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Magnetic resonance imaging reveals functional anatomy and biomechanics of a living dragon tree

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ABSTRACT

Magnetic resonance imaging (MRI) was used to gain in vivo insight into load-induced displacements of inner plant tissues making a non-invasive and non-destructive stress and strain analysis possible. The central aim of this study was the identification of a possible load-adapted orientation of the vascular bundles and their fibre caps as the mechanically relevant tissue in branch-stem-attachments of Dracaena marginata. The complex three-dimensional deformations that occur during mechanical loading can be analysed on the basis of quasi-three-dimensional data representations of the outer surface, the inner tissue arrangement (meristem and vascular system), and the course of single vascular bundles within the branch-stem-attachment region. In addition, deformations of vascular bundles could be quantified manually and by using digital image correlation software. This combination of qualitative and quantitative stress and strain analysis leads to an improved understanding of the functional morphology and biomechanics of D. marginata, a plant that is used as a model organism for optimizing branched technical fibre-reinforced lightweight trusses in order to increase their load bearing capacity.

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Experimental setup for applying mechanical loads to a ramification of Dracaena marginata during magnetic resonance imaging.The experimental setup is split into a non-magnetic skeletal structure (A1/A2) and a magnetic extension (B1/B2). A1/A2: A long aluminium beam is the base of the skeletal structure which also consists of a magnetic resonance imaging inactive plastic tip, two grooves for attaching the specimen and for guiding the load cable, holes for securing the specimen with cable straps and a bras-disk for locking the load cable into position after having applied a bending force. B1/B2: An aluminium beam, which can be attached to the skeletal structure, is the base of the extension. A holding for a spring scale, which is mounted to a screw handle, is fixed to the extension. The screw handle allows for precise adjustment of the applied force.
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f8: Experimental setup for applying mechanical loads to a ramification of Dracaena marginata during magnetic resonance imaging.The experimental setup is split into a non-magnetic skeletal structure (A1/A2) and a magnetic extension (B1/B2). A1/A2: A long aluminium beam is the base of the skeletal structure which also consists of a magnetic resonance imaging inactive plastic tip, two grooves for attaching the specimen and for guiding the load cable, holes for securing the specimen with cable straps and a bras-disk for locking the load cable into position after having applied a bending force. B1/B2: An aluminium beam, which can be attached to the skeletal structure, is the base of the extension. A holding for a spring scale, which is mounted to a screw handle, is fixed to the extension. The screw handle allows for precise adjustment of the applied force.

Mentions: The experimental setup chosen for the biomechanical experiments integrated the spatial limitation of the MR-bore and other constraints imposed by the plants and the technical materials. During the biomechanical tests, special attention needs to be given to the attachment of the plant to the skeletal structure (Fig. 8, A1 and A2). Small deviations from the parallel alignment in particularly of the branch-stem-attachment to the aluminium beam can lead to larger twisting deformations of the entire ramification (Fig. 1c–f) which also include the vascular bundles and their fibre caps (Fig. 3a,b). Furthermore, the distance of the applied force to the branch in respect to the main stem has a significant effect on the occurrence of shear strains which superimpose the bending strains. This is not a new finding in the field of plant biomechanics where span-to-depth ratios were routinely calculated for tests of biological beams303132. When testing the biomechanics of plant ramifications, however, comparable ratios need to be carefully considered. This is a crucial step as the influences of interior shear strains are barely apparent on the outer surface of the ramification (Fig. 1c,d) whereas they clearly affect single vascular bundles and their fibre caps (Fig. 3a,b). The differences of the vascular bundle displacements between individual DM09 and DM10 (compare Fig. 2c,d with Fig. 3a,b) can be led back to the varying lateral distance of the applied force to the main stem which is in the magnitude of roughly 1 cm (Supplementary Fig. S5). For experiments on mechanical loading of side branches in Salix and Picea both Beismann et al.30 and Müller et al.33 chose a distance of applied load from the main stem of approximately 1 cm, which is comparable to the distance chosen for individual DM09 showing the shear displacements (Figs 1, 3 and 6). However, the results of the electronic speckle pattern analysis of Müller et al.33 do not indicate shear displacements. Thus an appropriate distance of applied load should be determined individually for each species and for each individual specimen dependent on the morphometry of the branch-stem-attachment region.


Magnetic resonance imaging reveals functional anatomy and biomechanics of a living dragon tree
Experimental setup for applying mechanical loads to a ramification of Dracaena marginata during magnetic resonance imaging.The experimental setup is split into a non-magnetic skeletal structure (A1/A2) and a magnetic extension (B1/B2). A1/A2: A long aluminium beam is the base of the skeletal structure which also consists of a magnetic resonance imaging inactive plastic tip, two grooves for attaching the specimen and for guiding the load cable, holes for securing the specimen with cable straps and a bras-disk for locking the load cable into position after having applied a bending force. B1/B2: An aluminium beam, which can be attached to the skeletal structure, is the base of the extension. A holding for a spring scale, which is mounted to a screw handle, is fixed to the extension. The screw handle allows for precise adjustment of the applied force.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5015020&req=5

f8: Experimental setup for applying mechanical loads to a ramification of Dracaena marginata during magnetic resonance imaging.The experimental setup is split into a non-magnetic skeletal structure (A1/A2) and a magnetic extension (B1/B2). A1/A2: A long aluminium beam is the base of the skeletal structure which also consists of a magnetic resonance imaging inactive plastic tip, two grooves for attaching the specimen and for guiding the load cable, holes for securing the specimen with cable straps and a bras-disk for locking the load cable into position after having applied a bending force. B1/B2: An aluminium beam, which can be attached to the skeletal structure, is the base of the extension. A holding for a spring scale, which is mounted to a screw handle, is fixed to the extension. The screw handle allows for precise adjustment of the applied force.
Mentions: The experimental setup chosen for the biomechanical experiments integrated the spatial limitation of the MR-bore and other constraints imposed by the plants and the technical materials. During the biomechanical tests, special attention needs to be given to the attachment of the plant to the skeletal structure (Fig. 8, A1 and A2). Small deviations from the parallel alignment in particularly of the branch-stem-attachment to the aluminium beam can lead to larger twisting deformations of the entire ramification (Fig. 1c–f) which also include the vascular bundles and their fibre caps (Fig. 3a,b). Furthermore, the distance of the applied force to the branch in respect to the main stem has a significant effect on the occurrence of shear strains which superimpose the bending strains. This is not a new finding in the field of plant biomechanics where span-to-depth ratios were routinely calculated for tests of biological beams303132. When testing the biomechanics of plant ramifications, however, comparable ratios need to be carefully considered. This is a crucial step as the influences of interior shear strains are barely apparent on the outer surface of the ramification (Fig. 1c,d) whereas they clearly affect single vascular bundles and their fibre caps (Fig. 3a,b). The differences of the vascular bundle displacements between individual DM09 and DM10 (compare Fig. 2c,d with Fig. 3a,b) can be led back to the varying lateral distance of the applied force to the main stem which is in the magnitude of roughly 1 cm (Supplementary Fig. S5). For experiments on mechanical loading of side branches in Salix and Picea both Beismann et al.30 and Müller et al.33 chose a distance of applied load from the main stem of approximately 1 cm, which is comparable to the distance chosen for individual DM09 showing the shear displacements (Figs 1, 3 and 6). However, the results of the electronic speckle pattern analysis of Müller et al.33 do not indicate shear displacements. Thus an appropriate distance of applied load should be determined individually for each species and for each individual specimen dependent on the morphometry of the branch-stem-attachment region.

View Article: PubMed Central - PubMed

ABSTRACT

Magnetic resonance imaging (MRI) was used to gain in vivo insight into load-induced displacements of inner plant tissues making a non-invasive and non-destructive stress and strain analysis possible. The central aim of this study was the identification of a possible load-adapted orientation of the vascular bundles and their fibre caps as the mechanically relevant tissue in branch-stem-attachments of Dracaena marginata. The complex three-dimensional deformations that occur during mechanical loading can be analysed on the basis of quasi-three-dimensional data representations of the outer surface, the inner tissue arrangement (meristem and vascular system), and the course of single vascular bundles within the branch-stem-attachment region. In addition, deformations of vascular bundles could be quantified manually and by using digital image correlation software. This combination of qualitative and quantitative stress and strain analysis leads to an improved understanding of the functional morphology and biomechanics of D. marginata, a plant that is used as a model organism for optimizing branched technical fibre-reinforced lightweight trusses in order to increase their load bearing capacity.

No MeSH data available.


Related in: MedlinePlus