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146 A. Gefen
For example, we have designed, developed and produced a laboratory phantom
of an exuding sacral PU/PI which mimics an active wound environment in an
anatomically−and pathophysiologically-realistic form (Fig. 1a) (Lustig et al.,
2021b; Lustig and Gefen, 2022b). The robotic PU/PI includes a plastic replica of
the pelvis bones and soft tissue substitutes made of silicone casted to the shape of
an adult male buttocks. A cylindrical wound geometry has been carved at the sacral
region, into which disposable sponge components are inserted to simulate different
wound-beds, with either a crater shape or undermining. To simulate the secretion of
exudate, we embedded a hierarchal tubing system within the silicone volume which
is connected to an electromechanical syringe pump. This flow system allows the
release of exudate substitutes at controlled, pre-determined flow volumes and rates.
Replica fluids are synthetic, containing, e.g., a xanthan gum-based thickener, and
can be produced at a range of viscosities and pH levels which resemble those of real
exudates (Lustig et al., 2021b; Lustig and Gefen, 2022b). Five thermocouples are
further embedded around the simulated wound to monitor spatial temperatures
during testing, while an adjustable-distance infrared lamp stationed above the
phantom acts as a heat source (Lustig et al., 2021b; Lustig and Gefen, 2022b). This
PU/PI robotic wound system facilitated, for the first time, experiments that expose
treatment dressings to exudate-like fluids at the mechanical, thermodynamic and
use conditions which duplicate real-world settings, as opposed to simple immersion
and weighing tests that are commonly accepted in the wound dressing industry for
testing fluid handling (Lustig et al., 2021b; Lustig and Gefen, 2022b). Moreover,
pre-use and post-use physical and mechanical studies o f dressing products and
simulated wound-beds, such as measurements of the ratio of fluid mass returned to
the wound-bed versus the mass retained in the dressing, or tensile testing of the
used dressings, generate fundamental new efficacy data that shed light on the
expected performance of the relevant dressing products in a clinical setting, under
real-world conditions (Figs. 1, 2).
These robotic-based testing methods for advanced wound dressings, shown in
Fig. 1, focus on clinical relevance, as well as on the standardisation and automation
of contemporary laboratory measurements of dressing performance. Utilisation of
these novel robotic-based test methods for characterising the performance of gelling
fibre dressings is demonstrated in Fig. 2, and facilitates the identification of key
performance differences between products offered for similar clinical indications,
particularly sorptivity and durability. Specifically, the clinically-relevant testing
using robotic wounds revealed differences across products that apparently belong to
the same “gelling fibre” family, but differ rema rkably in materials, structure and
composition, and thereby, in laboratory and clinical performance (Fig.
et al., 2021b; Lustig and Gefen, 2022a, 2022b; Orlov et al., 2022
For example, a
).
2)
(Lustig
robotic phantom system containing six identical wound simulant units has been
developed and employed to determine the synergy in fluid handling of two commercially available silver-containing gelling fibre primary dressings when used with
a secondary foam -based dressing, as per clinical practice. The durability of the
primary dressings post simulated use was further investigated, through tensile
mechanical testing. The silver-containing gelli
ng fibre primary dressing
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Fig. 2 Example results obtained by means of the robotic wound systems: a Absorbency and
retention of a viscous exudate simulant and sharing of the exudate simulant between primary and
secondary wound dressings after 5 h of simulated use, in a diabetic foot ulcer (DFU) and a sacral
pressure ulcer/injury (PU/PI) robotic systems. The primary dressing was the Exufiber® gelling
fibre dressing (Mölnlycke Health Care, Gothenburg, Sweden) versus a comparator commercial
gelling fi bre dressing, and the secondary dressing was Mepilex® Border Flex or Mepilex® Border
Sacrum for the DFU and PU/PI robotic wound systems, respectively. b The durability of the tested
primary gelling fibre dressing after 5 h of simulated use in the DFU robotic wound, quantified as
the strain energy density to failure (Lustig et al., 2021b; Lustig and Gefen, 2022a, 2022b; Orlov
et al., 2022)
148 A. Gefen
incorporating polyvinyl alcohol (PVA) fibres (Exufiber® Ag + manufactured by
Mölnlycke Health Care, Gothenburg, Sweden) delivered greater fluid amounts for
absorbency and retention by the secondary foam dressing (sorptivity), approximately twofold and 1.5-fold more than the comparator silver-containing primary
dressing incorporating sodium carboxymethyl cellulose CMC) fibres, after 10 and
15 h of simulated use, respectively (Orlov et al., 2022). The above PVA fibre-based
primary dressing type further demonstrated greater post-use mechanical strength
that was *4-times and *6-times greater than that of the comparator primary
dressing, when the latter dressing was tested out-of-alignment with its seams, after
10 and 15 h of usage, respectively (Orlov et al.,
primary dressing type thus exhibited better sorptivity and durability than the
comparator product, but this could only be detected through the robotic
wound-based, clinically-relevan t testing approach (Orlov et al., 2022).
The above results exemplify that gelling fibre dressings, belonging to the same
product category but
constructed differently yield remarkably distinct performance metrics when tested
against each other. Accordingly, the robotic wound systems (Fig. 1) contribute
towards the development of clinically-relevant testing methods for wound dressings
and importantly, progress the standardisation and automation of the performance
measurements of dressings. These innovative robotic phantom studies reported in
our aforementioned published work are pivotal for improving the decision-making
process of clinicians and regulatory personnel, by basing their choices of wound
dressings on quantitative efficacy research. This should ultimately improve patient
safety, the effectiveness of treatments and the overall quality of the delivered wound
care.
made of different base materials (i.e., PVA versus CMC) and
2022). The PVA fibre-based
Computational Modelling Reveals the Efficacy of Wound
Dressings in Prophylactic Use
Non-invasive CPAP ventilation masks are commonly used for respiratory support
where intubation or surgical airway procedure can be avoided. The se masks were
massively used during the COVID-19 pandemic as a first line of respiratory support, in an attempt to avoid invasive ventilation in patients who responded to the
non-invasive respiration. However, prolonged use of CPAP masks involves risk to
the integrity and viability of facial tissues, which are subjected to sustained
deformations caused by tightening the mask and microclimate conditions (Gefen
et al., 2022b). The risk of developing such MDRPUs can be reduced by providing
additional cushioning at the mask -face contact areas. We determined differences in
facial skin and underlying soft tissue stresses while a CPAP mask is being used,
with or without cushioning using cuts of the Mepilex® Lite (Mölnlycke Health
Care, Gothenburg, Sweden) dressings (Peko Cohen et al., 2019). First, we developed a force measurement system consisting of five force sensors connected to a
microcontroller board. The aforementioned system was used to experimentally
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determine local forces applied to facial skin at the bridge of the nose, cheeks and
chin of healthy subjects while using a medium-size CPAP mask. Each subject was
tested with or without Mepilex® Lite dressings cut to the shape of their individual
face. Next, we used the Scan-IP module of Simpleware® to generate a
three-dimensional computational head model using the visible human project®
image database, and segmented and meshed the tissues, mask and dressing cuts
(Peko Cohen et al., 2019) (Fig. 3). Using the finite element (FE) method (FEBio
Fig. 3 The intensity of facial stress concentrations at the nasal bridge, cheeks and chin, visualised
by means of a computational (finite element) model of an adult male head with simulated
continuous positive airway pressure (CPAP) mask mounted and tightened to the face (the mask is
not shown here to visualise the facial stress concentrations). This modelling framework facilitates
quantitative investigations of the protective efficacy delivered by dressing cuts applied to avoid a
CPAP-related injury (e.g., using the foam-based Mepilex® Lite dressing type manufactured by
Mölnlycke Health Care, Gothenburg, Sweden) on the facial stress concentration levels (Peko
Cohen et al., 2019)
150 A. Gefen
software suite), we delivered the measured compressive forces per site of the face to
the respective skin sites in the model. We compared maximal effective, shear and
compressive tissue stresses, as well as strain energy densities (SED) in facial skin
and subdermally, with or without the dressing cuts applied as cushioning. Application of the Mepilex® Lite dressing cuts substantially alleviated the exposure of
facial skin and subdermal tissues to elevated stresses w
9). The Mepilex® Lite dressings have
case, as reported in Peko Cohen et al., (
shown substantial biomechanical effectiveness in alleviating facial skin and
underlying tissue deformations, by providing localised cushioning to the tissues
at-risk which is only possible if there is adequate stiffness matching between the
dressing and skin (Gefen, 2021b). Of note, use of the FE method for this purpose
(Fig. 3) not only identifies and visualises the tissue stress concentrations in compression, tension and shear, but also allows to determine their diffusion into subdermal tissues (Peko Cohen et al.,
measurements are not capable of achieving.
The ability of the aforementioned foam-based dressings to alleviate localised and
sustained facial soft tissue
gradients between the skin and the protecting dressing cuts, because the stiffness of
the foam material in the dressing is relatively close to that of native skin (Gefen,
2021b). In fact, the ratio of the compressive stiffness between the material of the
dressing intended for prophylaxis and that of native skin, termed the compressive
stiffness matching ratio (CSMR) is a highly useful, intuitive and easy-to-implement
biomechanical performance measure in this regard. Based on this CSMR criterion,
hydrocolloid-based wound dressings which are popular for facial skin protection
from MDRPUs, probably due to historical reasons and availability, exhibit poor
biomechanical prophylactic efficacy in protecting facial skin from MDRPUs
associated with use of CPAP masks (Gefen, 2021b). Foam-based dressings such as
the Mepilex® Lite dressing, which have substantially lower stiffness than hydrocolloids, are much more suitable for prevention of MDRPUs due to their good
stiffness matching with skin, i.e., foam-based dressings have a CSMR value which
is typically much closer to unity than that of hydrocolloid-based dressings (Gefen,
2021b).
loads (Fig. 3) is achieved by avoiding sharp stiffness
201
2019)
, which traditional interface pressure
ith respect to the no-dressing
Summary and Conclusions
The effectiveness of wound dressing performance in exudate management when
applied to treatment, and in the redistribution of skin and subdermal tissue loads
when used prophylactically, are commonly and typically gauged in oversimplified,
non-realistic setups. Examples of these are where wound dressing specimens are
submersed in vessels containing watery solution s to evaluate their absorbency, or
by means of interface pressure measurements in the context of PU/PI prevention.
We have developed a portfolio of clinically-relevant, experimental and
Innovation in Laboratory Evaluations of the Performance … 151
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computationally-based laboratory test configurations for dressings used in treatment
and preventative applications.
In the context of application of wound dressings for
treatment, we developed
advanced test methods and robotic wound systems for evaluating two key fluid–
structure interaction concepts, that is, sorptivity−the ability of wound dressings to
transfer exudate including viscous wound fluids away from the wound-bed by
capillary action; and durability−the capacity of dressings to maintain their structural
integrity over time and particularly, at removal events (Figs. 1, 2). In the PU/PI
prevention arena, we developed sophisticated, anatomically−accurate computational models of parts of the human body to evaluate the biomechanical protective
efficacy of dressings in redistributing and alleviating subdermal tissue loads due to
bodyweight or medical device-related forces (Fig. 3). Our published work referenced here details the specific materials and methods for each laboratory test type.
The purpose of this chapter is to provide a high-level review, with some illustrative
examples, regarding our recent published research concerning the development of
these testing methods for wound dressings, focusi ng on the clinical relevance of the
tests as well as on the standardisation and automation of the laboratory measurements of dressing performance. The current chapter further demonstrates that differences across product performance metrics can be detected by means of the above
advanced test methods, including for products that supposedly belong to the same
families, or products that are used for the same clinical purpose. According to the
fundamental structure–function principle in engineering, these differences in
dressing performance always relate to the materials, structure and composition of
the tested dressings, and our currently reported test methods are able to make these
connections between the structure and the performance metrics of wound dressings,
in either treatment or preventative clinical applications.
Acknowledgements The research work reviewed in this chapter was supported by Mölnlycke
Health Care (Gothenburg, Sweden).
References
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Atypical Wounds and Wounds
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Resulting from Infection
Massimo Papi and Ersilia Fiscarelli
Abstract
Atypical cutaneous ulcers are caused by inflammatory, neoplastic, vasculopathic,
haematological, drug-induced and infectious etiologies.They present in unusual
sites and have abnormal clinical aspects. They are underes timated. They may be
clinically difficult to recognize and complicated in their features by the possible
concurrent presence of mul tiple pathogenetic processes. The absence of response
of a chronic ulcer to standard therapies requires a more specific diagnostic
investigation. Diagnosis involves obtaining an accurate history and performing
clinical examination and additional tests. A skin biopsy is fundamental to have a
basic information on the type of atypical ulcer.
Keywords
Atypical ulcersInflammatory ulcersNeoplastic ulcersMicro-thrombotic
ulcers Infectious ulcers
M. Papi (&)
Chair ADOI (National Study Group Vascular Dermatology and Vulnology), Rome, Italy
e-mail: ma.papi57@gmail.com
E. Fiscarelli
Clinical Management and Technological Innovations, Research Center S. Paolo,
Bambin Gesù Hospital, IRCCS, Rome, Italy
R. Mani (ed.), Chronic Wound Management,
https://doi.org/10.1007/978-3-031-26110-7_9
153© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023
154 M. Papi and E. Fiscarelli
Introduction
Chronic skin ulcers are mainly diagnosed as venous, arterial, mixed
(venous-arterial), pressure on bone prominences-related or neuro-ischemic ulcers.
They represent most skin wounds.
Atypical wounds (AW) of the skin
accurate diagnosis, management, and specific treatment. Even if atypical ulcers for
their unusual aspect are likely difficult to obtain a standard care, the aim of our
present and future work will be to inform us about this delicate topic and to
standardize diagnostic strategies and treatmen ts (Mani et al. 2016).
AW are chronic skin ulcers which do not show clinical-histological aspects,
localization and response to therapies that are usually seen in most common ulcers
(Hoffman 2013). They may present features that the clinician has not previously
encountered. They are increasingly and properly diagnosed with the improvement
of investigative and diagnostic skills (Janowska et al. 2019).
AW result from several different pathogenetic processes. They can be summa-
rized as: neoplastic, haematologic (i.e. haemoglobin disorders, polycythaemia vera),
metabolic anomalies (i.e. calciphylaxis), inflammatory (i.e. vasculitis, pyoderma
gangrenosum), occlusive small vessel vasculopathies (i.e. coagulation anomalies,
micro-thrombosis, livedo vasculopathies), drug assumption (i.e. hydroxyurea) or
addiction (i.e. heroin-cocaine injection). Many other biological conditions may
determine difficult-to-diagnose atypical chronic skin ulcers above all in the case of
concurrent presence of venous-arterial insufficiency (double-hit effect).
A special chapter of atypical ulcers is primary cutaneous infection (Tang and
Kirsner 2012). Mycobacteria, Leishmania, Sporotrichum and skin parasites may be
the causative agents of many chronic and often disablin g wounds all over the world.
Gram + and gram-bacteria are responsible for severe complication of many skin
wounds but they may be the cause of primary-induced ulcers in immunocompromised, diabetic and elderly patients (i.e. ecthyma gangrenosum).
Clinical examination, specific diagnostic investigation, and additional tests are
required to diagnose AW. Despite recent emerging cutting-edge technologies
provide innovative pathways to make diagnose and to improve AW treatments skin
biopsy remains the first diagnostic step to obtain information about an undetermined chronic-cutaneous ulcer (Tottoli et al. 2020; Miteva and Romanelli 2012).
are a daily challenge for clinicians. They need
Neoplastic Ulcers
Chronic
non-melanoma skin
(Fig. 1).
skin ulcers can be caused by cutaneous neoplasms. They are mainly
cancer and, in a limited number of cases, cutaneous lymphoma
Atypical Wounds and Wounds Resulting from Infection 155
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Fig. 1 Cutaneous B-cell lymphoma initial presentation in a 45 yrs-old female
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