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Why are we here?
Material choice has a critical role in the success of an orthotic.
Diverse types and varieties and a myriad of trade names to further confuse.
Our aim:
To empower you with fundamental knowledge regarding material types, their key characteristics and performance traits so that you can confidently choose materials that meet your
3. Performance values & Technical Data typically used
4. Types :
•Textiles•Synthetic Leathers (Vita, Microfibre products etc)•Leathers (production of , forms of , qualities etc)•Thermoplastic polymers ( PEs, EVAs , PUs)
The top cover of an orthotic lies directly against the foot and so plays a critical role in the comfort of the patient, the health of the patients foot and the ultimate success of the orthosis.
PRACTITIONER/LAB• Elasticity• Drape• Ease of bonding• Ease of converting• Porosity• Yield• Ease to replace
TOP COVERSHeat Management (Thermoregulation)Our bodies actively try to regulate our temperature within a certain temperature range By various mechanisms.
Body heat is transferred by: Radiation Conduction Evaporation Convection
When the body can’t dissipate enough heat through conduction or convection , in for example an enclosed environment like shoes, it will use evaporation as an initial process.
Sweating is the most effective way of cooling the body.Rise in body temperature causes an increase in sweating and blood flow to the skin.As sweat evaporates the average temperature of the liquid left behind drops. When sweat evaporates from the skin, it carts heat away with it and naturally cools the skin.
This works well in an uncovered situation.Inside shoes there is little opportunity for convection and a lot of moisture builds up.
The most concentrated area of sweat glands is on the bottom of the feet. (over 250,000 sweat glands in each foot).
How much sweat are we talking about?
Each foot normally produces about 240ml per day.
Moisture alters the resistance of the epidermis to external forces by softening the skin’s surface and reducing the tensile strength. This in turn makes it more susceptible to pressure, shear and friction.
If there is not much evaporation or convection, then the ability of the hose, the lining within theshoe and the top cover of the orthotic to manage this constant production of moisture is critical.
The wicking performance of a fabric determines its effectiveness in drawing
moisture away from the foot, assisting with the cooling process and keeping
the foot surface dry.
Often measured as Moisture Vapour Transmission
Rate
generally related to hydrophilic fibre content.
The drying or desorption rate is equally important
to ensure water is not held in the fabric and it
dries.
This is also related to hydrophobic fibre
content of the fabric
MATERIALS INTELLIGENCE®
TOP COVERS
Friction
Fabric friction = resistance to motion• Can be detected when a fabric is rubbed mechanically against itself or tactually
between the finger and thumb. The level of friction is often measured by the Coefficient of Friction .
> coefficient = > the greater the resistance to motion
Type of fibre, blend, yarn structure, fabric structure, compressibility influence the coefficient of friction.
• Prolonged pressure, friction and shear forces, as well as humidity at the skin-textile interface are decisive physical factors in perceived comfort, generation of heat and development of blisters or other skin lesions.
• Whilst we generally seek a low coefficient of friction of top cover materials, if too low, then patient’s foot slides across the orthotic surface causing other issues.
Abrasion Resistance MeasurementTwo different test methods commonly used by the textile industry to assess
abrasion resistance: Wyzenbeek and Martindale .
These tests both apply constant flat rubbing with a specified fabric lined weight
against the material being tested and record the number of cycles until first signs of
wear under different conditions (Wet & Dry)
MATERIALS INTELLIGENCE®
TOP COVERS
Antibacterial propertiesA wide variety of antibacterial and antimicrobial fabric and textile finishes have been
developed.
These inhibit the grow of bacterial and other
microorganisms within the shoe or growing
on the foot itself.
Usually seen as a zone of inhibition in tests.
Foot odour is the result of metabolic products of these bacteria and microorganisms.
The moist environment encourages microbial growth.
These finishes need to withstand multiple washes.
Methods used include treating the fibres themselves prior to knitting, weaving, treating the finished fabric or using nanoparticles like silver or bamboo.
Elasticity = amount of stretch of a material , measured in terms of additional % of
original dimensions before it breaks.
For highly shaped orthotics – deep heel cups, good elasticity is required.
For top covers over contouring cushions (eg for diabetics, arthritic patients) high elasticity is required to follow the cushion contouring so that the gentle cushion and pressure reduction is retained.
Tensile Strength = Measure of tear strength of the material.
Where there are high torsional forces, shearing or friction forces, this will give an
indication of the likely longevity of the top cover material.
Drape = Conformability of a material or ability to flow over other materials. High drape assists with bonding to shell shape without creasing.
TOP COVERSTextilesVariety of fibres used : Nylon, Polyester, Polyamide
Polyamides are commonly used in textiles, automotives, carpet and sportswear due to their extreme durability and strength. Proliner is a non woven heat melted polyamide.
Knitted, Woven, Non WovenKnit fabric - one continuous yarn is looped repeatedly . eg Opulex Top Cover (good stretch)Woven fabric - multiple yarns cross each other at right angles. eg Cushmax
Non Woven - made from long fibres, bonded together by chemical, mechanical, heat or solvent treatment. (eg. Agotex, Proliner)
Synthetic Leathers : PVC • PU • MicrofibrePVC Synthetic LeathersLow costDo not breathe, exacerbate build up of moisture within the shoe, do not wick.PVC materials contain plasticisers that can leach out from fabric leading to stiffness, cracking and premature wear.
PU Synthetic Leather Generally provide better moisture & heat management.Various qualities available due to production process. Can be made by two processes:Dry-process PU synthetic leather and wet-process (coagulation process) PU synthetic leather.
MicrofibreHighest quality and costMicrofibre is 1/100th the diameter of a human hair and 1/20th the diameter of a strand of silk. The most common types of microfibers are made from polyesters and polyamides.Tough , soft to the touch, breathable and excellent wicking and drying.
High quality, lightweight, closed cell foam that is non allergenic
allowing direct contact against the skin even onto open
wounds and lesions.
Made by a unique process.
This produces a pure, chemically inert foam without blowing
agent residues and with a uniform cell structure
Excellent cushioning material for applications which require high conformability. Used to assist in reducing peak pressures.
Key FeaturesBiologically inertPure, low odourLightweight and durableClosed cell, water repellentNon Toxic and safeEasy to work with and safeContours easily
Typical Properties•Open cell•Excellent resistance to compression set•Outstanding energy absorption•PVC, Latex & solvent Free•USP Class VI Toxicology Tests : ISO 10993 Skin contact•NOT Thermoformable
CELL STRUCTURE IS KEY TO HIGH PERFORMANCE
Available in a range of formulations that vary firmness, energy absorption and rates of return. 1.6mm – 12.7mmUsed for: Top Covers, Arch Filling, Cushioning, & Postings
Firmness: Compression Force Deflection Shore Hardness (Durometer)Density (can be misleading – denser doesn’t mean firmer)
Resistance to compression set or bottoming out% Compression at room and elevated Temp & Humidity
Impact AbsorptionTear StrengthElongation
Shore DurometerUsed for measuring plastics, elastomers, EVAsA relative scale measure 0-100Measure of depth of indentation by a given forceA number of different scales which relate to the shapeof the pressure foot . Most common Shore A & D scales.Better to refer to Shore Hardness than density for EVA
Type of device required (& manufacturing method) will lead to choice in shell material
Broad Categories include:Thermoplastics – EVAs & PEs. Soften when heated and harden when cooled. EVAs are now also milled
Polypropylene – Plastics with low specific gravity and high stiffness. Thermoformed or milled. Homo & Copolymers.Shrinkage, drape, impact strength, end rigidity important.
Subortholens – High density polyethylenes. High melt strength and deep draw.
Acrylics – Rohadur, Polydur etc. Methyl methacrylatepolymenrs – first of the synthetics for rigid orthotics. Some cracking.
Composite Carbon Fibres – TL. Good for thin rigid orthotics , can be more difficult to work with. Higher softening temperature, faster vacuuming and accuracy during forming . Not reworked easily.
The Capron Direct Molding System utilises an extensive range of modules enabling the podiatrist to greatly reduce investment in materials, labour and time.
The modules have been developed after many years of clinical experience and comprise high performance materials specifically chosen to meet end function.
The 59 standard modules can be divided into broad families