Cerdak consists of microporous ceramic granules housed in an envelope of permeable, synthetic, non-woven fibre designed for medical application. The ceramic granules in the Cerdak wound dressings possess an exceptional capillary suction force as well as a very large absorbent and adsorbent surface. The ceramic siphons off excess wound exudate while bacteria, fungi and other micro organisms adhere to the surface of the ceramic. This non-selective action leads to favourable alteration of the wound environment and reduction of the bacterial load.
Cerdak leaves a micro-moist environment and optimises the work of the biochemical elements normally active in the fresh wound exudate. This leads to healing of skin defects irrespective of the cause of the skin defect.
The physics of absorption
The microporous ceramic spheres filling the sachets have an average diameter of 1mm and a porosity of 65% by volume. Their patented microstructure consists of a micro-porous α-alumina matrix that encloses cellular pores with an average intra-pore diameter of 0,1-5 μm. Resulting from the interconnectedness between the cellular pores and the micro-pores in the highly charged alumina matrix, the high total porosity is supplemented by a high permeability and a high surface area.
The absorption, transport and storage of the exudate from the wound bed to the pores inside the ceramic spheres is caused by the capillary pressure created at each pore by the surface tension of the exudate, the degree of wetting of the ceramic by the exudate and by the effective pore diameter. Because of the voids between the loosely stacked spheres, the wound retains contact with atmospheric oxygen even when the spheres become saturated with exudate.
The magnitude of the capillary pressure can be calculated from the Young-Laplace equation, ΔP = 4 γ cos Ɵ / d (N/m²), where ΔP = capillary suction pressure; γ = surface tension of exudate (= 0,7 N/m); Ɵ = wetting angle (=0ᵒ) and d = pore diameter in meter.
The ceramic-filled sachet as the medium of absorption remains permeable to atmospheric oxygen while old exudate is permanently separated from fresh exudate by a capillary suction force of approximately 100kPa.
The physics and chemistry of adsorption
Adsorption refers to the adhesive properties between charged suspended colloids in the exudate and the solid alumina surfaces. Because of its relevance to biomedical systems, this phenomenon is well researched, and it is for example known that suspended proteins adsorbs instantaneously onto wet alumina surfaces and that this adhesion is caused by ionic and electrostatic interaction, hydrogen bonding and charge-transfer interactions.
Charged colloidal cells, micro-organisms, molecules and other solids suspended in wound exudate are bound (adsorbed) onto a highly charged dry alumina surface. The alumina surfacesconsist of rough, easily wetted alumina (wetting angle = 0ᵒ) with a surface area of 0,5 m² per gram of alumina. This 1 gram of alumina consists of 3,5×10²¹ oxygen ions (O²⁻), and 2,4×10²¹ aluminium ions (Al³⁺). Every cell in a living body contains a tiny electrical charge, defined as the difference between charged atoms on either side of the cell’s membrane. A proton colloidal solid on the other hand, may develop a surface charge due to the ionization of side-chain amino acid groups. The highly charged alumina surface (5.9×10²¹ ionic charges per gram) is therefore continuously moistened by the exudate containing charged cellular material, microorganisms and colloids. Since the charged alumina surface will become progressively wetter as more exudate is absorbed, and since its surface texture and roughness are ideal for the purpose, strong adsorption takes place.
Bacterial binding properties of the ceramic ensures the reduction of the bacterial load in chronic and infected wounds, while the bacterial binding properties prevent colonisation and infection in acute wounds.
Clinical effect of absorption and adsorption
Effective control of moisture and the elements in the moisture is critical to wound management irrespective of the phase of healing. The main objective in wound management will be to reduce the duration of the inflammation phase and optimise the wound environment for the optimum cell proliferation.
Reduce duration of inflammation phase
By eliminating inflammation-causing elements like contaminants, bacteria, toxins and expired cells through absorption and adsorption, the inflammatory response is reduced, which assists the wound to proceed to next phase of healing.
Chronic wounds are typically locked in chronic inflammation due to several reasons that can include excessive bacterial load or the lack of oxygen supply to the wound.
The binding of bacteria by adsorption assists in lowering the bacterial load. Atmospheric oxygen is supplied to the clean wound through the loosely packed ceramic granules.
Optimise conditions for cell proliferation phase
Regeneration of lost and/or damaged tissue is optimised by removing proteins, fibroblasts and growth factors promoting the formation of scar tissue and contraction by cyclic separation of these elements from fresh exudate byway of absorption and adsorption. Optimisation of conditions on the wound bed allows for quality tissue regeneration, increased healing rate and the prevention of wound infection.