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Abstract Electrospinning is an outstanding manufacturing technique for producing nano-micro-scaled fibrous scaffolds comparable to biological tissues. However, the solvents used are normally hazardous for the health and the environment, which compromises the sustainability of the process and the industrial scaling. This novel study compares different machine learning models to predict how green solvents affect the morphology, topography and mechanical properties of gelatin-based scaffolds. Gelatin-based scaffolds were produced with different concentrations of distillate water (dH2O), acetic acid (HAc) and dimethyl sulfoxide (DMSO). 2214 observations, 12 machine learning approaches, including Generalised Linear Models, Generalised Additive Models, Generalised Additive Models for Location, Scale and Shape (GAMLSS), Decision Trees, Random Forest, Support Vector Machine and Artificial Neural Network, and a total of 72 models were developed to predict diameter of the fibres, inter-fibre separation, roughness, ultimate tensile strength, Young’s modulus and strain at break. The best GAMLSS models improved the performance of R2 with respect to the popular regression models by 6.868%, and the MAPE was improved by 21.16%. HAc highly influenced the morphology and topography; however, the importance of DMSO was higher in the mechanical properties. The addition of the morphological properties as covariates in the topographic and mechanical models enhanced their understanding.

Objectives Deep Brain Stimulation (DBS) is an effective, yet underused therapy for people living with Parkinson’s disease (PD) in whom tremor, motor fluctuations and/or dyskinesia are not satisfactorily controlled by oral medical therapy. Fear of vascular complications related to the operative procedure remains a strong reason for both the referrer and patient reluctance. We review the incidence of vascular complications in the first 600 patients with Parkinson’s disease treated at our centre by a single neurologist/neurosurgical team.Methods Surgical data routinely collected for patients who underwent DBS implantation for the management of PD between the years 2001–2023 was retrospectively reviewed. Incidences of vascular complication were analysed in detail, examining causal factors.Results Including reimplantations, 600 consecutive DBS patients underwent implantation with 1222 DBS electrodes. Three patients (0.50%) experienced vascular complications.Conclusion This vascular complication rate is at the low end of that reported in the literature. Risk mitigation strategies discussed include a consistent neurosurgical team, dual methodology target and trajectory planning, control of cerebrospinal fluid egress during the procedure, use of a specialised microelectrode recording (MER)/macrostimulation electrode without an introducing brain cannula and low number of MER passes. A reduced vascular complication rate may improve the acceptability of DBS therapy for both patients and referrers.

This paper aims to identify construction robotics' potential to reduce airborne virus transmission, review factors limiting the technology's adoption and highlight how similar barriers have been addressed in other industries. Construction robotics were identified and classified into 8 themes with 25 categories through a critical literature review. We undertook interviews with 4 construction contractors and conducted an online questionnaire with 32 experts from the UK (n=14) and China (n=18) who reviewed the robotic systems we identified and ranked the potential ability of each to reduce airborne virus transmission within the construction industry. The results of this study showed that construction robotics is not only beneficial to reduce airborne virus transmission, but may also help to reduce the spread of future contagious viruses. We found no significant difference (P>0.05) in practical usage and implementation barriers to construction robotics between the UK and China. Cost, training and limited awareness of robotic technologies were the main implementation barriers we identified in both countries. Both the UK and China may need to adopt strategies such as providing more financial support to small construction industries and skill training which are utilised successfully in other sectors to realise the potential of construction robotic technologies.

Summary: Percutaneous dilatational tracheostomy (PDT) is a bedside medical procedure which sites a new tracheostomy tube in the front of the neck. The critical first step is accurate placement of a needle through the neck tissues into the trachea. Misplacement occurs in around 5% of insertions, causing morbidity, mortality, and delays to recovery. We aimed to develop and evaluate a prototype medical device to improve precision of initial PDT-needle insertion. The Guidance for Tracheostomy (GiFT) system communicates the relative locations of intra-tracheal target sensor and PDT-needle sensor to the operator. In simulated “difficult neck” models, GiFT significantly improved accuracy (mean difference 10.0 mm, ANOVA p

Plantar shear stress may have an important role in the formation of a Diabetic Foot Ulcer, but its measurement is regarded as challenging and has limited research. This paper highlights the importance of anatomical specific shear sensor calibration and presents a feasibility study of a novel shear sensing system which has measured in-shoe shear stress from gait activity on both healthy and diabetic subjects. The sensing insole was based on a strain gauge array embedded in a silicone insole backed with a commercial normal pressure sensor. Sensor calibration factors were investigated using a custom mechanical test rig with indenter to exert both normal and shear forces. Indenter size and location were varied to investigate the importance of both loading area and position on measurement accuracy. The sensing insole, coupled with the calibration procedure, was tested one participant with diabetes and one healthy participant during two sessions of 15 minutes of treadmill walking. Calibration with different indenter areas (from 78.5 mm2 to 707 mm2) and different positions (up to 40 mm from sensor centre) showed variation in measurements of up to 80% and 90% respectively. Shear sensing results demonstrated high repeatability (>97%) and good accuracy (mean absolute error < ±18 kPa) in bench top mechanical tests and less than 21% variability within walking of 15-minutes duration. The results indicate the importance of mechanical coupling between embedded shear sensors and insole materials. It also highlights the importance of using an appropriate calibration method to ensure accurate shear stress measurement. The novel shear stress measurement system presented in this paper, demonstrates a viable method to measure accurate and repeatable in-shoe shear stress using the calibration procedure described. The validation and calibration methods outlined in this paper could be utilised as a standardised approach for the research community to develop and validate similar measurement technologies.

The production of scaffolds for bone tissue applications is requiring a combination of physical and biological properties, which are depending on the materials morphology and pro-cessing conditions during the production process. The aim of the paper is the investigation of rheological behaviour of polymer and composite blends regularly used for the production of scaffolds for bone tissue applications with the use of additive manufacturing. Poly-ε-caprolactone (PCL), hydroxyapatite (HA), β-tri-calcium phosphate (TCP) and Bioglass 45S5 blends containing different ceramic concentrations (10 wt%, 15 wt% and 20 wt%) were prepared with the use of melt blending procedure and investigated with the use of oscillation and rotational rheology tests. Results are showing that all blends are presenting viscoelastic behaviour with higher viscous modulus, compared with elastic modulus for low frequencies, with this difference reducing while the frequency is increasing. All blends are presenting shear-thinning behaviour suitable for use with additive manufacturing methods. Viscous and elastic modulus are increasing by adding ceramic particles. Results are presenting that PCL/HA blends of the same material concentration are presenting higher elastic modulus properties compared with the other blends, while PCL/Bioglass blends are presenting lower loss factor, lower relaxation time and lower shear viscosity making them easier to handle during the printing procedure.

Introduction: Gelatin is a natural polymer commonly used in biomedical applications in combination with other materials due to its high biocompatibility, biodegradability, and similarity to collagen, principal protein of the extracellular matrix (ECM). The aim of this study was to evaluate the suitability of gelatin as the sole material to manufacture tissue engineering scaffolds by electrospinning.Methods: Gelatin was electrospun in nine different concentrations onto a rotating collector and the resulting scaffold’s mechanical properties, morphology and topography were assessed using mechanical testing, scanning electron microscopy and white light interferometry, respectively. After characterizing the scaffolds, the effects of the concentration of the solvents and crosslinking agent were statistically evaluated with multivariate analysis of variance and linear regressions.Results: Fiber diameter and inter-fiber separation increased significantly when the concentration of the solvents, acetic acid (HAc) and dimethyl sulfoxide (DMSO), increased. The roughness of the scaffolds decreased as the concentration of dimethyl sulfoxide increased. The mechanical properties were significantly affected by the DMSO concentration. Immersed crosslinked scaffolds did not degrade until day 28. The manufactured gelatin-based electrospun scaffolds presented comparable mechanical properties to many human tissues such as trabecular bone, gingiva, nasal periosteum, oesophagus and liver tissue.Discussion: This study revealed for the first time that biomimetic electrospun scaffolds with gelatin alone can be produced for a significant number of human tissues by appropriately setting up the levels of factors and their interactions. These findings also extend statistical relationships to a form that would be an excellent starting point for future research that could optimize factors and interactions using both traditional statistics and machine learning techniques to further develop specific human tissue.

Large bone reconstruction following trauma poses significant challenges for reconstructive surgeons, leading to a healthcare burden for health systems, long-term pain for patients, and complex disorders such as infections that are difficult to resolve. The use of bone substitutes is suboptimal for substantial bone loss, as they induce localized atrophy and are generally weak, and unable to support load. A combination of strong polycaprolactone (PCL)-based scaffolds, with an average channel size of 330 µm, enriched with 20% w/w of hydroxyapatite (HA), β-tricalcium phosphate (TCP), or Bioglass 45S5 (Bioglass), has been developed and tested for bone regeneration in a critical-size ovine femoral condyle defect model. After 6 weeks, tissue ingrowth was analyzed using X-ray computed tomography (XCT), Backscattered Electron Microscopy (BSE), and histomorphometry. At this point, all materials promoted new bone formation. Histological analysis showed no statistical difference among the different biomaterials (p > 0.05), but PCL-Bioglass scaffolds enhanced bone formation in the center of the scaffold more than the other types of materials. These materials show potential to promote bone regeneration in critical-sized defects on load-bearing sites.

Objectives We aimed to design and produce a low-cost, ergonomic, hood-integrated powered air-purifying respirator (Bubble-PAPR) for pandemic healthcare use, offering optimal and equitable protection to all staff. We hypothesised that participants would rate Bubble-PAPR more highly than current filtering face piece (FFP3) face mask respiratory protective equipment (RPE) in the domains of comfort, perceived safety and communication.Design Rapid design and evaluation cycles occurred based on the identified user needs. We conducted diary card and focus group exercises to identify relevant tasks requiring RPE. Lab-based safety standards established against British Standard BS-EN-12941 and EU2016/425 covering materials; inward particulate leakage; breathing resistance; clean air filtration and supply; carbon dioxide elimination; exhalation means and electrical safety. Questionnaire-based usability data from participating front-line healthcare staff before (usual RPE) and after using Bubble-PAPR.Setting Overseen by a trial safety committee, evaluation progressed sequentially through laboratory, simulated, low-risk, then high-risk clinical environments of a single tertiary National Health Service hospital.Participants 15 staff completed diary cards and focus groups. 91 staff from a range of clinical and non-clinical roles completed the study, wearing Bubble-PAPR for a median of 45 min (IQR 30–80 (15–120)). Participants self-reported a range of heights (mean 1.7 m (SD 0.1, range 1.5–2.0)), weights (72.4 kg (16.0, 47–127)) and body mass indices (25.3 (4.7, 16.7–42.9)).Outcome measures Preuse particulometer ‘fit testing’ and evaluation against standards by an independent biomedical engineer.Primary:Perceived comfort (Likert scale).Secondary: Perceived safety, communication.Results Mean fit factor 16 961 (10 participants). Bubble-PAPR mean comfort score 5.64 (SD 1.55) vs usual FFP3 2.96 (1.44) (mean difference 2.68 (95% CI 2.23 to 3.14, p

Large bone defects are clinically challenging, with up to 15% of these requiring surgical intervention due to non-union. Bone grafts (autographs or allografts) can be used but they have many limitations, meaning that polymer-based bone tissue engineered scaffolds (tissue engineering) are a more promising solution. Clinical translation of scaffolds is still limited but this could be improved by exploring the whole design space using virtual tools such as mechanobiological modeling. In tissue engineering, a significant research effort has been expended on materials and manufacturing but relatively little has been focused on shape. Most scaffolds use regular pore architecture throughout, leaving custom or irregular pore architecture designs unexplored. The aim of this paper is to introduce a virtual design environment for scaffold development and to illustrate its potential by exploring the relationship of pore architecture to bone tissue formation. A virtual design framework has been created utilizing a mechanical stress finite element (FE) model coupled with a cell behavior agent-based model to investigate the mechanobiological relationships of scaffold shape and bone tissue formation. A case study showed that modifying pore architecture from regular to irregular enabled between 17 and 33% more bone formation within the 4–16-week time periods analyzed. This work shows that shape, specifically pore architecture, is as important as other design parameters such as material and manufacturing for improving the function of bone tissue scaffold implants. It is recommended that future research be conducted to both optimize irregular pore architectures and to explore the potential extension of the concept of shape modification beyond mechanical stress to look at other factors present in the body.

Introduction: Electrospinning is a manufacturing technique that creates a net of nano and microfibres able to mimic the natural extracellular matrix (ECM) of biological tissue. Electrospun scaffolds' morphology and mechanical behaviour can be tailored by modifying the environmental, solution and process parameters. This study aims to produce biomimetic vascular implants optimising the manufacturing set up through two machine learning techniques and statistical approaches.Methods: Polyvinyl alcohol (PVA) based scaffolds were produced by modifying the concentration of the polymer, flow rate, voltage, type of collector, diameter of the needle, distance between needle and collector and revolutions of the mandrel. The scaffolds were morphologically and mechanically characterised using scanning electron microscopy and mechanical testing respectively to inform the morphological model (simultaneously predicting diameter of the fibres and inter-fibre separation) and mechanical model (predicting strain at rupture and ultimate tensile strength).Results: Prediction and traditional techniques led to an optimum set up of: 12% PVA, 1 ml/h flow rate, 20 kV, 8 cm between the needle, 18 G gauge needle, rotational mandrel of 15 cm and 2000 rpm. Optimised PVA scaffolds replicated the mechanical properties and morphology of the vascular tissue with an ultimate tensile strength of 6.17 ± 0.18 MPa, a strain at break of 97.39 ± 5.06, fibre diameters of 126 ± 6.11 nm and inter-fibre separation of 1488 ± 91.99 nm.Discussion: This work revealed for the first time that machine learning Chi-squared Automatic Interaction Detection (CHAID) models are a novel and visual route to elect the optimum manufacturing set up to develop biomimetic vascular implants. Novel two-output Artificial Neural Networks (ANN) and multivariate analysis of variance and covariance (MANOVA, MANCOVA) models presented comparable prediction results (R2=0.91); however, two-output ANN predicted models demonstrated to be the most powerful tool for non-parametric conditions, showing cross-validation mean squared errors (MSE) of 0.0001943. Multi Linear Regression models (MLR) exhibited the lowest accuracy in their predictions (R2=0.6). Machine learning, statistical approaches and traditional characterisation methods were studied to successfully achieve vascular substitutes with analogous biomechanical behaviour and physical structure to the native vascular tissue.

Introduction: Osteoporosis is a skeletal disease that severely affects the mechanical properties of bone. It increases the porosity of cancellous bone and reduces the resistance to fractures. It has been reported in 2009 that there are approximately 500 million osteoporotic patients worldwide. Patients who suffer fractures due to fragility cost the National Healthcare Systems in the United Kingdom £4.4 billion in 2018, in Europe €56 billion in 2019, and in the United States $57 billion in 2018. Thus, osteoporosis is problematic for both patients and healthcare systems. Aim: This review is conducted for the purpose of presenting and discussing all articles introducing or investigating treatment solutions for osteoporotic patients undergoing total hip replacement. Methods: Searches were implemented using three databases, namely Scopus, PubMed, and Web of Science to extract all relevant articles. Predetermined eligibility criteria were used to exclude articles out of the scope of the study. Results: 29 articles out of 183 articles were included in this review. These articles were organised into three sections: (i) biomechanical properties and structure of osteoporotic bones, (ii) hip implant optimisations, and (iii) drug, cells, and bio-activators delivery through hydrogels. Discussion: The findings of this review suggest that diagnostic tools and measurements are crucial for understanding the characteristics of osteoporosis in general and for setting patient-specific treatment plans. It was also found that attempts to overcome complications associated with osteoporosis included design optimisation of the hip implant; however, only short-term success was reported, while the long-term stability of implants was compromised by the progressive nature of osteoporosis. Finally, it was also found that targeting implantation sites with cells, drugs, and growth factors has been outworked using hydrogels, where promising results have been reported regarding enhanced osteointegration and inhibited bacterial and osteoclastic activities. Conclusions: These results may encourage investigations that explore the effects of these impregnated hydrogels on osteoporotic bones beyond metallic scaffolds and implants.

This research investigates the accelerated hydrolytic degradation process of both anatomically designed bone scaffolds with a pore size gradient and a rectangular shape (biomimetically designed scaffolds or bone bricks). The effect of material composition is investigated considering poly-ε-caprolactone (PCL) as the main scaffold material, reinforced with ceramics such as hydroxyapatite (HA), β-tricalcium phosphate (TCP) and bioglass at a concentration of 20 wt%. In the case of rectangular scaffolds, the effect of pore size (200 μm, 300 μm and 500 μm) is also investigated. The degradation process (accelerated degradation) was investigated during a period of 5 days in a sodium hydroxide (NaOH) medium. Degraded bone bricks and rectangular scaffolds were measured each day to evaluate the weight loss of the samples, which were also morphologically, thermally, chemically and mechanically assessed. The results show that the PCL/bioglass bone brick scaffolds exhibited faster degradation kinetics in comparison with the PCL, PCL/HA and PCL/TCP bone bricks. Furthermore, the degradation kinetics of rectangular scaffolds increased by increasing the pore size from 500 μm to 200 μm. The results also indicate that, for the same material composition, bone bricks degrade slower compared with rectangular scaffolds. The scanning electron microscopy (SEM) images show that the degradation process was faster on the external regions of the bone brick scaffolds (600 μm pore size) compared with the internal regions (200 μm pore size). The thermal gravimetric analysis (TGA) results show that the ceramic concentration remained constant throughout the degradation process, while differential scanning calorimetry (DSC) results show that all scaffolds exhibited a reduction in crystallinity (Xc), enthalpy (Δm) and melting temperature (Tm) throughout the degradation process, while the glass transition temperature (Tg) slightly increased. Finally, the compression results show that the mechanical properties decreased during the degradation process, with PCL/bioglass bone bricks and rectangular scaffolds presenting higher mechanical properties with the same design in comparison with the other materials.

The design of scaffolds with optimal biomechanical properties for load-bearing applications is an important topic of research. Most studies have addressed this problem by focusing on the material composition and not on the coupled effect between the material composition and the scaffold architecture. Polymer–bioglass scaffolds have been investigated due to the excellent bioactivity properties of bioglass, which release ions that activate osteogenesis. However, material preparation methods usually require the use of organic solvents that induce surface modifications on the bioglass particles, compromising the adhesion with the polymeric material thus compromising mechanical properties. In this paper, we used a simple melt blending approach to produce polycaprolactone/bioglass pellets to construct scaffolds with pore size gradient. The results show that the addition of bioglass particles improved the mechanical properties of the scaffolds and, due to the selected architecture, all scaffolds presented mechanical properties in the cortical bone region. Moreover, the addition of bioglass indicated a positive long-term effect on the biological performance of the scaffolds. The pore size gradient also induced a cell spreading gradient.

Lumbar disc herniation is one of the most common degenerative spinal conditions resulting in lower back pain and sciatica. Surgical treatment options include microdiscectomy, lumbar fusion, total disc replacement, and other minimally invasive approaches. At present, microdiscectomy procedures are the most used technique; however, the annulus fibrosus is left with a defect that without treatment may contribute to high reherniation rates and changes in the biomechanics of the lumbar spine. This paper aims to review current commercially available products that mechanically close the annulus including the AnchorKnot® suture-passing device and the Barricaid® annular closure device. Previous studies and reviews have focused mainly on a biomimetic biomaterials approach and have described some mechanical and biological requirements for an active annular repair/regeneration strategy but are still far away from clinical implementation. Therefore, in this paper we aim to create a design specification for a mechanical annular closure strategy by identifying the most important mechanical and biological design parameters, including consideration of material selection, preclinical testing requirements, and requirements for clinical implementation.

The practice of combining external stimulation therapy alongside stimuli-responsive bio-scaffolds has shown massive potential for tissue engineering applications. One promising example is the combination of electrical stimulation (ES) and electroactive scaffolds because ES could enhance cell adhesion and proliferation as well as modulating cellular specialization. Even though electroactive scaffolds have the potential to revolutionize the field of tissue engineering due to their ability to distribute ES directly to the target tissues, the development of effective electroactive scaffolds with specific properties remains a major issue in their practical uses. Conductive polymers (CPs) offer ease of modification that allows for tailoring the scaffold’s various properties, making them an attractive option for conductive component in electroactive scaffolds. This review provides an up-to-date narrative of the progress of CPs-based electroactive scaffolds and the challenge of their use in various tissue engineering applications from biomaterials perspectives. The general issues with CP-based scaffolds relevant to its application as electroactive scaffolds were discussed, followed by a more specific discussion in their applications for specific tissues, including bone, nerve, skin, skeletal muscle and cardiac muscle scaffolds. Furthermore, this review also highlighted the importance of the manufacturing process relative to the scaffold’s performance, with particular emphasis on additive manufacturing, and various strategies to overcome the CPs’ limitations in the development of electroactive scaffolds.

Fixation devices are commonly used for bone fracture treatments. These implants are made of biocompatible materials such as stainless steel, cobalt, titanium and its alloys (e.g. CoCrMo and Ti-6Al-4V). However, metallic medical implants present higher stiffness compared to bone, contributing to the stress shielding phenomena compromising bone integrity. This paper explores the use of topology optimization to create novel bone fixation designs with reduced material volumes. Results show that for certain levels of volume reductions, which depends on the load condition, it is possible to obtain designs that minimise the stress shielding phenomena.

Electroactive biomaterials are fascinating for tissue engineering applications because of their ability to deliver electrical stimulation directly to cells, tissue, and organs. One particularly attractive conductive filler for electroactive biomaterials is silver nanoparticles (AgNPs) because of their high conductivity, antibacterial activity, and ability to promote bone healing. However, production of AgNPs involves a toxic reducing agent which would inhibit biological scaffold performance. This work explores facile and green synthesis of AgNPs using extract of Cilembu sweet potato and studies the effect of baking and precursor concentrations (1, 10 and 100 mM) on AgNPs’ properties. Transmission electron microscope (TEM) results revealed that the smallest particle size of AgNPs (9.95 ± 3.69 nm) with nodular morphology was obtained by utilization of baked extract and ten mM AgNO3. Polycaprolactone (PCL)/AgNPs scaffolds exhibited several enhancements compared to PCL scaffolds. Compressive strength was six times greater (3.88 ± 0.42 MPa), more hydrophilic (contact angle of 76.8 ± 1.7°), conductive (2.3 ± 0.5 × 10−3 S/cm) and exhibited anti-bacterial properties against Staphylococcus aureus ATCC3658 (99.5% reduction of surviving bacteria). Despite the promising results, further investigation on biological assessment is required to obtain comprehensive study of this scaffold. This green synthesis approach together with the use of 3D printing opens a new route to manufacture AgNPs-based electroactive with improved anti-bacterial properties without utilization of any toxic organic solvents.

Diabetic foot ulcers (DFUs) are a life-changing complication of diabetes that can lead to amputation. There is increasing evidence that long-term management with wearables can reduce incidence and recurrence of this condition. Temperature asymmetry measurements can alert to DFU development, but measurements of dynamic information, such as rate of temperature change, are under investigated. We present a new wearable device for temperature monitoring at the foot that is personalised to account for anatomical variations at the foot. We validate this device on 13 participants with diabetes (no neuropathy) (group name D) and 12 control participants (group name C), during sitting and standing. We extract dynamic temperature parameters from four sites on each foot to compare the rate of temperature change. During sitting the time constant of temperature rise after shoe donning was significantly (p < 0.05) faster at the hallux (p = 0.032, 370.4 s (C), 279.1 s (D)) and 5th metatarsal head (p = 0.011, 481.9 s (C), 356.6 s (D)) in participants with diabetes compared to controls. No significant differences at the other sites or during standing were identified. These results suggest that temperature rise time is faster at parts of the foot in those who have developed diabetes. Elevated temperatures are known to be a risk factor of DFUs and measurement of time constants may provide information on their development. This work suggests that temperature rise time measured at the plantar surface may be an indicative biomarker for differences in soft tissue biomechanics and vascularisation during diabetes onset and progression.

Electrostimulation and electroactive scaffolds can positively influence and guide cellular behaviour and thus has been garnering interest as a key tissue engineering strategy. The development of conducting polymers such as polyaniline enables the fabrication of conductive polymeric composite scaffolds. In this study, we report on the initial development of a polycaprolactone scaffold incorporating different weight loadings of a polyaniline microparticle filler. The scaffolds are fabricated using screw-assisted extrusion-based 3D printing and are characterised for their morphological, mechanical, conductivity, and preliminary biological properties. The conductivity of the polycaprolactone scaffolds increases with the inclusion of polyaniline. The in vitro cytocompatibility of the scaffolds was assessed using human adipose-derived stem cells to determine cell viability and proliferation up to 21 days. A cytotoxicity threshold was reached at 1% wt. polyaniline loading. Scaffolds with 0.1% wt. polyaniline showed suitable compressive strength (6.45 ± 0.16 MPa) and conductivity (2.46 ± 0.65 × 10−4 S/cm) for bone tissue engineering applications and demonstrated the highest cell viability at day 1 (88%) with cytocompatibility for up to 21 days in cell culture.

It was previously suggested that the flight ability of feathered fossils could be hypothesized from the diameter of their feather rachises. Central to the idea is the unvalidated assumption that the strength of a primary flight feather (i.e. its material and structural properties) may be consistently calculated from the external diameter of the feather rachis, which is the only dimension that is likely to relate to structural properties available from fossils. Here, using three-point bending tests, the relationship between feather structural properties (maximum bending moment, Mmax and Young's modulus, Ebend) and external morphological parameters (primary feather rachis length, diameter and second moment of area at the calamus) in 180 primary feathers from four species of bird of differing flight style was investigated. Intraspecifically, both Ebend and Mmax were strongly correlated with morphology, decreasing and increasing, respectively, with all three morphological measures. Without accounting for species, however, external morphology was a poor predictor of rachis structural properties, meaning that precise determination of aerial performance in extinct, feathered species from external rachis dimensions alone is not possible. Even if it were possible to calculate the second moment of area of the rachis, our data suggest that feather strength could still not be reliably estimated.