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Microenvironment of Materials used to Facilitate the Healing Process of Ulcers

Info: 14230 words (57 pages) Dissertation
Published: 11th Dec 2019

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Tags: Medicine

Contents

1. Introduction

1.1 Literature Review

1.1.1 Required Conditions for Optimal Wound Healing

1.1.2 Different Dressings for Different Wounds

1.1.2.1 Polyvinyl Film

1.1.2.2 Hydrocolloids

1.1.2.3 Alginates

1.1.2.4 Hydrofibers

1.1.2.5 Synthetic Fibres

1.1.2.6 Foam

1.1.2.6.1 Heelift® Suspension Boot

1.1.2.8 Silver

1.1.3 Textile Arrangements

1.1.4 Possible Textile Arrangement

1.1.5 Sensors

1.1.5.1 Sensors for Moisture Detection

1.1.5.1 Sensors for Infection Detection

1.2 Aims and Objectives

1.3 Summary

2. Materials and Methods

2.1 DuoDERM®

2.2 AQUACEL®

2.3 KALTOSTAT ®

2.4 DermaSilk ®

2.5 Microfiber

2.6 Spacer Fabric TF010

2.7 Spacer Fabric TF009

2.8 Heelift® Suspension Boot

2.9 Methodology

2.9.1 Sample Selection and Preparation

2.9.2 Planar Wicking Test

2.9.3 Temperature Test

2.9.4 Compression Test

3. Results

3.1 Wicking Test

3.2 Temperature Test

3.3 Compression Test

3.4 Summary of Results

3.4.1 Wicking

3.4.2 Absorption

3.4.3 Temperature of Material

3.4.4 Temperature of Foot

3.4.5 Compression of Material

4. Discussion of Results

4.1 Wicking Test

4.2 Temperature Test

4.3 Compression Test

4.4 Summary of Discussion

5. Conclusion and Future Work

5.1 Future Work

5.2 Final Summary

Table of Figures

Figure 1: Heelift® Suspension Boot

Figure 2: Variations of 2D Weaving

Figure 3: Spacer fabrics of varying thicknesses.

Figure 4: Flow of air and moisture through a spacer fabric.

Figure 5: DuoDERM®

Figure 6: AQUACEL®

Figure 7: KALTOSTAT®

Figure 8: DermaSilk

Figure 9: Microfibre

Figure 10: Spacer Fabric TF010

Figure 11: Spacer Fabric TF009

Figure 12: Heelift Suspension Boot

Figure 13: Vertical Wicking Test Set-Up

Figure 14: Temperature Gun

Figure 15: KALTOSTAT® Wicking Level

Figure 16: Microfiber Wicking Level

Figure 17: AQUACEL® Wicking Level

Figure 18: TF010 and TF009 Spacer Fabric

Figure 19: Stress-Strain Plot for a Specimen loaded in Compression

Figure 20: TF010 Post-Compression Test

Figure 21: TF010 Outer Layer

Figure 22: Microfiber Inner Layer

List of Tables

 

Table 1: Material Characteristics

Table 2: Wicking Value

Table 3: Absorption Value

Table 4: Temperature of Material

Table 5: Temperature of Foot

Table 6: Compression of Material

Nomenclature

 

MVTR Moisture Vapor Transition Rate
g grams
m2 Square Metre
ppm Parts Per Million
DNA Deoxyribonucleic Acid
RNA Ribonucleic Acid
MMP Matrix Metalloproteinase
3D Three Dimensional
2D Two Dimensional
Ag Silver
AgCl Silver Chloride
NPUAP National Pressure Ulcer Advisory Panel
EPUAP European Pressure Ulcer Advisory Panel
mm Millimetre
g/m2 Grams per Metre Square
W Width (mm)
L Length (mm)
ml Millimetre
oC Degree Celsius
Kg Kilogram
h Height (mm)
γ Liquid-air Surface Tension (N/m)
ρ Density of Liquid (kg/m3)
r Radius of Capillary (mm)
g Acceleration due to Gravity (m/s2)
θ Angle of Contact (o)
E Young’s Modulus (N)
σ Stress (N)
ϵ Strain
KPa Kilo Pascal
N Newton

Abstract

 

An investigation was carried out on the microenvironment of materials used to facilitate with the healing process of ulcers. In the past, the known contributing factors that were associated with ulcers were pressure, shear and friction. However recently, microenvironment has gained attention and it is important to know the behaviour of materials in order to improve wound healing.

Around 1 in 20 people who are admitted to hospital with a sudden illness will develop a pressure ulcer. Therefore, a medical device that can not only facilitate with the healing process, but also prevent the risk of ulcers occurring is required.

The most common medical device that is currently prescribed to patients with a foot ulcer is manufactured with a thick polyurethane foam, which can lead to patient discomfort with continuous wear-time. In order to find a new appropriate material, research was conducted on currently used medical dressings and textile arrangements of materials. Wicking, compression and absorption tests were carried out on potential materials in order to gain an understanding of the behaviour of materials when in contact with moisture and human skin.

The resulting material was a stitched combination of 100% polyester microfiber as the contact-layer to the skin, joint with a spacer fabric known as TF010. This combination of materials offer excellent wicking and absorption properties to ensure any excess wound fluid is removed from the area, preventing maceration. They will also allow for the surface temperature of the skin to be regulated which is important as temperature effects the rate of chemical and enzymatic processes. The cushioning effect then provided by TF010 will allow the patient to be comfortable as their ulcer is in a bony prominence, therefore to have cushioning below is vital.

 

Key words: Microenvironment; Ulcers; Polyester; Microfiber; Spacer

1.   Introduction

An ulcer is recognised as a localised injury that breaks down the skin and underlying tissue to areas where bones are close to the surface, because of pressure, shear, friction and microclimate [1].

The management of foot ulcers is a challenge that has been at the forefront of wound management for many years. There is a plethora of devices that exist to try to alleviate the problem and whilst many assist with the healing process there is a requirement for a fresh look at the problem to create a device that offers not only wound protection but also provides data feedback, such as temperature, humidity, and other measurable variables, as required whilst maintaining the most effective possible environment to facilitate the healing process. The contributing factors of pressure, shear and friction can be prevented by the physical design of a medical device which will be completed by the design drivers. This report will seek to investigate how to achieve, and maintain these optimum parameters within the microenvironment of appropriate materials in order to promote more effective healing.

It is estimated that approximately half a million people in the UK will develop at least one pressure ulcer in any given year. Around 1 in 20 people who are admitted to hospital with a sudden illness will develop a pressure ulcer [1]. As the severity of the ulcer increases, the treatment cost will be more expensive due to longer healing time and the possibility of more problems arising.  Therefore, it is important to try to eliminate the amount of severe cases of ulcers with the use of a preventable material dressing.

Pressure ulcers represent a significant cost burden in the UK as treatment is estimated to be £1.4 billion to £2.1 billion annually, which is approximately 4% of the NHS expenditure [2]. As the population of the world increases, this cost is likely to rise. This investigation will promote more effective healing in a shorter time frame, aiming to reduce the treatment cost, as a result of the shorter hospital stay. Pressure ulcers are not only a financial burden, but also a painful, incapacitating and potentially life threatening injury, therefore to improve patient comfort would be extremely beneficial.

Despite ulcers being a preventable injury, the number of occurrences is an increasing factor. For many years, pressure has been widely known to be the most significant external influence involved in the evolution of foot ulcers. It is evident that there is a lack of true knowledge with the relation of natural and external influences as the number of patients suffering with pressure ulcers is an increasing factor.  In order for prevention, patients who may be at risk of pressure ulcers must be identified, followed with implementation of prevention strategies for those patients at risk.

Those with diabetes and people with poor circulation are most likely to develop a foot ulcer. With these particular individuals, an infection can arise quite quickly if the ulcer does not heal sufficiently on time. If an infection is not immediately treated during the initial stages, it can lead to the development of:

  • A bone infection
  • Gangrene
  • An abscess, and/or,
  • A spreading infection of the skin and underlying fat

The significant role of microclimate alteration in the prevention of foot ulcers has been overlooked since the 1970s, although it is now regaining attention [3]. In relation to pressure ulcers, the term microclimate is defined as:

  • Tissue or skin surface temperature
  • Skin surface moisture at the body-support surface interface and/or humidity. [3]

The skin has an important role in regulating body temperature. Sweating is a mechanism which cools the skin through evaporation. Dermal vasodilation is also a mechanism which rises skin blood flow which creates heat loss by convection and conduction [3]. An increase in core body temperature may activate these responses. More perspiration is predominantly connected to the possible risk factor of pressure ulcers due to moisture on the surface of the skin as this can increase the coefficient of friction, resulting in it being more likely to pressure, friction and shear stresses. [3]

Elderly skin is less robust and further liable to harm compared to younger skin as it is usually weaker, thinner and drier. When skin is dry, it contains reduced water content, flexibility, liquid levels, and tensile strength.  Low ambient humidity causes a reduction in water content in the outermost layer of the skin. The material selected must be capable of promoting and maintaining the correct humidity levels in order to prevent excessive moisture, or dryness, whilst integrating the traditional protective role.

The chosen material will also be capable of incorporating sensors to provide a live feedback of temperature, humidity, or other measurable data as required to allow medical practitioners to act promptly with any change in situation. Sensor innovation has the potential to impact economic policy and patient outcomes. This will allow for a much more comprehensive treatment regime to be put in place with the prospect of hastening recovery time thus reducing associated costs.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1.1 Literature Review

There is an extensive range of dressing procedures and materials accessible to deal with the management of acute and chronic wounds. Dressings that provide the optimum environment surrounding the wound allow for a faster healing process. Advanced dressings are those that do this by simple physical or chemical means.

1.1.1 Required Conditions for Optimal Wound Healing

The chosen materials used in dressings should ideally increase the healing process and reduce the loss of electrolytes, fluid and protein from the wound, therefore assisting with the reduction of infection and pain. Dr. Sujata Sarabahi (2012) studied moist wound healing. Sarabahi’s studies show that a wound is open to complement, chemotactic, growth factors and proteinases from the fluid surrounding the wound when an occlusive dressing is used [4]. The original design of occlusive dressings was to protect and preserve a moist environment in the wound, although modern occlusive dressings also promote collagen synthesis, increase the rate of re-epithelialization, create a hypoxic environment at the wound bed in order to encourage angiogenesis and also decrease pH at the surface of the wound to create an environment unreceptive to bacterial growth, resulting in a decreased rate of wound infection [4].

Padma et al (2015) reviewed wound dressings, in this study it states that the selection of a dressing should be based on its ability to [5]:

  • Improve epidermal migration
  • Promote connective tissue synthesis and angiogenesis
  • Provide or maintain a moist environment
  • Maintain suitable tissue temperature to enhance epidermal migration and increase the blood flow to the wound bed
  • Should be non-inherent to the wound and easy to remove after healing
  • Allow gas exchange between wounded tissue and environment
  • Must provide debridement action to enhance leucocytes migration, and support the accumulation of enzyme
  • Provide protection against bacterial infection, and
  • Must be non-toxic, sterile, and non-allergic.

The material selection must offer the properties which are stated by both Sarabahi and Padma et al, and also include additional advanced properties, such as adaptable temperature/moisture conditions for the different stages of the healing process with the use of phase changing materials and sensors.

The term ‘microclimate’ was brought about from the growing evidence that the vulnerability of skin to pressure ulcers is intensely influenced by the thermodynamic conditions within and around skin tissue [6]. Amit Gefen (2011) developed the mathematical model for predicting the tolerance of skin to pressure ulcers, in the context of the microclimate to which the skin is exposed to [6]. This model allows for the determination of how changes in humidity, skin temperature, and air temperature affect skin tolerance. Gefen predicted that decreased permeability’s of the skin-contact materials, as well as an increase in ambient temperature, skin temperature, relative humidity, and the pressure delivered from the support to the skin all increase the risk of pressure ulcers [6].  Incorporating sensors within the material will allow the practitioner to know the exact live conditions of the wound and the surrounding area, ensuring that an increase in ambient temperature, humidity, etc. will be avoided, thus increasing the speed of the healing process.

In Sarabahi’s research it states that a moist environment is beneficial for healing as it supports autolytic debridement, absorbs exudate, and protects surrounding normal skin.  It is specified that a dressing is moisture retentive if its MVTR (Moisture Vapor Transition Rate) is less than 840 g/m2/24 hours [4]. Hydrocolloids have a MVTR less than 300g/m2/24 hours, which differs to gauze dressings that have a MVTR value of 1200g/m2/24 hours. MVTR is a beneficial tool for selecting dressings in accordance to the wound type [4]. It is important to note that maceration can occur when there is too much moisture, although when there is too little moisture this can result in the wound being dried out. Ideally, a phase change material should be selected as when the healing process of wounds progress, the conditions of the wound alternate. Therefore, if the device had materials that have the capabilities of changing from one phase to another at a designated temperature/moisture level then it would ensure optimal healing.

S.Mondal (2007) studied phase change materials and stated that textiles containing these react instantly with fluctuations in environmental temperatures, and the temperatures in different areas of the body [7]. The phase change material microcapsules react to a rise in temperature, by absorbing heat and storing this energy in the liquefied phase change materials [7]. The microcapsules then release this stored heat energy when the temperature drops again, causing the phase change materials to solidify [7]. These reactions improve the thermal insulation capacity which varies considerably from the insulation properties of any other material. Phase change material microcapsules may well be directly incorporated into fibres and foams, or applied as a coating on fabrics [7].

1.1.2 Different Dressings for Different Wounds

There are numerous dressings that are readily accessible, although none of these can be classified as suitable for all wounds. Daley et al (2016) and Sarabahi (2012) studied this issue of different dressings for different wounds/patients [8]. The fibres and polymers presently used to fabricate wound healing are numerous, such as modified and natural cellulose, alginates, collagen, hydrocolloid, chitin/chitosan, and hydrogels or synthetic fibres [9]. Subject to the material used, they can be separated into three categories, i.e., proteins, synthetic polymers and modified or natural polysaccharides [9].

It is important to investigate and identify the different materials and fibres currently used for wounds in order to have candidate commercial materials which can then undergo testing to find the most appropriate materials that could be used to suit all wound conditions ranging from acute wounds to chronic wounds.

1.1.2.1 Polyvinyl Film

Daley et al studies show that a polyvinyl film dressing such as OpSite™ or Tegaderm™, should be used for wounds that are neither highly exudative or dry [8]. Sarahbahi explains that transparent films are adhesive and semi-permeable. They are waterproof but allow atmospheric gases and water vapour to cross, however they are impermeable to contaminants and bacteria. Wounds can be reviewed without eliminating the dressing as these films are transparent [4]. Padma et al states that commercially available film dressings vary in terms of their adhesive characteristics, vapour permeability, extensibility and conformability [5].

1.1.2.2 Hydrocolloids

For wounds that are moderately desiccated, Daley et al states hydrocolloid dressings such as DuoDERM®, InstraSite™, Granuflex™, Comfeel™, or Tegasorb™ are suitable choices as they maintain a moist environment and also support autolytic debridement [8]. Sarabahi explains that hydrocolloids are composed of gel forming agents (carboxymethylcellulose, gelatine, and/or pectin) and function as a semi-occlusive dressing. Hydrocolloids are impermeable to bacteria, contaminants, and water; however, they are permeable to water vapour [4]. The most significant benefit is their extensive wear time, which allows for a reduction in inconvenience, local trauma with dressing changes and cost [4]. However, Padma et al specified that hydrocolloids are not a suitable dressing for highly exudative wounds or neuropathic ulcers, and are usually used as a secondary dressing [5].

1.1.2.3 Alginates

Daley at el specifies that for wounds that are exudative, calcium alginates such as Kaltostat® or Curasorb™ are suitable choices [8]. Horrocks et al (1997) reported that alginates are naturally occurring polysaccharides in seaweed. Alginates are appropriate for full thickness wounds, they are highly absorbent, and hemostatic [9]. Sarabahi’s research shows that alginates are made up of soft, non-woven fibres which contain sodium salts of alginic acid and calcium [4]. Peri-wound maceration can occur if the alginate is not cut to the size of the wound as they have a tendency of absorbing fluid across an entire surface [4].  Alginates promote moist healing and gelation, decrease the number of dressing changes required, however they are not suitable for dry wounds.

1.1.2.4 Hydrofibers

Hydrofiber dressings such as Aquacel® and Aquacel-AG® are also suitable choices for wounds that are exudative. The study produced by Sarabahi states that hydrofibers are sterile sodium carboxymethyl cellulose fibres [4]. Karen A.Gibbs (2010) stated that while alginates and hydrofibers are comparable, there are vital variances between them [10]. Alginate dressings serve as biodegradable, hemostatic agents which absorb up to 20 times their weight in fluid. Whereas, hydrofiber dressings provide less risk of maceration due to their vertical fluid absorption properties, and absorb up to 30 times their weight. Providing acceptable drainage, both dressings form a gel with absorption. Alginates and hydrofibers promote autolytic debridement, atraumatic removal, and a moist wound healing environment [10].

1.1.2.5 Synthetic Fibres

Synthetic fibres are a suitable choice for wounds that are exudative. Horrocks et al studied synthetic fibres and stated that they are incorporated or blended in many high-performance dressings in order to improve the properties of the final products, such as strength, antibacterial performance, absorbency, etc. [9]. Researchers at DuPont developed a biodegradable material named Coolmax®, which is based on a polyester containing a copolymer of a non-aromatic diacid[9]. Other synthetic fibres which are commercially offered are:

  • Dermasilk® – Made of a knitted medical grade silk which has been stripped of its outer coating and bonded with Microbe Shield technology [11]. It has advanced properties to cotton as it holds up to 30% of its own weight in moisture without feeling damp [11]. It is structurally weak, has very low frictional properties, although it has excellent antimicrobial properties when coated.
  • Baltex® Spacer Fabrics- Wide range of fabrics with a combination of different parameters such as polyester, Coolmax®, Lycra®, and cotton. Must complete tests on spacer fabrics regarding moisture control, as there is a lack of research in this area.
  • Microfiber- Microfibers are the finest of all fibres. Microfiber can be used for the application of children’s nappies as it has excellent absorbent and breathability properties.

1.1.2.6 Foam

Sarabahi states that foam is a material that is used for highly exudative wounds [4]. Foam dressings are highly absorbent polyurethane dressings, accessible as cavity dressings, sheets, and pads. They provide thermal insulation to the wound and produce a moist environment [4]. Foam dressings are non-adherent, resulting in easy application when applying and removing. Layering in arrangement with additional materials is possible with overlying compression bandages [4]. The thickness of the foam determines the fluid absorption capacity. Their MVTR ranges between 800-5000g/m2/24 hours [4]. Their cushioning effect is a suitable use for foam dressings, although they are not a substitute for devices which relieve pressure. An issue with foam is the possibility of producing extreme malodorous draining which would require regular dressing change [4]. According to Pereira et al (2007) foam dressings are uncomfortable to wear due to the closed cell structure as heat, water vapour, and moisture cannot escape easily [12].

Those with foot ulcers are currently supplied with the Heelift® Suspension Boot which is made from foam.

1.1.2.6.1 Heelift® Suspension Boot

Heelift® claims to relieve pressure from the heel by reallocating the pressure to the calf, hence preventing heel pressure ulcers from developing. [13]

This particular boot includes ventilation holes to provide air circulation, resulting in improved patient comfort.

 

Figure 1: Heelift® Suspension Boot

 

1.1.2.8 Silver

For wounds that are infected, Daley et al reported that a silver sulfadiazine or an ionic-silver hydrofiber dressing are suitable choices for infected wounds [8]. Sarabahi explains that silver is a recognised antiseptic agent (silver nitrate and silver sulfadiazine) [4]. The successful, widespread biological use of silver has been prevented due to the delivery system in the form a salt. Sarabahi reported that silver has been combined into various wound dressing products such as foams, alginates, hydrocolloids, gauzes, gels and creams although each of them vary in the way silver ions are released [4]. Sarabahi states that the discovery of the nanocrystalline structure of silver has enabled improvements in the delivery system [4]. Silver sulfadiazine and silver nitrate release silver at concentration of 3200ppm. The majority of pathogenic organisms are killed invitro at concentration 10-40ppm. The development of nanochemistry has produced micro-fine particles which increase silver’s solubility and releases silver ions in concentration of 70-100ppm [4].

Epidermal cells that absorb silver induces creation of metallotheine, which eventually rises the uptake of copper and zinc, thus increasing DNA and RNA synthesis [4]. This then generates tissue repair and cell proliferation. Sarabahi reported that an excess of matrix metalloproteinase (MMP) will result in a chronic wound not healing, as there is an increase of inflammatory cell exudates and degrades of growth factors.

Carville et al (2012) states that recommendations from clinical guidelines suggest that silver dressings are to be used for wounds where infection is already present or an excessive wound bioburden is causing a delay in healing[14].

1.1.3 Textile Arrangements

Gefen (2011) noted that textiles designed for protecting the skin must permit the clearance of perspiration or to be absorbed quickly, and have a low coefficient of friction with skin [6]. This means that the material properties and the textile designs are very important. The key difference is that the properties required can be achieved by utilising the materials alone in a standard plain weave or can be achieved with a more complex textile.

Schematics of woven composites (without matrix pockets).Mohamed et al (2009) compared analysis on different 3D weaving processes[15]. This study states that properties of any composite do not only depend on the reinforcing fibres and matrix materials, but also on the geometrical arrangement of the fibres. If the reinforcing fibres are aligned, the resulting composite is generally highly anisotropic with respect to modulus, thermal expansion, strength and other characteristics [15]. Whitcomb et al (2005) studied the micromechanics modelling of moisture diffusion in woven composites, it was reported in this study that although weaves are stated as 2D, their microstructure is indeed 3D [16].

Figure 2: Variations of 2D Weaving

In order to acquire the sufficient engineering properties such as thermal conductivities, moisture diffusivities, or effective moduli, micromechanics analyses are generally required [16]. Understanding the absorption and desorption of moisture is vital for estimating the structural performance of a long-term material, as moisture can cause degradation of the fibre/matrix interface, and plasticization of the polymer matrix [16].

Mohamed et al identified that 3D woven fabrics are composed of several series of warp yarns and filling yarns that form distinct layers, one above the other [15]. The fabrics can be woven as a thick dense structure or with a space between layers. Jennifer Woodson (2009) studied spacer fabrics for active wear, and reported that spacer fabrics have several attributes that make them ideal for a variety of uses including strength, insulation, breathability, and durability [17]. It states that spacer fabrics are knitted fabrics that have two, usually warp-knitted faces and a pile, of carrying thickness, between the two faces [17]. Yip et al (2008) studied three-dimensional spacer fabrics, in this research it states that there are two types of spacer fabrics which are warp-knitted spacer fabric and weft-knitted spacer fabric [18]. Pereira et al (2007) reported that the spacer fabric properties can be engineered in order to suit varying specific needs by manipulating the structures and yarns used in the three independent elements of spacer fabrics (face, back and spacer) [12]. Research produced by Woodson found that by hydroentangling a thin layer of wool on one side of a spacer fabric, the thermal conductivity of the fabric is reduced and the thermal resistance is increased [17].

Woodson states that a method of production, which has been greatly utilized in the upholstery and automotive markets, is to cut down the middle of the spacer portion (across the width) of a spacer fabric; this is how many common pile fabrics; such as velvet, are produced. This is known as Corduroy weaving.

Figure 3: Spacer fabrics of varying thicknesses.

 

Woodson stated that spacer fabrics are currently being used to replace such fabrics as polyurethane, neoprene, and other foam type products that are generally laminated, and utilized in end products that require flexible or bulky type characteristics in order to achieve the desirable outcomes [17]. Spacer fabrics have properties such as breathability and thermal regulation that are far superior to that of foam and foam type products.

According to Woodson, fibre selection is very important when determining the comfort level of the wearer, and optimizing the beneficial properties. For example, if cellulosic fibres, which are hydrophilic, are utilized in the face of the fabric in contact with skin, the fibres will hold moisture and will not wick it away quickly, heat transport will then be inhibited, thus leaving the wearer damp and uncomfortable [17].

Figure 4: Flow of air and moisture through a spacer fabric.

 

1.1.4 Possible Textile Arrangement

 

From studying previous research, there are a wide range of offerings accessible in the commercial sector. There are a number of themes that run throughout them and occur quite regularly:

  • Spacer fabrics- fabrics with a three-layer structure where the middle section acts to dry away moisture and the fabrics have a supporting role for the patient.
  • Synthetic and Natural fibre mixes- mixture of fibres to allow for moisture and temperature to be controlled.
  • Multilayer fabric structures- multiple layers of fabric with different types of weaves in order to provide a ‘best of both’ approach without utilising standard weaving or production techniques.

A spacer fabric appears to be a suitable structure to use due to the breathability and thermal regulation properties. A synthetic fibre could be used as the top layer which could be woven or manufactured in channels to allow air flow. Suitable phase change materials with a tight plain weave could be on the outside in order to absorb the heat generated during the moisture phase change which is experienced in the middle of the spacer fabric.

With a cooling air coming from below the phase change materials, this will actively draw heat from any zone within close proximity; actively cooling the skin contact area.

However, appropriate testing will have to be completed in order to ensure the appropriate materials and textile arrangements are chosen to allow for optimal wound healing. It is important to note that the textile arrangements will also have to enable sensor incorporation throughout.

1.1.5 Sensors

Ochoa et al (2014) studied flexible sensors for chronic wound management, in this research it states that therapies such as growth factor therapy, ultrasonic stimulation, oxygenation, and electrical stimulation have had limited success due to only utilizing a single chemical or physical parameter to improve the process of healing [19]. A major factor connected to the limited success is their open-loop nature; they do not allow modification or adjustment of treatment based on the wound physiochemical microenvironment due to not using physical or chemical feedback [19]. Integrating flexible, chemical and physical sensors which are capable of assessing the microenvironment of a wound to form a beneficial feedback loop would have a significant benefit to the current treatment methods [19]. In addition to this, Wang et al in 2012 also studied flexible sensors, and stated that wound management technologies lack sensory feedback control [20].

1.1.5.1 Sensors for Moisture Detection

Dargaville (2013) reported that the healing process is critically related to the moisture levels of the wound [21]. In 2007, an electrical impedance sensor was developed by McColl et al. This sensor produces a map of the wound to allow for real-time monitoring of the moisture levels. Wound fluid has an ionic nature which the sensor takes advantage of. It evaluates the fluid volume with the use of fluctuating frequency that has an alternating current, thus measuring the impedance across AgCl/Ag electrodes that have a silicone elastomer insulation included in a variety of dressings that are commercially available.

1.1.5.1 Sensors for Infection Detection

Dargaville et al reported that infection is one of the utmost common difficulties that prevent a wound from healing [21]. Swelling, heat, redness, epithelial bridging, tissue breakdown, pain, odour, purulent exudate, systemic illness, and contact bleeding are obvious signs of advanced infection, although it is difficult to distinguish infection prior to reaching these stages [21]. Infection is currently characterized by taking a swab from the wound site, followed by analysis in a microbiology laboratory. The issue with this method is that only superficial pathogenic organisms can be detected and an indication of what is occurring deeper in the wound is unachievable. Bacterial growth can be caused by moisture and not necessarily always due to an infection, causing the swabs to have a false positive reading.

Ochoa et al reported that actuators and sensors which are fabricated on flexible substrates can conformally cover the wound without applying excessive stress/force to the healing area, enabling them to be extremely beneficial for wound manipulation and monitoring [19]. Despite the unit cost being quite high for such a system, the ultimate efficacy can result in an outcome of decreased expenditure.

A range of flexible miniaturized pH sensors could be used to generate a high-density map of pH levels surrounding the wound. This would allow for the exact location of the infection to be allocated.

However, Wang et al stated that there may be concerns with flexible sensors that are incorporated in silver-based and organic materials with relation to the long-term durability in moist conditions within the body [20].

It is evident that there is the requirement for sensory feedback control in order to detect infection early and to offer guidance for the antibiotic treatments. A sensory system would also indicate when treatment is not required for infection, and as a result reduce the overuse of antibiotics and costs.

1.2 Aims and Objectives

Aims:

  • To investigate the microenvironment of materials used to prevent and facilitate the healing process of ulcers.
  • To identify the material or combination of materials which would provide the most appropriate environment to aid optimal wound healing.

Objectives:

  • To investigate the different conditions of wounds.
  • To explore and compare commercially available wound dressings.
  • To investigate sensors currently used in wound management.
  • Complete various material tests in order to obtain the most appropriate material.
  • Wicking testing
  • Temperature testing
  • Compression testing
  • Discuss any future work which may be required.

1.3 Summary

Further to the research reviewed, additional work needs to be completed in order to identify more appropriate materials to obtain a more suitable biological environment. This will encourage the most efficient healing environment possible which can be monitored remotely. Currently, the Heelift® Suspension Boot is generally provided by medical practitioners when a patient is diagnosed with a foot ulcer. This bulky design of a boot causes patient discomfort and excessive perspiration of the foot. It can take up to 20 weeks for a foot ulcer to heal [22]. An advanced dressing for ulcers is required in order to reduce this lengthy healing duration.

The following chapter will include the materials and methods used to test different fabrics and textile arrangements in order to find the most suitable which allows for a much more comprehensive treatment regime, with the prospect of hastening recovery time, thus reducing associated costs.

Chapter three will then comprise the results of the tests complete. Followed by Chapter four which include the discussion of results. This will explain the material properties of the test samples. A material, or a combination of materials with the appropriate textile arrangements will be chosen and discussed based on the results achieved.

The material selection must offer the following properties:

  • Promote and maintain the correct humidity levels
  • Maintain suitable tissue temperature
  • Allow gas exchange between the wound area and the environment
  • Provide protection against bacterial infection, and
  • Must be non-toxic, sterile and non-allergic.

Chapter five will include a conclusion and details of future work.

2.   Materials and Methods

From carrying out research on several materials that are presently used for wound dressings, the testing was based on eight materials.  The materials were selected from each researched category of dressings.

  • DuoDERM®: Hydrocolloid
  • AQUACEL®: Alginate
  • KALTOSTAT®: Hydrofiber
  • DermaSilk®: Synthetic fibre
  • Microfiber: Synthetic fibre
  • Spacer Fabric TF010: Warp knitted spacer
  • Spacer Fabric TF009: Warp knitted spacer
  • Heelift® Suspension Boot: Polyurethane foam

2.1 DuoDERM®

Figure 5: DuoDERM®

  • Designed to reduce the risk of further skin breakdown due to friction.
  • A viral and bacterial barrier is provided with the use of a thin polyurethane film when the dressing stays in contact with the wound and without leakage.
  • Advised by ‘ConvaTec’ to be used as a secondary dressing to protect an AQUACEL® dressing [23].
  • The National Pressure Ulcer Advisory Panel (NPUAP) and the European Pressure Ulcer Advisory Panel (EPUAP) promote hydrocolloids in order to manage pressure ulcers [24].

2.2 AQUACEL®

AQUACEL® https://scontent.xx.fbcdn.net/v/t34.0-12/18034829_10155271926513281_1868538790_n.jpg?oh=fab51d138f3317eadab905ad1c77f067&oe=58F8871Fis formed as a textile fibre held together by a needle bonding process, presented in the form of a fleece.

When interaction occurs with wound fluid, this dressing transforms into a gel, creating an adequate environment for wound healing.

This dressing contains ionic silver with the use of Hydrofiber™ Technology [25]. The use of silver is useful for a wound that may be at risk of infection, or already contains an infection.

Figure 6: AQUACEL®

https://scontent.xx.fbcdn.net/v/t35.0-12/18042959_10155271926588281_440904272_o.jpg?oh=e4c70ca534379e0f74761ec02403e635&oe=58F83E422.3 KALTOSTAT ®

KALTOSTAT®is formed with calcium and sodium salts of alginic acid presented in the form of a non-woven fibrous fleece [26].

This dressing is particularly useful for extremely exudative wounds.

Figure 7: KALTOSTAT®

2.4 DermaSilk ®

Dermasilk® claims that this particular silk retains up to 30% of its own weight in moisture without feeling damp [27]. Dermasilk® clothing is manufactured from of a unique, knitted medical grade silk that has been stripped of its outer coating and bonded with Microbe Shield technology [27]. https://scontent.xx.fbcdn.net/v/t35.0-12/17968026_10155271926583281_879055204_o.jpg?oh=58ad7d9d3561a46342a1536051aeceaf&oe=58F83E04Samples of this material will be used from a DermaSilk® eye mask as seen in Figure 8.

Figure 8: DermaSilk

https://scontent.xx.fbcdn.net/v/t34.0-12/18035306_10155274653168281_45920443_n.jpg?oh=03889c92a825a12d5e681f2e00590b7e&oe=58F97BB22.5 Microfiber

The specific microfiber put to test was 100% polyester. This is a synthetic fibre which is finer than one denier or decitex/thread.

Figure 9: Microfibre

2.6 Spacer Fabric TF010

http://i.ebayimg.com/images/g/16oAAOSwQTVWAXpq/s-l1600.jpg

Composition: 100% polyester
Construction: Warp knitted, double sided mesh
The holes are approximately 3 x 2mm in dimensions.
Area Density = 375 g/m2

Figure 10: Spacer Fabric TF010

http://i.ebayimg.com/images/g/iWwAAOSw2GlXFzky/s-l1600.jpg2.7 Spacer Fabric TF009

 

Composition: 100% polyester

Construction: Warp knitted, first grade

Hexagonal mesh

Thickness 4mm

Figure 11: Spacer Fabric TF009

2.8 Heelift® Suspension Boot

Manufactured from polyurethane foam.

Figure 12: Heelift Suspension Boot

2.9 Methodology

In order to obtain a true image of each material’s properties, a series of material tests were carried out. After consideration it was decided that the testing procedure should consist of the following tests:

  • Wicking
  • Temperature, and
  • Compression

These tests were chosen as the material for this specific boot must comply with certain requirements. It is important for the material to be capable of wicking away any excess moisture from the wounded area. However, moisture balance is also important as the wound requires an assessment of exudate levels. The material must not wick away too much resulting in the wound becoming dry as this will prolong recovery time. Therefore, a wicking test is suitable in order to identify the rate at which it absorbs liquid.

When evaporation occurs, the moisture is cooled from a surface, this results in the tissue of the wound not only loosing moisture, but also experiencing a temperature drop. The biological healing process of a wound can be affected with even a small temperature drop of approximately 2oC, as cells and enzymes work their best at normal body temperature. It is important to find a material/combination of materials that will be capable of maintaining the body’s surface temperature.

A compression test is also deemed as appropriate as it is important for the boot to perform adequately even when some part of the patient’s body weight is bearing down upon it.

The choice of test methods was an important decision as the results of these experiments will influence the choice of the material or combination of materials used for the ulcer boot.

2.9.1 Sample Selection and Preparation

Measurements for wicking, temperature, and compression were conducted on eight different fabrics, all of which were different in construction. Each fabric sample is a colour that allows for visual recording for the wicking test. Table 1 gives the complete characteristics of the eight selected samples.

Sample Fibre Type Thickness
DuoDERM® An outer layer of polyurethane film with an inner layer of hydrocolloid, consisting of an adhesive polymer matrix. 0.55mm
AQUACEL® Two layers of hydrofiber technology stitched together. 1.70mm
KALTOSTAT® Sterile non-woven dressing of calcium-sodium alginate fibre. 1.96mm
DermaSilk® A thin layer of polyurethane foam surrounded with knitted medical grade silk. 1.86mm
Microfiber 100% Polyester. 1.44mm
TF010 Spacer Fabric 100% Polyester warp knitted. 4.03mm
TF009 Spacer Fabric 100% Polyester warp knitted. 4.00mm
Heelift® Suspension Boot Polyurethane foam 10.00mm

Table 1: Material Characteristics

For each material test, all sample sizes are W10mm x L70mm.

 

2.9.2 Planar Wicking Test

Planar wicking occurs vertically and horizontally in the plane of a fabric, for example across the width of a fabric.

For this test, a sample was placed in 5ml of distilled water in a transparent 50ml beaker for a period of 5 seconds. The distance that the water travelled through the sample material was recorded.

Figure 13: Vertical Wicking Test Set-Up

5ml of water is an appropriate amount as the sample material is only 70mm in length, therefore the 5ml will cover 4mm of the material prior to any wicking.

It is important with wicking tests to measure the mass of the material before and after the test to the nearest 0.01 grams as it is evident to see how much water is absorbed by the material by just inspecting it, however it is important to know how much water is being held in that particular area in grams.

After holding the sample in water for 5 seconds, record the mass of the sample and using Vernier callipers measure how far the liquid was absorbed to. Subtract the dry mass from the wet mass in order to identify how much liquid was absorbed.

When the material is placed in the volume of water, 4mm of the material is covered. After the sample has been held in water, the total amount of material that is damp must be recorded in millimetres. Anything above 4mm is the wicking value for the material.

2.9.3 Temperature Test

The second method to be carried out is a temperature test. It is important to understand how the material reacts when in contact with human skin.

For this test, the sample material must be placed on the foot and held there for 3 minutes in total. After every 60 seconds the temperature must be recorded.

https://scontent.xx.fbcdn.net/v/t35.0-12/18053164_10155274957313281_955166232_o.jpg?oh=3e447c889f8ace39a2ca5816b811a648&oe=58F9534FFor this experiment, a temperature gun will be required. As seen in figure 15, the laser must be placed in the area where the temperature reading is required.

Figure 14: Temperature Gun

When holding the material in place, it is important to only hold the end of the sample. If the sample were to be covered entirely by the hand, this would affect the readings, as the heat will not only transfer from the foot, but also from the hand.

33oC is considered to be the normal temperature of human skin. The temperature must be maintained for each test sample in order to ensure accurate and fair testing conditions.

2.9.4 Compression Test

 

The compression test must be carried out in order to understand how the materials react under a compressive stress.

  •  The samples must be arranged on a flat surface.
  •  Using digital Vernier callipers, measure the thickness of the material prior to any compressive stresses being applied.
  •  Starting with a 1kg weight, place this on top of the material.
  • Allow the weight to rest on the material for 5 seconds.
  • Remove weight and record the thickness.
  • Continue adding 1kg weights, removing them, and recording the thickness until the material thickness is no longer decreasing.
  • This will allow the maximum compressive stress to be recorded.

 

The compression test will allow for a visual inspection of how the material reacts under a specific load. It will be evident to see if the material returns to its original shape and size, or if it reaches its maximum stress and does not return to its original state.

 

3.   Results

The results from all testing will be compared in order to narrow down the selection of materials to a chosen material which will be used for the product.

3.1 Wicking Test

It is important that all sample sizes are W10mm x L70mm.

See Appendix 1 for images of each of the materials tested as it is important to visualise how the materials react when in contact with a liquid.

Table 2 shows the amount of moisture that was wicked away after 5 seconds with the measurement units being millimetres.

Table 3 then shows the amount of liquid that was absorbed by the sample material. The measurement units being in grams.

Test Material Amount of Damp Material Wicked Amount Wicked Average Wicked Percentage
1 DuoDERM® 6.46mm 2.46mm 2.46mm 3.5%
2 6.48mm 2.48mm
3 6.46mm 2.46mm
4 6.45mm 2.45mm
5 6.46mm 2.46mm
1 AQUACEL® 10.70mm 6.70mm 6.95mm 9.9%
2 11.12mm 7.12mm
3 11.01mm 7.01mm
4 10.70mm 6.70mm
5 11.23mm 7.23mm
1 KALTOSTAT® 50.93mm 46.93mm 46.18mm 66.0%
2 50.76mm 46.76mm
3 50.01mm 46.01mm
4 49.20mm 45.20mm
5 50.01mm 46.01mm
1 DermaSilk® 8.29mm 4.29mm 4.26mm 6.1%
2 8.01mm 4.01mm
3 8.29mm 4.29mm
4 8.41mm 4.41mm
5 8.30mm 4.30mm
1 Microfiber 33.49mm 29.49mm 29.54mm 42.2%
2 34.01mm 30.01mm
3 33.21mm 29.21mm
4 33.50mm 29.50mm
5 33.49mm 29.49mm
1 TF010 Spacer Fabric 4.71mm 0.71mm 0.72mm 1.0%
2 4.83mm 0.83mm
3 4.64mm 0.64mm
4 4.72mm 0.72mm
5 4.71mm 0.71mm
1 TF009 Spacer Fabric 6.46mm 2.46mm 2.80mm 4.0%
2 6.01mm 2.01mm
3 8.50mm 4.50mm
4 6.54mm 2.54mm
5 6.47mm 2.47mm
1 Heelift® Suspension Boot 4.01mm 0.01mm 0.17mm 0.24%
2 4.20mm 0.20mm
3 4.51mm 0.51mm
4 4.12mm 0.12mm
5 4.02mm 0.02mm

Table 2: Wicking Value

Test Material Weight Before Test Weight After Test Average Weight After Test Average Absorbed Amount
1 DuoDERM® 0.35g 0.44g 0.44g 0.09g
2 0.45g
3 0.44g
4 0.42g
5 0.44g
1 AQUACEL® 0.08g 0.47g 0.48g 0.40g
2 0.50g
3 0.48g
4 0.47g
5 0.49g
1 KALTOSTAT® 0.09g 0.65g 0.56g 0.47g
2 0.56g
3 0.52g
4 0.53g
5 0.52g
1 DermaSilk® 0.31g 0.33g 0.33g 0.02g
2 0.32g
3 0.33g
4 0.34g
5 0.33g
1 Microfiber 0.15g 0.54g 0.54g 0.39g
2 0.55g
3 0.53g
4 0.54g
5 0.54g
1 TF010 Spacer Fabric 0.20g 0.22g 0.22g 0.02g
2 0.24g
3 0.21g
4 0.22g
5 0.23g
1 TF009 Spacer Fabric 0.28g 0.47g 0.45g 0.17g
2 0.30g
3 0.52g
4 0.48g
5 0.47g
1 Heelift® Suspension Boot 0.21g 0.25g 0.26g 0.05g
2 0.27g
3 0.28g
4 0.26g
5 0.25g

Table 3: Absorption Value

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.2 Temperature Test

It is important that the temperature of the foot remains a constant temperature for each test. The temperature of the foot being tested was 31.4oC. If this temperature dropped prior to starting a new test, an insulated sock was used to bring the temperature back up.

Table 4: Temperature of Material

The temperature of the foot for each test was 31.4oC.

Test Material Total Temperature Difference of the Foot After 3 Minutes Average Temp. Difference of Foot After 3 Minutes Average Temp. of inner contact layer of Material after Test Average Temp. of outer layer of Material after Test ΔT
1 DuoDERM® +0.6oC -0.56oC 23.2oC 23.0oC 0.2oC
2 +0.4oC
3 +0.6oC
4 +0.6oC
5 +0.6oC
1 AQUACEL® -0.2oC -0.24oC 23.2oC 23.0oC 0.2oC
2 -0.2oC
3 -0.3oC
4 -0.2oC
5 -0.3oC
1 KALTOSTAT® +0.2oC +0.16oC 23.5oC 23.1oC 0.4oC
2 +0.2oC
3 0oC
4 +0.3oC
5 +0.1oC
1 DermaSilk® +0.6oC +0.78oC 21.6oC 21.4oC 0.2oC
2 +0.5oC
3 +0.6oC
4 +1.5oC
5 +0.7oC
1 Microfiber +1oC +1.1oC 22.3oC 20.9oC 1.4oC
2 +0.9oC
3 +1.6oC
4 +1oC
5 +1oC
1 TF010 Spacer Fabric -0.4oC -0.56oC 23.3oC 22.9oC 0.4oC
2 -1.3oC
3 -0.3oC
4 -0.4oC
5 -0.4oC
1 TF009 Spacer Fabric -0.2oC -0.14oC 23.2oC 23.0oC 0.2oC
2 0oC
3 -0.1oC
4 -0.2oC
5 -0.2oC
1 Heelift® Suspension Boot +0.4oC +0.80oC 22.8oC 20.0oC 2.8oC
2 +0.4oC
3 +0.3oC
4 +0.5oC
5 +0.4oC

Minus (-) symbolising a drop of temperature. Positive (+) symbolising an in increase in temperature.

Table 5: Temperature of Foot

3.3 Compression Test

Test Material Thickness of Material Before Test Thickness of Material After:

1kg

2kg

3kg

Total Deflection Average Deflection %
1 DuoDERM® 0.55mm 0.36mm 0.27mm 0.26mm 0.29mm 50.2%
2 0.35mm 0.26mm 0.26mm 0.29mm
3 0.36mm 0.28mm 0.28mm 0.27mm
4 0.38mm 0.29mm 0.28mm 0.27mm
5 0.40mm 0.31mm 0.29mm 0.26mm
1 AQUACEL® 1.70mm 1.01mm 0.31mm 0.20mm 1.50mm 88.4%
2 0.99mm 0.33mm 0.21mm 1.49mm
3 1.20mm 0.25mm 0.19mm 1.51mm
4 0.98mm 0.27mm 0.19mm 1.51mm
5 0.99mm 0.28mm 0.20mm 1.50mm
1 KALTOSTAT® 1.96mm 0.92mm 0.33mm 0.18mm 1.78mm 90.7%
2 0.92mm 0.27mm 0.17mm 1.79mm
3 0.91mm 0.31mm 0.18mm 1.78mm
4 0.92mm 0.29mm 0.20mm 1.76mm
5 0.93mm 0.30mm 0.18mm 1.78mm
1 DermaSilk® 1.86mm 1.58mm 1.22mm 1.21mm 0.65mm 34.6%
2 1.55mm 1.22mm 1.20mm 0.66mm
3 1.56mm 1.21mm 1.21mm 0.65mm
4 1.55mm 1.22mm 1.22mm 0.64mm
5 1.57mm 1.31mm 1.24mm 0.62mm
1 Microfiber 1.44mm 1.00mm 0.44mm 0.44mm 1.00mm 70.8%
2 0.99mm 0.44mm 0.44mm 1.00mm
3 1.01mm 0.43mm 0.43mm 1.01mm
4 1.00mm 0.40mm 0.40mm 1.04mm
5 0.97mm 0.39mm 0.39mm 1.05mm
1 TF010 Spacer Fabric 4.03mm 3.81mm 2.32mm 2.31mm 1.72mm 42.5%
2 3.79mm 2.33mm 2.33mm 1.70mm
3 3.85mm 2.30mm 2.31mm 1.72mm
4 3.92mm 2.30mm 2.30mm 1.73mm
5 3.80mm 2.35mm 2.34mm 1.69mm
1 TF009 Spacer Fabric 4.00mm 3.91mm 3.30mm 3.22mm 0.78mm 19.2%
2 3.90mm 3.21mm 3.13mm 0.87mm
3 3.92mm 3.30mm 3.22mm 0.78mm
4 3.89mm 3.29mm 3.20mm 0.80mm
5 4.97mm 3.36mm 3.39mm 0.61mm
1 Heelift® Suspension Boot 10.00mm 8.99mm 7.84mm 7.70mm 2.30mm 23.1%
2 8.90mm 7.85mm 7.69mm 2.31mm
3 9.10mm 7.90mm 7.70mm 2.30mm
4 9.02mm 7.89mm 7.64mm 2.36mm
5 8.96mm 7.84mm 7.70mm 2.30mm

 

Table 6: Compression of Material

 

 

3.4           Summary of Results

 

3.4.1 Wicking

 

Material Wicked Percentage
KALTOSTAT® 66.0%
Microfiber 42.2%
AQUACEL® 9.9%
DermaSilk® 6.1%
TF009 Spacer Fabric 4.0%
DuoDERM® 3.5%
TF010 Spacer Fabric 1.0%
Heelift® Suspension Boot 0.24%

 

 

3.4.2 Absorption

Material Absorption Level
KALTOSTAT® 0.47g
AQUACEL® 0.40g
Microfiber 0.39g
TF009 Spacer Fabric 0.17g
DuoDERM® 0.09g
Heelift® Suspension Boot 0.05g
TF010 Spacer Fabric 0.02g
DermaSilk® 0.02g

 

3.4.3 Temperature of Material

Material Temperature Difference
Microfiber -1.20oC
Heelift® Suspension Boot +0.8oC
TF009 Spacer Fabric -0.40oC
DuoDERM® +0.40oC
DermaSilk® -0.40oC
TF010 Spacer Fabric -0.40oC
KALTOSTAT® +0.20oC
AQUACEL® 0oC

 

3.4.4 Temperature of Foot

Material Temperature Difference
Microfiber +1.1oC
Heelift® Suspension Boot +0.80oC
DermaSilk® +0.78oC
DuoDERM® -0.56oC
TF010 Spacer Fabric -0.56oC
AQUACEL® -0.24oC
KALTOSTAT® +0.16oC
TF009 Spacer Fabric -0.14oC

3.4.5 Compression of Material

Material Compressed Percentage
KALTOSTAT® 90.7%
AQUACEL® 88.4%
Microfiber 70.8%
DuoDERM® 50.2%
TF010 Spacer Fabric 42.5%
DermaSilk® 34.6%
Heelift® Suspension Boot 23.1%
TF009 Spacer Fabric 19.2%

4.   Discussion of Results

The results obtained give an understanding of the behaviour of each material. The results will be discussed within this section in order to find a suitable material for the ulcer boot design.

4.1 Wicking Test

The first test carried out was the wicking test. Wicking is when a material conveys liquid by capillary action [28]. It is the penetration of a liquid into the pores or openings of a solid body. The energy of attraction between a liquid and solid determines if wicking will occur. If the energy of attraction between the molecules of the liquid and the solid is less than the energy of attraction between the molecules of the liquid, wicking will not occur.

Capillary action:

[Accessed 23 November 2016].

[20] Wang et al. 2012. Thin, Flexible Sensors and Actuators as ‘Instrumented’ Surgical Sutures for Targeted Wound Monitoring and Therapy. [Journal Article] Available at: http://onlinelibrary.wiley.com/doi/10.1002/smll.201200933/pdf [Accessed 23 November 2016].

[21] Dargaville et al. 2013. Sensors and Imaging for Wound Healing: A review. [Journal Article] Available at: file:///G:/Final%20Year%20Project/Journals/Lit%20Review%20Journals/Sensors%20and%20Imaging%20for%20Wound%20Healing.pdf [Accessed 26 November 2016].

[22] Harvard Health Publications. 2010. Foot Ulcers. [Online] Available at: http://www.health.harvard.edu/diseases-and-conditions/foot-ulcers [Accessed 02 January 2017].

[23] ConvaTec. 2017. DuoDerm Extra Thin Dressing. [Online] Available at: https://www.convatec.co.uk/wound-skin/duoderm-dressings/duoderm-extra-thin-dressing/# [Accessed 13 January 2017].

[24] Wilson et al. 1998. Duoderm Extra Thin Dressing. [Online] Available at: https://www.convatec.co.uk/wound-skin/duoderm-dressings/duoderm-extra-thin-dressing/# [Accessed 18 April 2017]

[25] ConvaTec. 2017. AQUACEL. [Online] Available at: https://www.convatec.com/wound-skin/aquacel-dressings/aquacel-extra/ [Accessed 20 April 2017]

[26] Surgical Materials Testing Lab. 1997. Dressings Datacard. [Online] Available at: http://www.dressings.org/Dressings/kaltosta.html [Accessed 30 April 2017]

[27] The Healthy House. 2017. DermaSilk. [Online] Available at: https://www.healthy-house.co.uk/dermasilk-unisex-eye-mask

[28] Farlex. 2014. Wicking. [Online] Available at: http://www.thefreedictionary.com/wicking [Accessed 01 May 2017]

[29] Jonathan P. Fiene. 2017. Compressive Loading. Available at: https://alliance.seas.upenn.edu/~medesign/wiki/index.php/Courses/MEAM247-11C-P2P1-background [Accessed 01 May 2017]

[30] Cosmo. 2017. Heat Vs Temperature. Available at: http://coolcosmos.ipac.caltech.edu/cosmic_classroom/light_lessons/thermal/differ.html [Accessed 01 May 2017]

[31] Machine Design. 2017. Conduction, Convection, Radiation. Available at: http://www.machinedesign.com/whats-difference-between/what-s-difference-between-conduction-convection-and-radiation [Accessed 01 May 2017]

Figure 2:  Whitcomb et al. 2005. Micromechanics Modelling of Moisture Diffusion in Woven Composites. [Image] Available at: http://www.sciencedirect.com/science/article/pii/S0266353804000375 [Accessed 23 November 2016].

Figure 3: Jennifer Woodson. 2009. Spacer Fabrics Utilized in Active Wear. [Image] Available at: http://www.jennifermwoodson.com/Woodson-Spacer_Fabrics_Utilized_in_Active_Wear.pdf [Accessed 23 November 2016].

Figure 4: Jennifer Woodson. 2009. Spacer Fabrics Utilized in Active Wear. [Image] Available at: http://www.jennifermwoodson.com/Woodson-Spacer_Fabrics_Utilized_in_Active_Wear.pdf [Accessed 23 November 2016]

Figure 5: Jennifer Woodson. 2009. Spacer Fabrics Utilized in Active Wear. [Image] Available at: http://www.jennifermwoodson.com/Woodson-Spacer_Fabrics_Utilized_in_Active_Wear.pdf [Accessed 23 November 2016].

Include in Appendix http://www.nhs.uk/Conditions/Pressure-ulcers/Pages/Symptoms.aspx ( EPUAP Grades of Ulcers)

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