Injectable filler is a special type of substance made for injections into connective tissues, such as

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

or even

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

, 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 A hydrogel is a Phase (matter), biphasic material, a mixture of Porosity, porous and Permeation, permeable solids and at least 10% of water or other interstitial fluid. The solid phase is a water Solubility, insoluble three dimensional network ...

or gels made from pulverized

grafts Grafting refers to a surgical procedure to move tissue from one site to another on the body, or from another creature, without bringing its own blood supply with it. Instead, a new blood supply grows in after it is placed. A similar techniqu ...

. 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

wrinkle A wrinkle, also known as a rhytid, is a fold, ridge or crease in an otherwise smooth surface, such as on skin or fabric. Skin wrinkles typically appear as a result of ageing processes such as glycation, habitual sleeping positions, loss of b ...

s, provide facial volume, and augment facial features. Side effects include bruising or infections from improper sterilisation. This may include

HIV infection The human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a preventable disease. It can ...

, also allergic reactions, which may cause scarring and lumps. Blindness due to retrograde (opposite the direction of normal blood flow)

embolization Embolization refers to the passage and lodging of an embolus within the bloodstream. It may be of natural origin ( pathological), in which sense it is also called embolism, for example a pulmonary embolism; or it may be artificially induced ...

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 SCARS or S.C.A.R.S. is an acronym that may refer to: * SCARS (military) (Special Combat Aggressive Reactionary System), an American combat fighting system * Severe cutaneous adverse reactions Severe cutaneous adverse reactions (SCARs) are a gr ...

wrinkles A wrinkle, also known as a rhytid, is a fold, ridge or crease in an otherwise smooth surface, such as on skin or fabric. Skin wrinkles typically appear as a result of ageing processes such as glycation, habitual sleeping positions, loss of bo ...

, and enhancing facial features and specific anatomical sites like the

lips The lips are a horizontal pair of soft appendages attached to the jaws and are the most visible part of the mouth of many animals, including humans. Mammal lips are soft, movable and serve to facilitate the ingestion of food (e.g. sucklin ...

. 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 Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wat ...

such as hyaluronic acids (a naturally occurring

glycosaminoglycan Glycosaminoglycans (GAGs) or mucopolysaccharides are long, linear polysaccharides consisting of repeating disaccharide units (i.e. two-sugar units). The repeating two-sugar unit consists of a uronic sugar and an amino sugar, except in the case o ...

in skin and cartilage),

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

s 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 Hydroxyapatite (IMA name: hydroxylapatite) (Hap, HAp, or HA) is a naturally occurring mineral form of calcium apatite with the formula , often written to denote that the crystal unit cell comprises two entities. It is the hydroxyl endmember ...

polycaprolactone Polycaprolactone (PCL) is a synthetic, semi-crystalline, biodegradable polyester with a melting point of about 60 °C and a glass transition temperature of about −60 °C. The most common use of polycaprolactone is in the production ...

polymethylmethacrylate Poly(methyl methacrylate) (PMMA) is a synthetic polymer derived from methyl methacrylate. It is a transparent thermoplastic, used as an engineering plastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and bran ...

, and

polylactic acid Polylactic acid, also known as poly(lactic acid) or polylactide (PLA), is a plastic material. As a thermoplastic polyester (or polyhydroxyalkanoate) it has the backbone formula or . PLA is formally obtained by condensation of lactic acid with ...

. 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 Hyaluronic acid (; abbreviated HA; conjugate base hyaluronate), also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. It is unique among glycosaminog ...

(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 Bone resorption is resorption of bone tissue, that is, the process by which osteoclasts break down the tissue in bones and release the minerals, resulting in a transfer of calcium from bone tissue to the blood. The osteoclasts are multi-nuclea ...

gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

, 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 A facial cleft is an opening or gap in the face, or a malformation of a part of the face. Facial clefts is a collective term for all sorts of clefts. All structures like bone, soft tissue, skin etc. can be affected. Facial clefts are extremely rare ...

repair or cleft modification, treating fat loss secondary to

HIV The human immunodeficiency viruses (HIV) are two species of '' Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the im ...

: Fillers were found to give a temporary acceptable therapeutic effect in

‐infected patients with severe facial

lipodystrophy Lipodystrophy syndromes are a group of genetic or acquired disorders in which the body is unable to produce and maintain healthy fat tissue. The medical condition is characterized by abnormal or degenerative conditions of the body's adipose tissu ...

caused by highly active

antiretroviral The management of HIV/AIDS normally includes the use of multiple antiretroviral drugs as a strategy to control HIV infection. There are several classes of antiretroviral agents that act on different stages of the HIV life-cycle. The use of mu ...

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

s 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)

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 Autotransplantation is the transplantation of organs, tissues, or even particular proteins from one part of the body to another in the same person ('' auto-'' meaning "self" in Greek). The autologous tissue (also called autogenous, autogenei ...

fat is used as a filler, followed by

. 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 The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...

(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

neurotoxin Neurotoxins are toxins that are destructive to nervous tissue, nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insult (medical), insultsSpencer 2000 that can adversely affect function ...

s such as

Botox Botulinum toxin, or botulinum neurotoxin (commonly called botox), is a neurotoxic protein produced by the bacterium ''Clostridium botulinum'' and related species. It prevents the release of the neurotransmitter acetylcholine from axon endi ...

. 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.

References