# Injectable filler

Injectable filler is a special type of substance made for injections into connective tissues, such as skin, cartilage or even bone, for cosmetic or medical purposes. The most common application of injectable fillers is to change one's facial appearance, but they also are used to reduce symptoms of osteoarthritis, treat tendon or ligament injuries, support bone and gum regeneration, and for other medical applications. Injectable fillers can be in the form of hydrogel or gels made from pulverized grafts.
Injectable fillers have risen in popularity mostly due to the wide application of dermal fillers in 80's. Their premise is to help fill in facial wrinkles, provide facial volume, and augment facial features. Side effects include bruising or infections from improper sterilisation. This may include HIV infection, also allergic reactions, which may cause scarring and lumps. Blindness due to retrograde (opposite the direction of normal blood flow) embolization into the ophthalmic and retinal arteries can occur.
Injection of dermal fillers is the second most common nonsurgical cosmetic procedure in the USA, used for addressing volume deficiency, scars, wrinkles, and enhancing facial features and specific anatomical sites like the lips. The variety of available dermal fillers increases annually, requiring dermatologists and cosmetic surgeons to stay informed about the latest options to ensure safe and effective treatments.

## Materials used

Fillers are made of polysaccharides such as hyaluronic acids, a naturally occurring in skin and cartilage, collagens which may come from pigs, cows, cadavers, or may be generated in a laboratory, the person's own transplanted fat tissue, and/or biosynthetic polymers. Examples of the latter include calcium hydroxylapatite, polycaprolactone, polymethylmethacrylate, and polylactic acid. In 2012, "Artiste Assisted Injection System" was launched in the US market to assist in the delivery of dermal fillers. A study in 2013 concluded that the injecting device can achieve reductions in patient discomfort and adverse events by controlling the rate of flow of injection of the filler the practitioner is using to fill in the lips and frown lines.
Soft-tissue augmentation has grown in popularity recently, particularly with the use of hyaluronic acid (HA) based dermal fillers. These non-permanent injectables can restore lost volume, smooth fine lines and wrinkles, and enhance facial contours. Despite their widespread use since the late 1990s, there is limited comparative data and literature on the diverse range of HA fillers and their tissue performance.
The studies explore various methods and parameters for characterizing dermal fillers, providing key insights for clinicians to select the most suitable products for their patients. The aging face undergoes complex changes due to bone resorption, gravity, fat redistribution, and skin damage, which dermal fillers aim to counteract. HA fillers are considered medical devices rather than medicines, thus lacking stringent regulatory requirements for safety and efficacy data.
The scientific community emphasizes the importance of understanding the physico-chemical properties of fillers, such as their behavior under stress and deformation, and their performance over time. These properties are influenced by different crosslinking technologies used in manufacturing.
A literature search identified key studies on the rheological properties of HA fillers, focusing on FDA-approved products and others like Revolax. The review analyzes methodologies and critiques the existing literature to provide a comprehensive understanding of HA fillers' properties.

## Medical uses

Dermal fillers, also known as "injectables" or "soft-tissue fillers," fill in the area under the skin, and have some non-cosmetic uses, such as non-surgical facial cleft repair or cleft modification, treating fat loss secondary to HIV: Fillers were found to give a temporary acceptable therapeutic effect in HIV‐infected patients with severe facial lipodystrophy caused by highly active antiretroviral therapy. A 2009 review concluded that injectable fillers resulted in high satisfaction, but further research was needed to determine safety of its use.

## Pharmacokinetics

Most wrinkle fillers are temporary because they are eventually metabolized by the body. Some people may need more than one injection to achieve the wrinkle-smoothing effect. The effect lasts for about six months. Results depend on health of the skin, skill of the health care provider, and the type of filler used. Regardless of material (whether synthetic or organic) filler duration is highly dependent on amount of activity in the body area where it is injected. Exercise and high intensity activities such as manual labor can stimulate blood flow and shorten the lifespan of fillers.

## Side effects and risks

Risks of an improperly performed dermal filler procedure commonly include bruising, redness, pain, or itching. Less commonly, there may be infections or allergic reactions, which may cause scarring and lumps that may require surgical correction. In 2024, a cluster of HIV infections was described amongst clients receiving microneedling facials at a Spa. More rarely, serious adverse effects such as blindness due to retrograde (opposite the direction of normal blood flow) embolization into the ophthalmic and retinal arteries can occur. Delayed skin necrosis can also occur as a complication of embolization. Embolic complications are more frequently seen when autologous fat is used as a filler, followed by hyaluronic acid. Though rare, when vision loss does occur, it is usually permanent.

## Society and culture

In the US, fillers are approved as medical devices by the Food and Drug Administration (FDA) and the injection is prescribed and performed by a provider. What defines a qualified dermal injection provider varies by country and is a point of debate between board-certified doctors and injectors who operate under cosmetic or aesthetician licenses.
Fillers are not to be confused with neurotoxins such as Botox. Fillers are not approved for certain parts of the body where they can be unsafe, including the penis. In Europe and the UK, fillers are non-prescription medical devices that can be injected by anyone licensed to do so by the respective medical authorities. They require a CE mark, which regulates adherence to production standards, but does not require any demonstration of medical efficacy. As a result, there are over 140 injectable fillers in the UK/European market and only six approved for use in the US. In China, the market of cosmetic surgery increase in recent 10 years, NMPA (formerly CFDA) also has issued several guidance to regulate injectable filler.