This study is a single-blind intra-individual comparative study to evaluate the short and medium term tissue response after the injection of 2 brands of hyaluronic acid gels (HA), designed for deep injection, that have been used for several years on a worldwide scale.

The study will be disclosed to patients who present with an indication for either abdominoplasty or bilateral breast reduction with a Wise pattern skin excision (inverted T inframammary scar) Informed consent will be obtained from volunteers at their next consultation, during which the preoperative preparation is finalised and the surgery is booked.

Participants will receive injections for the first time three weeks to four months before the operation and for the second time five to nine days before the operation, in tissue that will be removed during the surgery.

In each session, through one single access point, a linear retrograde, subcutaneous injection will be performed with 0,5 ml of each of the studied hyaluronic acid gels, each in an opposite direction, each parallel to the skin surface.

Both sessions will be monitored by ultrasound examination. After the injections, the 2 cm of injected area which is most remote from the entrance point of the cannula will be remodelled by finger pressure and tissue pinching, to simulate remodelling as commonly performed after filler injection.

At the beginning of the operation, the injected subcutaneous fat will be removed with the overlying skin, to be sent for histologic examination.

The objective of the histologic examination is to assess the tissue response at one week versus three weeks to four months after the injection, as well as to assess the spread of the products, with and without remodelling after injection.

Inclusion Criteria:

• patients eligible for and requesting abdominoplasty
• patients eligible for and requesting bilateral breast reduction

Exclusion Criteria:

• Patients prone to hypertrophic scarring or keloids
• Hypersensitivity to hyaluronic acid
• Hypersensitivity to lidocaine or amide type local anaesthetics
• Autoimmune disease
• Severe, multiple allergies or anaphylactic shock
• Epilepsy
• Heart rhythm disorders
• Porphyria, congenital methemoglobinemia, glucose-6 phosphate dehydrogenase deficiencies, treatment with methaemoglobin-inducing substances.
• Previous streptococcal disease (acute rheumatic fever whether or not with heart valve involvement)
• Patients on medication which slows hepatic metabolism (such as cimetidine, beta-blockers)
• Diabetes requiring insulin treatment
• Major system disease.
• Coagulation disorders. Anticoagulation therapy. Chronic use of acetylsalicylic acid.
• Previous surgery in the areas eligible for injections.
• All contraindications to their surgical treatment (such as pregnancy or lactation).

pilot study on 5 patients: min, max, average measurements will be published