BRIT. J. SURG., 1965, Vol.
764
52,
No.
10,
OCTOBER
P. F., CROSS,C. E., RIEBEN, P. A., and
JAMISON,
W. L., GWEINHARDT,
W., ALAI,J., and BAILEY, SALISBURY,
LEWIN,R. J. (1960), ‘Comparison of Two Types sf
C . P. (1954), ‘Artificial Maintenance of the Systemi;
Mechanical Assistance in Experimental Heart Failure ,
Circulationwithout Participation of the Right Ventricle ,
Circulation Res., 8, 431.
Circulation Res., 2, 315.
J. H.,NEWMAN,
M. M., DENNIS,
C., BERG,E. H.,
LEIGHNINGER.
D. S.. DAVIDSON,
A. I. G.. and BECK,C. S. STUCKEY,
S. E.. FRIES,C. C., KARLSON,
K. E..
GOODMAN.
(1965), ‘Left Heart Bypass in Cardiac Resuscitation’,
BLUMENFIELD, M.,~WEI;ZNEU,
S. W., BINDER, L. s.,and
Amer. J . Cardiol., 15, 33.
A. (I957), The Use of the Heart-Lung
PATT,H. H., CLIFT,J. V., LOH,P. B., ROA,J. C., WEXLER, WINSTON,
Machine in Selected Cases of Acute Myocardial
J., and SELIGMAN,
A. M. (1960), ‘Veno-arterialPumpinf:
Infarction’, Surg. Forum, 8, 342.
in Normal Does and Does with Coronarv Occlusion
WATKINS,
D. H., and DUCHESNE,
E. R. (1961), ‘PostJ . thorac. Surg: 39, 464.
SALISBURY,
P. F., BOR,N., LEWIN,R. J., and RIEBEN, systolic Myocardial Augmentatton. I. Developmental
Considerations and Technique , Arch. Surg., Chicafo,
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Bypass on the Heart’,J. appl. Physiol., 14, 458.
82, 839.
.
-
THE MOBILE MICRO-ARCHITECTURE OF DERMAL COLLAGEN
A BIO-ENGINEERING STUDY
BY T. GIBSON
DEPARTMENT OF SURGERY, WESTERN INFIRMARY, GLASGOW
R. M. KENEDI
DEPARTMENT OF RIO-ENGINEERING,
AND
UNIVERSITY OF STRATiICLYDE. GLASGOW
J. E. CRAIK
DEPARTMENT OF PATHOLOGY, VICTORIA INI‘IRMARY, GLASGOW
HUMANskin is an extremely diversified structure;
there are obvious and extreme variations between
individuals and between different areas in the same
individual. The mechanical characteristics of skin
and, in particular, the range of naturally occurring
tensions, their regional and individual variations, and
their directional qualities have been studied (Kenedi
and Gibson, 1962; Gibson, 1965). Apparatus has
been designed and constructed to measure accurately
skin tension in vivo (Kenedi, Gibson, and Daly,
1965a, b), and it was hoped initially that it might
be possible to prepare ‘tension maps’ of the human
skin surface indicating the magnitude and orientation
of local tensions; such data, it is believed, might
greatly assist the design of incisions and skin-grafts.
However, the range of variations encountered to date
has been too wide to permit simple generalizations.
Skin tensions differ not only regionally but at different
ages and in different states of health and disease;
increasing adiposity of a part, for example, may alter
radically the directional properties of the tension in
the skin overlying it.
It seemed certain that these differences must be
related in some way to variations in the collagen and
elastic fibres of the dermis, but what these variations
were was not immediately obvious. Measuring the
thickness of the skin showed that there was often a
rough correlation between the bulk of the dermis and
the tensions to which it might naturally be subjected,
but there were many anomalies. It was only when
studies of the effect of increased tension on skin in
vivo and in detached specimens were undertaken that
a clue was obtained to the structural basis of the
underlying variations.
BEHAVIOUR OF SKIN UNDER LOAD
When a stretching force is apRlied to skin in situ
two effects can be observed: (I) the skin extends in
the direction of the applied force, while at the same
time (2) it contracts in a plane at right-angles to the
applied force. When skin is stretched in vitro a third
effect may be measured: (3) there occurs a progressive
decrease in the total volume of the stretched specimen.
It should be noted that all these data are timedependent; with any change in loading, a certain
period must elapse before the change in measurements
becomes stable. Considerable variations in the time
required have been noted in different individuals
for no obvious reason. The curves obtained on load
release are slightly different from those during loading, but the differences do not affect the present
argument.
I. Skin
Extension under Load.-Typical
examples of skin extension with increasing load are
shown in Fig. I . The curves may be conveniently
considered in three parts. Initially, there is a fairly
rapid increase in length for very small increments of
force. Terminally, only minor degrees of extension
result from relatively large increases in force. Between these two portions there is an ‘elbow’ representing the change from the first to the last parts
of the curve. Age variations are largely confined to
the initial fiat portion of the curve, which shortens
progressively with increasing age. The terminal,
almost linear portion of the curve is common to all
skin samples and is very similar to the extension
curve obtained with pure collagen (Fig. 2 ; Morgan,
1960). It seemed, therefore, as if some factor other
than the structural characteristics of collagen was
responsible for the behaviour of the Stretched skin at
the relatively low loads of normal activity.
2. Contraction at Right-angles to the Stretching Force.-This
effect may be readily observed on
one’s own skin; when measured and plotted against
extension a direct relationship is obtained (Fig. 3).
As would be expected, the amount of contraction is
greater at the smaller loads which produce the greater
extension.
GIBSON E T AL.: DERMAL COLLAGEN
3. Decrease in Volume.-When,
under laboratory conditions, a piece of skin is stretched and, in
addition to the length and width, the thickness is
3502
7-
1
P X T - MORTEM
SKIN,
A L L 4AMPLES A N T E R I O R
A g O O M l N A L REGION
300C
765
measured, there comes a point at which a decrease
in total volume occurs (Fig. 4). If the skin is being
stretched in air, this can be seen to be due to a
physical extrusion of fluid from the specimen.
HISTOLOGICAL CHANGES
Three collagenous layers can be distinguished in
sections of the dermis: a thin superficial layer of
rather fine bundles of collagen; a middle layer which
1 --
250C
0,
.c
_
2200c
I
b
2
1500
Ill
rk!
5
2
IOOC
7
2
0
500
0
EXTENSION
EXTENSION €- Y_-
Ed-
FIG. curves showing extension under load of post-mortem
samples of abdominal skin. Initially there is a rapid increase in
length for increments of force too small to be recorded on this
scale; the final part of the curve shows only minor degrees of
extension for very large force increases; a transitional ‘elbow’
joins the two portions of the curve.
W
POST- MORTEM SKIN
FIG.2.-1.oad extension curve for a single raw collagen fibre
taken from cow hide (Morgan, 1960). It is similar to the final
portion of the curves shown in Fi.y. I.
1
ABDOMINAL V E RT ICAL
MID-LINE, MALE AGE 67
24
-20
APPROXIMATE
.
CONTRACTION E
L E V E L OF
-
EXTENSION
EX
FIG.3.-Extension-~ontraction curve of detached abdominal skin under load. Extension of skin in one direction is accompanied by a
fimilar degree of contraction at right-angles to the stretching force. T h e ‘physiological load limit’ has been taken as the level at which
blanching’ of the skin occurs from constriction of the capillaries.
BRIT. J. SURG., 1965,Vol.
766
52, No.
10,OCTOBER
dermis; an arrangement which allows continual movements of the individual fibres to absorb the minor
stresses of normal activity and relies on the ultimate
strength of collagen to resist severe stretch. There is
in the dermis an intertwined meshwork of collagen
fibres so patterned that, in whatever direction it is
stretched, all the fibres eventually become parallel.
makes up most of the dermal bulk; a deep layer
consisting of fibres which are continuous with and
link the skin to the superficial fascia. Most of the
changes resulting from stretching of the skin occur
in the middle layer. In the relaxed state, the collagen
fibres are unorientated convoluted structures separated from each other by tissue fluid and amorphous
Y
POST-MORTEMSKIN
EXTENSION
IX
W.2-
-0.3
-0.2
-0.1
VOLUME
FIG.4.-When
CONTRACTION
0
t
-
..
0.1
STRAIN
0.2
&
skin is progressively extended, there comes a oint at which decrease in volume occurs. In detached specimens this caii
bc seen to be due to a pfysical extrusion of fluid.
ground substance (Fig. 5 ) . When teased out of
unfixed skin they are seen to be long, unbranched,
smooth, intertwined filaments (Fig. 6).
When subjected to considerable loads (i.e., to those
corresponding to the final part of the extension curve)
and fixed while in the stretched position, it is found
that the majority if not all of the collagen fibres have
become orientated along the line of stretch (Fig. 7).
This has been observed in all detached specimens
of skin, mainly from the trunk and limbs, which we
have examined in this way, and it has occurred no
matter in which direction the skin has been stretched.
Sections of skin subjected to the lower loads of the
initial part of the elbow of the extension curve show
an increasing number of fibres becoming orientated
parallel to the line of force (Fig. 8).
The fact that the collagen fibres change their
staining reaction when stressed has been described
elsewhere (Craik and McNeil, 1969,and is outside
the scope of the present paper.
THE MICRO-ARCHITECTURAL PATTERN
OF DERMAL COLLAGEN
We have, therefore, been led to a dynamic concept
of the arrangement of the collagen fibres in the
At rest, no fibres are under stretch and all appear
randomly orientated. When an increasing load is
applied, there is first of all a rearrangement of the
individual fibres as they move into alinement in the
ground substance which surrounds them. This phase
of straightening and redirection of the fibres corresponds to the first part of the extension curve. As more
and more fibres are orientated parallel to the line
of force, and ‘take up the strain’, the shape of the
graph approaches and is finally governed by that of
collagen. During this phase it is obvious histologically
that fluid has been displaced from the meshwork. It
has been observed during in vitro experiments that a
complete recovery of the original pattern, on removal
of the load, is unlikely even during the alinement
phase. Certainly, when all the collagen bundles have
been drawn parallel, they tend to remain so even
after relaxation, presumably because of loss of tissue
fluid and ground substances from between the fibres.
It must be remembered that the collagen fibre itself
is not constructed of inert isotropic material. Electron
microscopy of a typical fibre (Fig. 9) shows a highly
organized structure, which consists of parallel macromolecular collagen fibrils each surrounded by a
mucopolysaccharide sheath. The frequent presence
GIBSON E T AL.: DERMAL COLLAGEN
of a protoplasmic extension of a fibroblast at the
periphery suggests continued metabolic activity. The
precise structural characteristics of this organization
have still to be determined, but it obviously permits
readily the recurring bending and straightening of the
fibre which occur during movements of the collagen
fibre network.
FIG.S.-Normal unstretched skin. Beneath the epidermis the
relatively narrow superficial dermis is composed of compactly
arranged fine bundles of colla en In the middle layer, which is
the main mass of the dermis, t i e collagen bundles are thicker and
are arranged in an apparently haphazard three-dimensional loose
network. 11. and 1:. ( x 100.)
FIG.7.-Fully stretched skin fixed while under load. I n the
middle dermis the collagen bundles lie parallel to one another
along the line of stretch, which is in the plane of the photogra h
and parallel t o the surface. T h e narrow superficial layer of t t e
dermis is less affected. H. and H. ( x 100.)
767
THE
OF THE
Some mechanism must exist in vivo to restore the
status quo to the meshwork of collagen after it has
been deformed by a stretching force. Elsewhere in
the body, for example, in blood-vessels, this function
is served by elastic fibres which act as storers of the
energy required to return the structure to its resting
FIG.6.-Teased fresh specimen of dermal collagen. T h e fibres
tend to remain in bundles and the bundles retain their natural
convolutions. Unfixed preparations stained new red and photographed with reduced substage diaphragm to show finer fibres.
( y 36.)
FIG.8.--Partially
stretched skin fixed while under small load.
A number of collagen bundles have become orientated parallel to
the line of force. Trichrome. ( 1 loo.)
768
BRIT. J. SURG., 1965, Vol. 52, No.
10,
OCTOBER
collagen mesh in such a way that it can return the
collagen fibres to their resting pattern after they have
been stretched. A secondary factor necessary to
restore the meshwork to its relaxed state after severe
deformation is the reintroduction of fluid between the
fibres. In vivo this is probably only displaced into the
neighbouring tissues and is readily available on
relaxation; in detached skin it is lost and a return to
normal does not occur.
I ~ I G9.--Electron micrograph of a collagen fibre in the subserosal coat of the rat jejunum. T h e ground substance (G)lying
between the collagen fibrils (c) is stained heavily with lead.
Particles of colloidal iron ( I ) are dispersed uniformly throughou!
the ground substance and also coat the surface of the ‘fibrocyte
which is closely apposed to the collagen fibrils. ( x 30,000.)
(F\Tissue fixed in osmium tetroxide and section stained with
alkaline lead solution. Prior to embedding, the tissue was reacre:
in bulk with the colloidal iron solution which specifically ‘stains
acid mucopolysaccharides.)
(Reproduced b.v kind permissioii of Professor R . C . Curraii from
‘ Theyourno1 of Anatoiiiy”, 1965, 99, 427.)
MATHEMATICAL ANALYSIS OF THE
COLLAGEN FRAMEWORK
While in theory many of the variations in structural
characteristics of skin can be explained by variations
of pattern in the collagen network, the precise threedimensional architecture of the fibres in different
specimens is still to be determined. This is being
studied by microdissection of skin and by the construction of mathematical models which represent,
in a simplified form, one or more of the possible
patterns which may exist.
The simplest two-dimensional interwoven network, which Will satisfy the criterion of all the fibres
becoming parallel when stretched in any direction, is
shown in Fig. 12. While it must be emphasized that
FIG. Io.-Normal
skin showing arrangement of elastic fibres,
stained black. These fibres run between the collagen bundles;
in the superficial dermis they tend to be straight, but in the middle
dermis they are convoluted or spirillary, apparently looping around
the collagen. Elastica. ( x 100.)
FIG.I I .-Fully stretched skin to show elastic fibres which, for
the most part, have been straightened out and lie between the
collagen bundles. Elastica. ( x loo.)
state. It seems likely that the elastic fibres of the
dermis act in the same way. In relaxed skin they
form a secondary network looped around the collagen
fibres (Fig. 10). When the skin is fully stretched their
convolutions straighten out, and they lie between the
collagen bundles and are roughly orientated in the
same direction (Fig. 11).
Unlike collagen fibres, elastic fibres are branched
or, more accurately, show many end-to-side junctions.
It seems likely, therefore, that they form an interconnected network which is intertwined with the
the actual structure is much more compact and
complex, such a pattern is susceptible to mathematical
analysis and a mathematical model based on this and
incorporating an energy storing factor for restoration
to normal is shown in Fig. 13. Typical curves (Fig.
14) obtained from this model, which is being dcscribed in detail elsewhere (Kenedi, Gibson, and Daly,
1 9 6 5 ~ are
) ~ in many ways similar to those of skin.
As further evidence is obtained from microdissection,
additional analogue components can be incorporated
in the model so that a more accurate mathematical
GIBSON ET AL.: DERMAL COLLAGEN
769
each other and must be replaced before the relaxed
pattern is reestablished.
6. Variations in the architecture of the collagen
and elastic fibre networks probably underlie the
variations in mechanical characteristics of skin which
have been observed at different ages, at different
sites, and in different directions at thc same site.
analysis can be derived. It is hoped thereby to be
able to assess the presumptive collagen pattern and its
FIG.12.-The simplest two-dimensional interwoven network
which satisfies the criterion of all fibres becoming parallel when
stretched in any direction. T h e collagen pattern of the dermis is
much more complex and three-dimensional.
mechanical behaviour in any piece of skin, once
certain simple structural characteristics are known.
1
SUMlMARY
The collagen fibres of the dermis form an
intertwined meshwork which moves and changes
pattern during stretching and relaxation of the skin.
2. Considerable extension of relaxed skin can take
place with relatively small loads ; during this phase,
the collagen fibres of the network become successively
alined in the direction of the stretching force.
3. When the majority of the fibres are rearranged
parallel to the line of stretch, further extension in that
direction is resisted by the fibres themselves and very
little extension is obtained, even with great increase in
load.
4. The elastic fibres in the dermis form a secondary
network interconnected with that of collagen and
probably act as stores of the energy required to return
the collagen network to its relaxed state.
5. Interstitial fluid is displaced from the network
as the fibres are orientated and compacted parallel to
. + .
i
. . .
I.
.
,
I
.
-
i-._I.i
.
F I ~13.--r)iagram
.
of part of a mathematical model based on
the network pattern shown in Pi,.12. T h e full model consists of
a 15 Y 15 arrangement of 225 microscale units, each of which has
4 extensible side-limbs of finite thickness and a compressible
cross-link. T h e solution of the appropriate equation system is
obtained with the help of a digital computer.
Y
- -1
POST-MORTEM SKIN. ABDOMINAL I
-
2
NETWORK CONCEPT
0 - ~ DIRECTION,
~ ~ - ~MALE
~ ~
AGE 53.
TESTED IN RINGER SOCUllOrJ
EXPERIMENTAL RESULT
I5.-AT
P
a
--
2
10:
-
0
J
5---
-
A
A
21" C.
~
770
BRIT. J. SURG., 1965, Vol.
52,
No. 10,OCTOBER
KENEDI,
R. M., and GIBSON,T. (1962), ‘etude Experimentale des Tensions de la Peau dans le Corps I-fumain
-Systl.me de Mesure des Forces et Resultats , Rev.
franc. Mecan., 4, IZI.
- - - - and DALY,C. H. (1965a), ‘Bioengineering
Studies of the Human Skin-1’, N.A.T.O. Advanced
Acknowledgement.-We
are very grateful to
Study Courses on Connective Tissue, St. Andrews, June,
Professor R. C. Curran, Department of Pathology,
1964. London: Buttenvorths (in the press).
St. Thomas’s Hospital, London, for his continuing
(1965b), ‘Bioengineering Studies of
interest in our work and his permission to use the
the Human Skin-I1 ’, Symposium on Biomechanics and
electron micrograph in Fig. 9.
Related Bio-engineering Topics, University of Strathclyde,
Glasgow, September, 1964. Oxford : Pergamon Press
REFERENCES
(in the press).
CRAIK,
J. E., and MCNEIL,,I.
R. R. (1965), ‘Histological
(1965c), ‘The Determination, SigniStudies of Stressed Skin , Symposium on Biomechanics
ficance and Application of the Biomechanical Characand Related Bio-engineering Topics, University of
teristics of Human Skin’, 6th International Conference
Strathclyde, Glasgow, September, 1964. Oxford:
of Medical Electronics and Biological Engineering,
Pergamon Press (in the press).
Tokyo, August, 1965 (in the press).
GIBSON,T. (1965), ‘Biomechanics in Plastic Surgery’, MORGAN,
F. R. (1960), ‘The Mechanical,Properties of
Ibid., University of Strathclyde, Glasgow, September,
Collagen Fibres-Stress/Strain Curves , SOC. learh.
1964. Oxford: Pergamon Press (in the press).
Tr. Chem., 44, 170.
7. The experimental data, on which this dynamic
concept of the fibre construction of the dermis is
based, are detailed and methods suggested for the
further study of its micro-architecture.
_____-____-
CIRCULATING CANCER CELLS
THE EFFECT OF SURGICAL OPERATIONS
BY R. A. SELLWOOD
DEPARTMENT OF SURGERY, HAMMERSMITH HOSPITAL AND POSTGRADUATE MEDICAI. SCHOOL OF LONDON
S. W. A. KUPER
DEPARTMENTS OF PATHOLOGY, BROMPTON AND HAMMERSMITH HOSPITALS, LONDON
NOEL WALLACE
DEI’ARTMENT OF RADIOTHERAPY, ROYAL MARSDEN IIOSPITAL, LONDON
AND
J. I. BURN
DEPARTMENT OP SURGERY, HAMMERSMITH HOSPITAL AND POSTGRADUATE MEDICAL SCHOOL OF I.ONI)ON
PATIENTSwith previously slow-growing malignant of squamous-cell carcinoma they found that the incitumours may deteriorate rapidly and die of widespread dence of metastases was not increased by biopsy.
metastases shortly after surgical intervention, possibly Maun and Dunning (1946)found that biopsy did
as a result of the dissemination of tumour cells by the not alter significantly the incidence of metastases nor
trauma of operation. I n certain circumstances opera- the average survival period in experimental rats.
tive manipulation can release emboli of tumour cells Robbins, Brothers, Eberhart, and Quan (1954)could
into the circulation. Mimpriss and Birt (1949)and find no significant difference in the prognosis between
Masson and Rranwood (1955)described fatal pul- patients who were submitted to aspiration biopsy for
monary emboli of tumour fragments released from cancer of the breast and those who were not. Pierce,
the renal veins during mobilization of hyper- Clagett, McDonald, and Gage (1956)found no difnephromas, and various animal experiments seem to ference in the 5-year survivals between patients with
confirm that local trauma and manipulation of tumours breast cancer referred to the Mayo Clinic after biopsy
play a part in dissemination. Knox (1922)found a and a varying delay, and those referred without
significant increase in metastases when certain trans- biopsy. If is of interest, however, that those who had
plantable animal tumours were subjected to repeated excisional biopsies fared significantly better than those
massage, and Peyton (1940)found a similar increase who had incisional ones.
when tumours were removed after local infiltration
The recent development of techniques for the
with 0.5 per cent procaine. Young, Lumsden, and isolation of circulating cancer cells (Engell, 1955;
Stalker (1950)found that firm palpation of normal and Malmgren, Pruitt, Del Vecchio, and Potter, 1958;
neoplastic rabbit testes raised tissue pressure to levels Roberts, Watne, McGrath, McGrew, and Cole,
above that in veins. Thus trauma might increase dis- 1958;Kuper, Bignall, and Luckcock, 1961)has made
semination by forcing cells into vascular channels.
it possible to examine this problem by more direct
Biopsy of tumours might be dangerous if trauma methods. Observations by Cole and his colleagues
causes dissemination, and Czerny (1g13),quoted by at the University of Illinois have suggested that, in
Paterson and Nuttall (I939), has described it as ‘a some patients, cancer cells may appear in the bloodcriminal act ’. Paterson and Nuttall (1939)pointed stream during surgical operations, and in some cases
out that this view was based largely on observation of showers of cells appear to have been liberated at the
individual cases, and in a controlled study of 166cases time of operation (Cole, McDonald, Roberts, and