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.

Coaxial electrohydrodynamic printing of core–shell microfibrous scaffolds with layer-specific growth factors release for enthesis regeneration

The rotator cuff tear has emerged as a significant global health concern.However,existing therapies fail to fully restore the intricate bone-to-tendon gradients,resulting in compromised biomechanical functionalities of the reconstructed enthesis tissues.Herein,a tri-layered core–shell microfibrous scaffold with layer-specific growth factors(GFs)release is developed using coaxial electrohydrodynamic(EHD)printing for in situ cell recruitment and differentiation to facilitate gradient enthesis tissue repair.Stromal cell-derived factor-1(SDF-1)is loaded in the shell,while basic fibroblast GF,transforming GF-beta,and bone morphogenetic protein-2 are loaded in the core of the EHD-printed microfibrous scaffolds in a layer-specific manner.Correspondingly,the tri-layered microfibrous scaffolds have a core–shell fiber size of(25.7±5.1)μm,with a pore size sequentially increasing from(81.5±4.6)μm to(173.3±6.9)μm,and to(388.9±6.9μm)for the tenogenic,chondrogenic,and osteogenic instructive layers.A rapid release of embedded GFs is observed within the first 2 d,followed by a faster release of SDF-1 and a slightly slower release of differentiation GFs for approximately four weeks.The coaxial EHD-printed microfibrous scaffolds significantly promote stem cell recruitment and direct their differentiation toward tenocyte,chondrocyte,and osteocyte phenotypes in vitro.When implanted in vivo,the tri-layered core–shell microfibrous scaffolds rapidly restored the biomechanical functions and promoted enthesis tissue regeneration with native-like bone-to-tendon gradients.Our findings suggest that the microfibrous scaffolds with layer-specific GFs release may offer a promising clinical solution for enthesis regeneration.

Advanced strategies for 3D-printed neural scaffolds:materials,structure,and nerve remodeling

Nerve regeneration holds significant potential in the treatment of various skeletal and neurological disorders to restore lost sensory and motor functions.The potential of nerve regeneration in ameliorating neurological diseases and injuries is critical to human health.Three-dimensional(3D)printing offers versatility and precision in the fabrication of neural scaffolds.Complex neural structures such as neural tubes and scaffolds can be fabricated via 3Dprinting.This reviewcomprehensively analyzes the current state of 3D-printed neural scaffolds and explores strategies to enhance their design.It highlights therapeutic strategies and structural design involving neural materials and stem cells.First,nerve regeneration materials and their fabrication techniques are outlined.The applications of conductive materials in neural scaffolds are reviewed,and their potential to facilitate neural signal transmission and regeneration is highlighted.Second,the progress in 3D-printed neural scaffolds applied to the peripheral and central nerves is comprehensively evaluated,and their potential to restore neural function and promote the recovery of different nervous systems is emphasized.In addition,various applications of 3D-printed neural scaffolds in peripheral and neurological diseases,as well as the design strategies of multifunctional biomimetic scaffolds,are discussed.

Numerical Analysis of Permeability of Functionally Graded Scaffolds

In this work,we numerically study the hydrodynamic permeability of new-generation artificial porous materials used as scaffolds for cell growth in a perfusion bioreactor.We consider two popular solid matrix designs based on triply periodic minimal surfaces,the Schwarz P(primitive)and D(diamond)surfaces,which enable the creation of materials with controlled porosity gradients.The latter property is crucial for regulating the shear stress field in the pores of the scaffold,which makes it possible to control the intensity of cell growth.The permeability of functionally graded materials is studied within the framework of both a microscopic approach based on the Navier-Stokes equation and an averaged description of the liquid filtration through a porous medium based on the equations of the Darcy or Forchheimer models.We calculate the permeability coefficients for both types of solid matrices formed by Schwarz surfaces,study their properties concerning forward and reverse fluid flows,and determine the ranges of Reynolds number for which the description within the Darcy or Forchheimer model is applicable.Finally,we obtain a shear stress field that varies along the sample,demonstrating the ability to tune spatially the rate of tissue growth.

Recognizing and preventing complications regarding bioresorbable scaffolds during coronary interventions

The evolution of coronary intervention techniques and equipment has led to more sophisticated procedures for the treatment of highly complex lesions.However,as a result,the risk of complications has increased,which are mostly iatrogenic and often include equipment failure.Stent dislodgement warrants vigilance for the early diagnosis and a stepwise management approach is required to either expand or retrieve the lost stent.In the era of bioresorbable scaffolds that are not radiopaque,increased caution is required.Intravascular imaging may assist in detecting the lost scaffold in cases of no visibility fluoroscopically.Adequate lesion preparation is the key to minimizing the possibility of equipment loss;however,in the case that it occurs,commercially available and improvised devices and techniques may be applied.

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.

In vitro investigations on the effects of graphene and graphene oxide on polycaprolactone bone tissue engineering scaffolds

Polycaprolactone(PCL)scaffolds that are produced through additive manufacturing are one of the most researched bone tissue engineering structures in the field.Due to the intrinsic limitations of PCL,carbon nanomaterials are often investigated to reinforce the PCL scaffolds.Despite several studies that have been conducted on carbon nanomaterials,such as graphene(G)and graphene oxide(GO),certain challenges remain in terms of the precise design of the biological and nonbiological properties of the scaffolds.This paper addresses this limitation by investigating both the nonbiological(element composition,surface,degradation,and thermal and mechanical properties)and biological characteristics of carbon nanomaterial-reinforced PCL scaffolds for bone tissue engineering applications.Results showed that the incorporation of G and GO increased surface properties(reduced modulus and wettability),material crystallinity,crystallization temperature,and degradation rate.However,the variations in compressive modulus,strength,surface hardness,and cell metabolic activity strongly depended on the type of reinforcement.Finally,a series of phenomenological models were developed based on experimental results to describe the variations of scaffold’s weight,fiber diameter,porosity,and mechanical properties as functions of degradation time and carbon nanomaterial concentrations.The results presented in this paper enable the design of three-dimensional(3D)bone scaffolds with tuned properties by adjusting the type and concentration of different functional fillers.

Developing fibrin-based biomaterials/scaffolds in tissue engineering

Tissue engineering technology has advanced rapidly in recent years, offering opportunities to construct biologicallyactive tissues or organ substitutes to repair or even enhance the functions of diseased tissues and organs.Tissue-engineered scaffolds rebuild the extracellular microenvironment by mimicking the extracellular matrix.Fibrin-based scaffolds possess numerous advantages, including hemostasis, high biocompatibility, and gooddegradability. Fibrin scaffolds provide an initial matrix that facilitates cell migration, differentiation, proliferation,and adhesion, and also play a critical role in cell-matrix interactions. Fibrin scaffolds are now widelyrecognized as a key component in tissue engineering, where they can facilitate tissue and organ defect repair.This review introduces the properties of fibrin, including its composition, structure, and biology. In addition, themodification and cross-linking modes of fibrin are discussed, along with various forms commonly used in tissueengineering. We also describe the biofunctionalization of fibrin. This review provides a detailed overview of theuse and applications of fibrin in skin, bone, and nervous tissues, and provides novel insights into future researchdirections for clinical treatment.

Orthogonally woven 3D nanofiber scaffolds promote rapid soft tissue regeneration by enhancing bidirectional cell migration

Repairing large-area soft tissue defects caused by traumas is a major surgical challenge.Developing multifunctional scaffolds with suitable scalability and favorable cellular response is crucial for soft tissue regeneration.In this study,we developed an orthogonally woven three-dimensional(3D)nanofiber scaffold combining electrospinning,weaving,and modified gas-foaming technology.The developed orthogonally woven 3D nanofiber scaffold had a modular design and controlled fiber alignment.In vitro,the orthogonally woven 3D nanofiber scaffold exhibited adjustable mechanical properties,good cell compatibility,and easy drug loading.In vivo,for one thing,the implantation of an orthogonally woven 3D nanofiber scaffold in a full abdominal wall defect model demonstrated that extensive granulation tissue formation with enough mechanical strength could promote recovery of abdominal wall defects while reducing intestinal adhesion.Another result of diabetic wound repair experiments suggested that orthogonally woven 3D nanofiber scaffolds had a higher wound healing ratio,granulation tissue formation,collagen deposition,and re-epithelialization.Taken together,this novel orthogonally woven 3D nanofiber scaffold may provide a promising and effective approach for optimal soft tissue regeneration.

Enhanced axonal regeneration and functional recovery of the injured sciatic nerve in a rat model by lithium-loaded electrospun nanofibrous scaffolds

Increasing evidence indicates that engineered nerve grafts have great potential for the regeneration of peripheral nerve injuries(PNIs).While most studies have focused only on the topographical features of the grafts,we have considered both the biophysical and biochemical manipulations in our applied nanoscaffold.To achieve this,we fabricated an electrospun nanofibrous scaffold(ENS)containing polylactide nanofibers loaded with lithium(Li)ions,a Wnt/β-catenin signaling activator.In addition,we seeded human adipose-derived mesenchymal stem cells(hADMSCs)onto this engineered scaffold to examine if their differentiation toward Schwann-like cells was induced.We further examined the efficacy of the scaffolds for nerve regeneration in vivo via grafting in a PNI rat model.Our results showed that Li-loaded ENSs gradually released Li within 11 d,at concentrations ranging from 0.02 to(3.64±0.10)mmol/L,and upregulated the expression of Wnt/β-catenin target genes(cyclinD1 and c-Myc)as well as those of Schwann cell markers(growth-associated protein 43(GAP43),S100 calcium binding protein B(S100B),glial fibrillary acidic protein(GFAP),and SRY-box transcription factor 10(SOX10))in differentiated hADMSCs.In the PNI rat model,implantation of Li-loaded ENSs with/without cells improved behavioral features such as sensory and motor functions as well as the electrophysiological characteristics of the injured nerve.This improved function was further validated by histological analysis of sciatic nerves grafted with Li-loaded ENSs,which showed no fibrous connective tissue but enhanced organized myelinated axons.The potential of Li-loaded ENSs in promoting Schwann cell differentiation of hADMSCs and axonal regeneration of injured sciatic nerves suggests their potential for application in peripheral nerve tissue engineering.

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.

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.

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.

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.

Topology optimization of microstructure and selective laser meltingfabrication for metallic biomaterial scaffolds

The precise design and fabrication of biomaterial scaffolds is necessary to provide a systematic study for bone tissue engineering. Biomaterial scaffolds should have sufficient stiffness and large porosity. These two goals generally contradict since larger porosity results in lower mechanical properties. To seek the microstructure of maximum stiffness with the constraint of volume fraction by topology optimization method, algorithms and programs were built to obtain 2D and 3D optimized microstructure and then they were transferred to CAD models of STL format. Ti scaffolds with 30% volume fraction were fabricated using a selective laser melting （SLM） technology. The architecture and pore shape in the metallic biomaterial scaffolds were relatively precise reproduced and the minimum mean pore size was 231μm. The accurate fabrication of intricate microstructure has verified that the SLM process is suitable for fabrication of metallic biomaterial scaffolds.

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.