Mechanical properties of native and acellular temporal muscle fascia for surgical reconstruction and computational modelling purposes

Functional adaptation of the infant craniofacial system to mechanical loadings arising from masticatory forces

The morphology and biomechanics of infant crania undergo significant changes between the pre- and post-weaning phases due to increasing loading of the masticatory system. The aims of this study were to characterize the changes in muscle forces, bite forces and the pattern of mechanical strain and stress arising from the aforementioned forces across crania in the first 48 months of life using imaging and finite element methods. A total of 51 head computed tomography scans of normal individuals were collected and analysed from a larger database of 217 individuals. The estimated mean muscle forces of temporalis, masseter and medial pterygoid increase from 30.9 to 87.0 N, 25.6 to 69.6 N and 23.1 to 58.9 N, respectively (0-48 months). Maximum bite force increases from 90.5 to 184.2 N (3-48 months). There is a change in the pattern of strain and stress from the calvaria to the face during postnatal development. Overall, this study highlights the changes in the mechanics of the craniofacial system during normal development. It further raises questions as to how and what level of changes in the mechanical forces during the development can alter the morphology of the craniofacial system.

Finite element analysis of repairing tympanic membrane perforation using autologous graft material and biodegradable bionic cobweb scaffold

BACKGROUND AND OBJECTIVE

As for repairing the perforated tympanic membranes (TM), temporalis fascia and tragal cartilage are popular in clinics as autologous graft materials. However, there is a significant hearing loss after repairing the TM with autologous graft materials, which needs to be addressed in biomechanical engineering.

METHODS

The finite element model of normal middle ear is improved from two aspects: the repair method of tympanic fibrous layer and the bionic spider web tympanic scaffold. By creating the solid-shell coupling condition and strong coupling boundary condition to simulate the repair, TM umbo and stapes footplate displacement-frequency response are explored in 200-8000 Hz.

RESULTS

The tympanic membrane perforation (TMP) causes a significant conductive hearing loss in high frequency region, which is positively correlated with perforation area. Both temporalis fascia and tragal cartilage still perform a certain degree of high-frequency hearing loss after repairing TMP. The TM attachment the magnesium alloy scaffold (MAS) prevents appropriately the high frequency hearing loss after autologous graft repair and makes the sound transmission closer to the normal condition. Significantly, the density of graft material has a negative effect on high-frequency sound transmission without the MAS. The modal-motion of TM repaired with temporalis fascia and tragal cartilage is improved significantly after attaching the MAS. In addition, the MAS restores effectively the configuration and vibration frequency of the repaired TM, which is similar to that of the native TM.

CONCLUSION

The area size of TMP is studied through the finite element method, which includes autologous graft materials, the MAS, parameter sensitivity analysis, modal analysis of graft material and the MAS in biological form on the effect of middle ear sound transmission. Relevant conclusions provide some references for clinical trial protocol and the follow-up repair ideas of TM of tympanoplasty.

On a potential morpho-mechanical link between the gluteus maximus muscle and pelvic floor tissues

Stress urinary incontinence presents a condition not only found in female elderlies, but also in young athletes participating in high-impact sports such as volleyball or trampolining. Repeated jumps appear to be a predisposing factor. Yet the pathophysiology remains incompletely elucidated to date; especially with regard to the influence of the surrounding buttock tissues including gluteus maximus. The present study assessed the morpho-mechanical link between gluteus maximus and the pelvic floor female bodies. 25 pelves obtained from Thiel embalmed females were studied in a supine position. Strands of tissues connecting gluteus maximus with the pelvic floor obtained from 20 sides were assessed mechanically. Plastinates were evaluated to verify the dissection findings. In total, 49 hemipelves were included for data acquisition. The fascia of gluteus maximus yielded connections to the subcutaneous tissues, the fascia of the external anal sphincter and that of obturator internus and to the fascia of the urogenital diaphragm. The connection between gluteus maximus and the urogenital diaphragm withstood an average force of 23.6 ± 17.3 N. Cramér φ analyses demonstrated that the connections of the fasciae connecting gluteus maximus with its surroundings were consistent in the horizontal and sagittal planes, respectively. In conclusion, gluteus maximus is morphologically densely linked to the pelvic floor via strands of connective tissues investing the adjacent muscles. Though gluteus maximus has also been reported to facilitate urinary continence, the here presented morpho-mechanical link suggests that it may also have the potential to contribute to urinary stress incontinence. Future research combining clinical imaging with in-situ testing may help substantiate the potential influence from a clinical perspective.

Applied use of biomechanical measurements from human tissues for the development of medical skills trainers: a scoping review

OBJECTIVE

The objective of this review was to identify quantitative biomechanical measurements of human tissues, the methods for obtaining these measurements, and the primary motivations for conducting biomechanical research.

INTRODUCTION

Medical skills trainers are a safe and useful tool for clinicians to use when learning or practicing medical procedures. The haptic fidelity of these devices is often poor, which may be because the synthetic materials chosen for these devices do not have the same mechanical properties as human tissues. This review investigates a heterogeneous body of literature to identify which biomechanical properties are available for human tissues, the methods for obtaining these values, and the primary motivations behind conducting biomechanical tests.

INCLUSION CRITERIA

Studies containing quantitative measurements of the biomechanical properties of human tissues were included. Studies that primarily focused on dynamic and fluid mechanical properties were excluded. Additionally, studies only containing animal, in silico , or synthetic materials were excluded from this review.

METHODS

This scoping review followed the JBI methodology for scoping reviews and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sources of evidence were extracted from CINAHL (EBSCO), IEEE Xplore, MEDLINE (PubMed), Scopus, and engineering conference proceedings. The search was limited to the English language. Two independent reviewers screened titles and abstracts as well as full-text reviews. Any conflicts that arose during screening and full-text review were mediated by a third reviewer. Data extraction was conducted by 2 independent reviewers and discrepancies were mediated through discussion. The results are presented in tabular, figure, and narrative formats.

RESULTS

Data were extracted from a total of 186 full-text publications. All of the studies, except for 1, were experimental. Included studies came from 33 countries, with the majority coming from the United States. Ex vivo methods were the predominant approach for extracting human tissue samples, and the most commonly studied tissue type was musculoskeletal. In this study, nearly 200 unique biomechanical values were reported, and the most commonly reported value was Young's (elastic) modulus. The most common type of mechanical test performed was tensile testing, and the most common reason for testing human tissues was to characterize biomechanical properties. Although the number of published studies on biomechanical properties of human tissues has increased over the past 20 years, there are many gaps in the literature. Of the 186 included studies, only 7 used human tissues for the design or validation of medical skills training devices. Furthermore, in studies where biomechanical values for human tissues have been obtained, a lack of standardization in engineering assumptions, methodologies, and tissue preparation may implicate the usefulness of these values.

CONCLUSIONS

This review is the first of its kind to give a broad overview of the biomechanics of human tissues in the published literature. With respect to high-fidelity haptics, there is a large gap in the published literature. Even in instances where biomechanical values are available, comparing or using these values is difficult. This is likely due to the lack of standardization in engineering assumptions, testing methodology, and reporting of the results. It is recommended that journals and experts in engineering fields conduct further research to investigate the feasibility of implementing reporting standards.

REVIEW REGISTRATION

Open Science Framework https://osf.io/fgb34.

Sample size considerations in soft tissue biomechanics

Biomechanical experiments help link tissue morphology with load-deformation characteristics. A tissue-dependent minimum sample number is indispensable to obtain accurate material properties. Stress-strain properties were retrieved from human dura mater and scalp skin, exemplifying two distinct soft tissues. Minimum sample sizes necessary for a stable estimation of material properties were obtained in a simulation study. One-thousand random samples were sequentially drawn for calculating the point at which a majority of the estimators settled within a corridor of stability at given tolerance levels around a 'complete' reference for the mean, median and coefficient of variation. Stable estimations of means and medians can be achieved below sample sizes of 30 at a ± 20%-tolerance within 80%-conformity for scalp skin and dura. Lower tolerance levels or higher conformity dramatically increase the required sample size. Conformity was barely ever reached for the coefficient of variation. The parameter type appears decisive for achieving conformity. STATEMENT OF SIGNIFICANCE: Biomechanical trials utilizing human tissues are needed to obtain material properties for surgical repair, tissue engineering and modeling purposes. Linking tissue mechanics with morphology helps elucidate form-function relationships, the 'morpho-mechanical link'. For material properties to be accurate, it is vital to examine a minimum number of samples. This number may vary between tissues, and the effects of intrinsic tissue characteristics on data accuracy are unclear to date. This study used data obtained from human dura and skin to compute minimum sample sizes required for estimating material properties at a stable level. It was shown that stable estimations are possible at a ± 20%-tolerance within 80%-conformity below sample sizes of 30. Higher accuracy warrants much higher sample sizes for most material properties.

Choosing the optimal mandible position for inferior alveolar nerve block (IANB) using finite element analysis

BACKGROUND

One of the most popular methods of local anesthesia in dentistry, inferior alveolar nerve block (IANB) involves the blockade of the inferior alveolar nerve (IAN) and lingual nerve (LN) in the pterygomandibular space. Despite the large number of works describing the contents of this space, the spatial displacements of the anatomical structures of this area at different positions of the mandible have not been sufficiently studied. The aim of our study was to study the spatial movements of the IAN and inferior alveolar artery (IAA) at various positions of the mandible using computer simulation and finite element analysis to find the safest way to conduct IANB.

MATERIALS AND METHODS

Reverse engineering was used to create a model of the cranial base and the mandible based on computed tomography (CT) data obtained from patient N (male, 24 years old), the arteries of the head and neck were designed from the data of multiphase angiography of patient M (female, 61 years old). Masticatory muscles, sphenomandibular ligament, temporomandibular joint and mandibular nerve were modeled in the SolidWorks software package based on an open database of anatomical structures. The finite element grid was generated in the Solidworks software. In the first series of experiments, the displacement of the mandible was modeled along the vertical axis down by 48 mm (maximum opening of the mouth), in the second series, the jaw was displaced vertically by 48 mm with a simultaneous transversal movement of 10 mm, in the third series, the jaw was displaced along the vertical axis down by 34 mm and transversally by 22 mm.

RESULTS

The largest distance between IAN and IAA was noted in the third series of experiments. The distance between the nerve and the vessel was minimal in the first series, with an open mouth without lateral displacements.

CONCLUSION

The generated computer model opens new possibilities for studying the dynamic anatomy of the pterygomandibular space. The results of this study can be used for further experimental and clinical trials to find the safest approach to the implementation of IANB, as well as applied in the practice of the educational process.

Effect of closing material on hearing rehabilitation in stapedectomy and stapedotomy: A finite element analysis

Stapedotomy or stapedectomy operations are often performed to treat otosclerosis. During the operation, the space created by bone removal is usually filled with a closing material such as fat or fascia. In this study, the effect of the Young's modulus of the closing material on the hearing level was investigated through the 3D finite element model of a human head including auditory periphery. The Young's moduli of the closing material used to implement stapedotomy and stapedectomy conditions in the model were varied from 1 kPa to 24 MPa. The results showed that the hearing level improved when the closing material was more compliant after stapedotomy. Therefore, when the stapedotomy was performed using fat whose Young's modulus is lowest among the potential closing materials, the hearing level recovered the best among all simulated cases. On the other hand, in stapedectomy, the Young's modulus did not have the linear relationship between the hearing level and the compliance of the closing material. Hence, the Young's modulus causing the best hearing rehabilitation in stapedectomy was found not at the end of the investigated range of Young's modulus but somewhere in the middle of the given range.

Fatigue Testing of Human Flexor Tendons Using a Customized 3D-Printed Clamping System

Improved surgical procedures and implant developments for ligament or tendon repair require an in-depth understanding of tissue load-deformation and fatigue properties. Cyclic testing will provide crucial information on the behavior of these materials under reoccurring loads and on fatigue strength. Sparse data are available describing soft tissue behavior under cyclic loading. To examine fatigue strength, a new technology was trialed deploying 3D-printing to facilitate and standardize cyclic tests aiming to determine tendon fatigue behavior. Cadaveric flexor digitorum tendons were harvested and mounted for tensile testing with no tapering being made, using 3D-printed clamps and holder arms, while ensuring a consistent testing length. Loads ranging between 200 to 510 N were applied at a frequency of 4 Hz, and cycles to failure ranged between 8 and >260,000. S–N curves (Woehler curves) were generated based on the peak stresses and cycles to failure. Power regression yielded a combined coefficient of determination of stress and cycles to failure of R2 = 0.65, while the individual coefficients for tissues of single donors ranged between R2 = 0.54 and R2 = 0.88. The here-presented results demonstrate that S–N curves of human tendons can be obtained using a standardized setting deploying 3D-printing technology.

Experimental characterisation of porcine subcutaneous adipose tissue under blunt impact up to irreversible deformation

A deeper understanding of the mechanical characteristics of adipose tissue under large deformation is important for the analysis of blunt force trauma, as adipose tissue alters the stresses and strains that are transferred to subjacent tissues. Hence, results from drop tower tests of subcutaneous adipose tissue are presented (i) to characterise adipose tissue behaviour up to irreversible deformation, (ii) to relate this to the microstructural configuration, (iii) to quantify this deformation and (iv) to provide an analytical basis for computational modelling of adipose tissue under blunt impact. The drop tower experiments are performed exemplarily on porcine subcutaneous adipose tissue specimens for three different impact velocities and two impactor geometries. An approach based on photogrammetry is used to derive 3D representations of the deformation patterns directly after the impact. Median values for maximum impactor acceleration for tests with a flat cylindrical impactor geometry at impact velocities of 886 mm/s, 1253 mm/s and 2426 mm/s amount to 61.1 g, 121.6 g and 264.2 g, respectively, whereas thickness reduction of the specimens after impact amount to 16.7%, 30.5% and 39.3%, respectively. The according values for tests with a spherically shaped impactor at an impact velocity of 1253 mm/s are 184.2 g and 78.7%. Based on these results, it is hypothesised that, in the initial phase of a blunt impact, adipose tissue behaviour is mainly governed by the behaviour of the lipid inside the adipocytes, whereas for further loading, contribution of the extracellular collagen fibre network becomes more dominant.

On the correlations of biomechanical properties of super-imposed temporal tissue layers and their age-, sex-, side- and post-mortem interval dependence

Obtaining biomechanical properties of biological tissues for simulation purposes or graft developments is time and resource consuming. The number of samples required for biomechanical tests could be reduced if the load-deformation properties of a given tissue layer could be estimated from adjacent layers or if the biomechanical parameters were unaffected by age, bodyside, sex or post-mortem interval. This study investigates for the first time potential correlations of multiple super-imposed tissue layers using the temporal region of the human head as an area of broad interest in biomechanical modelling. Spearman correlations between biomechanical properties of the scalp, muscle fascia, muscle, bone and dura mater from up to 83 chemically unfixed cadavers were investigated. The association with age, sex and post-mortem interval was assessed. The results revealed sporadic correlations between the corresponding layers, such as the maximum force (r = 0.43) and ultimate tensile strength (r = 0.33) between scalp and muscle. Side- and age-dependence of the biomechanical properties were different between the tissue types. Strain at maximum force of fascia (r = -0.37) and elastic modulus of temporal muscle (r = 0.26) weakly correlated with post-mortem interval. Only strain at maximum force of scalp differed significantly between sexes. Uniaxial biomechanical properties of individual head tissue layers can thus not be estimated solely based on adjacent layers. Therefore, correlations between the tissues' biomechanical properties, anthropometric data and post-mortem interval need to be established independently for each layer. Sex seems not to be a relevant influencing factor for the passive tissue mechanics of the here investigated temporal head tissue layers.

Elastic Fibres in the subcutaneous tissue: Is there a difference between superficial and muscular fascia? A cadaver study

BACKGROUND

In last years the role of fascia in proprioception and pain has been confirmed in numerous papers, but the real structure of fasciae is not still entirely known. To date, many studies have evaluated the elastic fibres in arteries, ligaments, lungs, epidermis and dermis, but only two studies exist about the elastic fibres in the fasciae, and they did not distinguish between superficial (in the subcutaneous tissue) and deep/muscular fasciae. The aim of the study was to assess the percentage of elastic fibres between superficial and deep fascia.

MATERIALS AND METHODS

Three full thickness specimens (proximal, middle and distal respectively) were taken from each of four regions of the thigh of three non-embalmed cadavers: the anterior (Ant), the lateral (Lat), the posterior (Post) and the medial (Med) aspect. Thus, a total of 12 specimens were collected from each analysed thigh and histological Weigert Van Gieson stains was performed. Three sections per specimen were considered for the morphometric analysis.

RESULTS

In all the specimens the superficial and deep fasciae were clearly recognizable. The difference in percentage of elastic fibres between superficial and deep fasciae in same region for all four was highly significant (p < 0.001). They are abundant in the superficial fascia than deep fascia.

CONCLUSIONS

In the light of these findings is evident that the superficial (in the subcutaneous tissue) and deep fasciae have different elasticity. This difference may improve grading of fascial dysfunction in dermatological diseases as burns, scars and lymphedema to better plan treatments.

Why heel spurs are traction spurs after all

It is unclear whether plantar and posterior heel spurs are truly pathological findings and whether they are stimulated by traction or compression forces. Previous histological investigations focused on either one of the two spur locations, thereby potentially overlooking common features that refer to a uniform developmental mechanism. In this study, 19 feet from 16 cadavers were X-ray scanned to preselect calcanei with either plantar or posterior spurs. Subsequently, seven plantar and posterior spurs were histologically assessed. Five spur-free Achilles tendon and three plantar fascia entheses served as controls. Plantar spurs were located either intra- or supra-fascial whereas all Achilles spurs were intra-fascial. Both spur types consistently presented a trabecular architecture without a particular pattern, fibrocartilage at the tendinous entheses and the orientation of the spur tips was in line with the course of the attached soft tissues. Spurs of both entities revealed tapered areas close to their bases with bulky tips. Achilles and plantar heel spurs seem to be non-pathological calcaneal exostoses, which are likely results of traction forces. Both spur types revealed commonalities such as their trabecular architecture or the tip direction in relation to the attached soft tissues. Morphologically, heel spurs seem poorly adapted to compressive loads.

The dynamic impact behavior of the human neurocranium

Realistic biomechanical models of the human head should accurately reflect the mechanical properties of all neurocranial bones. Previous studies predominantly focused on static testing setups, males, restricted age ranges and scarcely investigated the temporal area. This given study determined the biomechanical properties of 64 human neurocranial samples (age range of 3 weeks to 94 years) using testing velocities of 2.5, 3.0 and 3.5 m/s in a three-point bending setup. Maximum forces were higher with increasing testing velocities (p ≤ 0.031) but bending strengths only revealed insignificant increases (p ≥ 0.052). The maximum force positively correlated with the sample thickness (p ≤ 0.012 at 2.0 m/s and 3.0 m/s) and bending strength negatively correlated with both age (p ≤ 0.041) and sample thickness (p ≤ 0.036). All parameters were independent of sex (p ≥ 0.120) apart from a higher bending strength of females (p = 0.040) for the 3.5 -m/s group. All parameters were independent of the post mortem interval (p ≥ 0.061). This study provides novel insights into the dynamic mechanical properties of distinct neurocranial bones over an age range spanning almost one century. It is concluded that the former are age-, site- and thickness-dependent, whereas sex dependence needs further investigation.

Assessment of plantaris and peroneus tertius tendons as graft materials for ankle ligament reconstructions - A cadaveric biomechanical study

Both the plantaris tendon and the peroneus tertius tendon are used as auto- and allogenous graft materials to reconstruct the ankle ligament complex. However, it is unclear to what extent these graft materials resemble the load-deformation behavior of the ankle ligaments. A total of 34 human ankle ligaments and 35 tendons were assessed mechanically deploying a quasi-static tensile testing setup. Tendons were significantly stiffer (median elastic moduli: plantaris tendon = 465.7 MPa, peroneus tertius tendon = 338.5 MPa, medial ligament = 61.4 MPa, lateral ligament = 49.3 MPa; p ≤ 0.035), but more distensible (median strain at maximum force: plantaris tendon = 15.1%, peroneus tertius tendon = 15.3%, medial ligament = 9.3%, lateral ligament = 9.6%; p ≤ 0.008) and mechanically tougher (median ultimate tensile strength: plantaris tendon = 51.0 MPa, peroneus tertius tendon = 40.5 MPa, medial ligament = 4.1 MPa, lateral ligament = 3.5 MPa; p ≤ 0.033) when compared to medial and lateral ankle ligaments. The lateral ligaments of the right ankle were significantly tougher compared to the left side (p = 0.015). The elastic modulus of the medial ligament (r = 0.489, p = 0.045) and the peroneus tertius tendon (r = 0.517, p = 0.014) yielded an age-dependent increase. Both tendons seem biomechanically suitable graft materials to replace the medial and lateral ankle ligaments during physiological loading. The age-dependent increase in tissue elastic properties of the medial vs. lateral ankle ligaments, and differences in ultimate tensile strength between the lateral ligaments left vs. right, may reflect the complex asymmetric loading behavior of both ankle ligaments.

Surface coating and speckling of the human iliotibial tract does not affect its load-deformation properties

Stochastic surface patterns form an important requirement to facilitate digital image correlation and to subsequently quantify material properties of various tissues when loaded and deformed without artefacts arising from material slippage. Depending on the samples' natural colour, a surface pattern is created by speckling with colour or dye only, or it requires combined surface coating and speckling before to enhance the contrast, to facilitate high-quality data recording for mechanical evaluation. However, it is unclear to date if the colours deployed for coating and speckling do significantly alter the biomechanical properties of soft tissues. The given study investigated the biomechanical properties of 168 human iliotibial tract samples as a model for collagen-rich soft tissues, separated into four groups: untreated, graphite speckling only, water-based coating plus graphite speckling and solvent-based coating plus graphite speckling following a standardized approach of application and data acquisition. The results reveal that elastic modulus, ultimate tensile strength and strain at maximum force of all groups were similar and statistically non-different (p ≥ 0.69). Qualitatively, the speckle patterns revealed increasing contrast differences in the following order: untreated, graphite speckling only, water-based coating plus graphite speckling and solvent-based coating plus graphite speckling. Conclusively, both coating by water- and solvent-based paints, as well as exclusive graphite speckling, did not significantly influence the load-deformation parameters of the here used human iliotibial tract as a model for collagen-rich soft tissues. In consequence, water- and solvent-based coating paints seem equally suitable to coat collagen-rich soft tissues for digital image correlation, resulting in suitable speckle patterns and unbiased data acquisition.

Load-deformation characteristics of acellular human scalp: assessing tissue grafts from a material testing perspective

Acellular matrices seem promising scaffold materials for soft tissue regeneration. Biomechanical properties of such scaffolds were shown to be closely linked to tissue regeneration and cellular ingrowth. This given study investigated uniaxial load-deformation properties of 34 human acellular scalp samples and compared these to age-matched native tissues as well as acellular dura mater and acellular temporal muscle fascia. As previously observed for human acellular dura mater and temporal muscle fascia, elastic modulus (p = 0.13) and ultimate tensile strength (p = 0.80) of human scalp samples were unaffected by the cell removal. Acellular scalp samples showed a higher strain at maximum force compared to native counterparts (p = 0.02). The direct comparison of acellular scalp to acellular dura mater and temporal muscle fascia revealed a higher elasticity (p < 0.01) and strain at maximum force (p = 0.02), but similar ultimate tensile strength (p = 0.47). Elastic modulus and ultimate tensile strength of acellular scalp decreased with increasing post-mortem interval. The elongation behavior formed the main biomechanical difference between native and acellular human scalp samples with elastic modulus and ultimate tensile strength being similar when comparing the two.