Microstructure design of biodegradable scaffold and its effect on tissue regeneration

3D-Printed Scaffolds for Cranial Bone Regeneration: A Systematic Review of Design, Materials, and Computational Optimization

Cranial bone defects from trauma, congenital conditions, or surgery are challenging to treat due to the skull's limited regeneration. Traditional methods like autografts and allografts have drawbacks, including donor site issues and poor integration. 3D-printed scaffolds provide a patient-specific alternative, improving bone regeneration and integration. This review evaluates advancements in 3D-printed scaffolds for cranial bone regeneration, focusing on fabrication techniques, material innovations, and structural optimization while assessing their preclinical and clinical potential. A systematic literature search (2014-2024) was conducted using PubMed and other databases. Studies addressing scaffold properties such as porosity, pore interconnectivity, and mechanical stability were included, while non-cranial scaffold studies were excluded. Advances in 3D printing have enabled patient-specific scaffolds with optimized architecture to enhance bone regeneration, mechanical support, and nutrient transport. Bioceramics, polymers, and composites mimic native bone properties, while bioactive coatings further improve osteogenesis. However, limited clinical translation and insufficient customization remain challenges. Further preclinical and clinical trials are crucial to overcoming barriers in mechanical optimization and patient-specific scaffold fabrication, bridging the gap between research and clinical applications.

Biomechanical properties of tetrahedral microstructure for design of the porous stem in total hip arthroplasty

Different internal strut architectures affect the biomechanical performance of porous lattice structures. This study aims to investigate these properties under various conditions using different methods.The finite element simulations of tetrahedral microstructures were conducted with varying internal strut thicknesses under different loads. The effective elastic modulus from compression tests aligned with the homogenization results. However, both the number and size of unit cells can influence the modulus at identical porosity levels. Smaller unit cell sizes demonstrated superior mechanical properties while utilizing less material.

Stem Cell-Laden Engineered Patch: Advances and Applications in Tissue Regeneration

Stem cell-based therapies are emerging as significant approaches in tissue engineering and regenerative medicine, applicable to both fundamental scientific research and clinical practice. Despite remarkable results in clinical studies, challenges such as poor standardization of graft tissues, limited sources, and reduced functionality have hindered the effectiveness of these therapies. In this review, we summarize the engineering approaches involved in fabricating stem cell assisted patches and the substantial strategies for designing stem cell-laden engineered patches (SCP) to complement the existing stem cell-based therapies. We then outline the potential applications of SCP in advancing tissue regeneration and regenerative medicine. By combining living stem cells with engineered patches, SCP can enhance the functions of both components, particularly for tissue engineering applications. Finally, we addressed current challenges, such as ethical considerations, high costs, and regulatory hurdles and proposed future research directions to overcome these barriers.

A review of computational optimization of bone scaffold architecture: methods, challenges, and perspectives

The design and optimization of bone scaffolds are critical for the success of bone tissue engineering (BTE) applications. This review paper provides a comprehensive analysis of computational optimization methods for bone scaffold architecture, focusing on the balance between mechanical stability, biological compatibility, and manufacturability. Finite element method (FEM), computational fluid dynamics (CFD), and various optimization algorithms are discussed for their roles in simulating and refining scaffold designs. The integration of multiobjective optimization and topology optimization has been highlighted for developing scaffolds that meet the multifaceted requirements of BTE. Challenges such as the need for consideration of manufacturing constraints and the incorporation of degradation and bone regeneration models into the optimization process have been identified. The review underscores the potential of advanced computational tools and additive manufacturing techniques in evolving the field of BTE, aiming to improve patient outcomes in bone tissue regeneration. The reliability of current optimization methods is examined, with suggestions for incorporating non-deterministic approaches andin vivovalidations to enhance the practical application of optimized scaffolds. The review concludes with a call for further research into artificial intelligence-based methods to advance scaffold design and optimization.

3D Bilayered Hydrogel and Nanofiber Multifunctional Sponge Dressing: An Efficacious Healing Agent for Chronic Wound Healing

Chronic wound management using biomaterial-based dressings has significantly impacted the standard and efficiency of wound healing. However, various available wound healing aids are ineffective in treating deep open injuries and chronic wounds such as diabetic wounds. Herein, we developed a 3D bilayered multifunctional sponge, which addresses the structural and functional issues faced by biomaterial dressings in treating deep and chronic wounds. The 3D bilayered sponge consists of a hydrogel base functionalized with wound healing peptide (Tylotoin)-carrying nanoparticles and topped with a nanofiber layer functionalized with an antimicrobial peptide (LLKKK18). The 3D bilayered sponge, with its highly porous, elastic, and enhanced fluid absorption ability, makes it a suitable wound treatment aid. The developed multifunctional 3D sponge shows antibacterial action and promotes a microenvironment similar to the extracellular matrix (ECM) in regulating dermal cell survival and migration. Study in a full-thickness skin defect diabetic mouse model has shown that the developed 3D bilayered sponge accelerated wound closure and promoted functional skin regeneration through reduced inflammation, faster granulation tissue formation, re-epithelialization, neovascularization, and skin appendage restoration, which make the developed 3D bilayered multifunctional sponge an efficient and advanced chronic wound management aid with potential for future clinical application.

Computational models of bone fracture healing and applications: a review

Fracture healing is a very complex physiological process involving multiple events at different temporal and spatial scales, such as cell migration and tissue differentiation, in which mechanical stimuli and biochemical factors assume key roles. With the continuous improvement of computer technology in recent years, computer models have provided excellent solutions for studying the complex process of bone healing. These models not only provide profound insights into the mechanisms of fracture healing, but also have important implications for clinical treatment strategies. In this review, we first provide an overview of research in the field of computational models of fracture healing based on CiteSpace software, followed by a summary of recent advances, and a discussion of the limitations of these models and future directions for improvement. Finally, we provide a systematic summary of the application of computational models of fracture healing in three areas: bone tissue engineering, fixator optimization and clinical treatment strategies. The application of computational models of bone healing in clinical treatment is immature, but an inevitable trend, and as these models become more refined, their role in guiding clinical treatment will become more prominent.

Multiscale topology optimization of pelvic bone for combined walking and running gait cycles

We propose a multiscale topology optimization procedure of pelvic bone using weighted compliance minimization. In macroscale optimization, a level set-based method is used, which gives a binary structure. In microscale optimization, cubic lattice-based homogenization is done while keeping the global geometry fixed. For the macroscale, a volume constraint equal to the volume of the pelvic bone is imposed, whereas, for the microscale, a mass constraint equal to the mass of the pelvic bone is imposed. The optimal geometries are compared with pelvic bone using different metrics and show good similarity with the same. Designed geometries are additively manufactured and experimentally tested for stiffness.

A 3D-Printed Scaffold for Repairing Bone Defects

The treatment of bone defects has always posed challenges in the field of orthopedics. Scaffolds, as a vital component of bone tissue engineering, offer significant advantages in the research and treatment of clinical bone defects. This study aims to provide an overview of how 3D printing technology is applied in the production of bone repair scaffolds. Depending on the materials used, the 3D-printed scaffolds can be classified into two types: single-component scaffolds and composite scaffolds. We have conducted a comprehensive analysis of material composition, the characteristics of 3D printing, performance, advantages, disadvantages, and applications for each scaffold type. Furthermore, based on the current research status and progress, we offer suggestions for future research in this area. In conclusion, this review acts as a valuable reference for advancing the research in the field of bone repair scaffolds.

Multifunctional polydopamine/hemin-cyclodextrin reinforced chitosan nanocomposite hydrogel: A synergistic platform for wound healing

Chronic cutaneous wounds present a significant challenge for healthcare providers globally, with the risk of bacterial infections emerging as a particularly concerning issue. There is an increasing need to employ a combination of diverse antibacterial strategies to address infections comprehensively in chronic wounds. This study introduces a highly efficient antibacterial platform that encapsulates the NO precursor (BNN6) into β-cyclodextrin-modified hemin-bearing polydopamine nanoparticles called NO/CHPDA. These nanoparticles are seamlessly integrated into a hydrogel composite comprised of L-arginine grafted chitosan (Arg-CS) and oxide dextrans (oDex). The amalgamation of photothermal therapy (PTT), chemodynamic therapy (CDT), and nitric oxide (NO) antibacterial strategies within the NO/CHPDA@Arg-CS/oDex nanocomposite hydrogel demonstrates a synergistic and highly effective capacity to eradicate bacteria and accelerate the wound healing process in vivo. Remarkably, this nanocomposite hydrogel maintains excellent biocompatibility and induces minimal side effects. The resulting nanocomposite hydrogel represents a promising therapeutic solution for treating bacterial infections in wound healing applications.

Bone Regeneration Induced by Patient-Adapted Mg Alloy-Based Scaffolds for Bone Defects: Present and Future Perspectives

Treatment of bone defects resulting after tumor surgeries, accidents, or non-unions is an actual problem linked to morbidity and the necessity of a second surgery and often requires a critical healthcare cost. Although the surgical technique has changed in a modern way, the treatment outcome is still influenced by patient age, localization of the bone defect, associated comorbidities, the surgeon approach, and systemic disorders. Three-dimensional magnesium-based scaffolds are considered an important step because they can have precise bone defect geometry, high porosity grade, anatomical pore shape, and mechanical properties close to the human bone. In addition, magnesium has been proven in in vitro and in vivo studies to influence bone regeneration and new blood vessel formation positively. In this review paper, we describe the magnesium alloy's effect on bone regenerative processes, starting with a short description of magnesium's role in the bone healing process, host immune response modulation, and finishing with the primary biological mechanism of magnesium ions in angiogenesis and osteogenesis by presenting a detailed analysis based on a literature review. A strategy that must be followed when a patient-adapted scaffold dedicated to bone tissue engineering is proposed and the main fabrication technologies are combined, in some cases with artificial intelligence for Mg alloy scaffolds, are presented with examples. We emphasized the microstructure, mechanical properties, corrosion behavior, and biocompatibility of each study and made a basis for the researchers who want to start to apply the regenerative potential of magnesium-based scaffolds in clinical practice. Challenges, future directions, and special potential clinical applications such as osteosarcoma and persistent infection treatment are present at the end of our review paper.

Virtual Design of 3D-Printed Bone Tissue Engineered Scaffold Shape Using Mechanobiological Modeling: Relationship of Scaffold Pore Architecture to Bone Tissue Formation

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

Silk fibroin-hydroxyapatite scaffolds promote the proliferation of adipose-derived mesenchymal stem cells by activating the ERK signal

Adipose-derived mesenchymal stem cell (Ad-MSC) with capacities of releasing trophic factors and chondrogenic differentiation was a promising candidate for tracheal reconstruction. Silk fibroin (SF)- hydroxyapatite (HA) scaffolds were fabricated by the freeze-drying method. And Ad-MSCs were co-cultured on the scaffolds for 14 days in vitro. The role of the SF-HA scaffold in regulating the adhesion, growth, and proliferation of Ad-MSCs, and its potential mechanisms were investigated. The identity of Ad-MSCs was confirmed by cell morphology, surface markers, and differentiation characteristics. Cell proliferation, viability, and morphology were observed via CCK-8, live/dead assay, and scanning electron microscopy (SEM). Gene mRNA and protein levels were examined using quantitative real-time polymerase chain reaction and western blotting, respectively. SF-HA scaffolds showed excellent properties of promoting Ad-MSCs adhesion, growth, and proliferation for at least 14 days. In the CCK-8 assay, the relative OD value of Ad-MSCs cultured on SF-HA scaffolds increased (p < 0.001). Furthermore, live/dead staining showed that the fluorescent coverage increased with time (p < 0.05). SEM also showed that 3 days after inoculation, the coverage of Ad-MSCs on the SF-HA scaffolds was 78.15%, increased to 92.91% on day 7, and reached a peak of 94.38% on day 14. Extracellular signal-regulated kinase (ERK) mRNA and phosphorylated ERK (pERK) protein expression increased at day 3 (p < 0.05), followed by a significant decline at day 7 (p < 0.05). And ERK mRNA expression was positively correlated with Ad-MSCs proliferation (p < 0.05). In summary, the SF-HA scaffold co-cultured with Ad-MSCs is a promising biomaterial for tracheal repair by activating the ERK signal pathway.

Review on Bioinspired Design of ECM-Mimicking Scaffolds by Computer-Aided Assembly of Cell-Free and Cell Laden Micro-Modules

Tissue engineering needs bioactive drug delivery scaffolds capable of guiding cell biosynthesis and tissue morphogenesis in three dimensions. Several strategies have been developed to design and fabricate ECM-mimicking scaffolds suitable for directing in vitro cell/scaffold interaction, and controlling tissue morphogenesis in vivo. Among these strategies, emerging computer aided design and manufacturing processes, such as modular tissue unit patterning, promise to provide unprecedented control over the generation of biologically and biomechanically competent tissue analogues. This review discusses recent studies and highlights the role of scaffold microstructural properties and their drug release capability in cell fate control and tissue morphogenesis. Furthermore, the work highlights recent advances in the bottom-up fabrication of porous scaffolds and hybrid constructs through the computer-aided assembly of cell-free and/or cell-laden micro-modules. The advantages, current limitations, and future challenges of these strategies are described and discussed.

A review on design of scaffold for osteoinduction: Toward the unification of independent design variables

Biophysical stimulus quantifies the osteoinductivity of the scaffold concerning the mechanoregulatory mathematical models of scaffold-assisted cellular differentiation. Consider a set of independent structural variables ($) that comprises bulk porosity levels ([Formula: see text]) and a set of morphological features of the micro-structure ([Formula: see text]) associated with scaffolds, i.e., [Formula: see text]. The literature suggests that biophysical stimulus ([Formula: see text]) is a function of independent structural variables ($). Limited understanding of the functional correlation between biophysical stimulus and structural features results in the lack of the desired osteoinductivity in a scaffold. Consequently, it limits their broad applicability to assist bone tissue regeneration for treating critical-sized bone fractures. The literature indicates the existence of multi-dimensional independent design variable space as a probable reason for the general lack of osteoinductivity in scaffolds. For instance, known morphological features are the size, shape, orientation, continuity, and connectivity of the porous regions in the scaffold. It implies that the number of independent variables ([Formula: see text]) is more than two, i.e., [Formula: see text], which interact and influence the magnitude of [Formula: see text] in a unified manner. The efficiency of standard engineering design procedures to analyze the correlation between dependent variable ([Formula: see text]) and independent variables ($) in 3D mutually orthogonal Cartesian coordinate system diminishes proportionally with the increase in the number of independent variables ([Formula: see text]) (Deb in Optimization for engineering design-algorithms and examples, PHI Learning Private Limited, New Delhi, 2012). Therefore, there is an immediate need to devise a framework that has the potential to quantify the micro-structural's morphological features in a unified manner to increase the prospects of scaffold-assisted bone tissue regeneration.

Nondeterministic multiobjective optimization of 3D printed ceramic tissue scaffolds

Despite significant advances in the design optimization of bone scaffolds for enhancing their biomechanical properties, the functionality of these synthetic constructs remains suboptimal. One of the main challenges in the structural optimization of bone scaffolds is associated with the large uncertainties caused by the manufacturing process, such as variations in scaffolds' geometric features and constitutive material properties after fabrication. Unfortunately, such non-deterministic issues have not been considered in the existing optimization frameworks, thereby limiting their reliability. To address this challenge, a novel multiobjective robust optimization approach is proposed here such that the effects of uncertainties on the optimized design can be minimized. This study first conducted computational analyses of a parameterized ceramic scaffold model to determine its effective modulus, structural strength, and permeability. Then, surrogate models were constructed to formulate explicit mathematical relationships between the geometrical parameters (design variables) and mechanical and fluidic properties. The Non-Dominated Sorting Genetic Algorithm II (NSGA-II) was adopted to generate the robust Pareto solutions for an optimal set of trade-offs between the competing objective functions while ensuring the effects of the noise parameters to be minimal. Note that the nondeterministic optimization of tissue scaffold presented here is the first of its kind in open literature, which is expected to shed some light on this significant topic of scaffold design and additive manufacturing in a more realistic way.

A mechanobiological computer optimization framework to design scaffolds to enhance bone regeneration

The treatment of large bone defects is a clinical challenge. 3D printed scaffolds are a promising treatment option for such critical-size defects. However, the design of scaffolds to treat such defects is challenging due to the large number of variables impacting bone regeneration; material stiffness, architecture or equivalent scaffold stiffness—due it specific architecture—have all been demonstrated to impact cell behavior and regeneration outcome. Computer design optimization is a powerful tool to find optimal design solutions within a large parameter space for given anatomical constraints. Following this approach, scaffold structures have been optimized to avoid mechanical failure while providing beneficial mechanical stimulation for bone formation within the scaffold pores immediately after implantation. However, due to the dynamics of the bone regeneration process, the mechanical conditions do change from immediately after surgery throughout healing, thus influencing the regeneration process. Therefore, we propose a computer framework to optimize scaffold designs that allows to promote the final bone regeneration outcome. The framework combines a previously developed and validated mechanobiological bone regeneration computer model, a surrogate model for bone healing outcome and an optimization algorithm to optimize scaffold design based on the level of regenerated bone volume. The capability of the framework is verified by optimization of a cylindrical scaffold for the treatment of a critical-size tibia defect, using a clinically relevant large animal model. The combined framework allowed to predict the long-term healing outcome. Such novel approach opens up new opportunities for sustainable strategies in scaffold designs of bone regeneration.

The Degradation of Synthetic Polymeric Scaffolds With Strut-like Architecture Influences the Mechanics-dependent Repair Process of an Osteochondral Defect in Silico

Current clinical treatments of osteochondral defects in articulating joints are frequently not successful in restoring articular surfaces. Novel scaffold-based tissue engineering strategies may help to improve current treatment options and foster a true regeneration of articulating structures. A frequently desired property of scaffolds is their ability to degrade over time and allow a full restoration of tissue and function. However, it remains largely unknown how scaffold degradation influences the mechanical stability of the tissue in a defect region and, in turn, the regenerative process. Such differing goals–supporting regeneration by degrading its own structure–can hardly be analyzed for tissue engineered constructs in clinical trials and in vivo preclinical experiments. Using an in silico analysis, we investigated the degradation-induced modifications in material and architectural properties of a scaffold with strut-like architecture over the healing course and their influence on the mechanics-dependent tissue formation in osteochondral defects. The repair outcome greatly varied depending on the degradation modality, i.e. surface erosion or bulk degradation with and without autocatalysis, and of the degradation speed, i.e. faster, equal or slower than the expected repair time. Bulk degradation with autocatalysis, independently of degradation speed, caused the mechanical failure of the scaffold prior to osteochondral defect repair and was thereby deemed inappropriate for further application. On the other hand, scaffolds with strut-like architecture degrading by both surface erosion and bulk degradation with slow degradation speed resulted in comparably good repair outcomes, thereby indicating such degradation modalities as favorable for the application in osteochondral defects.

Biphasic mineralized collagen based composite scaffold for cranial bone regeneration in developing sheep

Appropriate mechanical support and excellent osteogenic capability are two essential prerequisites of customized implants for regenerating large-sized cranial bone defect. Although porous bone scaffolds have been widely proven to promote bone regeneration, their weak mechanical properties limit the clinical applications in cranioplasty. Herein, we applied two previously developed mineralized collagen-based bone scaffolds (MC), porous MC (pMC) and compact MC (cMC) to construct a biphasic MC composite bone scaffold (bMC) to repair the large-sized cranial bone defect in developing sheep. A supporting frame composed of cMC phase in the shape of tic–tac–toe structure was fabricated first and then embedded in pMC phase. The two phases had good interfacial bond, attributing to the formation of an interfacial zone. The in vivo performance of the bMC scaffold was evaluated by using a cranial bone defect model in 1-month-old sheep. The computed tomography imaging, X-ray scanning and histological evaluation showed that the pMC phase in the bMC scaffold, similar to the pMC scaffold, was gradually replaced by the regenerative bone tissues with comprehensively increased bone mineral density and complete connection of bone bridge in the whole region. The cMC frame promoted new bone formation beneath the frame without obvious degradation, thus providing appropriate mechanical protection and ensuring the structural integrity of the implant. In general, the sheep with bMC implantation exhibited the best status of survival, growth and the repair effect. The biphasic structural design may be a prospective strategy for developing new generation of cranioplasty materials to regenerate cranial bone defect in clinic.

Lotus root and osteons-inspired channel structural scaffold mediate cell biomineralization and vascularized bone tissue regeneration

The interconnectivity of porous scaffold is vital for cell and tissue infiltration, and vascular networks formation, determining the successful bone regeneration in large bone defects. Here, inspired by the lotus-root and Haversian system of natural bone, a nano-hydroxyapatite/polyurethane (n-HA/PU) lotus root-like scaffold inlaid with micro holes on the wall of the adjacent channel was utilized to mediate cell biomineralization and vascularized bone tissue regeneration. Such a particular lotus-type structure remarkably promoted cells to proliferate and infiltrate into the center of the entire scaffold, serving as a clue to account for regulating cell alignment and differentiation physically. In vitro studies suggested that apatite accumulated dramatically on the channel wall in the lotus-type scaffold, probably promoting specific osteogenic differentiation of cells by the orientated channels, even in the absence of osteogenic factors. In vivo creation of critical bone defects (15-mm segments) was done in the radius of rabbits and implanted with the scaffold of different geometry to assess the structural parameters on the efficacy of new bone regeneration. The more extensive positive staining of BMP-2, more considerable amount of infiltrated capillary, more robust new bone formation, particularly the biomechanical strength of lotus-type scaffold group could reach the level of the control group without surgery, indicating that the lotus-type scaffold was more favorable for new bone tissue formation along tube-like channels. These results highlighted the potential of this biomimetic scaffold for cell and tissue infiltration and thus repair large bony defects.

Modeling the biomechanics of the lamina cribrosa microstructure in the human eye

Glaucoma is among the leading causes of blindness worldwide that is characterized by irreversible damage to the retinal ganglion cell axons in the lamina cribrosa (LC) region of the optic nerve head (ONH), most often associated with elevated intraocular pressure (IOP). The LC is a porous, connective tissue structure that provides mechanical support to the axons as they exit the eye and the biomechanics of the LC microstructure likely play a crucial role in protecting the axons passing through it. There is a limited knowledge of the IOP-driven biomechanics of the LC microstructure, primarily due to its small size and the difficulty with imaging the LC both in vitro and in vivo. We present finite element (FE) models of three human eye posterior poles that include the LC microstructure and interspersed neural tissues (NT) composed of retinal axons that are constructed directly from segmented, binary images of the LC. These models were used to estimate the stresses and strains in the LC and NT for an acute IOP elevation from 0 to 45 mmHg and compared with identical models except that the LC was represented as a homogenized continuum material with either homogeneous isotropic neo-Hookean properties or heterogeneous properties derived from local connective tissue volume fraction (CTVF) and predominant LC beam orientation. Stresses and strains in the LC and NT microstructure were investigated, and results were compared against those from the models wherein the LC was represented as a homogenized continuum. The regionalized volumetric average stresses and strains showed that the microstructural model yielded similar patterns to our prior approach using an LC continuum representation with mapped LC CTVF/anisotropy, but the microstructural modeling approach allows analysis of the stresses and strains in the LC and NT separately. As expected, the LC beams carried most of the IOP load in the microstructural models but exhibited less strain, while the encapsulated NT exhibited lower stresses and much higher strains. Results also revealed that the continuum models underestimate the maximum strains in the LC beams and NT by a factor of 2-3. Microstructural modeling should provide greater insight into the biomechanical factors driving damage to the axons (NT) and LC connective tissue remodeling that occur in glaucoma. The methods presented are ideal for modeling any structure with a complex microstructure composed of different materials, such as trabecular bone, lung, and tissue engineering scaffolds such as decellularized LC. Matlab code for mesh generation from a segmented image stack of the microstructure is included as Supplemental Material. STATEMENT OF SIGNIFICANCE: Glaucoma is among the leading causes of blindness worldwide that is characterized by axon damage in the lamina cribrosa (LC) region of the eye. We present a new approach for finite element modeling the entire eye-specific 3D LC microstructure and the interspersed neural tissues, incorporated into an eye-specific posterior eye model that provides appropriate boundary and loading conditions. Results are presented for three human donor eyes, showing that prior modeling approaches underestimate the stresses and strains in the laminar microstructure. We constructed models from image stacks of the segmented microstructure (Matlab code included) using an approach that is ideal for modeling any structure with a complex microstructure composed of different materials, such as trabecular bone, lung, and tissue engineering scaffolds.

A machine learning-based multiscale model to predict bone formation in scaffolds

Computational modeling methods combined with non-invasive imaging technologies have exhibited great potential and unique opportunities to model new bone formation in scaffold tissue engineering, offering an effective alternate and viable complement to laborious and time-consuming in vivo studies. However, existing numerical approaches are still highly demanding computationally in such multiscale problems. To tackle this challenge, we propose a machine learning (ML)-based approach to predict bone ingrowth outcomes in bulk tissue scaffolds. The proposed in silico procedure is developed by correlating with a dedicated longitudinal (12-month) animal study on scaffold treatment of a major segmental defect in sheep tibia. Comparison of the ML-based time-dependent prediction of bone ingrowth with the conventional multilevel finite element (FE2) model demonstrates satisfactory accuracy and efficiency. The ML-based modeling approach provides an effective means for predicting in vivo bone tissue regeneration in a subject-specific scaffolding system.

Initial mechanical conditions within an optimized bone scaffold do not ensure bone regeneration - an in silico analysis

Large bone defects remain a clinical challenge because they do not heal spontaneously. 3-D printed scaffolds are a promising treatment option for such critical defects. Recent scaffold design strategies have made use of computer modelling techniques to optimize scaffold design. In particular, scaffold geometries have been optimized to avoid mechanical failure and recently also to provide a distinct mechanical stimulation to cells within the scaffold pores. This way, mechanical strain levels are optimized to favour the bone tissue formation. However, bone regeneration is a highly dynamic process where the mechanical conditions immediately after surgery might not ensure optimal regeneration throughout healing. Here, we investigated in silico whether scaffolds presenting optimal mechanical conditions for bone regeneration immediately after surgery also present an optimal design for the full regeneration process. A computer framework, combining an automatic parametric scaffold design generation with a mechano-biological bone regeneration model, was developed to predict the level of regenerated bone volume for a large range of scaffold designs and to compare it with the scaffold pore volume fraction under favourable mechanical stimuli immediately after surgery. We found that many scaffold designs could be considered as highly beneficial for bone healing immediately after surgery; however, most of them did not show optimal bone formation in later regenerative phases. This study allowed to gain a more thorough understanding of the effect of scaffold geometry changes on bone regeneration and how to maximize regenerated bone volume in the long term.

Evaluation of mechanical properties of Ti-25Nb BCC porous cell structure and their association with structure porosity: A combined finite element analysis and analytical approach for orthopedic application

Ti-based alloys have been commonly employed in manufacturing implants for orthopedic applications. Binary Titanium-Niobium (Ti-25Nb) alloy is a promising material for potential applications in orthopedics because of their lower elastic moduli and superior biocompatibility than the conventional Ti-based alloys. Implants with porous structures encourage bone ingrowth and reduce the effect of stress-shielding further. This study is aimed at establishing the relationship between the mechanical performance and structural parameters of porous body-centered-cubic (BCC) structures made up of Ti-25Nb (25% by wt.). Solid models of BCC porous structures were constructed (unit cell size: 2 mm; overall size: 8 × 8 × 8 mm³). Finite element analysis (FEA) of the BCC structures with porosity ranging from 29% to 79% (seven porosities) was conducted under tension, bending, and torsional loads. The Gibson-Ashby model and Exponential regression model were also employed to determine the stiffness of the above porous structures. The functional relationships between effective Young's modulus, effective yield strength, and porosity generated from both the models were found to match the FEA results well. Results indicated that porosity in the range of 50%-70% can be used to design graded porous stems to mimic the mechanical properties of cortical bone.

Mechano-driven regeneration predicts response variations in large animal model based on scaffold implantation site and individual mechano-sensitivity

It is well founded that the mechanical environment may regulate bone regeneration in orthopedic applications. The purpose of this study is to investigate the mechanical contributions of the scaffold and the host to bone regeneration, in terms of subject specificity, implantation site and sensitivity to the mechanical environment. Using a computational approach to model mechano-driven regeneration, bone ingrowth in porous titanium scaffolds was simulated in the distal femur and proximal tibia of three goats and compared to experimental results. The results showed that bone ingrowth shifted from a homogeneous distribution pattern, when scaffolds were in contact with trabecular bone (max local ingrowth 12.47%), to a localized bone ingrowth when scaffolds were implanted in a diaphyseal location (max local ingrowth 20.64%). The bone formation dynamics revealed an apposition rate of 0.37±0.28%/day in the first three weeks after implantation, followed by limited increase in bone ingrowth until the end of the experiment (12 weeks). According to in vivo data, we identified one animal whose sensitivity to mechanical stimulation was higher than the other two. Moreover, we found that the stimulus initiating bone formation was consistently higher in the femur than in the tibia for all the individuals. Overall, the dependence of the osteogenic response on the host biomechanics means that, from a mechanical perspective, the regenerative potential depends on both the scaffold and the host environment. Therefore, this work provides insights on how the mechanical conditions of both the recipient and the scaffold contribute to meet patient and location-specific characteristics.

Berberine-releasing electrospun scaffold induces osteogenic differentiation of DPSCs and accelerates bone repair

The repair of skeletal defects in maxillofacial region remains an intractable problem, the rising technology of bone tissue engineering provides a new strategy to solve it. Scaffolds, a crucial element of tissue engineering, must have favorable biocompatibility as well as osteoinductivity. In this study, we prepared berberine/polycaprolactone/collagen (BBR/PCL/COL) scaffolds with different concentrations of berberine (BBR) (25, 50, 75 and 100 μg/mL) through electrospinning. The influence of dosage on scaffold morphology, cell behavior and in vivo bone defect repair were systematically studied. The results indicated that scaffolds could release BBR stably for up to 27 days. Experiments in vitro showed that BBR/PCL/COL scaffolds had appropriate biocompatibility in the concentration of 25-75 μg/mL, and 50 and 75 μg/mL scaffolds could significantly promote osteogenic differentiation of dental pulp stem cells. Scaffold with 50 μg/mL BBR was implanted into the critical bone defect of rats to evaluate the ability of bone repair in vivo. It was found that BBR/PCL/COL scaffold performed more favorable than polycaprolactone/collagen (PCL/COL) scaffold. Overall, our study is the first to evaluate the capability of in vivo bone repair of BBR/PCL/COL electrospun scaffold. The results indicate that BBR/PCL/COL scaffold has prospective potential for tissue engineering applications in bone regeneration therapy.

A time-dependent mechanobiology-based topology optimization to enhance bone growth in tissue scaffolds

Scaffold-based bone tissue engineering has been extensively developed as a potential means to treatment of large bone defects. To enhance the biomechanical performance of porous tissue scaffolds, computational design techniques have gained growing popularity attributable to their compelling efficiency and strong predictive features compared with time-consuming trial-and-error experiments. Nevertheless, the mechanical stimulus necessary for bone regeneration, which characterizes dynamic nature due to continuous variation in the bone-scaffold construct system as a result of bone-ingrowth and scaffold biodegradation, is often neglected. Thus, this study proposes a time-dependent mechanobiology-based topology optimization framework for design of tissue scaffolds, thereby developing an ongoing favorable microenvironment and ensuring a long-term outcome for bone regeneration. For the first time, a level-set based topology optimization algorithm and a time-dependent shape derivative are developed to optimize the scaffold architecture. In this study, a large bone defect in a simulated 2D femur model and a partial defect in a 3D femur model are considered to demonstrate the effectiveness of the proposed design method. The results are compared with those obtained from stiffness-based topology optimization, time-independent design and typical scaffold constructs, showing significant advantages in continuing bone ingrowth outcomes.

Challenges on optimization of 3D-printed bone scaffolds

Advances in biomaterials and the need for patient-specific bone scaffolds require modern manufacturing approaches in addition to a design strategy. Hybrid materials such as those with functionally graded properties are highly needed in tissue replacement and repair. However, their constituents, proportions, sizes, configurations and their connection to each other are a challenge to manufacturing. On the other hand, various bone defect sizes and sites require a cost-effective readily adaptive manufacturing technique to provide components (scaffolds) matching with the anatomical shape of the bone defect. Additive manufacturing or three-dimensional (3D) printing is capable of fabricating functional physical components with or without porosity by depositing the materials layer-by-layer using 3D computer models. Therefore, it facilitates the production of advanced bone scaffolds with the feasibility of making changes to the model. This review paper first discusses the development of a computer-aided-design (CAD) approach for the manufacture of bone scaffolds, from the anatomical data acquisition to the final model. It also provides information on the optimization of scaffold's internal architecture, advanced materials, and process parameters to achieve the best biomimetic performance. Furthermore, the review paper describes the advantages and limitations of 3D printing technologies applied to the production of bone tissue scaffolds.

Relationship between the morphological, mechanical and permeability properties of porous bone scaffolds and the underlying microstructure

Bone scaffolds are widely used as one of the main bone substitute materials. However, many bone scaffold microstructure topologies exist and it is still unclear which topology to use when designing scaffold for a specific application. The aim of the present study was to reveal the mechanism of the microstructure-driven performance of bone scaffold and thus to provide guideline on scaffold design. Finite element (FE) models of five TPMS (Diamond, Gyroid, Schwarz P, Fischer-Koch S and F-RD) and three traditional (Cube, FD-Cube and Octa) scaffolds were generated. The effective compressive and shear moduli of scaffolds were calculated from the mechanical analysis using the FE unit cell models with the periodic boundary condition. The scaffold permeability was calculated from the computational fluid dynamics (CFD) analysis using the 4×4×4 FE models. It is revealed that the surface-to-volume ratio of the Fischer-Koch S-based scaffold is the highest among the scaffolds investigated. The mechanical analysis revealed that the bending deformation dominated structures (e.g., the Diamond, the Gyroid, the Schwarz P) have higher effective shear moduli. The stretching deformation dominated structures (e.g., the Schwarz P, the Cube) have higher effective compressive moduli. For all the scaffolds, when the same amount of change in scaffold porosity is made, the corresponding change in the scaffold relative shear modulus is larger than that in the relative compressive modulus. The CFD analysis revealed that the structures with the simple and straight pores (e.g., Cube) have higher permeability than the structures with the complex pores (e.g., Fischer-Koch S). The main contribution of the present study is that the relationship between scaffold properties and the underlying microstructure is systematically investigated and thus some guidelines on the design of bone scaffolds are provided, for example, in the scenario where a high surface-to-volume ratio is required, it is suggested to use the Fischer-Koch S based scaffold.

Multiobjective Design Optimization of a Biconcave Mobile-Bearing Lumbar Total Artificial Disk Considering Spinal Kinematics, Facet Joint Loading, and Metal-on-Polyethylene Contact Mechanics

Total disk arthroplasty (TDA) using an artificial disk (AD) is an attractive surgical technique for the treatment of spinal disorders, since it can maintain or restore spinal motion (unlike interbody fusion). However, adverse surgical outcomes of contemporary lumbar TDAs have been reported. We previously proposed a new mobile-bearing AD design concept featuring a biconcave ultrahigh-molecular-weight polyethylene (UHMWPE) mobile core. The objective of this study was to develop an artificial neural network (NN) based multiobjective optimization framework to refine the biconcave-core AD design considering multiple TDA performance metrics, simultaneously. We hypothesized that there is a tradeoff relationship between the performance metrics in terms of range of motion (ROM), facet joint force (FJF), and polyethylene contact pressure (PCP). By searching the resulting three-dimensional (3D) Pareto frontier after multiobjective optimization, it was found that there was a "best-tradeoff" AD design, which could balance all the three metrics, without excessively sacrificing each metric. However, for each single-objective optimum AD design, only one metric was optimal, and distinct sacrifices were observed in the other two metrics. For a commercially available biconvex-core AD design, the metrics were even worse than the poorest outcomes of the single-objective optimum AD designs. Therefore, multiobjective design optimization could be useful for achieving native lumbar segment biomechanics and minimal PCPs, as well as for improving the existing lumbar motion-preserving surgical treatments.

Material Characterization of PCL:PLLA Electrospun Fibers Following Six Months Degradation In Vitro

The annulus fibrosus-one of the two tissues comprising the intervertebral disc-is susceptible to injury and disease, leading to chronic pain and rupture. A synthetic, biodegradable material could provide a suitable scaffold that alleviates this pain and supports repair through tissue regeneration. The transfer of properties, particularly biomechanical, from scaffold to new tissue is essential and should occur at the same rate to prevent graft failure post-implantation. This study outlines the effect of hydrolytic degradation on the material properties of a novel blend of polycaprolactone and poly(lactic acid) electrospun nanofibers (50:50) over a six-month period following storage in phosphate buffered saline solution at 37 °C. As expected, the molecular weight distribution for this blend decreased over the 180-day period. This was in line with significant changes to fiber morphology, which appeared swollen and merged following observation using Scanning Electron Microscopy. Similarly, hydrolysis resulted in considerable remodeling of the scaffolds' polymer chains as demonstrated by sharp increases in percentage crystallinity and tensile properties becoming stiffer, stronger and more brittle over time. These mechanical data remained within the range reported for human annulus fibrosus tissue and their long-term efficacy further supports this novel blend as a potential scaffold to support tissue regeneration.

Numerical Simulation of the Posterior Malleolus Fracture with the Finite Element Method

The high demand for biodegradable implants in bone fracture fixations has dramatically increased the use of polymers for biomedical applications as well. However, the replacement of stainless steel and titanium screws by biodegradable materials represents one of the most critical aspects of biomechanics. In this study, the mechanical behavior of polycaprolactone (PCL) in tension and compression is examined. Driven by the advanced technology of computational mechanics, the fixation of the posterior malleolus fracture has been designed and analyzed. The core idea depicts the static analysis of screws made of PCL fixed in the ankle joint. The focus of the study is on this bio-absorbable, polymer-based material performance under constant compression. Parametric analysis is employed for the optimization of the PCL scaffold. Future studies will focus on the experimental verification of the numerical analysis results.

A Review of Topology Optimisation for Fluid-Based Problems

This review paper provides an overview of the literature for topology optimisation of fluid-based problems, starting with the seminal works on the subject and ending with a snapshot of the state of the art of this rapidly developing field. “Fluid-based problems” are defined as problems where at least one governing equation for fluid flow is solved and the fluid–solid interface is optimised. In addition to fluid flow, any number of additional physics can be solved, such as species transport, heat transfer and mechanics. The review covers 186 papers from 2003 up to and including January 2020, which are sorted into five main groups: pure fluid flow; species transport; conjugate heat transfer; fluid–structure interaction; microstructure and porous media. Each paper is very briefly introduced in chronological order of publication. A quantititive analysis is presented with statistics covering the development of the field and presenting the distribution over subgroups. Recommendations for focus areas of future research are made based on the extensive literature review, the quantitative analysis, as well as the authors’ personal experience and opinions. Since the vast majority of papers treat steady-state laminar pure fluid flow, with no recent major advancements, it is recommended that future research focuses on more complex problems, e.g., transient and turbulent flow.

Towards multi-dynamic mechano-biological optimization of 3D-printed scaffolds to foster bone regeneration

Substantial tissue loss, such as in large bone defects, represents a clinical challenge for which regenerative therapies and tissue engineering strategies aim at offering treatment alternatives to conventional replacement approaches by metallic implants. 3D printing technologies provide endless opportunities to shape scaffold structures that could support endogenous regeneration. However, it remains unclear which of the numerous parameters at hand eventually enhance tissue regeneration. In the last decades, a significant effort has been made in the development of computer tools to optimize scaffold designs. Here, we aim at giving a more comprehensive overview summarizing current computer optimization framework technologies. We confront these with the most recent advances in scaffold mechano-biological optimization, discuss their limitations and provide suggestions for future development. We conclude that the field needs to move forward to not only optimize scaffolds to avoid implant failures but to improve their mechano-biological behaviour: providing an initial stimulus for fast tissue organisation and healing and accounting for remodelling, scaffold degradation and consecutive filling with host tissue. So far, modelling approaches fall short in including the various scales of tissue dynamics. With this review, we wish to stimulate a move towards multi-dynamic mechano-biological optimization of 3D-printed scaffolds. STATEMENT OF SIGNIFICANCE: Large bone defects represent a clinical challenge for which tissue engineering strategies aim at offering alternatives to conventional treatment strategies. 3D printing technologies provide endless opportunities to shape scaffold structures that could support endogenous regeneration. However, it remains unclear which of the numerous parameters at hand eventually enhance tissue regeneration. In the last decades, a significant effort has been made in the development of computer tools to optimize scaffold designs. This review summarizes current computer optimization frameworks and most recent advances in mechano-biological optimization of bone scaffolds to better stimulate bone regeneration. We wish to stimulate a move towards multi-dynamic mechano-biological optimization of 3D-printed scaffolds.

Additive manufacturing of biodegradable metals: Current research status and future perspectives

The combination of biodegradable metals and additive manufacturing (AM) leads to a revolutionary change of metal implants in many aspects including materials, design, manufacturing, and clinical applications. The AM of nondegradable metals such as titanium and CoCr alloys has proven to be a tremendous success in clinical applications. The AM of biodegradable metals including magnesium (Mg), iron (Fe), and zinc (Zn) is still in its infancy, although much progress has been made in the research field. Element loss and porosity are common processing problems for AM of biodegradable metals like Zn and Mg, which are mainly caused by evaporation during melting under a high-energy beam. The resulting formation quality and properties are closely related to material, design, and processing, making AM of biodegradable metals a typical interdisciplinary subject involving biomaterials, mechanical engineering, and medicine. This work reviews the state of research and future perspective on AM of biodegradable metals from extensive viewpoints such as material, processing, formation quality, design, microstructure, and properties. Effects of powder properties and processing parameters on formation quality are characterized in detail. The microstructure and metallurgical defects encountered in the AM parts are described. Mechanical and biodegradable properties of AM samples are introduced. Design principles and potential applications of biodegradable metal implants produced by AM are discussed. Finally, current research status is summarized together with some proposed future perspectives for advancing knowledge about AM of biodegradable metals. STATEMENT OF SIGNIFICANCE: Rapid development of research and applications on biodegradable metals and additive manufacturing (AM) has been made in recent years. Customized geometric shapes of medical metals with porous structure can be realized accurately and efficiently by laser powder bed fusion (L-PBF), which is beneficial to achieve reliable stress conduction and balanced properties. This review introduces the development history and current status of AM of biodegradable metals and then critically surveys L-PBF of Mg-, Fe-, and Zn-based metals from multiple viewpoints including materials, processing, formation quality, structural design, microstructure, and mechanical and biological properties. The present findings are summarized together with some proposed future challenges for advancing AM of biodegradable metals into real clinical applications.

Tuning pore features of mineralized collagen/PCL scaffolds for cranial bone regeneration in a rat model

Porosity is indispensable for a bone tissue-engineered scaffold for facilitating endogenous cell migration and nascent bone ingrowth. In large-sized cranial bone defect repair, porous scaffolds meet great challenges to match cranial bone regeneration and provide sufficient protection with structural integrity. Therefore, the pore features of the scaffolds for cranial bone regeneration should differ from those typical porous scaffolds used in tubular bone repair and be finely tuned. In this study, a series of porous mineralized collagen/PCL scaffolds with different pore features were fabricated via freeze-drying and applied in a Sprague Dawley rat cranial bone calvarial defect model. The pore size for four groups increased from 10-45 μm to 40-130 μm. As scaffold porosity increased, the compressive strength decreased from 2.09 ± 0.12 MPa to 0.51 ± 0.04 MPa. The micro-computed tomography three-dimensional reconstruction images showed that as pore size and porosity increased, the amount of new bone formation had a maximum in group 3 (pore size: 20-100 μm, compressive strength: 1.06 ± 0.03 MPa). In addition, the histological and histomorphometric analyses showed a consistent tendency which confirmed the Micro-CT results. Meanwhile, histological findings including bony bridging, tissue response at the bone-implant interface and fibrous capsule thickness indicated that the dura mater pathway played the most important role in the regenerative process of this calvarial defect model.

Graphene-based 3D scaffolds in tissue engineering: fabrication, applications, and future scope in liver tissue engineering

Tissue engineering embraces the potential of recreating and replacing defective body parts by advancements in the medical field. Being a biocompatible nanomaterial with outstanding physical, chemical, optical, and biological properties, graphene-based materials were successfully employed in creating the perfect scaffold for a range of organs, starting from the skin through to the brain. Investigations on 2D and 3D tissue culture scaffolds incorporated with graphene or its derivatives have revealed the capability of this carbon material in mimicking in vivo environment. The porous morphology, great surface area, selective permeability of gases, excellent mechanical strength, good thermal and electrical conductivity, good optical properties, and biodegradability enable graphene materials to be the best component for scaffold engineering. Along with the apt microenvironment, this material was found to be efficient in differentiating stem cells into specific cell types. Furthermore, the scope of graphene nanomaterials in liver tissue engineering as a promising biomaterial is also discussed. This review critically looks into the unlimited potential of graphene-based nanomaterials in future tissue engineering and regenerative therapy.

The anisotropic elastic behavior of the widely-used triply-periodic minimal surface based scaffolds

The Triple Periodic Minimal Surface (TPMS) has emerged as a new approach for producing open cell porous scaffolds for biomedical applications. However, different from the traditional scaffolds, the TPMS scaffolds always exhibit anisotropic elastic behaviors and consequently the simple mechanical testing is not capable to provide a full characterization of their mechanical behaviors. Additionally, it is still unclear if the TPMS scaffolds possess the similar anisotropic behaviors as the natural bones. The aim of the present study was to analyze the anisotropic elastic behaviors of TPMS based scaffolds using the numerical homogenization method and the analytical analysis approach. Five widely-used TPMS scaffold topologies (Diamond, Gyroid, Fischer-Koch S, Schwarz P and F-RD) were investigated. The independent elastic constants were determined from the analytical analysis and then, the values for these independent constants were determined using the finite element (FE) unit cell models of the scaffolds combined with the periodic boundary condition. The analytical analysis revealed that the Diamond, Gyroid and Fischer-Koch S topologies are threefold rotational symmetric and consequently have seven independent elastic constants. The Schwarz P and F-RD topologies are cubic symmetric and have three independent elastic constants. The FE analysis showed that the Diamond, Gyroid and Fischer-Koch S based scaffolds have only three non-zero independent elastic constants, implying the cubic symmetric property of these scaffolds. All the independent elastic constants decreased quadratically with the increase of scaffold porosity. The absolute difference between the Zener anisotropic factor and one increased the most for the Gyroid based scaffold, while the value for the Fischer-Koch S based scaffold increased the least. The present study revealed that all the five TPMS scaffolds possess cubic symmetry, limiting their anisotropic behaviors. The information on the Zener anisotropic factor and the relationship between the scaffold elastic constants and the porosity can facilitate the selection and design of scaffolds in biomedicine and relevant fields.

Architectural Design of 3D Printed Scaffolds Controls the Volume and Functionality of Newly Formed Bone

The successful regeneration of functional bone tissue in critical-size defects remains a significant clinical challenge. To address this challenge, synthetic bone scaffolds are widely developed, but remarkably few are translated to the clinic due to poor performance in vivo. Here, it is demonstrated how architectural design of 3D printed scaffolds can improve in vivo outcomes. Ceramic scaffolds with different pore sizes and permeabilities, but with similar porosity and interconnectivity, are implanted in rabbit calvaria for 12 weeks, and then the explants are harvested for microcomputed tomography evaluation of the volume and functionality of newly formed bone. The results indicate that scaffold pores should be larger than 390 µm with an upper limit of 590 µm to enhance bone formation. It is also demonstrated that a bimodal pore topology-alternating large and small pores-enhances the volume and functionality of new bone substantially. Moreover, bone formation results indicate that stiffness of new bone is highly influenced by the scaffold's permeability in the direction concerned. This study demonstrates that manipulating pore size and permeability in a 3D printed scaffold architecture provides a useful strategy for enhancing bone regeneration outcomes.

Three-dimensional porous poly(propylene fumarate)-co-poly(lactic-co-glycolic acid) scaffolds for tissue engineering

Three-dimensional structural scaffolds have played an important role in tissue engineering, especially broad applications in areas such as regenerative medicine. We have developed novel biodegradable porous poly(propylene fumarate)-co-poly(lactic-co-glycolic acid) (PPF-co-PLGA) scaffolds using thermally induced phase separation, and determined the effects of critical parameters such as copolymer concentration (6, 8, and 10 wt %) and the binary solvent ratio of dioxane:water (78/22, 80/20, 82/18 wt/wt %) on the fabrication process. The cloud-point temperatures of PPF-co-PLGA changed in parallel with increasing copolymer concentration, but inversely with increasing dioxane content. The compressive moduli of the scaffolds increased with greater weight composition and dioxane:water ratio. Scaffolds formed using high copolymer concentrations and solvent ratios exhibited preferable biomineralization. All samples showed biodegradation capability in both accelerated solution and phosphate-buffered saline (PBS). Cell toxicity testing indicated that the scaffolds had good biocompatibility with bone and nerve cells, which adhered well to the scaffolds. Variations in the copolymer concentration and solvent ratio exercised a remarkable influence on morphology, mechanical properties, biomineralization, and biodegradation, but not on the cell viability and adhesion of the cross-linked scaffolds. An 8 to 10 wt % solute concentration and 80/20 to 82/18 wt/wt dioxane:water ratio were the optimum parameters for scaffold fabrication. PPF-co-PLGA scaffolds thus possess several promising prospects for tissue engineering applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2507-2517, 2018.

Angiogenic Self-Assembling Peptide Scaffolds for Functional Tissue Regeneration

Implantation of acellular biomimetic scaffolds with proangiogenic motifs may have exciting clinical utility for the treatment of ischemic pathologies such as myocardial infarction. Although direct delivery of angiogenic proteins is a possible treatment option, smaller synthetic peptide-based nanostructured alternatives are being investigated due to favorable factors, such as sustained efficacy and high-density epitope presentation of functional moieties. These peptides may be implanted in vivo at the site of ischemia, bypassing the first-pass metabolism and enabling long-term retention and sustained efficacy. Mimics of angiogenic proteins show tremendous potential for clinical use. We discuss possible approaches to integrate the functionality of such angiogenic peptide mimics into self-assembled peptide scaffolds for application in functional tissue regeneration.

Porous Three-Dimensional Silk Fibroin Scaffolds for Tracheal Epithelial Regeneration in Vitro and in Vivo

The regeneration of functional epithelial lining is critical for artificial grafts to repair tracheal defects. Although silk fibroin (SF) scaffolds have been widely studied for biomedical application (e.g., artificial skin), its potential for tracheal substitute and epithelial regeneration is still unknown. In this study, we fabricated porous three-dimensional (3D) silk fibroin scaffolds and cocultured them with primary human tracheobronchial epithelial cells (HBECs) for 21 days in vitro. Examined by scanning electronic microscopy (SEM) and calcein-AM staining with inverted phase contrast microscopy, the SF scaffolds showed excellent properties of promoting cell growth and proliferation for at least 21 days with good viability. In vivo, the porous 3D SF scaffolds (n = 18) were applied to repair a rabbit anterior tracheal defect. In the control group (n = 18), rabbit autologous pedicled trachea wall without epithelium, an ideal tracheal substitute, was implanted in situ. Observing by endoscopy and computed tomography (CT) scan, the repaired airway segment showed no wall collapse, granuloma formation, or stenosis during an 8-week interval in both groups. SEM and histological examination confirmed the airway epithelial growth on the surface of porous SF scaffolds. Both the epithelium repair speed and the epithelial cell differentiation degree in the SF scaffold group were comparable to those in the control group. Neither severe inflammation nor excessive fibrosis occurred in both groups. In summary, the porous 3D SF scaffold is a promising biomaterial for tracheal repair by successfully supporting tracheal wall contour and promoting tracheal epithelial regeneration.

Efficient Computational Design of a Scaffold for Cartilage Cell Regeneration

Due to the sensitivity of mammalian cell cultures, understanding the influence of operating conditions during a tissue generation procedure is crucial. In this regard, a detailed study of scaffold based cell culture under a perfusion flow is presented with the aid of mathematical modelling and computational fluid dynamics (CFD). With respect to the complexity of the case study, this work focuses solely on the effect of nutrient and metabolite concentrations, and the possible influence of fluid-induced shear stress on a targeted cell (cartilage) culture. The simulation set up gives the possibility of predicting the cell culture behavior under various operating conditions and scaffold designs. Thereby, the exploitation of the predictive simulation into a newly developed stochastic routine provides the opportunity of exploring improved scaffold geometry designs. This approach was applied on a common type of fibrous structure in order to increase the process efficiencies compared with the regular used formats. The suggested topology supplies a larger effective surface for cell attachment compared to the reference design while the level of shear stress is kept at the positive range of effect. Moreover, significant improvement of mass transfer is predicted for the suggested topology.

Tissue Engineering to Improve Immature Testicular Tissue and Cell Transplantation Outcomes: One Step Closer to Fertility Restoration for Prepubertal Boys Exposed to Gonadotoxic Treatments

Despite their important contribution to the cure of both oncological and benign diseases, gonadotoxic therapies present the risk of a severe impairment of fertility. Sperm cryopreservation is not an option to preserve prepubertal boys’ reproductive potential, as their seminiferous tubules only contain spermatogonial stem cells (as diploid precursors of spermatozoa). Cryobanking of human immature testicular tissue (ITT) prior to gonadotoxic therapies is an accepted practice. Evaluation of cryopreserved ITT using xenotransplantation in nude mice showed the survival of a limited proportion of spermatogonia and their ability to proliferate and initiate differentiation. However, complete spermatogenesis could not be achieved in the mouse model. Loss of germ cells after ITT grafting points to the need to optimize the transplantation technique. Tissue engineering, a new branch of science that aims at improving cellular environment using scaffolds and molecules administration, might be an approach for further progress. In this review, after summarizing the lessons learned from human prepubertal testicular germ cells or tissue xenotransplantation experiments, we will focus on the benefits that might be gathered using bioengineering techniques to enhance transplantation outcomes by optimizing early tissue graft revascularization, protecting cells from toxic insults linked to ischemic injury and exploring strategies to promote cellular differentiation.