Device forOpening andClosing MagentaVessels forMicropropagation

Loren D. Gautz and

Charles W. Wong

Additional index words. tissueculture, repetitive work injury

Summary. A device is described thatcan be used to open and close Ma-genta vessels used for micropropaga-tion. Performance of the device isreported and compared favorably tounassisted manual opening and clos-ing of vessels. Benefits include elimi-nation of a potentially physically dam-aging (e.g., carpal tunnel syndrome)manual operation.

Micropropagation is the invitroculture of small (micro) cut-tings for propagation of

plants. The cuttings are induced toproduce multiple new shoots throughmanipulation of the chemical and physi-cal environment. By this process, plantmaterial of the same genotype can bereproduced rapidly and can be keptfree of viral, bacterial, and fungal dis-eases. Because of these benefits,micropropagation has been adoptedwidely. More then 250 laboratories inthe United States are engaged inmicropropagation of many types ofplants. Five to 10 of these laboratoriesproduce more than 5 million plantsannually (Wochock, 1987). Many ofthese laboratories use the MagentaGA-7 vessel.

In Hawaii, the Hawaiian SugarPlanters’ Assn. (HSPA) was usingmicropropagation to supply sugarplanters with micropropagated sugar-cane transplants at rates as high as

Agricultural Engineering, University of Hawaii atManoa, Honolulu, HI 96822.

Hawaii Inst. of Tropical Agriculture and Human Re-sources Journal Series no. 3790. Mention of brand namesis for clarity only and is not an endorsement. Fundingwas made available for this research by the Office of theVice President for Research and Graduate Studies, Univ.of Hawaii at Manoa, Honolulu.

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100,000 plants/week. Current prac-tice is to use five generations for mul-tiplication, including the rooting phase.Each generation takes 14 days andgives a shoot multiplication of fourtimes. A vessel must be opened at thebeginning, at the middle to change thegrowing medium, and at the end ofeach generation. This means that, forsustained production, 21,826 vesselswere opened per week with a crew ofsix people. Workers have complainedof pain similar to the onset of carpaltunnel syndrome from repetitive open-ing of vessels. In a study to determinethe optimal conditions for microprop-agation of sugarcane, Walker et al.(1991) determined that the liquidgrowing medium should be changedtwice during the 14-day growing cycle.Using two medium changes instead ofone would increase the number ofvessels that must be opened per weekby 25%.

Similar to many other microprop-agation laboratories, HSPA uses theMagenta GA-7 vessel. Several factorslead to the selection of this vessel andare outside the scope of this study.

Other than many recommenda-tions to automate the handling of ves-sels used for micropropagation, noreferences were found relating to theopening of vessels. More than 800U.S. patents related to openers werefound in the U.S. Patent Office Ga-zette. These consist of openers for ev-erything from bags, bottles, and cans,to oysters and wooden boxes. Thereare 54 patents for opening containers.The U.S. Patent Office does not havea classification for plastic container orplastic box. Of the patented openers,none were found that related to open-ing a friction-fit lid on a plastic boxsuch as the GA-7 vessel used formicropropagation.

Basic dataThe GA-7 vessel is made from

polycarbonate plastic and is nearly cu-bical in shape; nominally 80 mm on aside. The lid is a polyethylene materialthat has a friction-fit to the vessel.When the lid is closed completely, agap between the lid and the vessel ≈1mm wide and 1 mm deep extendsaround the outside of the vessel at theinterface. Although the lips on thevessel and the lid make accidental con-tact with the interior of the vessel or lidduring opening by hand highly un-likely, the force exerted during the

opening of some vessels causes occa-sional mishaps such as dropping the lidor spilling the contents of the vessel.

The force required to pull a lidstraight off from a vessel was deter-mined using an Instron Universal Test-ing machine. The vessel was held downby a fixture gripping two oppositesides. The lid was fastened to the cross-head using a gripper with graspingjaws in the lid-vessel gap on either twoopposing sides or two opposing cor-ners.

Tests were run with four vesselsand four lids chosen at random fromthe current stock. The sample includedboth old and new vessels and tops. All16 possible combinations of the ves-sels and lids were tested at two cross-headspeeds: 0.4 and 10.6 mm·s-1. Themaximum, minimum, and mean peakforce attained during opening the 16combinations is shown in Table 1.Because only 16 tests were made, theforce used for engineering design cal-culations should be taken as at least themaximum force experienced for thetype of gripper used.

The force using the opposing sidegrip was independent of pull rate. Be-cause the force using the opposingcorner grip was not independent ofpull rate and greater than when usingthe opposing side grip, opposing cor-ner gripping was not considered fordevelopment of an opening device.

Description of deviceThe device is a hand-held tool to

assist in opening friction-fit containers(Fig. 1). The prototype was designedto open Magenta GA-7 containers,but can be modified easily to openother containers. The device consistsof a handles and two grippers; onestationary and the other movable. Thehandle is a pistol grip shape with aknob at the top to aid in control whilenot gripping a vessel. The grippers aremade of strips of 0.9-mm (20 USStd.ga.) stainless steel sheet metal that isbent at the ends at right angles to forma small jaw to engage the lid at the gapbetween it and the vessel. The station-ary gripper is attached to the bottomof the handle and grabs one side of thelid. The movable gripper is a simplecantilevered beam mounted to the topof the handle. A jaw at the free (lower)end of the movable gripper grabs thefar side of the lid. The operator holdsthe device with the stationary gripperadjacent to the heel of the hand and

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Table 1. Peak forcer (N) to open vessels at two pull rates (mm·s–1).

the movable gripper under the fingers.The shape of the handle makes it pos-sible to hold the device with the thumband palm without applying pressure tothe movable gripper with the fingers.

After clasping the vessel with onehand, the operator places the device

Fig. 1. Device for opening and closing Magenta Gtion to opening (bottom).

on top of the lid with a forward slidingmotion to engage the lid at the gap onthe side of the vessel closest to theoperator. Then, as the operatorsqueezes the cantilever with the fin-gers to close the movable gripper, pres-sure is applied to the top of the handle

A-7 vessels (top) andproper initial applica-

with the base of the thumb, causingthe device to rotate slightly and thenear side of the lid to slide up. Theoperator then lifts the lid off with alittle force. Depending on the labora-tory practice, the lid and device can beplaced aside by setting them down onthe lip of the lid or rotating the deviceforward to hold the lid in a verticalposition. The lid may remain in thedevice. Suspending the device on somesort of hanger is not recommended.The lid cannot remain securely in thedevice, and no savings in motion isobtained.

The lid can be replaced using thedevice. Because the friction-fit is suffi-ciently tight to hold the vessel, theclosed vessel can be placed aside withthe device while the other hand ac-quires another vessel. This gives a bal-anced motion to the hands, necessaryfor optimal working efficiency. Withtraining and properworkspace arrange-ment, placing the device aside is un-necessary except when this hand isneeded for pouring media, or someother peripheral task.

EvaluationThe device was evaluated by tim-

ing only the lid removal and handmovement to the next vessel to beopened. For each trial, 11 vessels wereplaced in an arc at an easy reach fromthe operator. Timing started at thecompletion of opening the first vesseland ended. with the completion ofopening the last vessel. Therefore, 10vessels were opened during the timedinterval. The timer was accurate to0.01 s. More than 10 trials were madewith each subject using the device, anda similar number of trials with eachsubject opening vessels manually. Sometrials were not used for the averagebecause of various avoidable errors inthe trial. A complete test session for agive subject took >50 min and >200vessels were opened.

Six subjects volunteered for thetime study. Subjects 1–4 were maleand subjects 5 and 6 were female.Subject 1 was trained with the device,but had very little experience with thehand-opening ofvessels. Subject 2 wastrained with the device and was expe-rienced with both the device and hand-opening. Subject 3 was a total novice,with no training or experience prior tothe trials. Subjects 4-6 had openedmany vessels by hand in a researchlaboratory, but had never used the

device before. The last three subjectswere first tested without training withthe device. Following initial trials, theywere given instruction and supervisedpractice using the device and thenwere tested with the device again. In-struction and practice did not exceed15 min. Hand and device trials wereinterspersed randomly. Unfortunately,once trained, the subject cannot betested as untrained, making random-ization of trained and untrained con-ditions impossible.

Mean times for a subject to openvessels by hand and with the device(Table 2) were compared statisticallyusing Student’s t test. All four subjectswho had not been trained with thedevice had slower times with the de-vice compared to manual opening. Foronly one of these four (subject 4) wasthe difference not highly significantstatistically (99% confidence). Threeof these subjects were given training,bringing the total number of trainedsubjects to five. All subjects trainedwith the device had lower opening

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times compared to hand-opening. Onlyone subject (subject 4) did not exhibita statistically significant difference.Even though this is a small sample, theprobability for all subjects to lowertheir times purely by random effectswould be similar to getting five headsin five tosses with a fair coin (i.e., 3%).This indicates that some training isrequired even with this simple device.Also, with training, there is a timeadvantage when using the device. In-terestingly, all subjects believed thatthe device made them faster even be-fore training. The also believed thatusing the device made them less fa-tigued than did manual opening.

Although forces applied by handwhen using the device were not mea-sured, only enough grip force to over-come the cantilevered beam resistanceis required. This force is <1 N and isadjustable. The grip force in manualopening must be great enough to ob-tain sufficient friction with the lid tocause the lid to move. The force ap-plied by hand to the top of the handle

is less than pulling force applied duringmanual opening, because of the leveraction of the handle. The hand hold-ing the vessel experiences the sameforces with either method, but theuncertain forces observed duringmanual opening are not experiencedusing the device.

ConclusionThe device described here can be

used to make the opening of MagentaGA-7 vessels, used commonly formicropropagation, less fatiguing. Thereis no time penalty for using the device.In fact, there is good probability thatsome time will be saved with the de-vice. Because the gripping force thatmust be applied is substantially lessthan without, and because the wristtakes a more natural position duringopening of the vessels, there is muchless chance for repetitive stress injuriesthat are presently the cause for com-plaint by workers. Also, when usingthe device, the vessel remains stableand the lid does not suddenly pop outof tightly gripped fingers as it iswrenched off the vessel by hand.

Literature CitedWalker, P.N., J.P. Harris, and L.D. Gautz.1991. Optimal environment for sugarcanemicropropagation. Trans. of ASAE 34:2609-2614.

Wochock, Z.S. 1987. Status of crop im-provement through tissue culture. Comb.Proc. Intl. Plant Prop. Soc. 36:72-77.

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