therapies range widely by clinic, condition, and cell type, but most commonly range between $10,000-$20,000. insurance does not cover stem cell injections at clinics so patients often use on-line fundraising. in 2018, the us federal trade commission found health centers and an individual physician making unsubstantiated claims for stem cell therapies, and forced refunds of some $500,000. the fda filed suit against two stem cell clinic firms around the same time, seeking permanent injunctions against their marketing and use of unapproved adipose stem cell products. covid-19-related marketing and government agency responses although according to the nih no stem cell treatments have been approved for covid-19, and the agency recommends against the use of mscs for the disease, some stem cell clinics began marketing both unproven and non-fda-approved stem cells and exosomes for covid-19 in 2020. the fda took prompt action by sending letters to the firms in question. the ftc also warned a stem cell firm for misleading covid-19-related marketing.