• Absorption: > 1.5 g/cm² (physiological Ringer’s solution or 0.9% saline)
• Retention: approx. 70%
• Logarithmic reduction factor of the BTBS: > 10⁷
• Microbial retention: almost 100%
• WVTR (water vapour transmission rate): 3500 g ± 1000 g/m²/24h

• Adhesive- and binder-free absorption core -> SuperCore^®
• Vertical absorption (prevents the distribution of exudate to the periwound area)
• Very good absorption of fluids, even under compression therapy at 46 mmHg
• Secure retention (even under compression)
• Avoids maceration (due to the retention of exudate)
• The BTBS acts as a sterile barrier against germs (to protect the surrounding area of the wound and the environment of the patient)
• Binds germs in SuperCore^® (MRSA, as well) and reduces the number of germs in the wound
• Modulates MMPs (matrix metalloproteases)
• Minimises wound odours (by inactivating germs and MMPs)
• Less frequent dressing changes
• More cost-efficient than standard wound care
• Improves the psycho-social situation of the patient
• Reduces traumata during dressing changes (especially in the granulation phase)

MMPs are enzymes, which are produced by the body in the periwound tissue as part of the immune system. Normally, they regulate the decomposition of body tissue in the phase of inflammation to create space for new cells. Thus, in a healthy wound they help in the process of wound healing.

In chronic wounds the body wrongly assumes to be in the inflammation phase and the signal to produce MMPs is not stopped. As a result, the high level of MMPs acts against the body and inhibits the regrowth of new skin.

MMPs are enzymes that play an essential role in “normal” wound healing. MMPs are produced by activated inflammatory immune cells (e.g. neutrophils and macrophages) and by cells of the skin like epithelial cells, fibroblasts and vascular endothelial cells. During wound healing MMPs are responsible for the controlled decomposition of extracellular matrix proteins (e.g. collagen) and they influence the activity and bioavailability of cytokines and growth factors. For their enzymatic activity MMPs need metal ions (e.g. zinc). In chronic wounds excessive amounts of MMPs can be detected. These high levels of out-of-balance MMPs affect the formation of granulation tissue, because newly synthesized extracellular matrix and cytokines are decomposed. Without growth factors, receptors or a stable extracellular matrix, wound cells (e.g. fibroblasts) are not able to react to “normal” growth and repair signals, which leads to diminished adhesion and migration. Wound healing stagnates.

MMPs have been named according to their two main characteristics: 1) the ability to decompose an extracellular matrix and 2) for this these enzymes require a metal ion like zinc.

The expert report from the Medical School of Göttingen³ verifies that curea P1 and curea P2 are able to absorb whole blood. It is in the interest of good wound healing to absorb blood to avoid the aggregation of blood particles which would be good nutrition for microbes and a source of cytokines. Cytokines can e.g. raise the level of MMP (see matrix metalloproteases), thus impairing wound healing.

The ideal wound dressing…

– removes surplus exudate and toxic components

• SuperCore^® binds exudate, germs and toxins safely, due to its absorption- and retention qualities.

– provides a humid wound environment

• The pulp within SuperCore^® stores the moisture and releases it as required.

– allows a continuous gas exchange

• The backsheet BTBS of curea P1 and curea P2 allows a gas exchange of 3.5 l/m² in 24h and acts as a sterile barrier.

– offers thermic insulation

• The multi-layer construction of the curea P1 and curea P2 thermally insulates, thus retaining body temperature.

– protects against secondary infection

• The BTBS acts as a sterile barrier against germs from the surrounding area. SuperCore^® molecularly binds germs from the exudate. It retains the microbes, thus inhibiting secondary proliferation².

– is free from particulate or toxic contamination

• The polypropylene nonwoven is widely particle-free. SuperCore^® consists of native pulp and sodium polyacrylate only. It is free of adhesives and binders (allergens). The wound dressings curea P1 and curea P2 are adhesive- and latex-free.

– causes no traumata during dressing changes

• The hydrophobic nonwoven of curea P1 reduces traumata during dressing changes. The perforated polyethylene wound contact layer of curea P2 enables an atraumatic dressing change.

Compared with PU foams curea medical dressings provide the essential advantage of fluid retention, while foams can be simply squeezed out like a blackboard sponge under pressure. A commonly observed side effect of foams is maceration due to the low retention.

Germs are bound to the sodium polyacrylate, hereby impairing the vital functions of the germs and inhibiting the causes of bad odours and secondary infections. Another advantage is the filtering of coarse particles (e.g. blood cells or detritus) by the pulp. That is why the wound dressings curea P1 and curea P2 also provide the ability to absorb whole blood.

Taking into account a longer wearing time and the reduced danger of maceration, the use of curea polyacrylate dressings generally costs less than using foams.

Wound dressings containing polyacrylate are NOT able to desiccate a wound, because a dynamic balance arises between the cellulose and the body tissue:

Body tissue binds exudate by adsorption like cellulose. Both “materials” have similar adsorption forces, because the chemistry of body tissue is not very different from the chemistry of cellulose. Thus, only free fluid can be exchanged. Free fluid is transported to the sodium polyacrylate due to the capillary effect (as a result of adsorption on cellulose). In this case, the cellulose acts physically to store the fluid. If there is no more free fluid available, the capillary effect collapses and the sodium polyacrylate will not absorb any more fluid while the cellulose and the body tissue remain moist to some extent.

Only a qualitative but not a quantitative description of exudate exists in scientific literature. Wound exudate, basically, is similar to blood plasma. Wound exudate derives from liquid migrating from blood vessels into the tissue. Wound exudate consists of mainly water and contains electrolytes, nutrients, inflammatory mediators, white blood cells, proteases (enzymes), growth factors and decomposition products. Different aspects define the amount and composition of exudate, among other things, the nutrition of patients, the inflammation- and infection level as well as the wound healing phase. The absorption capacity of a wound dressing depends on its size or area. Because the wearing time of the wound dressing determines the weight of the wound dressing, the absorption capacity of SAP-dressings should be between 1.0 and 2.0 g/cm² of core area. Less than 1 g/cm² could result in shortened changing intervals, while more than 2.0 g/cm² may cause that the dressings to become too heavy and chafing of the wound dressing could cause destruction of freshly grown tissue and reduce the comfort for the patient. A polyacrylate wound dressing of the size 20 x 30 cm can absorb between 0.5 and 1 l of exudate, which corresponds to a weight of 0.5 to 1 kg. Such a weight on the leg, for example, during the care of a venous lower leg ulcer would not be desirable in “clinical reality”.

For wound dressings a basic standard EN 13726 exists which describes, among other things, a test method for absorption (3.1 free swell)¹. With regard to this standard, absorption is tested with physiological Ringer’s solution for 30 minutes at a temperature of 37°C. Technically comparable are tests with 0.9% saline, which is a defined solution of salt (NaCl) and water (app. 9.08 g salt/l). The reason for determining the absorption of wound dressings with defined test solutions is that free ions in liquids influence the binding activity of chemical substances like polyacrylate. By comparison, tap water has a regionally different ionic content, which means that the amount of free ions is unknown. Because tap water isn`t a standardized test solution, measurements of absorbency with tap water are purely speculative. The temperature and pH of the test solution also influence the absorption measurement and can be controlled for Ringer’s solution and saline in contrast to tap water.

Unfortunately, no official test with synthetic exudate exists, so that the information about capacities is speculative.

The various wound dressings based on polyacrylate differ significantly from each other. This is due to many factors. On the one hand, there are the raw materials and the manufacturing method of the core material, on the other hand the materials of the covering. Based on these various factors, there are differences in terms of absorption, capacity, wound contact, haptics and purity of the wound dressing.

The ability to bind germs and to absorb blood is based on the manufacturing process of SuperCore^®. The materials of the back side (see BTBS) of the wound dressings curea P1 and P2 act as a sterile barrier, thus protecting the patient and the user.

The materials on the wound side have different effects: The nonwoven generates a soft debridement, whereas the 3D-PE foil guarantees non-adherent wound contact.

Sodium polyacrylates differ significantly from each other based on the chemical manufacturing process. Depending on the crosslinking and surface linking of the molecules, polyacrylates have different absorption rates as well as different absorption capacities. Because of the crosslinking, the space in which the sodium polyacrylate is able to expand is limited (see capacity). The surface linking causes a change in the accessibility of the sodium polyacrylate. The larger the surface of the molecule, the faster it is able to absorb. The shape and the size of the polyacrylate grains are also relevant.

Sodium polyacrylate is a hydrophilic artificial material. It is made by polymerisation (“endless connection”) of acrylic acid and sodium acrylate. The polymer chains are crosslinked with a difunctional molecule, which makes them insoluble in water. When in contact with water this network swells to a volume several hundred times larger than that of the dry substance (compare absorption). Because of the formation of molecular bonds (hydrogen bonds) and their high binding energies, the water molecules remain trapped in the polymer network and are not released, even under mechanical pressure, which makes sodium polyacrylate very suitable for compression therapy.

SuperCore^® describes a fluid-absorbing core, which is manufactured without any adhesives or binders by a manufacturing process. SuperCore^® consists of two components – sodium polyacrylate (plastic) and pulp (cellulose fibres). SuperCore^® is manufactured by a so-called airlaid process. In the airlaid process the two components are layered by an air flow and then bonded point by point by two heated and structured rollers under pressure. The result is the characteristic pixel structure of SuperCore^®.

Retention is described as the ability of a material to bind and hold a substance even under pressure. For curea P1 and P2 the retention of thin exudate under a pressure of 46 mmHg is approximately two thirds of the unweighted swollen wound dressing.

A question is often asked about how much fluid in terms of ml or g of exudate can be absorbed by a wound dressing containing polyacrylate. The wound dressings curea P1 and curea P2 are able to store 1.5 g of exudate per cm2. Depending on the size of the core there are different maximum capacities. Please be aware of the fact that the wound dressings become heavy, respectively. A 20 x 30 cm wound dressing can weigh more than 750 g at maximum absorption.

The term adsorption is used to describe the accumulation of gases or fluids to the surface of a solid body. For example, the process by which polyurethane foam takes up fluid is defined as adsorption. Fluid accumulates at the edges of the foam pores. The binding of fluid to cellulose fibres is also an example of adsorption. Adsorption has approximately one tenth of the binding force of absorption. Therefore, adsorbed fluids can be wrung out again (see retention).

A nonwoven is a sheet of undirected fibres that have been formed into a web through compaction by two heated rollers (calendering). The nonwoven of the wound dressings curea P1 and curea P2 consists of polypropylene.

A BTBS (breathable textile backsheet) is a laminate of a PP nonwoven (for reinforcement) and a microporous PE film. The PE film provides micropores that are smaller than water drops but large enough for water vapour, thus being waterproof but still permeable for gases. The water vapour permeability (technical breathing activity) is 3.5 l/m² in 24 hours. As a side effect the micropores also act as a sterile filter for germs and thus function as a sterile barrier.

Polypropylene (PP) is a plastic that originates through polymerisation (“endless connection”) of its monomer propene (C₃H₆).  As a macromolecule PP is chemically insoluble in water, thus largely reaction-free in the human body. PP is used as a hydrophobic material to avoid adherence to the wound bed.

Will I know if there is a leak?

• the Nexa device doesn’t have a leak alarm. Due to the unique action of the device, it will continue to remove wound fluid irrespective of vacuum levels.

How will I know if there is a blockage?

• a blockage will cause the machine to make an uncharacteristic slapping noise. Check there is no kinking in the tubing or that the tube is occluded. If there is either straighten the kink or replace the dressing/fluid container.

How do I know the fluid container is full?

• the red light will come on. Change the fluid container.

Can I shower with the pump and dressing in place?

• No, you must first turn off the pump and disconnect it from the dressing before showering; the dressing is water resistant however do not expose it to direct jets of water or soak it.

Can I remove the dressing?

• No, this should be done by your nurse or doctor.

How will I know if the device needs charging?

• The battery is LOW when the orange light is ON. Plug the Nexa into the mains, the orange light flashes while the battery is charging.

Why has the pump stopped working?

• The battery needs to be charged or the pump has stopped working after fifty-six days of use.

Can I switch the device off to take a shower and if so for how long?

• there is no maximum permissible time limit for the machine to be switched off for activities such as showering.
• The manufacturer recommends  the least amount of time possible to be disconnected from the device as this will have a clinical impact on the therapy provision and should be considered on a case by case basis by the clinician.

Call your nurse or doctor immediately if you notice a change in the colour or amount of fluid in the dressing. For example:

• If it changes from clear to cloudy or bright red or you see the dressing fills rapidly with blood
• Your wound looks more red than usual or has a foul smell
• The skin around your wound looks reddened or irritated
• The dressing feels or appears loose
• You experience pain

If you have any other questions, please speak to your nurse or doctor.