De novo topology optimization of total ossicular replacement prostheses

Optimization of functionally graded solid-network TPMS meta-biomaterials

The current study enhances the performance of solid-network triply periodic minimal surface (TPMS) cellular materials through using cell size grading along with the Taguchi method. Cell size grading is a novel technique used to control the size of pores and the surface area without changing the relative density. In this context, experimental compression testing was conducted on six distinct geometries of cell size graded TPMS structures (Diamond, Fischer-Koch S, Gyroid, IWP, Primitive, and Schoen-F-RD) manufactured with dental resin using a masked stereolithography (MSLA) printer. The findings indicated that mean total energy absorption was greater for smaller initial cell sizes (4 and 6 mm) compared to larger sizes (12 mm). Consistent patterns were also observed with respect to final cell sizes. Upon examination of the stress-strain relationships between D and I-WP, it is evident that D exhibits a higher initial peak stress point. However, subsequent to a significant decline, it exhibits a tremendous degree of volatility before recovering. Conversely, I-WP demonstrated greater stability throughout the experiments, with a notably greater maximum stress effect. A significant influence was observed from the initial cell size on stress, with larger sizes leading to a reduction in absorbed energy. The acquired results serve as an essential basis for the identification of optimized designs that may be implemented to enhance the structures' durability.

Mechanical effect of reconstructed shapes of autologous ossicles on middle ear acoustic transmission

Conductive hearing loss is caused by a variety of defects, such as chronic otitis media, osteosclerosis, and malformation of the ossicles. In such cases, the defective bones of the middle ear are often surgically reconstructed using artificial ossicles to increase the hearing ability. However, in some cases, the surgical procedure does not result in increased hearing, especially in a difficult case, for example, when only the footplate of the stapes remains and all of the other bones are destroyed. Herein, the appropriate shapes of the reconstructed autologous ossicles, which are suitable for various types of middle-ear defects, can be determined by adopting an updating calculation based on a method that combines numerical prediction of the vibroacoustic transmission and optimization. In this study, the vibroacoustic transmission characteristics were calculated for bone models of the human middle ear by using the finite element method (FEM), after which Bayesian optimization (BO) was applied. The effect of the shape of artificial autologous ossicles on the acoustic transmission characteristics of the middle ear was investigated with the combined FEM and BO method. The results suggested that the volume of the artificial autologous ossicles especially has a great influence on the numerically obtained hearing levels.

3D Printability of Silk/Hydroxyapatite Composites for Microprosthetic Applications

Micro-prosthetics requires the fabrication of mechanically robust and personalized components with sub-millimetric feature accuracy. Three-dimensional (3D) printing technologies have had a major impact on manufacturing such miniaturized devices for biomedical applications; however, biocompatibility requirements greatly constrain the choice of usable materials. Hydroxyapatite (HA) and its composites have been widely employed to fabricate bone-like structures, especially at the macroscale. In this work, we investigate the rheology, printability, and prosthetic mechanical properties of HA and HA-silk protein composites, focusing on the roles of composition and water content. We correlate key linear and nonlinear shear rheological parameters to geometric outcomes of printing and explain how silk compensates for the inherent brittleness of printed HA components. By increasing ink ductility, the inclusion of silk improves the quality of printed items through two mechanisms: (1) reducing underextrusion by lowering the required elastic modulus and, (2) reducing slumping by increasing the ink yield stress proportional to the modulus. We demonstrate that the elastic modulus and compressive strength of parts fabricated from silk-HA inks are higher than those for rheologically comparable pure-HA inks. We construct a printing map to guide the manufacturing of HA-based inks with excellent final properties, especially for use in biomedical applications for which sub-millimetric features are required.

Computational Design and Manufacturing of Sustainable Materials through First-Principles and Materiomics

Engineered materials are ubiquitous throughout society and are critical to the development of modern technology, yet many current material systems are inexorably tied to widespread deterioration of ecological processes. Next-generation material systems can address goals of environmental sustainability by providing alternatives to fossil fuel-based materials and by reducing destructive extraction processes, energy costs, and accumulation of solid waste. However, development of sustainable materials faces several key challenges including investigation, processing, and architecting of new feedstocks that are often relatively mechanically weak, complex, and difficult to characterize or standardize. In this review paper, we outline a framework for examining sustainability in material systems and discuss how recent developments in modeling, machine learning, and other computational tools can aid the discovery of novel sustainable materials. We consider these through the lens of materiomics, an approach that considers material systems holistically by incorporating perspectives of all relevant scales, beginning with first-principles approaches and extending through the macroscale to consider sustainable material design from the bottom-up. We follow with an examination of how computational methods are currently applied to select examples of sustainable material development, with particular emphasis on bioinspired and biobased materials, and conclude with perspectives on opportunities and open challenges.

Development of the Customized Asymmetric Fixation Plate to Resist Postoperative Relapse of Hemifacial Microsomia Following BSSO: Topology Optimization and Biomechanical Testing

Hemifacial microsomia (HFM), one of the most common congenital facial anomalies, was usually treated with the bilateral sagittal split osteotomy (BSSO) procedure to correct the asymmetric appearance and malocclusion of the mandible. However, the frequent post-operative relapse incidents would lead to the restoration of the mandibular segment to its preoperative position and failure of the BSSO procedure. In this study, a customized asymmetric fixed plate (CAF plate) was developed to resist relapse due to hemifacial microsomia occlusal forces and the different muscular traction forces on both sides of the mandible. For the actual HFM case in this study, the reconstructed mandibular segmental bone model was fixed using BSSO with a rectangular plate (the original CAF plate appearance) in the topology optimization analysis. With the topology optimization technique, the CAF plate was designed with a lightweight profile and excellent structural strength in consideration of the HFM asymmetrical muscle traction and occlusal force. Using biomechanical simulations, the von-Mises stress and CAF plate mandibular segment displacement and the miniplate were compared to evaluate which had superior relapse resistance. In the in-vitro biomechanical test, a fatigue force of 250,000 cycles and a constant muscle traction force were applied to the HFM mandibular model, which was fixed with the CAF plate fabricated using metal 3D printing (selective laser melting, SLM) to obtain the mandibular segment displacement as a relapse assessment. The topology optimization analysis showed that the CAF plate has the best characteristics, light weight and structural strength with 30% volume retention. The biomechanical analysis showed that the maximum von Mises stress of the mini-plate was 2.71 times higher than that of the CAF plate. The relapse displacement of the mandibular segment fixed with the mini-plate was 1.62 times higher than that fixed with the CAF plate. The CAF plate ability to resist relapse was confirmed by the biomechanical testing results so that only 0.29 mm of recurrence displacement was observed in the mandibular segment. The results indicated that the CAF plate structural strength and resistance to relapse was significantly better than that of the mini-plate. This study developed a customized asymmetric fixation plate for hemifacial microsomia, integrating topology optimization, metal 3D printing, and in vitro biomechanical testing to resist occlusal forces and differential muscle traction on both sides of the mandible to reduce relapse and improve fixation stability.

Sensing Devices for Detecting and Processing Acoustic Signals in Healthcare

Acoustic signals are important markers to monitor physiological and pathological conditions, e.g., heart and respiratory sounds. The employment of traditional devices, such as stethoscopes, has been progressively superseded by new miniaturized devices, usually identified as microelectromechanical systems (MEMS). These tools are able to better detect the vibrational content of acoustic signals in order to provide a more reliable description of their features (e.g., amplitude, frequency bandwidth). Starting from the description of the structure and working principles of MEMS, we provide a review of their emerging applications in the healthcare field, discussing the advantages and limitations of each framework. Finally, we deliver a discussion on the lessons learned from the literature, and the open questions and challenges in the field that the scientific community must address in the near future.

Chitin Nanofibril Application in Tympanic Membrane Scaffolds to Modulate Inflammatory and Immune Response

Chitin nanofibrils (CNs) are an emerging bio-based nanomaterial. Due to nanometric size and high crystallinity, CNs lose the allergenic features of chitin and interestingly acquire anti-inflammatory activity. Here we investigate the possible advantageous use of CNs in tympanic membrane (TM) scaffolds, as they are usually implanted inside highly inflamed tissue environment due to underlying infectious pathologies. In this study, the applications of CNs in TM scaffolds were twofold. A nanocomposite was used, consisting of poly(ethylene oxide terephthalate)/poly(butylene terephthalate) (PEOT/PBT) copolymer loaded with CN/polyethylene glycol (PEG) pre-composite at 50/50 (w/w %) weight ratio, and electrospun into fiber scaffolds, which were coated by CNs from crustacean or fungal sources via electrospray. The degradation behavior of the scaffolds was investigated during 4 months at 37 °C in an otitis-simulating fluid. In vitro tests were performed using cell types to mimic the eardrum, i.e., human mesenchymal stem cells (hMSCs) for connective, and human dermal keratinocytes (HaCaT cells) for epithelial tissues. HMSCs were able to colonize the scaffolds and produce collagen type I. The inflammatory response of HaCaT cells in contact with the CN-coated scaffolds was investigated, revealing a marked downregulation of the pro-inflammatory cytokines. CN-coated PEOT/PBT/(CN/PEG 50:50) scaffolds showed a significant indirect antimicrobial activity.

Trends in Managing Cardiac and Orthopaedic Device-Associated Infections by Using Therapeutic Biomaterials

Over the years, there has been an increasing number of cardiac and orthopaedic implanted medical devices, which has caused an increased incidence of device-associated infections. The surfaces of these indwelling devices are preferred sites for the development of biofilms that are potentially lethal for patients. Device-related infections form a large proportion of hospital-acquired infections and have a bearing on both morbidity and mortality. Treatment of these infections is limited to the use of systemic antibiotics with invasive revision surgeries, which had implications on healthcare burdens. The purpose of this review is to describe the main causes that lead to the onset of infection, highlighting both the biological and clinical pathophysiology. Both passive and active surface treatments have been used in the field of biomaterials to reduce the impact of these infections. This includes the use of antimicrobial peptides and ionic liquids in the preventive treatment of antibiotic-resistant biofilms. Thus far, multiple in vivo studies have shown efficacious effects against the antibiotic-resistant biofilm. However, this has yet to materialize in clinical medicine.

Molecular origin of viscoelasticity in mineralized collagen fibrils

Bone is mineralized tissue constituting the skeletal system, supporting and protecting the body's organs and tissues. In addition to such fundamental mechanical functions, bone also plays a remarkable role in sound conduction. From a mechanical standpoint, bone is a composite material consisting of minerals and collagen arranged in multiple hierarchical structures, with a complex anisotropic viscoelastic response, capable of transmitting and dissipating energy. At the molecular level, mineralized collagen fibrils are the basic building blocks of bone tissue, and hence, understanding bone properties down to fundamental tissue structures enables better identification of the mechanisms of structural failures and damage. While efforts have focused on the study of micro- and macro-scale viscoelasticity related to bone damage and healing based on creep, mineralized collagen has not been explored at the molecular level. We report a study that aims at systematically exploring the viscoelasticity of collagenous fibrils with different mineralization levels. We investigate the dynamic mechanical response upon cyclic and impulsive loads to observe the viscoelastic phenomena from either shear or extensional strains via molecular dynamics. We perform a sensitivity analysis with several key benchmarks: intrafibrillar mineralization percentage, hydration state, and external load amplitude. Our results show an increase of the dynamic moduli with an increase of the mineral percentage, pronounced at low strains. When intrafibrillar water is present, the material softens the elastic component, but considerably increases its viscosity, especially at high frequencies. This behavior is confirmed from the material response upon impulsive loads, in which water drastically reduces the relaxation times throughout the input velocity range by one order of magnitude, with respect to the dehydrated counterparts. We find that, upon transient loads, water has a major impact on the mechanics of mineralized fibrillar collagen, being able to improve the capability of the tissue to passively and effectively dissipate energy, especially after fast and high-amplitude external loads. Our study provides knowledge of bone mechanics in relation to pathologies deriving from dehydration or traumas. Moreover, these findings show the potential for being used in designing new bioinspired materials not limited to tissue engineering applications, in which passive mechanisms for dissipating energy can prevent structural failures.

Topology optimization of a mandibular reconstruction plate and biomechanical validation

OBJECTIVES

Reconstruction plates, used to bridge segmental defects of the mandible after tumor resection or traumatic bone tissue loss, are subjected to repeated stresses of mastication. High stress concentrations in these plates can result in hardware failure. Topology optimization (TO) could reduce the peak stress by computing the most optimal material distribution in a patient-specific implant (PSI) used for mandibular reconstruction. The objective of this study was biomechanical validation of a TO-PSI.

METHODS

A computer-aided design (CAD) model with a segmental defect was created based on the geometry of a polyurethane mandible model. A standard-PSI was designed to bridge the defect. A TO-PSI was then designed with a maximum stress equal to the ultimate tensile stress of Ti6Al4V (930 MPa) during a loading condition of 378 N. Finite element analysis (FEA) was used to analyze stresses in both PSI designs during loading. The standard-PSI and TO-PSI designs were produced in triplicate by selective laser melting of Ti6Al4V, fixated to polyurethane mandible models with segmental defects identical to the CAD model, and subsequently subjected to continuous compression with a speed of 1 mm/min on a universal testing machine, while recording the load. Peak loads before failure in the TO-PSI group within a 30% range of the predicted peak load (378 N) were considered a successful biomechanical validation.

RESULTS

Fracture of the TO-PSI occurred at a median peak load of 334 N (range 304-336 N). These values are within the 30% range of the predicted peak load. Fracture of the mandible model in the standard-PSI group occurred at a median peak load of 1100 N (range 1010-1460 N). Failure locations during biomechanical testing of TO-PSI and standard-PSI samples corresponded to regions in the FEA where stresses exceeded the ultimate tensile strength of titanium and polyurethane, respectively.

CONCLUSION

This study demonstrates a successful preliminary biomechanical validation of TO in the design process for mandibular reconstruction plates. Further work is needed to refine the finite element model, which is necessary to ultimately design TO-PSIs for clinical use.

Biodegradable Polymeric Micro/Nano-Structures with Intrinsic Antifouling/Antimicrobial Properties: Relevance in Damaged Skin and Other Biomedical Applications

Bacterial colonization of implanted biomedical devices is the main cause of healthcare-associated infections, estimated to be 8.8 million per year in Europe. Many infections originate from damaged skin, which lets microorganisms exploit injuries and surgical accesses as passageways to reach the implant site and inner organs. Therefore, an effective treatment of skin damage is highly desirable for the success of many biomaterial-related surgical procedures. Due to gained resistance to antibiotics, new antibacterial treatments are becoming vital to control nosocomial infections arising as surgical and post-surgical complications. Surface coatings can avoid biofouling and bacterial colonization thanks to biomaterial inherent properties (e.g., super hydrophobicity), specifically without using drugs, which may cause bacterial resistance. The focus of this review is to highlight the emerging role of degradable polymeric micro- and nano-structures that show intrinsic antifouling and antimicrobial properties, with a special outlook towards biomedical applications dealing with skin and skin damage. The intrinsic properties owned by the biomaterials encompass three main categories: (1) physical–mechanical, (2) chemical, and (3) electrostatic. Clinical relevance in ear prostheses and breast implants is reported. Collecting and discussing the updated outcomes in this field would help the development of better performing biomaterial-based antimicrobial strategies, which are useful to prevent infections.

Mechanics of Mineralized Collagen Fibrils upon Transient Loads

Collagen is a key structural protein in the human body, which undergoes mineralization during the formation of hard tissues. Earlier studies have described the mechanical behavior of bone at different scales, highlighting material features across hierarchical structures. Here we present a study that aims to understand the mechanical properties of mineralized collagen fibrils upon tensile/compressive transient loads, investigating how the kinetic energy propagates and it is dissipated at the molecular scale, thus filling a gap of knowledge in this area. These specific features are the mechanisms that nature has developed to passively dissipate stress and prevent structural failures. In addition to the mechanical properties of the mineralized fibrils, we observe distinct nanomechanical behaviors for the two regions (i.e., overlap and gap) of the D-period to highlight the effect of the mineralization. We notice decreasing trends for both wave speeds and Young's moduli over input velocity with a marked strengthening effect in the gap region due to the accumulation of the hydroxyapatite. In contrast, the dissipative behavior is not affected by either loading conditions or the mineral percentage, showing a stronger damping effect upon faster inputs compatible to the bone behavior at the macroscale. Our results offer insights into the dissipative behavior of mineralized collagen composites to design and characterize bioinspired composites for replacement devices (e.g., prostheses for sound transmission or conduction) or optimized structures able to bear transient loads, for example, impact, fatigue, in structural applications.

Wave Propagation and Energy Dissipation in Collagen Molecules

Collagen is the key protein of connective tissue (i.e., skin, tendons and ligaments, and cartilage, among others), accounting for 25-35% of the whole-body protein content and conferring mechanical stability. This protein is also a fundamental building block of bone because of its excellent mechanical properties together with carbonated hydroxyapatite minerals. Although the mechanical resilience and viscoelasticity have been studied both in vitro and in vivo from the molecular to tissue level, wave propagation properties and energy dissipation have not yet been deeply explored, in spite of being crucial to understanding the vibration dynamics of collagenous structures (e.g., eardrum, cochlear membranes) upon impulsive loads. By using a bottom-up atomistic modeling approach, here we study a collagen peptide under two distinct impulsive displacement loads, including longitudinal and transversal inputs. Using a one-dimensional string model as a model system, we investigate the roles of hydration and load direction on wave propagation along the collagen peptide and the related energy dissipation. We find that wave transmission and energy-dissipation strongly depend on the loading direction. Also, the hydrated collagen peptide can dissipate five times more energy than dehydrated one. Our work suggests a distinct role of collagen in term of wave transmission of different tissues such as tendon and eardrum. This study can step toward understanding the mechanical behavior of collagen upon transient loads, impact loading and fatigue, and designing biomimetic and bioinspired materials to replace specific native tissues such as the tympanic membrane.