Customized scaffolds for large bone defects using 3D‑printed modular blocks from 2D‑medical images

Additive manufacturing(AM)has revolutionized the design and manufacturing of patient-specific,three-dimensional(3D),complex porous structures known as scaffolds for tissue engineering applications.The use of advanced image acquisition techniques,image processing,and computer-aided design methods has enabled the precise design and additive manufacturing of anatomically correct and patient-specific implants and scaffolds.However,these sophisticated techniques can be timeconsuming,labor-intensive,and expensive.Moreover,the necessary imaging and manufacturing equipment may not be readily available when urgent treatment is needed for trauma patients.In this study,a novel design and AM methods are proposed for the development of modular and customizable scaffold blocks that can be adapted to fit the bone defect area of a patient.These modular scaffold blocks can be combined to quickly form any patient-specific scaffold directly from two-dimensional(2D)medical images when the surgeon lacks access to a 3D printer or cannot wait for lengthy 3D imaging,modeling,and 3D printing during surgery.The proposed method begins with developing a bone surface-modeling algorithm that reconstructs a model of the patient’s bone from 2D medical image measurements without the need for expensive 3D medical imaging or segmentation.This algorithm can generate both patient-specific and average bone models.Additionally,a biomimetic continuous path planning method is developed for the additive manufacturing of scaffolds,allowing porous scaffold blocks with the desired biomechanical properties to be manufactured directly from 2D data or images.The algorithms are implemented,and the designed scaffold blocks are 3D printed using an extrusion-based AM process.Guidelines and instructions are also provided to assist surgeons in assembling scaffold blocks for the self-repair of patient-specific large bone defects.

Insights into Nano-and Micro-Structured Scaffolds for Advanced Electrochemical Energy Storage

Adopting a nano-and micro-structuring approach to fully unleashing the genuine potential of electrode active material benefits in-depth understandings and research progress toward higher energy density electrochemical energy stor-age devices at all technology readiness levels.Due to various challenging issues,especially limited stability,nano-and micro-structured(NMS)electrodes undergo fast electrochemical performance degradation.The emerging NMS scaffold design is a pivotal aspect of many electrodes as it endows them with both robustness and electrochemical performance enhancement,even though it only occupies comple-mentary and facilitating components for the main mechanism.However,extensive efforts are urgently needed toward optimizing the stereoscopic geometrical design of NMS scaffolds to minimize the volume ratio and maximize their functionality to fulfill the ever-increasing dependency and desire for energy power source supplies.This review will aim at highlighting these NMS scaffold design strategies,summariz-ing their corresponding strengths and challenges,and thereby outlining the potential solutions to resolve these challenges,design principles,and key perspectives for future research in this field.Therefore,this review will be one of the earliest reviews from this viewpoint.

3D-printed Mg-1Ca/polycaprolactone composite scaffolds with promoted bone regeneration

In bone tissue engineering,polycaprolactone(PCL)is a promising material with good biocompatibility,but its poor degradation rate,mechanical strength,and osteogenic properties limit its application.In this study,we developed an Mg-1Ca/polycaprolactone(Mg-1Ca/PCL)composite scaffolds to overcome these limitations.We used a melt blending method to prepare Mg-1Ca/PCL composites with Mg-1Ca alloy powder mass ratios of 5,10,and 20 wt%.Porous scaffolds with controlled macro-and microstructure were printed using the fused deposition modeling method.We explored the mechanical strength,biocompatibility,osteogenesis performance,and molecular mechanism of the Mg-1Ca/PCL composites.The 5 and 10 wt%Mg-1Ca/PCL composites were found to have good biocompatibility.Moreover,they promoted the mechanical strength,proliferation,adhesion,and osteogenic differentiation of human bone marrow stem cells(hBMSCs)of pure PCL.In vitro degradation experiments revealed that the composite material stably released Mg_(2)+ions for a long period;it formed an apatite layer on the surface of the scaffold that facilitated cell adhesion and growth.Microcomputed tomography and histological analysis showed that both 5 and 10 wt%Mg-1Ca/PCL composite scaffolds promoted bone regeneration bone defects.Our results indicated that the Wnt/β-catenin pathway was involved in the osteogenic effect.Therefore,Mg-1Ca/PCL composite scaffolds are expected to be a promising bone regeneration material for clinical application.Statement of significance:Bone tissue engineering scaffolds have promising applications in the regeneration of critical-sized bone defects.However,there remain many limitations in the materials and manufacturing methods used to fabricate scaffolds.This study shows that the developed Ma-1Ca/PCL composites provides scaffolds with suitable degradation rates and enhanced boneformation capabilities.Furthermore,the fused deposition modeling method allows precise control of the macroscopic morphology and microscopic porosity of the scaffold.The obtained porous scaffolds can significantly promote the regeneration of bone defects.

3D/4D printed bio-piezoelectric smart scaffolds for next-generation bone tissue engineering

Piezoelectricity in native bones has been well recognized as the key factor in bone regeneration.Thus,bio-piezoelectric materials have gained substantial attention in repairing damaged bone by mimicking the tissue’s electrical microenvironment(EM).However,traditional manufacturing strategies still encounter limitations in creating personalized bio-piezoelectric scaffolds,hindering their clinical applications.Three-dimensional(3D)/four-dimensional(4D)printing technology based on the principle of layer-by-layer forming and stacking of discrete materials has demonstrated outstanding advantages in fabricating bio-piezoelectric scaffolds in a more complex-shaped structure.Notably,4D printing functionality-shifting bio-piezoelectric scaffolds can provide a time-dependent programmable tissue EM in response to external stimuli for bone regeneration.In this review,we first summarize the physicochemical properties of commonly used bio-piezoelectric materials(including polymers,ceramics,and their composites)and representative biological findings for bone regeneration.Then,we discuss the latest research advances in the 3D printing of bio-piezoelectric scaffolds in terms of feedstock selection,printing process,induction strategies,and potential applications.Besides,some related challenges such as feedstock scalability,printing resolution,stress-to-polarization conversion efficiency,and non-invasive induction ability after implantation have been put forward.Finally,we highlight the potential of shape/property/functionality-shifting smart 4D bio-piezoelectric scaffolds in bone tissue engineering(BTE).Taken together,this review emphasizes the appealing utility of 3D/4D printed biological piezoelectric scaffolds as next-generation BTE implants.

Mg alloy cardio-/cerebrovascular scaffolds: Developments and prospects

Vascular scaffolds are one of the important application fields of biodegradable Mg alloys, and related research has been carried out for more than 20 years. In recent years, the application expansion of Mg alloy vascular scaffolds has brought new challenges to the research of related fields. This review focuses on the relevant advances in the field of Mg alloys for both cardio-/cerebrovascular scaffolds. The frequently investigated alloy series for vascular scaffolds were reviewed. The bottleneck of processing of Mg alloy minitubes was elucidated.The idea of functionalized surface modification was also pointed out in this review, and the authors put forward guidelines based on research experience in terms of scaffold structural design and degradation behavior evaluation. Finally, suggestions for further research directions of Mg alloy vascular scaffolds were provided.

Effect of Sr^(2+)on 3D gel-printed Sr_(3-x)Mg_(x)(PO_(4))_(2)composite scaffolds for bone tissue engineering

Porous magnesium strontium phosphate(Sr_(3-x)Mg_(x)(PO_(4))_(2))(x=2,2.5,3)composite scaffolds were successfully prepared by three dimension gel-printing(3DGP)method in this study.The results show that Sr_(0.5)Mg_(2.5)(PO_(4))_(2)scaffolds had good compressive strength,and Sr_(1.0)Mg_(2.0)(PO_(4))_(2)scaffolds had good degradation rate in vitro.The weight loss rate of Sr_(1.0)Mg_(2.0)(PO_(4))_(2)scaffolds soaked in simulated body fluid(SBF)or 6 weeks was 6.96%,and pH value varied between 7.50 and 8.61,which was within the acceptable range of human body.Preliminary biological experiment shows that MC3T3-E1 cells had good adhesion and proliferation on the surface of Sr_(3-x)Mg_(x)(PO_(4))_(2)scaffolds.Compared with pure Mg3(PO_(4))_(2)scaffolds,strontium doped scaffolds had excellent comprehensive properties,which explain that Sr_(3-x)Mg_(x)(PO_(4))_(2)composite scaffolds can be used for bone tissue engineering.

Fabrication of Porous Polycaprolactone/Carboxymethylcellulose Scaffolds by using Salt Leaching Technique

The purpose of this work was to fabricate three-dimensional porous scaffolds by using the salt leaching technique.This technique is simple and it does not need the pressure or dislike expensive equipment.The study selected polycaprolactone blended with carboxymethylcellulose that is the additive.The ratios of them were derived from mixture design in Minitab program that was 98/2(P1),93.5/6.5(P2),89/11(P3),84.5/15.5(P4),and 80/20(P5),respectively.The scanning electron microscopy(SEM)was applied to assess the physical properties and the pore size dimension of the scaffold from SEM micrographs.The results of SEM present the scaffolds happened interconnected porous structures that are found in all of the P1-P5 samples.The pore size dimension of all sample scaffolds is in the range of 264.11-348.28μm.Whereas the largest and the smallest of pore size are the sample of P3 and P2,respectively,while the porosity ranges from 98.06%-98.88%that the sample of P5 is the greatest and the sample of P4 is the slightly lowest.In conclusion,the blended PCL/CMC scaffolds P1-P5 were formed by salt leaching technique suitable to use in tissue engineering application.However,the amount of CMC blended with PCL should be reasonable in order to adjust the hydrophilic of the scaffold.

Bioengineering liver tissue by repopulation of decellularised scaffolds

Liver transplantation is the only curative therapy for end stage liver disease,but is limited by the organ shortage,and is associated with the adverse consequences of immunosuppression.Repopulation of decellularised whole organ scaffolds with appropriate cells of recipient origin offers a theoretically attractive solution,allowing reliable and timely organ sourcing without the need for immunosuppression.Decellularisation methodologies vary widely but seek to address the conflicting objectives of removing the cellular component of tissues whilst keeping the 3D structure of the extra-cellular matrix intact,as well as retaining the instructive cell fate determining biochemicals contained therein.Liver scaffold recellularisation has progressed from small rodent in vitro studies to large animal in vivo perfusion models,using a wide range of cell types including primary cells,cell lines,foetal stem cells,and induced pluripotent stem cells.Within these models,a limited but measurable degree of physiologically significant hepatocyte function has been reported with demonstrable ammonia metabolism in vivo.Biliary repopulation and function have been restricted by challenges relating to the culture and propagations of cholangiocytes,though advances in organoid culture may help address this.Hepatic vasculature repopulation has enabled sustainable blood perfusion in vivo,but with cell types that would limit clinical applications,and which have not been shown to have the specific functions of liver sinusoidal endothelial cells.Minority cell groups such as Kupffer cells and stellate cells have not been repopulated.Bioengineering by repopulation of decellularised scaffolds has significantly progressed,but there remain significant experimental challenges to be addressed before therapeutic applications may be envisaged.

Pressureless all-solid-state Na/S batteries with self-supporting Na_(5)YSi_(4)O_(12) scaffolds

The development of reliable and affordable all-solid-state sodium metal batteries(ASS-SMBs)requires suitable solid-state electrolytes with cost-efficient processing and stabilized electrode/electrolyte interfaces.Here,an integrated porous/dense/porous Na_(5)YSi_(4)O_(12)(NYS)trilayered scaffold is designed and fabricated by tape casting using aqueous slurries.In this template-based NYS scaffold,the dense layer in the middle serves as a separator and the porous layers on both sides accommodate the active materials with their volume changes during the charge/discharge processes,increasing the contact area and thus enhancing the utilization rate and homogenizing the current distribution.The Na/NYS/Na symmetric cells with the Pb-coated NYS scaffold exhibit significantly reduced interfacial impedance and superior critical current density of up to 3.0 mA cm^(-2)against Na metal owing to enhanced wettability.Furthermore,the assembled Na/NYS/S full cells operated without external pressure at room temperature showed a high initial discharge capacity of 970 mAh g^(-1)and good cycling stability with a capacity of 600 mAh g^(-1)after 150 cycles(based on the mass of sulfur).This approach paves the way for the realization of economical and practical ASS-SMBs from the perspective of ceramic manufacturing.

Collagen matrix scaffolds:Future perspectives for the management of chronic liver diseases

Approximately 1.5 billion chronic liver disease(CLD)cases have been estimated worldwide,encompassing a wide range of liver damage severities.Moreover,liver disease causes approximately 1.75 million deaths per year.CLD is typically characterized by the silent and progressive deterioration of liver parenchyma due to an incessant inflammatory process,cell death,over deposition of extracellular matrix proteins,and dysregulated regeneration.Overall,these processes impair the correct function of this vital organ.Cirrhosis and liver cancer are the main complications of CLD,which accounts for 3.5%of all deaths worldwide.Liver transplantation is the optimal therapeutic option for advanced liver damage.The liver is one of the most common organs transplanted;however,only 10%of liver transplants are successful.In this context,regenerative medicine has made significant progress in the design of biomaterials,such as collagen matrix scaffolds,to address the limitations of organ transplantation(e.g.,low donation rates and biocompatibility).Thus,it remains crucial to continue with experimental and clinical studies to validate the use of collagen matrix scaffolds in liver disease.

Anisotropic characterization of different materialized scaffolds:A numerical study

Ideal bone scaffold requires its mechanical properties to match those of natural bone.This work aimed to develop an anisotropic scaffold architecture,investigate the mechanical properties and anisotropy of the scaffold made of six biomedical materials by finite element method,and further compare them with the counterparts of natural bones for scaffold selection.The results showed that the mechanical properties of the scaffold constituent materials were positively correlated to those of the scaffolds but negatively correlated to the porosity.The modulus anisotropy was independent of materials at low porosity,and the strength anisotropy was weakly changed for high-strength materials but negatively correlated to porosity for low-strength materials.Plus,the modulus-strength chart of these materialized scaffolds against those of selected bones indicated that the mechanical match could be obtained by varying the anisotropic index.This work provided a constructing method for an anisotropic scaffold according to the structure-mechanical relationship of bone and could be helpful for scaffold design and selection to regenerate defective bones in clinical applications.

Recent advances in nano scaffolds for bone repair

Biomedical applications of nanomaterials are exponentially increasing every year due to analogy to various cell receptors, ligands, structural proteins, and genetic materials(that is, DNA). In bone tissue, nanoscale materials can provide scaffold for excellent tissue repair via mechanical stimulation, releasing of various loaded drugs and mediators, 3D scaffold for cell growth and differentiation of bone marrow stem cells to osteocytes. This review will therefore highlight recent advancements on tissue and nanoscale materials interaction.

The effect of the fibre orientation of electrospun scaffolds on the matrix production of rabbit annulus fibrosus-derived stem cells

Annulus fibrosus （AF） tissue engineering has recently received increasing attention as a treatment for intervertebral disc 0VD） degeneration; however, such engineering remains challenging because of the remarkable complexity of AF tissue. In order to engineer a functional AF replacement, the fabrication of cell-scaffold constructs that mimic the cellular, biochemical and structural features of native AF tissue is critical. In this study, we fabricated aligned fibroua polyurethane scaffolds using an electrospinning technique and used them for culturing AF-derived-stem/progenitor cells （AFSCs）. Random fibrous scaffolds, also prepared via electrospinningy were used as a control. We compared the morphology, proliferation, gene expression and matrix production of AFSCs on aligned scaffolds and random scaffolds. There was no apparent difference in the attachment or proliferation of cells cultured on aligned scaffolds and random scaffolds. However, compared to cells on random scaffolds, the AFSCs on aligned scaffolds were more elongated and better aligned, and they exhibited higher gene expression and matrix production of coUagen-I and aggrecan. The gene expression and protein production of coUagen-II did not appear to differ between the two groups. Together, these findings indicate that aligned fibrous scaffolds may provide a favourable microenvironment for the differentiation of AFSCs into cells similar to outer AF cells, which predominantly produce collagen-I matrix.

Restoring nervous system structure and function using tissue engineered living scaffolds

Neural tissue engineering is premised on the integration of engineered living tissue with the host nervous system to directly restore lost function or to augment regenerative capacity following ner- vous system injury or neurodegenerative disease. Disconnection of axon pathways - the long-distance fibers connecting specialized regions of the central nervous system or relaying peripheral signals - is a common feature of many neurological disorders and injury. However, functional axonal regenera- tion rarely occurs due to extreme distances to targets, absence of directed guidance, and the presence of inhibitory factors in the central nervous system, resulting in devastating effects on cognitive and sensorimotor function. To address this need, we are pursuing multiple strategies using tissue engi- neered ＂living scaffolds＂, which are preformed three-dimensional constructs consisting of living neural cells in a defined, often anisotropic architecture. Living scaffolds are designed to restore function by serving as a living labeled pathway for targeted axonal regeneration - mimicking key developmental mechanisms- or by restoring lost neural circuitry via direct replacement of neurons and axonal tracts. We are currently utilizing preformed living scaffolds consisting of neuronal dusters spanned by long axonal tracts as regenerative bridges to facilitate long-distance axonal regeneration and for targeted neurosurgical reconstruction of local circuits in the brain. Although there are formidable challenges in predinical and clinical advancement, these living tissue engineered constructs represent a promising strategy to facilitate nervous system repair and functional recovery.

Design and criteria of electrospun fibrous scaffolds for the treatment of spinal cord injury

The complex pathophysiology of spinal cord injury may explain the current lack of an effective therapeutic approach for the regeneration of damaged neuronal cells and the recovery of motor functions. Many efforts have been performed to design and develop suitable scaffolds for spinal cord regeneration, keeping in mind that the reconstruction of a pro-regenerative environment is the key challenge for an effective neurogenesis. The aim of this review is to outline the main features of an ideal scaffold, based on biomaterials, produced by the electrospinning technique and intended for the spinal cord regeneration. An overview of the poly- mers more investigated in the production of neural fibrous scaffolds is also provided.

3D printing of tissue engineering scaffolds:a focus on vascular regeneration

Tissue engineering is an emerging means for resolving the problems of tissue repair and organ replacement in regenerative medicine.Insufficient supply of nutrients and oxygen to cells in large-scale tissues has led to the demand to prepare blood vessels.Scaffold-based tissue engineering approaches are effective methods to form new blood vessel tissues.The demand for blood vessels prompts systematic research on fabrication strategies of vascular scaffolds for tissue engineering.Recent advances in 3D printing have facilitated fabrication of vascular scaffolds,contributing to broad prospects for tissue vascularization.This review presents state of the art on modeling methods,print materials and preparation processes for fabrication of vascular scaffolds,and discusses the advantages and application fields of each method.Specially,significance and importance of scaffold-based tissue engineering for vascular regeneration are emphasized.Print materials and preparation processes are discussed in detail.And a focus is placed on preparation processes based on 3D printing technologies and traditional manufacturing technologies including casting,electrospinning,and Lego-like construction.And related studies are exemplified.Transformation of vascular scaffolds to clinical application is discussed.Also,four trends of 3D printing of tissue engineering vascular scaffolds are presented,including machine learning,near-infrared photopolymerization,4D printing,and combination of self-assembly and 3D printing-based methods.

Physical and degradation properties of PLGA scaffolds fabricated by salt fusion technique

Tissue engineering scaffolds require a controlled pore size and interconnected pore structures to support the host tissue growth. In the present study, three dimensional （3D） hybrid scaffolds of poly lactic acid （PLA） and poly glycolic acid （PGA） were fabricated using solvent casting/particulate leaching. In this case, partially fused NaCl particles were used as porogen （200-300μ） to improve the overall porosity （≥90%） and internal texture of scaffolds. Differential scanning calorimeter （DSC） analysis of these porous scaffolds revealed a gradual reduction in glass transition temperature （Tg） （from 48°C to 42.5°C） with increase in hydrophilic PGA content. The potential applications of these scaffolds as implants were further tested for their biocompatibility and biodegradability in four simulated body fluid （SBF） types in vitro. Whereas, simulated body fluid （SBF） Type1 with the optimal amount of HCO 3 ions was found to be more appropriate and sensible for testing the bioactivity of scaffolds. Among three combinations of polymer scaffolds, sample B with a ratio of 75：25 of PLA： PGA showed greater stability in body fluids （pH 7.2） with an optimum degradation rate （9% to 12% approx）. X-ray diffractogram also confirmed a thin layer of hydroxyapatite deposition over sample B with all SBF types in vitro.

Preparation of polypyrrole-embedded electrospun poly(lactic acid) nanofibrous scaffolds for nerve tissue engineering

Polypyrrole （PPy） is a biocompatible polymer with good conductivity. Studies combining PPy with electrospinning have been reported; however, the associated decrease in PPy conductivity has not yet been resolved. We embedded PPy into poly（lactic acid） （PLA） nanofibers via electrospinning and fabricated a PLA/PPy nanofibrous scaffold containing 15% PPy with sustained conductivity and aligned topog- raphy, qhere was good biocompatibility between the scaffold and human umbilical cord mesenchymal stem cells as well as Schwann cells. Additionally, the direction of cell elongation on the scaffold was parallel to the direction of fibers. Our findings suggest that the aligned PLA/PPy nanofibrous scaffold is a promising biomaterial for peripheral nerve regeneration.

3D-cubic interconnected porous Mg-based scaffolds for bone repair

Mg-based porous materials,as potential bone tissue engineering scaffolds,are considered an attractive strategy for bone repair owing to favorable biodegradability,good biocompatibility and suitable mechanical properties.In this work,3D-cubic interconnected porous Mg–xZn–0.3Ca(x=0,3,6)scaffolds were prepared to obtain desirable pore structures with a mean porosity up to 73%and main pore size of 400–500μm,which pore structures were close to the human cancellous bone.The structure–property relationships in the present scaffolds were analyzed by experiments and theoretical models of generalized method of cells(GMC).Mg–xZn–0.3Ca scaffolds exhibited good compression properties with a maximum above 5MPa in yield strength and about 0.4GPa in elastic modulus.This was attributed to not only the alloy strengthening but also the large minimum solid area.On the other hand,the scaffolds showed undesirable and relatively serious degradation behavior in Hank’s solution,resulting from Zn addition in Mg-based scaffolds and the high surface area ratio in the pore structure.Therefore,surface modifications are worth studying for controlled degradation in the future.In conclusion,this research would explore a novel attempt to introduce 3D-cubic pore structure for Mg-based scaffolds,and provide new insights into the preparations of Mg-based scaffolds with good service performances for bone repair.

Morphology of spinal cord extracellular matrix-derived acellular scaffolds fabricated in rats

Acellular peripheral allograft scaffolds can be fabricated using chemical extraction techniques,but methods for producing acellular scaffold derived from spinal cord tissue are not currently available.The present study demonstrated that chemical extraction using Triton X-100 and sodium deoxycholate could be used to completely remove the cells,axons and neural sheaths in spinal cord extracellular matrix-derived scaffolds.The matrix fibers were longitudinally arranged in a wave-like formation,and were connected by fiber junctions.Lattice-shaped fiber cages appeared and developed into bone trabecula-like changes.The natural structure of matrix fibers in the scaffolds was maintained;this helps to guide the differentiation and migration of implanted stem cells.Decellularized spinal cord extracellular matrix-derived scaffolds can provide an ideal substance for fabricating tissue-engineered spinal cord.