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CUSHION USING NATURAL MATERIALS - A PRELIMINARY STUDY USING THE LEAVES OF THE YAU KAM CHI TREE

Dominic P.K. Cheng Rehabilitation Engineering Centre The Hong Kong Polytechnic University

ABSTRACT

The potential advantages of using natural materials for seat cushions were explored. Preliminary results using the leaves of the Yau Kam Chi Tree in home trials and in the laboratory were presented. Home trials by two able bodied volunteers were promising , especially in hot, humid weather, but inconclusive high pressure maps were obtained using the FSA. Simple material properties of the leaves were also presented.

BACKGROUND

Pressure sore is a common problem for the disabled world-wide. In affluent countries, expensive hi-tech ready- made cushions and custom contoured cushions have been used to minimize this problem. In developing countries, this is a serious problem pending appropriate technology solutions.

One successful example is a custom contoured cushion made with corrugated cardboard from discarded cardboard boxes used for packaging commercial goods. However, making a contoured cushion requires considerable skill and as the originator of the cardboard cushion pointed out, a supply of suitable cardboard boxes can not be taken for granted (1).

Using natural materials for bedding and cushions is not new. Human beings have been using fur from mammals, feather and down from birds, silk from silk-worms and cotton from the cotton-plant for such purposes throughout history. With the invention of modern materials such as polyester fibres and polyurethane foam, the use of natural materials has been decreasing. This decline is not only due to the desirable properties of man-made materials such as ease of use and hygiene but also due to the high cost of materials such as fur, silk and down.

In this city, where the summer months have temperatures around 30 C and humidity in the 90s, the leaves of the Yau Kam Chi tree have been used by some people as stuffing for summer-pillows. The dried leaves are still available in some bedding shops in older districts. The author spend about US$5 to made a pillow using the leaves and un-bleached cotton cloth. The pillow has a stiff, lumpy feel but is otherwise quite acceptable as a pillow, considering that the face is quite sensitive to irritation. One outstanding quality of the pillow is that it is not hot like a polyester or foam pillow (even with a cotton pillow case). It seems natural to try out the leaves for seat cushions. The Yau Kam Chi tree is often found in this city along country roads and in country parks. There is no known toxicity and the fruit from this tree is edible but not delicious (2,3).

RATIONALE

Essential and desirable cushion properties

Cushions for poor regions of the world must satisfy the following criteria:

1. Acceptable pressure distribution: Prolonged high pressure over a bony prominence is a major contributing factor of pressure sore formation. One of the major functions of a cushion is to keep the interfacial pressure within an acceptable level.

2. Low cost: With low financial resources, the cushions must be very low in cost to be affordable.

3. Easy to produce: With low financial resources, scarce capital is unlikely to be used in low demand special seating for the disabled. In addition, the disabled are most likely in the lower income bracket of rural society. Under these circumstances, special cushions are most likely either made by the users themselves or by people with limited skill.

4. Easy to use and maintain: Some hi-tech cushions requires pumping up air-sac compartments to appropriate pressures for good performance. Fluid filled cushions are subjected to puncture. Open cell foam cushions needs a good water-proof covering to prevent body fluid infiltration. All the above increases the difficulty in using and maintaining a cushion.

5. Other considerations: A lot of poor regions in world are hot and humid. Foam is a good insulator and trapped heat between the body and the cushion causes sweating. Shear stress is produced when a foam cushion deforms to conform to body shape. Sweating and shear are contributing factors of tissue damage. Low shear and low heat built-up are desirable properties of a cushion, especially for use in hot and humid climate.

Tree leaves as a potential candidate

For low cost, the cushion material has to be available locally as well as of low commercial value. In this regard, materials with high commercial value, such as fur and silk may not be appropriate even if available locally. Tree leaves are good potential candidates because they are in abundant supply and usually has no commercial value. If a particular type of tree leave can be identified with acceptable pressure distribution property, the cost will be essentially nil if it is available locally in abundance and maintenance will also be minimal because soiled or spent leaves can be replenished freely.

Cushions made with loose leaves will likely not trap much heat like a foam cushion and shear stress may likely be low if the leaves are able to slide over each other. One perceived advantage of this type of cushion is that it can be fluffed and pre-shaped if desired before each use

Making a cushion out of leaves will be very simple. All that is required is to sew a cotton bag and stuff it with the dried leaves. Collecting and drying the leaves should not be a problem because time, space and sun are not usually in short supply especially in rural areas.

In rural areas, people commonly possess knowledge on local poisonous plants. Toxicity should not be a problem if any potentially suitable tree leave is checked against published data and local folklore.

Method and Approach

Two cushions were made with un-bleached cotton and stuffed with Yau Kam Chi tree (phyllanthus emblica L.) leaves. The cotton case was simply made by sewing two pieces of material together with a zipper on the back edge for convenience. The cushions were stuffed to a thickness of about 40mm. Two able bodied users, one being the author, would use the cushion from July to November, 1995 in the home without air-conditioning on and with the cushion on a flat wooden chair.

In early December, 1995, the cushions were taken back to our centre for pressure mapping with the FSA system calibrated for 200mmHg with the author as the single subject. The cushions were placed on a wheelchair fitted with a plywood seat. Simple physical properties of the leaves from the cushions were measured for comparison with unused leaves. The following procedure was taken for leaves from each source: 1. 200ml of leaves was obtained by gradually putting leaves in a 400ml beaker and tapping on the side of the beaker until the 200ml mark was reached. 2. The beaker was taken to a material tester with a flat plastic disk of 74mm to provide about 1mm of clearance with respect to the internal diameter of the beaker. The disk was driven down at 6mm/min. The disk was stopped at pre-determined loads just long enough to manually take down the displacement reading. 3. The leaves were weighed.

OBSERVATIONS AND RESULTS

Qualitative evaluation

Cushion 1 was used by the author for an average of one hour per day mainly when using the computer at home while cushion 2 was used by a volunteer for an average of four hours a day while watching TV or reading. The author always sat on the cushion with both feet touching the floor. The other volunteer sat, kneeled and squatted on the cushion. Both users found that the cushions were firm but reasonably comfortable and can tolerate sitting on the cushion for about 1-1/2 hours a time. Both found perspiration, a common problem with foam and fibre filled cushions from experience, was not a problem in the area in contact with the leave cushion.

The author found that the cushion had some moulding property similar to that of a bean bag. An impression of the buttock remained after getting out of the cushion. Acceptable comfort was achieved not by sitting on a sat on cushion but by fluffing the cushion slightly and patting the cushion gently flat before each use. To prevent skin irritation, removing larger, stiff stalks of branchlets was desirable.

Appearance and densities of the leaves (Fig. 1)

Fresh leaves were a bit curly. The amount of flattening and breakage corresponded to the amount and style of use. The weight for 200ml of leaves were: unused (12gm), cushion 1 (18gm), cushion 2 (28 gm). Flattened and broken leaves packed better.

Pressure mapping with FSA (Fig. 2)

Cushion 1 and 2 both had a thickness of about 31mm. Relative to the flat plywood, the cushions did spread out loading. The amount of spreading decreased with the amount of use. The pressure under the ischia were high. For comparison, a 2" foam slab didn't give better results. Measurement using a single sensor of an Oxford Pressure Monitor showed a difference of about 100mmHg under the ischia when sitting on flat plywood and cushion 2.

Compression test (Table 1, Fig. 3)

A crackling noise, probably due to fibers breaking, was noticeable for the unused leaves and that from cushion 1 when the applied pressure exceeded 150mmHg. Downward displacement was taken relative to that at 10mmHg to allow for a bit of pre-compression. The leaves were compliant even at a pressure of 300mmHg. Compliance decreased with increasing pressure. The longer the leaves were used, the higher the decrease in compliance. Unused leaves had a much more uniform compliance.

DISCUSSION

The leave cushions are found to be acceptable by two able bodied volunteers, specially during hot humid weather. In contrast, inconclusive high pressures maps are obtained with the FSA. Evaluation by disabled subjects will be crucial but much care has to be exercised and volunteers may be difficult to find in this modern city. Interfacial pressure measurements using other techniques, such as the Dynamic Pressure Monitor or the Oxford Pressure Monitor will be useful to counter check the FSA results. A better protocol for pressure measurements has to be established. Simple material testing is done to characterise this loose aggregate material. But a better procedure, such as automatic data collection, has to be established especially for comparing different materials. Cyclic compression tests can be done in the laboratory to minimize the need for long term home trials.

REFERENCES

1. International Appropriate Technology SIG group meeting, 1995 RESNA annual meeting, Vancouver, BC, Canada.

2. Thrower, Hong Kong Trees (Omnibus Volume), Hong Kong Urban Council, Hong Kong, 1988.

3. Ho, Hong Kong Poisonous Plants, Hong Kong Urban Council, Hong Kong 1981.

ACKNOWLEDGEMENT

This work was supported by The Hong Kong Polytechnic University

Dominic P.K. Cheng REC, The Hong Kong Polytechnic University Hung Hom, Kln. Hong Kong email rcdpkc@polyu.edu.hk

Fig. 1 A pressed branchlet of a Yau Kam Chi tree