Biomechanics of trabecular bone

Clinical translation of polycaprolactone-based tissue engineering scaffolds, fabricated via additive manufacturing: A review of their craniofacial applications

The craniofacial region is characterized by its intricate bony anatomy and exposure to heightened functional forces presenting a unique challenge for reconstruction. Additive manufacturing has revolutionized the creation of customized scaffolds with interconnected pores and biomimetic microarchitecture, offering precise adaptation to various craniofacial defects. Within this domain, medical-grade poly(ε-caprolactone) (PCL) has been extensively used for the fabrication of 3D printed scaffolds, specifically tailored for bone regeneration. Its adoption for load-bearing applications was driven mainly by its mechanical properties, adjustable biodegradation rates, and high biocompatibility. The present review aims to consolidating current insights into the clinical translation of PCL-based constructs designed for bone regeneration. It encompasses recent advances in enhancing the mechanical properties and augmenting biodegradation rates of PCL and PCL-based composite scaffolds. Moreover, it delves into various strategies improving cell proliferation and the osteogenic potential of PCL-based materials. These strategies provide insight into the refinement of scaffold microarchitecture, composition, and surface treatments or coatings, that include certain bioactive molecules such as growth factors, proteins, and ceramic nanoparticles. The review critically examines published data on the clinical applications of PCL scaffolds in both extraoral and intraoral craniofacial reconstructions. These applications include cranioplasty, nasal and orbital floor reconstruction, maxillofacial reconstruction, and intraoral bone regeneration. Patient demographics, surgical procedures, follow-up periods, complications and failures are thoroughly discussed. Although results from extraoral applications in the craniofacial region are encouraging, intraoral applications present a high frequency of complications and related failures. Moving forward, future studies should prioritize refining the clinical performance, particularly in the domain of intraoral applications, and providing comprehensive data on the long-term outcomes of PCL-based scaffolds in bone regeneration. Future perspective and limitations regarding the transition of such constructs from bench to bedside are also discussed.

Effects of MgO nanoparticle addition on the mechanical properties, degradation properties, antibacterial properties and in vitro and in vivo biological properties of 3D-printed Zn scaffolds

Bone tissue engineering is the main method for repairing large segment bone defects. In this study, a layer of bioactive MgO nanoparticles was wrapped on the surface of spherical Zn powders, which allowed the MgO nanoparticles to be incorporated into 3D-printed Zn matrix and improved the biodegradation and biocompatibility of the Zn matrix. The results showed that porous pure Zn scaffolds and Zn/MgO scaffolds with skeletal-gyroid (G) model structure were successfully prepared by selective laser melting (SLM). The average porosity of two porous scaffolds was 59.3 and 60.0%, respectively. The pores were uniformly distributed with an average pore size of 558.6-569.3 μm. MgO nanoparticles regulated the corrosion rate of scaffolds, resulting in a more uniform corrosion degradation behavior of the Zn/MgO scaffolds in simulated body fluid solution. The degradation ratio of Zn/MgO composite scaffolds in vivo was increased compared to pure Zn scaffolds, reaching 15.6% at 12 weeks. The yield strength (10.8 ± 2.4 MPa) of the Zn/MgO composite scaffold was comparable to that of cancellous bone, and the antimicrobial rate were higher than 99%. The Zn/MgO composite scaffolds could better guide bone tissue regeneration in rat cranial bone repair experiments (completely filling the scaffolds at 12 weeks). Therefore, porous Zn/MgO scaffolds with G-model structure prepared with SLM are a promising biodegradable bone tissue engineering scaffold.

A probabilistic approach for assessing the mechanical performance of intertrochanteric fracture stabilized with proximal femoral nail antirotation

Maintaining post-operative mechanical stability is crucial for successfully healing intertrochanteric fractures treated with the Proximal Femoral Nail Antirotation (PFNA) system. This stability is primarily dependent on the bone mineral density (BMD) and strain on the fracture. Current PFNA failure analyses often overlook the uncertainties related to BMD and body weight (BW). Therefore, this study aimed to develop a probabilistic model using finite element modeling and engineering reliability analysis to assess the post-operative performance of PFNA under various physiological loading conditions. The model predictions were validated through a series of experimental test. The results revealed a negative nonlinear relationship between the BMD and compressive strain. Conversely, the BW was positively and linearly correlated with the compressive strain. Importantly, the compressive strain was more sensitive to BW than to BMD when the BMD exceeded 0.6 g/cm3. Potential trabecular bone compression failure is also indicated if BMD is equal to or below 0.15 g/cm3 and BW increases to approximately 2.5 times the normal or higher. This study emphasizes that variations in the BMD significantly affect the probability of failure of a PFNA system. Thus, careful planning of post-operative physical therapy is essential. For patients aged > 50 years restrictions on high-intensity activities are advised, while limiting strenuous movements is recommended for those aged > 65 years.

Lactobacillus helveticus-Derived Whey-Calcium Chelate Promotes Calcium Absorption and Bone Health of Rats Fed a Low-Calcium Diet

This study investigated the characteristics of Lactobacillus helveticus-derived whey-calcium chelate (LHWCC) and its effect on the calcium absorption and bone health of rats. Fourier-transform infrared spectroscopy showed that carboxyl oxygen atoms, amino nitrogen atoms, and phosphate ions were the major binding sites with calcium in LHWCC, which has a sustained release effect in simulated in vitro digestion. LHWCC had beneficial effects on serum biochemical parameters, bone biomechanics, and the morphological indexes of the bones of calcium-deficient rats when fed at a dose of 40 mg Ca/kg BW for 7 weeks. In contrast to the inorganic calcium supplement, LHWCC significantly upregulated the gene expression of transient receptor potential cation V5 (TRPV5), TRPV6, PepT1, calcium-binding protein-D9k (Calbindin-D9k), and a calcium pump (plasma membrane Ca-ATPase, PMCA1b), leading to promotion of the calcium absorption rate, whereas Ca3(PO4)2 only upregulated the TRPV6 channel in vivo. These findings illustrate the potential of LHWCC as an organic calcium supplement.

A Gellan Gum, Polyethylene Glycol, Hydroxyapatite Composite Scaffold with the Addition of Ginseng Derived Compound K with Possible Applications in Bone Regeneration

Engineered bone scaffolds should mimic the natural material to promote cell adhesion and regeneration. For this reason, natural biopolymers are becoming a gold standard in scaffold production. In this study, we proposed a hybrid scaffold produced using gellan gum, hydroxyapatite, and Poly (ethylene glycol) within the addition of the ginseng compound K (CK) as a candidate for bone regeneration. The fabricated scaffold was physiochemically characterized. The morphology studied by scanning electron microscopy (SEM) and image analysis revealed a pore distribution suitable for cells growth. The addition of CK further improved the biological activity of the hybrid scaffold as demonstrated by the MTT assay. The addition of CK influenced the scaffold morphology, decreasing the mean pore diameter. These findings can potentially help the development of a new generation of hybrid scaffolds to best mimic the natural tissue.

Magnetic biocomposite scaffold based on decellularized tendon ECM and MNP-deposited halloysite nanotubes: physicochemical, thermal, rheological, mechanical andin vitrobiological evaluations

The development of new three-dimensional biomaterials with advanced versatile properties is critical to the success of tissue engineering (TE) applications. Here, (a) bioactive decellularized tendon extracellular matrix (dECM) with a sol-gel transition feature at physiological temperature, (b) halloysite nanotubes (HNT) with known mechanical properties and bioactivity, and (c) magnetic nanoparticles (MNP) with superparamagnetic and osteogenic properties were combined to develop a new scaffold that could be used in prospective bone TE applications. Deposition of MNPs on HNTs resulted in magnetic nanostructures without agglomeration of MNPs. A completely cell-free, collagen- and glycosaminoglycan- rich dECM was obtained and characterized. dECM-based scaffolds incorporated with 1%, 2% and 4% MNP-HNT were analysed for their physical, chemical, andin vitrobiological properties. Fourier-transform infrared spectroscopy, x-ray powder diffractometry and vibrating sample magnetometry analyses confirmed the presence of dECM, HNT and MNP in all scaffold types. The capacity to form apatite layer upon incubation in simulated body fluid revealed that dECM-MNP-HNT is a bioactive material. Combining dECM with MNP-HNT improved the thermal stability and compressive strength of the macroporous scaffolds upto 2% MNP-HNT.In vitrocytotoxicity and hemolysis experiments showed that the scaffolds were essentially biocompatible. Human bone marrow mesenchymal stem cells adhered and proliferated well on the macroporous constructs containing 1% and 2% MNP-HNT; and remained metabolically active for at least 21 din vitro. Collectively, the findings support the idea that magnetic nanocomposite dECM scaffolds containing MNP-HNT could be a potential template for TE applications.

Additive manufactured gyroid-based cell structures under compression: design, testing and simulation for biomedical applications

The mechanical behaviour of a DMLS Ti-6Al-4V gyroid-based cellular structure (CS), with potential application in the fabrication of implants, was studied under compressive conditions. The influence of the CS volumetric fraction on the elastic modulus was experimentally evaluated in cubic and cylindrical samples. The experimental results showed that the selected parameters allowed approximating the mechanical behaviour of the CS to that of trabecular bone. Finite element analysis was employed to study the mechanical behaviour of the CS. The model presented a good approximation of the experimental results, being useful to predict the mechanical behaviour of the CS.

Effects of using collagen and aloe vera grafted fibroin scaffolds on osteogenic differentiation of rat bone marrow mesenchymal stem cells in SBF-enriched cell culture medium

In the study, collagen and aloe vera were grafted onto silk fibroin with two different methods, and 3D-microporous scaffolds (1F5C4A1 and 2F5C4A1) were formed by lyophilization. Three osteogenic cultures were started by seeding rat bone marrow mesenchymal stem cells (MSCs) and pre-induced MSC (osteoblast (OB)) on biopolymeric scaffolds. The osteogenic medium was enriched with 10% (v/v) simulated body fluid (SBF) to promote mineralization and osteogenic differentiation in one of the MSC cultures and the OB culture. X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning electron microscopy- energy dispersive spectrum (SEM-EDS) analyses on cellular samples and histochemical (alizarin red, safranin-O, alcian blue) and immunohistochemical (anti-collagen-1, anti-osteocalcin, anti-osteopontin) staining showed that bone-like mineralization was occurred by both chemically and cellular activity. In addition, pre-osteogenic induction of MSCs in 2D-cultured was found to promote osteogenesis more rapidly when started 3D-cultured. These results indicated that enrichment of the cell culture medium with SBF is sufficient forin vitromineralization rather than using high concentrations of SBF. The findings showed that OB cells on the 2F5C4A1 scaffold obtained the best osteogenic activity. Still, other culture media with 10% SBF content could be used for bone tissue engineering under osteogenic induction.

The effect of zoledronic acid on hip geometry in renal transplant recipients: a double-blind placebo-controlled randomized study

BACKGROUND

In renal transplant patients, bisphosphonates may prevent bone loss, but little is known about their effects on bone microarchitecture and geometrical hip parameters, as the key factors of bone stability. This study aimed to analyze the effect of zoledronic acid on the mentioned parameters in kidney transplant patients.

METHODS

In this double-blind, randomized trial, 33 patients were followed for six months after administering either 4mg of zoledronic acid or a placebo. Bone mineral density (BMD) measurement of the spine, hip, radius, and whole body was obtained, and trabecular bone score (TBS) was evaluated using the software. Geometric assessment at the proximal femur was performed by the HSA program.

RESULTS

Eighteen patients in the intervention group and 15 in the control group completed the study. The mean percentages of the changes in the BMD at the lumbar spine and whole body were significantly different between the placebo and intervention groups (-0.23% vs. 4.91% and -2.03% vs. 1.23%) (P < 0.05). Zoledronic acid appeared to enhance the subperiosteal diameter, endocortical diameter, and cross-sectional moment of inertia (CSMI) at the narrow neck in comparison with placebo (P < 0.05); however, no difference in TBS was observed between both groups (P > 0.05).

CONCLUSIONS

We concluded that a single administration of zoledronic acid might ameliorate bone loss at the lumbar spine and the whole body and maintain the subperiosteal diameter, endocortical diameter, and CSMI as parameters of bone strength at the narrow neck of the proximal femur after six months in renal-transplant recipients.

TRIAL REGISTRATION

This study was registered in IRCT (ID: IRCT20181202041821N1) on 04-05-2019.

A Comprehensive Mechanical Characterization of Subject-Specific 3D Printed Scaffolds Mimicking Trabecular Bone Architecture Biomechanics

This study presents a polymeric scaffold designed and manufactured to mimic the structure and mechanical compressive characteristics of trabecular bone. The morphological parameters and mechanical behavior of the scaffold were studied and compared with trabecular bone from bovine iliac crest. Its mechanical properties, such as modulus of elasticity and yield strength, were studied under a three-step monotonic compressive test. Results showed that the elastic modulus of the scaffold was 329 MPa, and the one for trabecular bone reached 336 MPa. A stepwise dynamic compressive test was used to assess the behavior of samples under various loading regimes. With microcomputed tomography (µCT), a three-dimensional reconstruction of the samples was obtained, and their porosity was estimated as 80% for the polymeric scaffold and 88% for trabecular bone. The full-field strain distribution of the samples was measured using in situ µCT mechanics and digital volume correlation (DVC). This provided information on the local microdeformation mechanism of the scaffolds when compared to that of the tissue. The comprehensive results illustrate the potential of the fabricated scaffolds as biomechanical templates for in vitro studies. Furthermore, there is potential for extending this structure and fabrication methodology to incorporate suitable biocompatible materials for both in vitro and in vivo clinical applications.

Biomechanical Performance of Total Wrist Arthrodesis Plates With and Without Arthrodesis of the Carpometacarpal Joint

BACKGROUND

It is unknown whether total wrist arthrodesis (TWA) should be performed with or without arthrodesis of the carpometacarpal joint (CMCJ). The aim of this study is to compare CMCJ-spanning TWA plates using 3D printed wrist arthrodesis model with and without arthrodesis of the CMCJ.

METHODS

Total wrist arthrodesis plates mounted to 3D printed models were tested under a 4-N bending load at 4 Hz for 50 000 cycles, increased by 15% every 10 000 cycles until failure.

RESULTS

Plates with arthrodesis CMCJ were stiffer and failed at a significantly greater load and number of cycles than plates mounted to models without CMCJ arthrodesis. The Synthes stainless steel locking TWA plate performed better than the Trimed plate applied to the model without CMCJ arthrodesis and the Acumed plate applied to the model with CMCJ arthrodesis. Based on these findings, we recommend arthrodesis of the CMCJ in TWA.

CONCLUSIONS

Incorporation of the CMCJ in TWA may protect against plate failure. If arthrodesis of the CMCJ is not performed, plate removal should be considered before breakage occurs.

LEVEL OF EVIDENCE

IV.

Comparison of osteogenic capability of 3D-printed bioceramic scaffolds and granules with different porosities for clinical translation

Pore parameters, structural stability, and filler morphology of artificial implants are key factors influencing the process of bone tissue repair. However, the extent to which each of these factors contributes to bone formation in the preparation of porous bioceramics is currently unclear, with the two often being coupled. Herein, we prepared magnesium-doped wollastonite (Mg-CSi) scaffolds with 57% and 70% porosity (57-S and 70-S) via a 3D printing technique. Meanwhile, the bioceramic granules (57-G and 70-G) with curved pore topography (IWP) were prepared by physically disrupting the 57-S and 70-S scaffolds, respectively, and compared for in vivo osteogenesis at 4, 10, and 16 weeks. The pore parameters and the mechanical and biodegradable properties of different porous bioceramics were characterized systematically. The four groups of porous scaffolds and granules were then implanted into a rabbit femoral defect model to evaluate the osteogenic behavior in vivo. 2D/3D reconstruction and histological analysis showed that significant bone tissue production was visible in the central zone of porous granule groups at the early stage but bone tissue ingrowth was slower in the porous scaffold groups. The bone tissue regeneration and reconstruction capacity were stronger after 10 weeks, and the porous architecture of the 57-S scaffold was maintained stably at 16 weeks. These experimental results demonstrated that the structure-collapsed porous bioceramic is favorable for early-stage osteoconduction and that the 3D topological scaffolds may provide more structural stability for bone tissue growth for a long-term stage. These findings provide new ideas for the selection of different types of porous bioceramics for clinical bone repair.

Porous metal implants: processing, properties, and challenges

Porous and functionally graded materials have seen extensive applications in modern biomedical devices-allowing for improved site-specific performance; their appreciable mechanical, corrosive, and biocompatible properties are highly sought after for lightweight and high-strength load-bearing orthopedic and dental implants. Examples of such porous materials are metals, ceramics, and polymers. Although, easy to manufacture and lightweight, porous polymers do not inherently exhibit the required mechanical strength for hard tissue repair or replacement. Alternatively, porous ceramics are brittle and do not possess the required fatigue resistance. On the other hand, porous biocompatible metals have shown tailorable strength, fatigue resistance, and toughness. Thereby, a significant interest in investigating the manufacturing challenges of porous metals has taken place in recent years. Past research has shown that once the advantages of porous metallic structures in the orthopedic implant industry have been realized, their biological and biomechanical compatibility-with the host bone-has been followed up with extensive methodical research. Various manufacturing methods for porous or functionally graded metals are discussed and compared in this review, specifically, how the manufacturing process influences microstructure, graded composition, porosity, biocompatibility, and mechanical properties. Most of the studies discussed in this review are related to porous structures for bone implant applications; however, the understanding of these investigations may also be extended to other devices beyond the biomedical field.

Printing tissue-engineered scaffolds made of polycaprolactone and nano-hydroxyapatite with mechanical properties appropriate for trabecular bone substitutes

BACKGROUND

Bone tissue engineering, based on three-dimensional (3D) printing technology, has emerged as a promising approach to treat bone defects using scaffolds. The objective of this study was to investigate the influence of porosity and internal structure on the mechanical properties of scaffolds.

METHODS

We fabricated composite scaffolds (which aimed to replicate trabecular bone) from polycaprolactone (PCL) reinforced with 30% (wt.) nano-hydroxyapatite (nHAp) by extrusion printing. Scaffolds with various porosities were designed and fabricated with and without an interlayer offset, termed as staggered and lattice structure, respectively. Mechanical compressive testing was performed to determine scaffold elastic modulus and yield strength. Linear regression was used to evaluate mechanical properties as a function of scaffold porosity.

RESULTS

Different relationships between mechanical properties and porosities were noted for the staggered and lattice structures. For elastic moduli, the two relationships intersected (porosity = 55%) such that the lattice structure exhibited higher moduli with porosity values greater than the intersection point; vice versa for the staggered structure. The lattice structure exhibited higher yield strength at all porosities. Mechanical testing results also indicated elastic moduli and yield strength properties comparable to trabecular bone (elastic moduli: 14-165 MPa; yield strength: 0.9-10 MPa).

CONCLUSIONS

Taken together, this study demonstrates that scaffolds printed from PCL/30% (wt.) nHAp with lattice and staggered structure offer promise for treating trabecular bone defects. This study identified the effect of porosity and internal structure on scaffold mechanical properties and provided suggestions for developing scaffolds with mechanical properties for substituting trabecular bone.

Tumor-associated macrophages induce inflammation and drug resistance in a mechanically tunable engineered model of osteosarcoma

The tumor microenvironment is a complex and dynamic ecosystem composed of various physical cues and biochemical signals that facilitate cancer progression, and tumor-associated macrophages are especially of interest as a treatable target due to their diverse pro-tumorigenic functions. Engineered three-dimensional models of tumors more effectively mimic the tumor microenvironment than monolayer cultures and can serve as a platform for investigating specific aspects of tumor biology within a controlled setting. To study the combinatorial effects of tumor-associated macrophages and microenvironment mechanical properties on osteosarcoma, we co-cultured human osteosarcoma cells with macrophages within biomaterials-based bone tumor niches with tunable stiffness. In the first 24 h of direct interaction between the two cell types, macrophages induced an inflammatory environment consisting of high concentrations of tumor necrosis factor alpha (TNFα) and interleukin (IL)-6 within moderately stiff scaffolds. Expression of Yes-associated protein (YAP), but not its homolog, transcriptional activator with PDZ-binding motif (TAZ), in osteosarcoma cells was significantly higher than in macrophages, and co-culture of the two cells slightly upregulated YAP in both cells, although not to a significant degree. Resistance to doxorubicin treatment in osteosarcoma cells was correlated with inflammation in the microenvironment, and signal transducer and activator of transcription 3 (STAT3) inhibition diminished the inflammation-related differences in drug resistance but ultimately did not improve the efficacy of doxorubicin. This work highlights that the biochemical cues conferred by tumor-associated macrophages in osteosarcoma are highly variable, and signals derived from the immune system should be considered in the development and testing of novel drugs for cancer.

Osteogenic differentiation of human adipose-derived mesenchymal stem cells in a bisphosphonate-functionalized polycaprolactone/gelatin scaffold

Recent trends in bone tissue engineering have focused on the development of biomimetic constructs with appropriate mechanical and physiochemical properties. Here, we report the fabrication of an innovative biomaterial scaffold based on a new bisphosphonate-containing synthetic polymer combined with gelatin. To this end, zoledronate (ZA)-functionalized polycaprolactone (PCL-ZA) was synthesized by a chemical grafting reaction. After adding gelatin to the PCL-ZA polymer solution, the porous PCL-ZA/gelatin scaffold was fabricated by the freeze-casting method. A scaffold with aligned pores and a porosity of 82.04 % was obtained. During in vitro biodegradability test, 49 % of its initial weight lost after 5 weeks. The elastic modulus of the PCL-ZA/gelatin scaffold was 31.4 MPa, and its tensile strength was 4.2 MPa. Based on the results of MTT assay, the scaffold had good cytocompatibility with human Adipose-Derived Mesenchymal Stem Cells (hADMSCs). Furthermore, cells grown in PCL-ZA/gelatin scaffold showed the highest mineralization and ALP activity compared to other test groups. Results of the RT-PCR test revealed that RUNX2, COL 1A1, and OCN genes were expressed in PCL-ZA/gelatin scaffold at the highest level, suggesting its good osteoinductive capacity. These results revealed that PCL-ZA/gelatin scaffold could be considered a proper biomimetic platform for bone tissue engineering.

Biomechanical properties and clinical significance of cancellous bone in proximal femur: A review

Trabecular bone plays an important role in the load-bearing capacity of the femur. Understanding the structural characteristics, biomechanics, and mechanical conduction of the trabecular bone is of great value in studying the mechanism of fractures and formulating surgical plans. The past decade has witnessed unprecedented progress in imaging, biomechanics and finite element analysis techniques, translating into a better understanding of trabecular bone. This article reviews the research progress achieved over the years regarding femoral trabecular bone, especially on factors influencing the strength of the proximal femoral cancellous bone and cancellous bone microfractures and provides a comprehensive overview of the latest findings on proximal femoral trabecular bone and their clinical significance.

Numerical analysis of the influence of triply periodic minimal surface structures morphometry on the mechanical response

BACKGROUND AND OBJECTIVE

Design of bone scaffolds requires a combination of material and geometry to fulfil requirements of mechanical properties, porosity and pore size. Triply Periodic Minimal Surface (TPMS) structures have gained attention due to their similarities to cancellous bone. In this work, we aim at exploring relationships between morphometry and mechanical properties for TPMS configurations.

METHODS

Eight TPMS structures are defined considering six porosity levels and their morphometry is characterized. The stiffness matrix of each structure is assessed and related to morphometry through a statistical analysis.

RESULTS

An orthotropic mechanical behavior has been derived from the numerical homogenization. Properties decay exponentially for decreasing volume fraction. Through volume fraction variation, TPMS mechanical properties can be selected to match bone properties in a range of 0.2% to 70% of the bulk material properties.

CONCLUSIONS

The comparison between cancellous bone and TPMS morphometry, considering a unit cell size of 1.5 mm, reveals that the configurations analyzed in this work match the requirements of volume fraction, mean thickness and pore size. However, the TPMS studied in this work differ from cancellous bone anisotropy. The results in this paper provide a framework to select the proper TPMS configuration and its geometry for patient-specific applications.

Fracture in porous bone analysed with a numerical phase-field dynamical model

A dynamic phase-field fracture finite element model is applied to discretized high-resolution three-dimensional computed tomography images of human trabecular bone to analyse rapid bone fracture. The model is contrasted to quasi-static experimental results and a quasi-static phase-field finite element model. The experiment revealed complex stepwise crack evolution with multiple crack fronts, and crack arrests, as the global tensile displacement load was incrementally increased. The quasi-static phase-field fracture model captures the fractures in the experiment reasonably well, and the dynamic model converges towards the quasi-static model when mechanically loaded at low rates. At higher load rates, i.e., at larger impulses, inertia effects significantly contribute to an increased initial global stiffness, higher peak forces and a larger number of cracks spread over a larger volume. Since the fracture process clearly is different at large impulses compared to small impulses, it is concluded that dynamic fracture models are necessary when simulating rapid bone fracture.

Titanium Lattice Structures Produced via Additive Manufacturing for a Bone Scaffold: A Review

The progress in additive manufacturing has remarkably increased the application of lattice materials in the biomedical field for the fabrication of scaffolds used as bone substitutes. Ti6Al4V alloy is widely adopted for bone implant application as it combines both biological and mechanical properties. Recent breakthroughs in biomaterials and tissue engineering have allowed the regeneration of massive bone defects, which require external intervention to be bridged. However, the repair of such critical bone defects remains a challenge. The present review collected the most significant findings in the literature of the last ten years on Ti6Al4V porous scaffolds to provide a comprehensive summary of the mechanical and morphological requirements for the osteointegration process. Particular attention was given on the effects of pore size, surface roughness and the elastic modulus on bone scaffold performances. The application of the Gibson–Ashby model allowed for a comparison of the mechanical performance of the lattice materials with that of human bone. This allows for an evaluation of the suitability of different lattice materials for biomedical applications.

Effects of Calcium Carbonate Microcapsules and Nanohydroxyapatite on Properties of Thermosensitive Chitosan/Collagen Hydrogels

Thermosensitive chitosan/collagen hydrogels are osteoconductive and injectable materials. In this study, we aimed to improve these properties by adjusting the ratio of nanohydroxyapatite particles to calcium carbonate microcapsules in a β-glycerophosphate-crosslinked chitosan/collagen hydrogel. Two hydrogel systems with 2% and 5% nanohydroxyapatite particles were studied, each of which had varying microcapsule content (i.e., 0%, 1%, 2%, and 5%). Quercetin-incorporated calcium carbonate microcapsules were prepared. Calcium carbonate microcapsules and nanohydroxyapatite particles were then added to the hydrogel according to the composition of the studied system. The properties of the hydrogels, including cytotoxicity and biocompatibility, were investigated in mice. The calcium carbonate microcapsules were 2-6 µm in size, spherical, with rough and nanoporous surfaces, and thus exhibited a burst release of impregnated quercetin. The 5% nanohydroxyapatite system is a solid particulate gel that supports homogeneous distribution of microcapsules in the three-dimensional matrix of the hydrogels. Calcium carbonate microcapsules increased the mechanical and physical strength, viscoelasticity, and physical stability of the nanohydroxyapatite hydrogels while decreasing their porosity, swelling, and degradation rates. The calcium carbonate microcapsules-nanohydroxyapatite hydrogels were noncytotoxic and biocompatible. The properties of the hydrogel can be tailored by adjusting the ratio of calcium carbonate microcapsules to the nanohydroxyapatite particles. The 1% calcium carbonate microcapsules containing 5% nanohydroxyapatite particle-chitosan/collagen hydrogel exhibited mechanical and physical strength, permeability, and prolonged release profiles of quercetin, which were superior to those of the other studied systems and were optimal for promoting bone regeneration and delivering natural flavonoids.

Open-porous magnesium-based scaffolds withstand in vitro corrosion under cyclic loading: A mechanistic study

The successful application of magnesium (Mg) alloys as biodegradable bone substitutes for critical-sized defects may be comprised by their high degradation rate resulting in a loss of mechanical integrity. This study investigates the degradation pattern of an open-porous fluoride-coated Mg-based scaffold immersed in circulating Hanks' Balanced Salt Solution (HBSS) with and without in situ cyclic compression (30 N/1 Hz). The changes in morphological and mechanical properties have been studied by combining in situ high-resolution X-ray computed tomography mechanics and digital volume correlation. Although in situ cyclic compression induced acceleration of the corrosion rate, probably due to local disruption of the coating layer where fatigue microcracks were formed, no critical failures in the overall scaffold were observed, indicating that the mechanical integrity of the Mg scaffolds was preserved. Structural changes, due to the accumulation of corrosion debris between the scaffold fibres, resulted in a significant increase (p < 0.05) in the material volume fraction from 0.52 ± 0.07 to 0.47 ± 0.03 after 14 days of corrosion. However, despite an increase in fibre material loss, the accumulated corrosion products appear to have led to an increase in Young's modulus after 14 days as well as lower third principal strain (εp3) accumulation (−91000 ± 6361 με and −60093 ± 2414 με after 2 and 14 days, respectively). Therefore, this innovative Mg scaffold design and composition provide a bone replacement, capable of sustaining mechanical loads in situ during the postoperative phase allowing new bone formation to be initially supported as the scaffold resorbs.

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First report on in vitro cyclic loading of MgF₂ coated open-porous Mg scaffolds in HBSS simulating 2–3 months in humans.

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Fluoride-coating slows down corrosion under cyclic loading in vitro.

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Entangled scaffold structure accumulates local corrosion debris which keeps the mechanical integrity over 14 days in vitro.

Repairing a critical cranial defect using WISP1-pretreated chondrocyte scaffolds

In cranial flat bone fractures, spontaneous bone repair will occur only when the fracture ends are in close contact. However, in cases wherein bone discontinuity is extensive, surgical interventions are often required. To this end, autologous bone is harvested and surgically integrated into the site of fracture. Here we propose to use cartilage, as an alternative autologous source, to promote cranial fracture repair. The advantage of this approach is the potential reduction in donor site morbidity, likely due to the avascular and aneural nature of cartilage. As a first step we attempted to induce cartilage mineralization in vitro, using micromass primary chondrocyte cultures, incubated with BMP2 and/or WISP1, which were examined histologically following a 3-week culture period. Next, chondrocyte seeded collagen scaffolds were evaluated in vitro for expression profiles and ALP activity. Finally, chondrocyte-seeded collagen scaffolds were implanted in a Lewis rats 8 mm critical calvaria defect model, which was imaged via live CT for 12 weeks until sacrifice. End points were analyzed for microCT, histology, and serum levels of bone related markers. Micromass cultures exhibited an osseous inducing trend following WISP1 administration, which was maintained in chondrocyte seeded scaffolds. Accordingly, in vivo analysis was carried out to assess the impact of WISP1-pretreated chondrocytes (WCS) versus untreated chondrocytes (UCS) in calvaria defect model and compared to untreated control comprised of a defect-associated blood clot (BC) or empty collagen scaffold (CS) implant. Live CT and microCT exhibited higher mineralization volumes in critical defect implanted with UCS, with some structural improvements in WCS. Histological analysis exhibited higher anabolic bone formation in WCS and trabecular bone was detected in WCS and UCS groups. Chondrocytes implanted into critical cranial defect expedite the formation of native-like osseous tissue, especially after WISP1 priming in culture. Ultimately, these data support the use of autologous chondrocytes to repair critical maxillofacial defects.

A Bioinspired Orthopedic Biomaterial with Tunable Mechanical Properties Based on Sintered Titanium Fibers

Inadequate mechanical compliance of orthopedic implants can result in excessive strain of the bone interface, and ultimately, aseptic loosening. It is hypothesized that a fiber-based biometal with adjustable anisotropic mechanical properties can reduce interface strain, facilitate continuous remodeling, and improve implant survival under complex loads. The biometal is based on strategically layered sintered titanium fibers. Six different topologies are manufactured. Specimens are tested under compression in three orthogonal axes under 3-point bending and torsion until failure. Biocompatibility testing involves murine osteoblasts. Osseointegration is investigated by micro-computed tomography and histomorphometry after implantation in a metaphyseal trepanation model in sheep. The material demonstrates compressive yield strengths of up to 50 MPa and anisotropy correlating closely with fiber layout. Samples with 75% porosity are both stronger and stiffer than those with 85% porosity. The highest bending modulus is found in samples with parallel fiber orientation, while the highest shear modulus is found in cross-ply layouts. Cell metabolism and morphology indicate uncompromised biocompatibility. Implants demonstrate robust circumferential osseointegration in vivo after 8 weeks. The biometal introduced in this study demonstrates anisotropic mechanical properties similar to bone, and excellent osteoconductivity and feasibility as an orthopedic implant material.

The effects of force application on the compressive properties of femoral spongious bone

BACKGROUND

End artefacts play a major role in uniaxial compression tests with cancellous bone specimens. They lead to misinterpretation of mechanical parameters of bones due to uncontrolled introduction of bending moments into the free ends of trabeculae. This work aims to simplify current methods preventing end-artefacts and furthermore to investigate the influence of end artefacts on plateau stress.

METHODS

176 cylindrical cancellous bone specimens were taken from human femoral condyles and tested in uniaxial compression. The specimens were divided into 2 groups (direct, end-cap) and compressive modulus, maximum stress, plateau stress, energy absorbtion as well as apparent density were evaluated. Density values are from separate specimens which are immediately adjacent to the mechanical specimen.

FINDINGS

All mechanical parameters were significantly higher in the end-cap specimens than in the direct ones by about 30 - 40 %, thus reaching similar differences as the previous studies. Greatest differences between groups were determined for compressive modulus (45 %) and plateau stress (35 %). Energy absorbtion can be explained with great accuracy by plateau stress (P < 0.001; R² = 0.95). Among all parameters plateau stress can be best explained by apparent density using an exponential function (P < 0.001; R² = 0.38).

INTERPRETATION

The end-cap method used here to prevent end artefacts showed variations consistent with the literature when compared to the direct method. Additionally it was shown that the way in which the force is applied to the specimen has a major influence on the failure progression behavior, which was characterized using the plateau stress.

Strontium-doped apatitic bone cements with tunable antibacterial and antibiofilm ability

Injectable calcium phosphate cements (CPCs) represent promising candidates for the regeneration of complex-shape bone defects, thanks to self-hardening ability, bioactive composition and nanostructure offering high specific surface area for cell attachment and conduction. Such features make CPCs also interesting for functionalization with various biomolecules, towards the generation of multifunctional devices with enhanced therapeutic ability. In particular, strontium-doped CPCs have been studied in the last years due to the intrinsic antiosteoporotic character of strontium. In this work, a SrCPC previously reported as osteointegrative and capable to modulate the fate of bone cells was enriched with hydroxyapatite nanoparticles (HA-NPs) functionalized with tetracycline (TC) to provide antibacterial activity. We found that HA-NPs functionalized with TC (NP-TC) can act as modulator of the drug release profile when embedded in SrCPCs, thus providing a sustained and tunable TC release. In vitro microbiological tests on Escherichia coli and Staphylococcus aureus strains proved effective bacteriostatic and bactericidal properties, especially for the NP-TC loaded SrCPC formulations. Overall, our results indicate that the addition of NP-TC on CPC acted as effective modulator towards a tunable drug release control in the treatment of bone infections or cancers.

3D printed trabeculae conditionally reproduce the mechanical properties of the actual trabeculae - A preliminary study

Three-dimensional (3D) printing has been used to fabricate synthetic trabeculae models and to test mechanical behavior that cannot be recognized in the actual sample, but the extent to which 3D printed trabeculae replicate the mechanical behavior of the actual trabeculae remains to be quantified. The aim of this study was to evaluate the accuracy of 3D printed trabeculae in reproducing the mechanical properties of the corresponding actual trabeculae. Twelve human trabecular cubes (5 × 5 × 5 mm) were scanned by micro-CT to form the trabecular 3D model. Each trabecular 3D model was scaled ×2-, ×3-, ×4- and ×5-fold and then printed twice at a layer thickness of 60 μm using poly (lactic acid) (PLA). The actual trabecular cubes and the 3D-printed trabecular cubes were first compressed under a loading rate of 1 mm/min; another replicated stack of 3D-printed trabecular cubes was compressed under a strain rate of 0.2/min. The results showed that the stiffness of the printed cubes tended to increase, while the strength tended to converge when the magnification increased under the two loading conditions. The strain rate effect was found in the printed cubes. The correlation coefficient (R²) of the mechanical properties between the printed and actual trabeculae can reach up to 0.94, especially under ×3-, ×4- and ×5-fold magnification. In conclusion, 3D printing could be a potential tool to evaluate the mechanical behavior of actual trabecular tissue in vitro and may help in the future to predict the risk of fracture and even personalize the treatment evaluation for osteoporosis and other trabecular bone pathologies.

The role of bone marrow on the mechanical properties of trabecular bone: a systematic review

Background

Accurate evaluation of the mechanical properties of trabecular bone is important, in which the internal bone marrow plays an important role. The aim of this systematic review is to investigate the roles of bone marrow on the mechanical properties of trabecular bone to better support clinical work and laboratory research.

Methods

A systematic review of the literature published up to June 2022 regarding the role of bone marrow on the mechanical properties of trabecular bone was performed, using PubMed and Web of Science databases. The journal language was limited to English. A total of 431 articles were selected from PubMed (n = 186), Web of Science (n = 244) databases, and other sources (n = 1).

Results

After checking, 38 articles were finally included in this study. Among them, 27 articles discussed the subject regarding the hydraulic stiffening of trabecular bone due to the presence of bone marrow. Nine of them investigated the effects of bone marrow on compression tests with different settings, i.e., in vitro experiments under unconfined and confined conditions, and computer model simulations. Relatively few controlled studies reported the influence of bone marrow on the shear properties of trabecular bone.

Conclusion

Bone marrow plays a non-neglectable role in the mechanical properties of trabecular bone, its contribution varies depending on the different loading types and test settings. To obtain the mechanical properties of trabecular bone comprehensively and accurately, the solid matrix (trabeculae) and fluid-like component (bone marrow) should be considered in parallel rather than tested separately.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12938-022-01051-1.

Yak (Bos grunniens) milk improves bone mass and microarchitecture in mice with osteoporosis

The effect of milk on bone health is controversial. In this study, the effects of yak milk in mice with retinoic acid-induced osteoporosis (OP) were evaluated. Yak milk was provided to OP mice as a nutrition supplement for 6 wk. The results showed that yak milk significantly reduced bone turnover markers (tartrate acid phosphatase and alkaline phosphatase). The yak milk treatment was also associated with remarkably increased bone mineral density, bone volume, trabecular thickness, and trabecular number, as well as improved biomechanical properties (maximum load and stress) of the tibia. Furthermore, yak milk mitigated the deterioration of the network and thickness of trabecular bone in treated OP mice compared with the OP model group. The results indicated that yak milk could improve bone mass and microarchitecture through the inhibition of bone resorption in OP mice.

An open-access plug-in program for 3D modelling distinct material properties of cortical and trabecular bone

BACKGROUND

Finite element modelling the material behavior of bone in-silico is a powerful tool to predict the best suited surgical treatment for individual patients.

RESULTS

We demonstrate the development and use of a pre-processing plug-in program with a 3D modelling image processing software suite (Synopsys Simpleware, ScanIP) to assist with identifying, isolating, and defining cortical and trabecular bone material properties from patient specific computed tomography scans. The workflow starts by calibrating grayscale values of each constituent element with a phantom - a standardized object with defined densities. Using an established power law equation, we convert the apparent density value per voxel to a Young's Modulus. The resulting "calibrated" scan can be used for modeling and in-silico experimentation with Finite Element Analysis.

CONCLUSIONS

This process allows for the creation of realistic and personalized simulations to inform a surgeon's decision-making. We have made this plug-in program open and accessible as a supplemental file.

Application of phase-field fracture theories and digital volume correlation to synchrotron X-ray monitored fractures in human trabecular bone: A case study

Fracture processes of trabecular bone have been studied using various approaches over the years. However, reliable methods to analyse fracture at the single trabecula level are limited. In this study, a digital volume correlation (DVC) and a phase-field fracture model are applied and contrasted for human trabecular bone to analyse its failure under global compression at high resolution. A human trabecular bone sample was fractured in situ under synchrotron-based X-ray micro computed tomography (CT). Reconstructed CT data was then used in DVC algorithms to obtain high-resolution displacement fields in the bone at different load steps. A high-resolution specimen-specific structural mesh was discretized from the CT data and used for the phase-field simulation of the fracturing bone. The DVC analysis showed opening mode cracks as well as shear mode cracks. Strains in cracked regions were analysed. The load distribution in the trabecular structure resulted in two completely separated fracture regions in the sample body. A phenomenon that was also captured in the phase-field model. The results encourage us to believe improvements in boundary conditions and material models are worthwhile pursuing. Findings in this study support further development of a phase-field method to analyse fracture in samples with complex morphology, such as trabecular bone, and the capacity of DVC to quantify strains and slowly growing stable fractures during step-wise loading of trabecular bone.

Preparation and Characterization of Chitosan and Inclusive Compound-Layered Gold Nanocarrier to Improve the Antiproliferation Effect of Tamoxifen Citrate in Colorectal Adenocarcinoma (Caco-2) and Breast Cancer (MCF-7) Cells

Objectives

Cancer diseases have been linked to a huge number of causes that led to deaths in this century along with cardiovascular and lung diseases. Most death-leading types of cancer are colon, lung, breast, and prostate cancers. Due to the remarkable properties of gold (Au) nanocarrier, they are used to deliver and improve tamoxifen (Tam) citrate activity in Caco-2 and MCF-7 cells.

Materials and Methods

In this study, preparation of Au nanoparticles (NPs), zeta-potential and size, high resolution transient electron microscopy (HRTEM), high-performance liquid chromatography, ultraviolet-visible spectra, fluorescence microscopy, fourier infrared spectroscopy, and real-time cellular analysis xCELLigence technology were investigated.

Results

The zeta-average size of the Tam- β-cyclodextrin (β-CD)-hyaluronic acid (HA)-chitosan (Chi)-Au nanocomposite is 82.02 nm with a negative zeta potential of -23.6. Furthermore, HRTEM images showed that, successful formulation of polymer shell around Au core and the Au NP shape is mostly spherical, triangle and irregular. Furthermore, the fluorescence microscope image showed proper cellular uptake of the Tam-β-CD-HA-Chi-Au nanocomposite in MCF-7 and Caco-2 cells. Additionally, Tam-β-CD-HA-Chi-Au nanocomposite significantly improved the cytotoxic activity of Tam citrate on Caco-2 cells. IC₅₀ value of Tam reduced from 8.55 µM to 5.32 µM, after 48 h of incubation time (p value <0.00001).

Conclusion

This study showed that Tam-β-CD-HA-Chi-Au nanocomposite is a potential nanocarrier for delivering the drug to Caco-2 and MCF-7 cancer cells, since it has improved Tam citrate activity on colorectal cancer cells. After all, the developed formula showed more effect on Caco-2 than MCF-7. The prepared nanocomposite could be used to improve the cancer therapy in clinical trials.

Biomechanical validation of additively manufactured artificial femoral bones

Replicating the mechanical behavior of human bones, especially cancellous bone tissue, is challenging. Typically, conventional bone models primarily consist of polyurethane foam surrounded by a solid shell. Although nearly isotropic foam components have mechanical properties similar to cancellous bone, they do not represent the anisotropy and inhomogeneity of bone architecture. To consider the architecture of bone, models were developed whose core was additively manufactured based on CT data. This core was subsequently coated with glass fiber composite. Specimens consisting of a gyroid-structure were fabricated using fused filament fabrication (FFF) techniques from different materials and various filler levels. Subsequent compression tests showed good accordance between the mechanical behavior of the printed specimens and human bone. The unidirectional fiberglass composite showed higher strength and stiffness than human cortical bone in 3-point bending tests, with comparable material behaviors being observed. During biomechanical investigation of the entire assembly, femoral prosthetic stems were inserted into both artificial and human bones under controlled conditions, while recording occurring forces and strains. All of the artificial prototypes, made of different materials, showed analogous behavior to human bone. In conclusion, it was shown that low-cost FFF technique can be used to generate valid bone models and selectively modify their properties by changing the infill.

Improvement of osteogenic properties using a 3D-printed graphene oxide/hyaluronic acid/chitosan composite scaffold

Oral and maxillofacial tumors, trauma and infections are the main causes of jaw defects, whose clinical treatment is very complicated. With the development of biological tissue engineering, many biological materials have been widely used in various fields of stomatology, and they play a very important role in the repair and replacement of maxillofacial bone defects. In this study, we intended to prepare a graphene oxide/hyaluronic acid/chitosan (GO/HA/CS) composite hydrogel with different mass ratios of GO: 0.1% (0.1% GO/HA/CS), 0.25% (0.25% GO/HA/CS), 0.5% (0.5% GO/HA/CS), and 1% (1% GO/HA/CS), prepare it into a multilayered and stable composite scaffold through 3D-printing technology, observe the surface morphology of the composite scaffold through scanning electron microscopy (SEM), and then test its physical and chemical properties, mechanical properties, water swelling rate, in vitro degradation and other material properties. Moreover, the biological performance of the GO/HA/CS composite scaffold was studied through experiments, such as cell morphology observation, cell adhesion, cell proliferation, and live-dead cell staining. The results showed that through chemical cross-linking and 3D-printing technology, a porous (pore size: 450–580 μm) and multilayered GO/HA/CS biological scaffold could be successfully constructed, and its surface was an interconnected microporous structure, and the porosity decreased (94%−40%) gradually with the increase of GO. Meanwhile, with the change in GO concentration, some mechanical properties of the scaffold could be improved, such as water swelling rate, degradation rate, and elastic modulus. In addition, the composite scaffold with the appropriate amount of GO had almost no cytotoxicity and could promote cell growth and proliferation, especially 0.25% GO/HA/CS composite scaffold. Consequently, the 0.25% GO/HA/CS composite scaffold had excellent biological material properties and good biocompatibility with osteoblasts, which may provide a new idea for the repair of jaw defects.

Mechanical and morphometric characterization of custom-made trabecular bone surrogates

Synthetic bones for biomechanical testing and surgeon training have become more important due to their numerous advantages compared to human bones. Several bone models are already available on the market, but most of them do not reflect the full range of versatile properties that characterize human bone like population-level influences, size, stiffness, bone-implant-interface or morphometry. Thus, the objectives of this study were to develop synthetic trabecular bone surrogates from polyurethane and varying additives and to determine their elastic and plastic mechanical compressive and additionally morphometric properties. Another aim was to investigate the influence of varying additives on aforementioned properties and finally compare the results with published data from human trabecular bone. Additives used were blowing agents to create a porous structure, mineral fillers to manipulate the basic polyurethane resin, and cell stabilizers to achieve an open porous composition. Mechanical properties were obtained from static compression tests until failure while morphometric analysis was carried out using microcomputed tomography. Thereby, the blowing agent showed the strongest influence on mechanical and morphometric properties with mean Young's moduli ranging from 627 ± 37 MPa (0% blowing agent) to 154 ± 15 MPa (0.25% blowing agent) while the variation of mineral filler content resulted in small standard deviations of approximately 10-20 MPa with a constant proportion of blowing agent. The achieved mechanical properties of the developed synthetic bones, such as the Young's modulus, ultimate stress and yield stress were in accordance with human trabecular bone, while yield strain for all groups was noticeably higher compared to human trabecular bone. Additionally, morphometric analysis showed results indicating similar morphometry of the custom-made synthetic bone and human cancellous bone. Although recreating bone structures in physiological conditions is not simple, the results of the current study show the possibility of developing synthetic bone materials with characteristics like human trabecular bone.

Optimization of a Tricalcium Phosphate-Based Bone Model Using Cell-Sheet Technology to Simulate Bone Disorders

Bone diseases such as osteoporosis, delayed or impaired bone healing, and osteoarthritis still represent a social, financial, and personal burden for affected patients and society. Fully humanized in vitro 3D models of cancellous bone tissue are needed to develop new treatment strategies and meet patient-specific needs. Here, we demonstrate a successful cell-sheet-based process for optimized mesenchymal stromal cell (MSC) seeding on a β-tricalcium phosphate (TCP) scaffold to generate 3D models of cancellous bone tissue. Therefore, we seeded MSCs onto the β-TCP scaffold, induced osteogenic differentiation, and wrapped a single osteogenically induced MSC sheet around the pre-seeded scaffold. Comparing the wrapped with an unwrapped scaffold, we did not detect any differences in cell viability and structural integrity but a higher cell seeding rate with osteoid-like granular structures, an indicator of enhanced calcification. Finally, gene expression analysis showed a reduction in chondrogenic and adipogenic markers, but an increase in osteogenic markers in MSCs seeded on wrapped scaffolds. We conclude from these data that additional wrapping of pre-seeded scaffolds will provide a local niche that enhances osteogenic differentiation while repressing chondrogenic and adipogenic differentiation. This approach will eventually lead to optimized preclinical in vitro 3D models of cancellous bone tissue to develop new treatment strategies.

Fixture Length and Primary Stability: An In Vitro Study on Polyurethane Foam

(1) Background: Recently, novel dental implants that are characterized by different levels of surface roughness in the distinct parts of the fixture’s body have been introduced in the market. These surface characteristics could affect the primary stability of the implants. The aim of this in vitro study was to compare the primary stability of short and long implants, characterized by multiscale surface roughness, inserted on polyurethane blocks. The secondary aim was to understand if the implant length could be a crucial factor in the decision-making in immediate or rather than delayed loading protocol in the different bone densities. (2) Methods: A total of 20 cylindrical dental implants with a diameter of 5.0 mm were tested for the lengths 6.0 mm (short implants) versus 13.0 mm (long implants) on two different solid rigid polyurethane blocks (20 and 30 PCF). The primary stability was evaluated by measuring the insertion torque value (ITV), the removal torque (RTV), and the resonance frequency analysis RFA. (3) Results: The values of ITV, RTV, and RFA showed the same trend in all measurements. Long implants showed a significantly higher primary stability on 30 PCF blocks that present mechanical properties similar to high-density bone. On the contrary, no relevant differences were found on 20 PCF blocks, which mimic trabecular bone density. (4) Conclusions: The impact of fixture length on the primary stability of implants with multiscale surface roughness is significant in 30 PCF polyurethane corresponding to higher bone density, but not in lower ones.

A shrewd inspection of vertebral regionalization in large shrews (Soricidae: Crocidurinae)

The regionalization of the mammalian spinal column is an important evolutionary, developmental, and functional hallmark of the clade. Vertebral column regions are usually defined using transitions in external bone morphology, such as the presence of transverse foraminae or rib facets, or measurements of vertebral shape. Yet the internal structure of vertebrae, specifically the trabecular (spongy) bone, plays an important role in vertebral function, and is subject to the same variety of selective, functional, and developmental influences as external bone morphology. Here we investigated regionalization of external and trabecular bone morphology in the vertebral column of a group of shrews (family Soricidae). The primary goals of this study were to: 1) determine if vertebral trabecular bone morphology is regionalized in large shrews, and if so, in what configuration relative to external morphology; 2) assess correlations between trabecular bone regionalization and functional or developmental influences; and 3) determine if external and trabecular bone regionalization patterns provide clues about the function of the highly modified spinal column of the hero shrew Scutisorex.

Trabecular bone is regionalized along the soricid vertebral column, but the configuration of trabecular bone regions does not match that of the external vertebral morphology, and is less consistent across individuals and species. The cervical region has the most distinct and consistent trabecular bone morphology, with dense trabeculae indicative of the ability to withstand forces in a variety of directions. Scutisorex exhibits an additional external morphology region compared to unmodified shrews, but this region does not correspond to a change in trabecular architecture.

Although trabecular bone architecture is regionalized along the soricid vertebral column, and this regionalization is potentially related to bone functional adaptation, there are likely aspects of vertebral functional regionalization that are not detectable using trabecular bone morphology. For example, the external morphology of the Scutisorex lumbar spine shows signs of an extra functional region that is not apparent in trabecular bone analyses. It is possible that body size and locomotor mode affect the degree to which function is manifest in trabecular bone, and broader study across mammalian size and ecology is warranted to understand the relationship between trabecular bone morphology and other measures of vertebral function such as intervertebral range of motion.

Vertebral trabecular bone mechanical properties vary among functional groups of cetaceans

Since their appearance in the fossil record 34 million years ago, modern cetaceans (dolphins, whales, and porpoises) have radiated into diverse habitats circumglobally, developing vast phenotypic variations among species. Traits such as skeletal morphology and ecologically linked behaviors denote swimming activity; trade-offs in flexibility and rigidity along the vertebral column determine patterns of caudal oscillation. Here, we categorized 10 species of cetaceans (families Delphinidae and Kogiidae; N = 21 animals) into functional groups based on vertebral centra morphology, swimming speeds, diving behavior, and inferred swimming patterns. We quantified trabecular bone mechanical properties (yield strength, apparent stiffness, and resilience) among functional groups and regions of the vertebral column (thoracic, lumbar, and caudal). We extracted 6 mm³ samples from vertebral bodies and tested them in compression in 3 orientations (rostrocaudal, dorsoventral, and mediolateral) at 2 mm min⁻¹. Overall, bone from the pre-fluke/fluke boundary had the greatest yield strength and resilience, indicating that the greatest forces are translated to the tail during caudal oscillatory swimming. Group 1, composed of 5 shallow-diving delphinid species, had the greatest vertebral trabecular bone yield strength, apparent stiffness, and resilience of all functional groups. Conversely, Group 3, composed of 2 deep-diving kogiid species, had the least strong, stiff, and resilient bone, while Group 2 (3 deep-diving delphinid species) exhibited intermediate values. These data suggest that species that incorporate prolonged glides during deep descents in the water column actively swim less, and place relatively smaller loads on their vertebral columns, compared with species that execute shallower dives. We found that cetacean vertebral trabecular bone properties differed from the properties of terrestrial mammals; for every given bone strength, cetacean bone was less stiff by comparison. This relative lack of material rigidity within vertebral bone may be attributed to the non-weight-bearing locomotor modes of fully aquatic mammals.

How Artificial Intelligence and Machine Learning Is Assisting Us to Extract Meaning from Data on Bone Mechanics?

Dramatic advancements in interdisciplinary research with the fourth paradigm of science, especially the implementation of computer science, nourish the potential for artificial intelligence (AI), machine learning (ML), and artificial neural network (ANN) algorithms to be applied to studies concerning mechanics of bones. Despite recent enormous advancement in techniques, gaining deep knowledge to find correlations between bone shape, material, mechanical, and physical responses as well as properties is a daunting task. This is due to both complexity of the material itself and the convoluted shapes that this complex material forms. Moreover, many uncertainties and ambiguities exist concerning the use of traditional computational techniques that hinders gaining a full comprehension of this advanced biological material. This book chapter offers a review of literature on the use of AI, ML, and ANN in the study of bone mechanics research. A main question as to why to implement AI and ML in the mechanics of bones is fully addressed and explained. This chapter also introduces AI and ML and elaborates on the main features of ML algorithms such as learning paradigms, subtypes, main ideas with examples, performance metrics, training algorithms, and training datasets. As a frequently employed ML algorithm in bone mechanics, feedforward ANNs are discussed to make their taxonomy and working principles more readily comprehensible to researchers. A summary as well as detailed review of papers that employed ANNs to learn from collected data on bone mechanics are presented. Reviewing literature on the use of these data-driven tools is essential since their wider application has the potential to: improve clinical assessments enabling real-time simulations; avoid and/or minimize injuries; and, encourage early detection of such injuries in the first place.

Sesamoid bones also show functional adaptation in their microanatomy-The example of the patella in Perissodactyla

The patella is the largest sesamoid bone of the skeleton. It is strongly involved in the knee, improving output force and velocity of the knee extensors, and thus plays a major role in locomotion and limb stability. However, the relationships between its structure and functional constraints, that would enable a better understanding of limb bone functional adaptations, are poorly known. This contribution proposes a comparative analysis, both qualitative and quantitative, of the microanatomy of the whole patella in perissodactyls, which show a wide range of morphologies, masses, and locomotor abilities, in order to investigate how the microanatomy of the patella adapts to evolutionary constraints. The inner structure of the patella consists of a spongiosa surrounded by a compact cortex. Contrary to our expectations, there is no increase in compactness with bone size, and thus body size and weight, but only an increase in the tightness of the spongiosa. No particular thickening of the cortex associated with muscle insertions is noticed but a strong thickening is observed anteriorly at about mid-length, where the strong intermediate patellar ligament inserts. The trabeculae are mainly oriented perpendicularly to the posterior articular surface, which highlights that the main stress is anteroposteriorly directed, maintaining the patella against the femoral trochlea. Conversely, anteriorly, trabeculae are rather circumferentially oriented, following the insertion of the patellar ligament and, possibly also, of the quadriceps tendon. A strong variation is observed among perissodactyl families but also intraspecifically, which is in accordance with previous studies suggesting a higher variability in sesamoid bones. Clear trends are nevertheless observed between the three families. Equids have a much thinner cortex than ceratomorphs. Rhinos and equids, both characterized by a development of the medial border, show an increase in trabecular density laterally suggesting stronger stresses laterally. The inner structure in tapirs is more homogeneous despite the absence of medial development of the medial border with no "compensation" of the inner structure, which suggests different stresses on their knees associated with a different morphology of their patellofemoral joint.

Gluing Living Bone Using a Biomimetic Bioadhesive: From Initial Cut to Final Healing

Osteoporotic fractures are a growing issue due to the increasing incidence of osteoporosis worldwide. High reoperation rates in osteoporotic fractures call for investigation into new methods in improving fixation of osteoporotic bones. In the present study, the strength of a recently developed bone bioadhesive, OsStic^tm, was evaluated in vivo using a novel bone core assay in a murine animal model at 0, 3, 7, 14, 28, and 42 days. Histology and micro-CT were obtained at all time points, and the mean peak pull-out force was assessed on days 0–28. The adhesive provided immediate fixation to the bone core. The mean peak bone core pull-out force gradually decreased from 6.09 N (σ 1.77 N) at day 0 to a minimum of 3.09 N (σ 1.08 N) at day 7, recovering to 6.37 N (σ 4.18 N) by day 28. The corresponding fibrin (Tisseel) control mean peak bone core pull-out characteristic was 0.27 N (σ 0.27 N) at day 0, with an abrupt increase from 0.37 N (σ 0.28) at day 3, 6.39 N (σ 5.09 N) at day 7, and continuing to increase to 11.34 N (σ 6.5 N) by day 28. The bone cores failed either through core pull-out or by the cancellous part of the core fracturing. Overall, the adhesive does not interrupt healing with pathological changes or rapid resorption. Initially, the adhesive bonded the bone core to the femur, and over time, the adhesive was replaced by a vascularised bone of equivalent quality and quantity to the original bone. At the 42 day time point, 70% of the adhesive in the cancellous compartment and 50% in the cortical compartment had been replaced. The adhesive outwith the bone shell was metabolized by cells that are only removing the material excess with no ectopic bone formation. It is concluded that the adhesive is not a physical and biochemical barrier as the bone heals through the adhesive and is replaced by a normal bone tissue. This adhesive composition meets many of the clinical unmet needs expressed in the literature, and may, after further preclinical assessments, have potential in the repair of bone and osteochondral fragments.

Fabrication and characterization of a bioactive polymethylmethacrylate-based porous cement loaded with strontium/calcium apatite nanoparticles

Polymethylmethacrylate (PMMA)-based cements are used for bone reparation due to their biocompatibility, suitable mechanical properties, and mouldability. However, these materials suffer from high exothermic polymerization and poor bioactivity, which can cause the formation of fibrous tissue around the implant and aseptic loosening. Herein, we tackled these problems by adding Sr²⁺ -substituted hydroxyapatite nanoparticles (NPs) and a porogenic compound to the formulations, thus creating a microenvironment suitable for the proliferation of osteoblasts. The NPs resembled the structure of the bone's apatite and enabled the controlled release of Sr²⁺ . Trends in the X-ray patterns and infrared spectra confirmed that Sr²⁺ replaced Ca²⁺ in the whole composition range of the NPs. The inclusion of an effervescent additive reduced the polymerization temperature and lead to the formation of highly porous cement exhibiting mechanical properties comparable to the trabecular bone. The formation of an opened and interconnected matrix allowed osteoblasts to penetrate the cement structure. Most importantly, the gas formation confined the NPs at the surface of the pores, guaranteeing the controlled delivery of Sr²⁺ within a concentration sufficient to maintain osteoblast viability. Additionally, the cement was able to form apatite when immersed into simulated body fluids, further increasing its bioactivity. Therefore, we offer a formulation of PMMA cement with improved in vitro performance supported by enhanced bioactivity, increased osteoblast viability and deposition of mineralized matrix assigned to the loading with Sr²⁺ -substituted hydroxyapatite NPs and the creation of an interconnected porous structure. Altogether, our results hold promise for enhanced bone reparation guided by PMMA cements.

Bone Organic-Inorganic Phase Ratio Is a Fundamental Determinant of Bone Material Quality

Background

Bone mineral density is widely used by clinicians for screening osteoporosis and assessing bone strength. However, its effectiveness has been reported unsatisfactory. In this study, it is demonstrated that bone organic-inorganic phase ratio is a fundamental determinant of bone material quality measured by stiffness, strength, and toughness.

Methods and Results

Two-hundred standard bone specimens were fabricated from bovine legs, with a specialized manufacturing method that was designed to reduce the effect of bone anisotropy. Bone mechanical properties of the specimens, including Young's modulus, yield stress, peak stress, and energy-to-failure, were measured by mechanical testing. Organic and inorganic mass contents of the specimens were then determined by bone ashing. Bone density and organic-inorganic phase ratio in the specimens were calculated. Statistical methods were applied to study relationships between the measured mechanical properties and the organic-inorganic phase ratios. Statistical characteristics of organic-inorganic phase ratios in the specimens with top material quality were investigated. Bone organic-inorganic phase ratio had strong Spearman correlation with bone material properties. Bone specimens that had the highest material quality had a very narrow scope of organic-inorganic phase ratio, which could be considered as the “optimal” ratio among the tested specimens.

Conclusion

Bone organic-inorganic phase ratio is a fundamental determinant of bone material quality. There may exist an “optimal” ratio for the bone to achieve top material quality. Deviation from the “optimal” ratio is probably the fundamental cause of various bone diseases. This study suggests that bone organic-inorganic phase ratio should be considered in clinical assessment of fracture risk.

3D printing of hierarchical porous biomimetic hydroxyapatite scaffolds: Adding concavities to the convex filaments

Porosity plays a key role on the osteogenic performance of bone scaffolds. Direct Ink Writing (DIW) allows the design of customized synthetic bone grafts with patient-specific architecture and controlled macroporosity. Being an extrusion-based technique, the scaffolds obtained are formed by arrays of cylindrical filaments, and therefore have convex surfaces. This may represent a serious limitation, as the role of surface curvature and more specifically the stimulating role of concave surfaces in osteoinduction and bone growth has been recently highlighted. Hence the need to design strategies that allow the introduction of concave pores in DIW scaffolds. In the current study, we propose to add gelatin microspheres as a sacrificial material in a self-setting calcium phosphate ink. Neither the phase transformation responsible for the hardening of the scaffold nor the formation of characteristic network of needle-like hydroxyapatite crystals was affected by the addition of gelatin microspheres. The partial dissolution of the gelatin resulted in the creation of spherical pores throughout the filaments and exposed on the surface, increasing filament porosity from 0.2 % to 67.9 %. Moreover, the presence of retained gelatin proved to have a significant effect on the mechanical properties, reducing the strength but simultaneously giving the scaffolds an elastic behavior, despite the high content of ceramic as a continuous phase. Notwithstanding the inherent difficulty of in vitro cultures with this highly reactive material an enhancement of MG-63 cell proliferation, as well as better spreading of hMSCs was recorded on the developed scaffolds. STATEMENT OF SIGNIFICANCE: Recent studies have stressed the role that concave surfaces play in tissue regeneration and, more specifically, in osteoinduction and osteogenesis. Direct ink writing enables the production of patient-specific bone grafts with controlled architecture. However, besides many advantages, it has the serious limitation that the surfaces obtained are convex. In this article, for the first time we develop a strategy to introduce concave pores in the printed filaments of biomimetic hydroxyapatite by incorporation and partial dissolution of gelatin microspheres. The retention of part of the gelatin results in a more elastic behavior compared to the brittleness of hydroxyapatite scaffolds, while the needle-shaped nanostructure of biomimetic hydroxyapatite is maintained and gelatin-coated concave pores on the surface of the filaments enhance cell spreading.