Scientific Characteristics of Hyaluronic Acid Dermal Filler Injections

Dermal filler injections using hyaluronic acid are one of the most common non-invasive cosmetic procedures performed today. There are many different varieties of hyaluronic acid fillers on the market, so it's important to understand the differences so you can choose the best option for your patient. Hyaluronic acid fillers are generally safe, but can cause serious complications, especially if used incorrectly; most complications are reversible if caught and treated early.

HA is a naturally occurring sugar that can bind 1,000 times its volume of water. It plumps the skin and aids in cell-to-cell communication. In its unmodified (not cross-linked) form, natural hyaluronic acid has a half-life of approximately 24 hours before it is enzymatically broken down by hyaluronidase and metabolized in the liver.

This article will briefly discuss the distinguishing characteristics of various hyaluronic acid fillers, read on to learn more.

Fillers with a high concentration of hyaluronic acid have greater volume, viscosity, and firmness/hardness, as well as longer duration, than the same HA with a lower concentration. Theoretically, the higher the concentration of hyaluronic acid in a filler, the harder the filler will be and the longer it will last. Fillers are labeled as containing a certain amount of mg/mL hyaluronic acid; this number includes both cross-linked and non-cross-linked hyaluronic acid. Only cross-linked hyaluronic acid helps extend the life of fillers, as uncross-linked hyaluronic acid degrades in approximately 24 hours. Uncross-linked hyaluronic acid is often added to dermal fillers to make it easier and smoother to squeeze out of the syringe. Although the concentration of hyaluronic acid in a dermal filler is important, other factors also come into play when considering longevity, including the amount of cross-linking, viscosity/spreadability, hardness, and cohesion.

HA is rapidly degraded by naturally occurring hyaluronidase enzymes. To extend longevity, hyaluronic acid is chemically modified and "cross-linked" to form a hydrogel. The higher the cross-linking percentage, the stronger the product will be and last longer, but it will be less flexible.

Chemical cross-linking holds hyaluronic acid chains together, but not all cross-links are complete. As shown in the picture, complete cross-links combine at least two different hyaluronic acid chains, while incomplete cross-links (also called pendant cross-links because they look like pendants on a necklace) only attach to one chain. The stability and duration of pendant cross-linking is lower than that of full cross-linking. Practitioners have no way of knowing how much cross-linking is complete or incomplete; therefore, when the package insert states that a product is 11% cross-linked, this information may be misleading.

The hardness of a product or G' (G prime) is a measure of gel hardness. It defines the gel's total resistance to deformation, or the amount of stress required to produce a given amount of deformation. It is measured by placing the gel on one plate, then placing a second plate on top of it, and applying a lateral force. The higher the G' of a product, the harder it is. The modulus of elasticity, along with other factors such as product cohesion, determines the appropriate product placement of hyaluronic acid fillers. For example, gels with a higher G' (such as Restylane Lyft) are stiffer and resistant to dynamic facial movements. These products provide a better lift and should be used on deeper lines such as nasolabial folds, and nasal folds, as well as lifting lateral brows or correcting the bridge and tip of the nose. Low-G' products, such as Juvederm Volbella, are typically used on areas that require a softer product, such as lips, tear troughs, or fine lines and superficial wrinkles.

Complex viscosity (ŋ) is defined as the resistance to flow. Cross-linked hyaluronic acid is more viscous than natural hyaluronic acid, and products with higher complex viscosity are difficult to spread. Products with lower viscosity have a greater ability to flow and spread through tissues. Ideally, a spreadable product will be used on large areas that need to feel soft, such as cheeks.

Cohesion has to do with the forces between particles of a material, allowing it to stick to itself. This defines the property of the gel to spread in tissue (low viscosity) or remain intact (high viscosity) when injected. In addition to viscosity, this allows the hyaluronic acid filler to mold easily after injection without causing the gel to break.

Squeeze force is important because the force with which the hyaluronic acid exits the syringe affects the risk of bruising and tissue damage and vessel occlusion. Syringe design, the addition of uncross-linked hyaluronic acid to the filler, the needle gauge used, and the amount of pressure the esthetician applies to the plunger all affect extrusion force.

Bruising and swelling are common complications of hyaluronic acid dermal filler injections. The risk of bruising can be reduced by asking patients to avoid NSAIDs, aspirin, salmon, green tea, vitamin E, and other anticoagulants for 10 days before the injection. Bruising and swelling can also be reduced with proper pre- and post-operative skin care. Using gentle squeezing pressure, avoiding blood vessels, using careful massage techniques, and warning patients to avoid heat, pressure, and exercise for 48 hours after surgery can help minimize complications.

The following are serious complications that can result from filler injections. Before injecting a patient, you must know how to handle the following:

Vascular Occlusion. Vascular damage is the most serious complication associated with dermal filler injections. Arterial occlusion may be caused by embolization of filler material directly into the artery, immediately manifesting as skin blanching and pain. If left untreated, it can result in loss of deep tissue through necrosis, or worse, loss of vision.

Vein occlusion, on the other hand, may be caused by injecting large amounts of filler into a small area. This may manifest as prolonged pain and swelling with dark discoloration. Damage to blood vessels can be prevented by understanding facial anatomy and appropriate injection depth, as well as slower injection techniques using minimal pressure; small bolus injections are also recommended. Treatment includes hyaluronidase injections, heat, massage, and applying nitroglycerin paste to the affected area.

Delayed Nodule Formation. Late-onset nodules present as subcutaneous, nonvolatile masses, usually located in the dermis or subcutaneous space. These can appear weeks to months after the injection and may be caused by an infection or an autoimmune reaction. These nodules are very disturbing and can be disfiguring to the patient.

Some nodules are caused by aggregates of polymer-secreting bacteria that form biofilms on injected materials and cause them to adhere irreversibly to the product. Not only does this biofilm create inflammatory nodules, but it can also release bacteria in the surrounding tissue, leading to infection or other inflammatory nodules. This can be avoided by using an aseptic technique during injections and a thorough review of the patient's history.

Some nodules are caused by the activation of the immune system. We're not sure why this is happening. Therefore, do not inject hyaluronic acid fillers into patients if they have received vaccinations within the past two weeks. Many doctors believe this may increase the chance of delayed-type hypersensitivity reactions. Treatment of these nodules is beyond the scope of this article.

Angioedema. Some patients may develop IgE-mediated allergic reactions to injected fillers. It is characterized by the swelling, erythema, pain, and itching seen in allergic reactions. This usually occurs within an hour of the injection but may last for several weeks. Angioedema usually resolves with antihistamines, but refractory cases may require treatment with oral prednisone. Rapidly progressive angioedema must be closely monitored because it may lead to airway obstruction.

With hyaluronic acid filler injections rapidly gaining popularity, an extensive understanding of dermal fillers is fundamental to any cosmetic injectable. For optimal results, cosmetic providers and injectors need to have a thorough understanding of facial anatomy, an in-depth understanding of dermal filler rheology, and the ability to avoid, recognize, and manage potential complications.

The above briefly introduces the distinguishing characteristics of different hyaluronic acid fillers. If you want to order or are looking for a reliable hyaluronic acid product manufacturer, please contact us.

Hyamax is a professional custom hyaluronic acid products manufacturer. Committed to safety, effectiveness and innovation, our products are rigorously tested and adhere to strict regulatory standards to ensure the highest level of quality and patient satisfaction. Whether you want to enhance facial contours, restore volume, or smooth wrinkles, Hyamax hyaluronic acid dermal fillers provide natural-looking, long-lasting results. Contact us somewhere and experience the difference in superior aesthetics. Our team of experts have many years of experience in dermatology, plastic surgery and pharmaceuticals, and we are passionate about using our knowledge to create products that make a real difference to people's lives. We continue to push the boundaries of aesthetic medicine and are proud to offer a range of treatments that are backed by scientific evidence and proven to be safe and effective.