Biodegradable metals for bone defect repair: A systematic review and meta-analysis based on animal studies

[Biocompatibility of 3D printed biodegradable WE43 magnesium alloy scaffolds and treatment of bone defects]

OBJECTIVE

To investigate the biocompatibility of porous WE43 magnesium alloy scaffolds manufactured by 3D printing technology and to observe its effect in treating femoral defects in New Zealand white rabbits.

METHODS

In vitro cytotoxicity test was performed using bone marrow mesenchymal stem cells from Sprague Dawley (S-D) rats. According to the different culture media, the cells were divided into 100% extract group, 50% extract group, 10% extract group and control group. After culturing for 1, 3 and 7 days, the cell activity of each group was determined by cell counting kit-8 (CCK-8). In the in vivo experiment, 3.0-3.5 kg New Zealand white rabbits were randomly divided into three groups: Experimental group, bone cement group and blank group, with 9 rabbits in each group. Each rabbit underwent surgery on the left lateral femoral condyle, and a bone defect with a diameter of 5 mm and a depth of 6 mm was created using a bone drill. The experimental group was implanted with WE43 magnesium alloy scaffolds, the bone cement group was implanted with calcium sulfate bone cement, and the blank group was not implanted. Then 4, 8 and 12 weeks after surgery, 3 rabbits in each group were euthanized by carbon dioxide anesthesia, and the femur and important internal organs were sampled. Micro-computed tomography (Micro-CT) scanning was performed on the left lateral femoral condyle. Sections of important internal organs were prepared and stained with hematoxylin-eosin (HE). Hard tissue sections were made from the left lateral femoral condyle and stained with methylene blue acid fuchsin and observed under a microscope.

RESULTS

In the cytotoxicity test, the cell survival rate in the 100% extract group was higher than that in the control group (140.56% vs. 100.00%, P < 0.05) on 1 day of culture; there was no statistically significant difference (P>0.05) in cell survival rate among the groups on 3 days of culture; the cell survival rate in the 100% extract group was lower than that in the control group (68.64% vs. 100.00%, P < 0.05) on 7 days of culture. Micro-CT scanning in the in vivo experiment found that most of the scaffolds in the experimental group had been degraded in 4 weeks, with very few high-density scaffolds remaining. In 12 weeks, there was no obvious stent outline. In 4 weeks, a certain amount of gas was generated around the WE43 magnesium alloy scaffold, and the gas was significantly reduced from 8 to 12 weeks. Hard tissue sections showed that a certain amount of extracellular matrix and osteoid were generated around the scaffolds in the experimental group in 4 weeks. In the bone cement group, most of the calcium sulfate bone cement had been degraded. In 8 weeks, the osteoid around the scaffold and its degradation products in the experimental group increased significantly. In 12 weeks, new bone was in contact with the scaffold around the scaffold in the experimental group. There was less new bone in the bone cement group and the blank group.

CONCLUSION

The porous WE43 magnesium alloy scaffold fabricated by 3D printing process has good biocompatibility and good osteogenic properties, and has the potential to become a new material for repairing bone defects.

Piezoelectric biomaterials for providing electrical stimulation in bone tissue engineering: Barium titanate

With the increasing clinical demand for orthopedic implants, bone tissue engineering based on a variety of bioactive materials has shown promising applications in bone repair. And various physiological cues, such as mechanical, electrical, and magnetic stimulation, can influence cell fate and participate in bone regeneration. Natural bone has a piezoelectric effect due to the non-centrosymmetric nature of collagen, which can aid in cell adhesion, proliferation and differentiation, and bone growth by converting mechanical stimuli into electrical stimuli. Piezoelectric materials have the same piezoelectric effect as human bone, and they are able to deform in response to physiological movement, thus providing electrical stimulation to cells or damaged tissue without the need for an external power source. Among them, Barium titanate (BaTiO3) is widely used in tumor therapy, tissue engineering, health detection and drug delivery because of its good biocompatibility, low cytotoxicity and good piezoelectric properties. This review describes the piezoelectric effect of natural bone and the characteristics of various types of piezoelectric materials, from the synthesis and physicochemical characteristics of BaTiO3 and its application in biomedicine. And it highlights the great potential of BaTiO3 as piezoelectric biomaterials in the field of bone tissue engineering in anticipation of providing new ideas and opportunities for researchers. The translational potential of this article: This review systematically discusses barium titanate, a bioactive material that can mimic the piezoelectric effect of natural bone tissue, which can intervene in the regenerative repair of bone by providing a sustained electrical microenvironment for bone repair scaffolds. This may help to solve the current problem of poor osteogenic properties of bioactive materials by utilizing barium titanate.

Engineering Stimuli-Responsive Materials for Precision Medicine

Over the past decade, precision medicine has garnered increasing attention, making significant strides in discovering new therapeutic drugs and mechanisms, resulting in notable achievements in symptom alleviation, pain reduction, and extended survival rates. However, the limited target specificity of primary drugs and inter-individual differences have often necessitated high-dosage strategies, leading to challenges such as restricted deep tissue penetration rates and systemic side effects. Material science advancements present a promising avenue for these issues. By leveraging the distinct internal features of diseased regions and the application of specific external stimuli, responsive materials can be tailored to achieve targeted delivery, controllable release, and specific biochemical reactions. This review aims to highlight the latest advancements in stimuli-responsive materials and their potential in precision medicine. Initially, we introduce disease-related internal stimuli and capable external stimuli, elucidating the reaction principles of responsive functional groups. Subsequently, we provide a detailed analysis of representative pre-clinical achievements of stimuli responsive materials across various clinical applications, including enhancements in the treatment of cancers, injury diseases, inflammatory diseases, infection diseases, and high-throughput microfluidic biosensors. Finally, we discuss some clinical challenges, such as off-target effects, long-term impacts of nano-materials, potential ethical concerns, and offer insights into future perspectives of stimuli-responsive materials.

Mussel-inspired multi-bioactive microsphere scaffolds for bone defect photothermal therapy

Hydrogel microspheres hold great promise as scaffolds for bone repair. Their hydrated matrix, biocompatibility, and functional properties make them an attractive choice in regenerative medicine. However, the irregularity of defect requires shape adaptability of the microspheres. Additionally, there is still room for improvement regarding the component of the microspheres to achieve sufficient bioactivity. Here, we prepare multi-bioactive microspheres composed of methacrylated silk fibroin (SFMA) via microfluidic electrospray. Magnesium ascorbyl phosphate (MAP) is encapsulated within the microspheres, whose sustained release facilitates angiogenesis and osteogenic differentiation. The microspheres are further coated with a polydopamine (PDA) layer, allowing them to assemble in situ into a scaffold that conforms to the non-uniform contours of bone defects. The photothermal conversion capability of PDA also provides mild photothermal stimulation to further promote bone regeneration. Based on the synergistic effects, our in vivo experiments demonstrated that the microsphere scaffold effectively promotes bone defect healing. Thus, this multi-bioactive scaffold offers a versatile strategy for bone repair with promising clinical potential.

A biodegradable, osteo-regenerative and biomechanically robust polylactide bone screw for clinical orthopedic surgery

Poly (L-lactic acid) (PLLA) has emerged as a promising orthopedic implant material due to its favorable strength and biodegradability. However, challenges such as low toughness and limited osteoinductivity hinder its widespread use in bone fixation. This study focuses on enhancing the toughness and osteogenic activity of PLLA-based orthopedic implants. Inspired by reinforcement techniques in the construction industry, we designed a structure comprising flexible fibers enveloped by PLLA/hydroxyapatite (HA) crystalline phases. Initially, PLLA/poly (butylene succinate-co-adipate) (PBSA)/HA composites with "sea-island" morphology were prepared through melt-compounding. Subsequently, the highly oriented PBSA fibers were in situ formed during microinjection molding for bone screw fabrication. Comprehensive investigation into the structural-mechanical property relationship revealed a significant increase in elongation at break (from 5.4 % to 59.4 % with an optimal PBSA/HA ratio), while maintaining a high stiffness and a slight decrease in tensile strength (from 62.0 MPa to 56.0 MPa). The flexural tests of the resulting composite bone screws demonstrated a significant increase in toughness. Additionally, the in vivo studies corroborated the osteogenic potential of the microinjection molded bone screws by using hematoxylin and eosin (HE) and Masson staining. The methodology presented in this study offers a promising approach for advancing PLLA-based fixation devices in bone repair applications.

Personalized bioceramic grafts for craniomaxillofacial bone regeneration

The reconstruction of craniomaxillofacial bone defects remains clinically challenging. To date, autogenous grafts are considered the gold standard but present critical drawbacks. These shortcomings have driven recent research on craniomaxillofacial bone reconstruction to focus on synthetic grafts with distinct materials and fabrication techniques. Among the various fabrication methods, additive manufacturing (AM) has shown significant clinical potential. AM technologies build three-dimensional (3D) objects with personalized geometry customizable from a computer-aided design. These layer-by-layer 3D biomaterial structures can support bone formation by guiding cell migration/proliferation, osteogenesis, and angiogenesis. Additionally, these structures can be engineered to degrade concomitantly with the new bone tissue formation, making them ideal as synthetic grafts. This review delves into the key advances of bioceramic grafts/scaffolds obtained by 3D printing for personalized craniomaxillofacial bone reconstruction. In this regard, clinically relevant topics such as ceramic-based biomaterials, graft/scaffold characteristics (macro/micro-features), material extrusion-based 3D printing, and the step-by-step workflow to engineer personalized bioceramic grafts are discussed. Importantly, in vitro models are highlighted in conjunction with a thorough examination of the signaling pathways reported when investigating these bioceramics and their effect on cellular response/behavior. Lastly, we summarize the clinical potential and translation opportunities of personalized bioceramics for craniomaxillofacial bone regeneration.

Hierarchical Integration of Curcumin-Loaded CaCO3 Nanoparticles and Black Phosphorus Nanosheets in Core/Shell Nanofiber for Cranial Defect Repair

Reconstruction and healing of large craniofacial bone defects are major clinical challenges due to high risk of chronic inflammation and reduced cell mineralization levels. Herein, a core-shell nanofiber-based implant with significant pro-osteogenesis capability for treating skull defects is reported, which is hierarchically integrated with curcumin-loaded calcium carbonate nanoparticles (CaCO3@Cur NPs) in the outer layers and black phosphorus nanosheets (BPNSs) in the core compartments. The radical alignment of the integrated nanocomponents allows the sequential in situ release of the therapeutic agents in a controlled manner after implantation. Curcumin can repolarize M1 macrophages into M2 phenotypes for anti-inflammation purposes. Meanwhile, the released calcium and phosphate ions can promote the biomineralization of hydroxyapatite at the defect site and facilitate bone regeneration. Evaluations on cranial defect-bearing rat models demonstrated that the electrospun fibers in the present study substantially promoted restoration of the damaged skulls and inhibited inflammation in the wound bed. This strategy provides a new idea for the treatment of skull defects in the clinic.

Innovations in three-dimensional-printed individualized bone prosthesis materials: revolutionizing orthopedic surgery: a review

The advent of personalized bone prosthesis materials and their integration into orthopedic surgery has made a profound impact, primarily as a result of the incorporation of three-dimensional (3D) printing technology. By leveraging digital models and additive manufacturing techniques, 3D printing enables the creation of customized, high-precision bone implants tailored to address complex anatomical variabilities and challenging bone defects. In this review, we highlight the significant progress in utilizing 3D-printed prostheses across a wide range of orthopedic procedures, including pelvis, hip, knee, foot, ankle, spine surgeries, and bone tumor resections. The integration of 3D printing in preoperative planning, surgical navigation, and postoperative rehabilitation not only enhances treatment outcomes but also reduces surgical risks, accelerates recovery, and optimizes cost-effectiveness. Emphasizing the potential for personalized care and improved patient outcomes, this review underscores the pivotal role of 3D-printed bone prosthesis materials in advancing orthopedic practice towards precision, efficiency, and patient-centric solutions. The evolving landscape of 3D printing in orthopedic surgery holds promise for revolutionizing treatment approaches, enhancing surgical outcomes, and ultimately improving the quality of care for orthopedic patients.

Biodegradable PMMA coated Zn-Mg alloy with bimodal grain structure for orthopedic applications - A promising alternative

The study examines the impact of microstructure and polymethyl methacrylate (PMMA) grafting on the degradability of Zn-Mg alloys. The mechanical properties of a Zn alloy containing 0.68 wt% Mg and extruded at 200 °C are enhanced for degradable load-bearing applications, addressing a crucial need in the field. The material exhibits a bimodal grain size distribution that is random texture, consisting of secondary phases, grains, and sub-grains. With an elongation to failure of 16 %, the yield and ultimate tensile strengths are 325.9 and 414.5 MPa, respectively, and the compressive yield strength is 450.5 MPa. The "grafting-from" method was used to coat a few micrometers thick of PMMA on both bulk and scaffold Zn alloys to mitigate the corrosion rate. The last one is a porous structure, with a porosity of 65.8 %, considered as in the first approach of an orthopedic implant. After being immersed for 720 h, the PMMA-grafted bulk alloy's corrosion rate decreased from 0.43 to 0.25 mm/y. Similarly, the scaffold alloy's corrosion rate reduced from 1.24 to 0.49 mm/y. These results indicate that the method employed could be used for future orthopedic applications.

Regulatory science promotes the translation of transcatheter tricuspid valve repair/replacement devices

For patients with symptomatic and severe tricuspid regurgitation but inoperable with open surgery, transcatheter tricuspid valve intervention (TTVI) is a procedure of great clinical value. TTVI products include repair and replacement devices. TTVI products are one of the hotspots of investigation now, with different innovative biomaterials and structural designs in trials to satisfy divergent indications and reduce complications. With the emerging biomaterials, the technical difficulty of structural design will be greatly reduced, spurring further product innovation and development. The innovativeness and complexity of TTVI products have brought challenges to academia, industry, and regulatory agencies. Regulatory science provides a bridge to address these difficulties and challenges. This perspective article introduces the latest development of the TTVI products. With traditional methods, regulatory agencies face challenges in evaluating the safety and efficacy of TTVr/TTVR devices given the uncertainty of clinical use and the diversity of innovative structural design. This perspective article analyzes the regulatory challenges and discusses regulatory science that can be developed to assess the safety, efficacy, quality and performance of such products: including new approaches for innovative devices, pre-review path, computer modeling and simulation, accelerated wear testing methods for transcatheter heart valves and evidence-based research. This article reveals for the first time how to apply regulatory science systematically to TTVI products, which is of great relevance to their development and translation.

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

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

T. gondii excretory proteins promote the osteogenic differentiation of human bone mesenchymal stem cells via the BMP/Smad signaling pathway

BACKGROUND

Bone defects, resulting from substantial bone loss that exceeds the natural self-healing capacity, pose significant challenges to current therapeutic approaches due to various limitations. In the quest for alternative therapeutic strategies, bone tissue engineering has emerged as a promising avenue. Notably, excretory proteins from Toxoplasma gondii (TgEP), recognized for their immunogenicity and broad spectrum of biological activities secreted or excreted during the parasite's lifecycle, have been identified as potential facilitators of osteogenic differentiation in human bone marrow mesenchymal stem cells (hBMSCs). Building on our previous findings that TgEP can enhance osteogenic differentiation, this study investigated the molecular mechanisms underlying this effect and assessed its therapeutic potential in vivo.

METHODS

We determined the optimum concentration of TgEP through cell cytotoxicity and cell proliferation assays. Subsequently, hBMSCs were treated with the appropriate concentration of TgEP. We assessed osteogenic protein markers, including alkaline phosphatase (ALP), Runx2, and Osx, as well as components of the BMP/Smad signaling pathway using quantitative real-time PCR (qRT-PCR), siRNA interference of hBMSCs, Western blot analysis, and other methods. Furthermore, we created a bone defect model in Sprague-Dawley (SD) male rats and filled the defect areas with the GelMa hydrogel, with or without TgEP. Microcomputed tomography (micro-CT) was employed to analyze the bone parameters of defect sites. H&E, Masson and immunohistochemical staining were used to assess the repair conditions of the defect area.

RESULTS

Our results indicate that TgEP promotes the expression of key osteogenic markers, including ALP, Runx2, and Osx, as well as the activation of Smad1, BMP2, and phosphorylated Smad1/5-crucial elements of the BMP/Smad signaling pathway. Furthermore, in vivo experiments using a bone defect model in rats demonstrated that TgEP markedly promoted bone defect repair.

CONCLUSION

Our results provide compelling evidence that TgEP facilitates hBMSC osteogenic differentiation through the BMP/Smad signaling pathway, highlighting its potential as a therapeutic approach for bone tissue engineering for bone defect healing.

Imidazole functionalized photo-crosslinked aliphatic polycarbonate drug-eluting coatings on zinc alloys for osteogenesis, angiogenesis, and bacteriostasis in bone regeneration

Zinc (Zn) alloys have demonstrated significant potential in healing critical-sized bone defects. However, the clinical application of Zn alloys implants is still hindered by challenges including excessive release of zinc ions (Zn2+), particularly in the early stage of implantation, and absence of bio-functions related to complex bone repair processes. Herein, a biodegradable aliphatic polycarbonate drug-eluting coating was fabricated on zinc-lithium (Zn-Li) alloys to inhibit Zn2+ release and enhance the osteogenesis, angiogenesis, and bacteriostasis of Zn alloys. Specifically, the photo-curable aliphatic polycarbonates were co-assembled with simvastatin and deposited onto Zn alloys to produce a drug-loaded coating, which was crosslinked by subsequent UV light irradiation. During the 60 days long-term immersion test, the coating showed distinguished stable drug release and Zn2+ release inhibition properties. Benefiting from the regulated release of Zn2+ and simvastatin, the coating facilitated the adhesion, proliferation, and differentiation of MC3T3-E1 cells, as well as the migration and tube formation of EA.hy926 cells. Astonishingly, the coating also showed remarkable antibacterial properties against both S. aureus and E. coli. The in vivo rabbit critical-size femur bone defects model demonstrated that the drug-eluting coating could efficiently promote new bone formation and the expression of platelet endothelial cell adhesion molecule-1 (CD31) and osteocalcin (OCN). The enhancement of osteogenesis, angiogenesis, and bacteriostasis is achieved by precisely controlling of the released Zn2+ at an appropriate level, as well as the stable release profile of simvastatin. This tailored aliphatic polycarbonate drug-eluting coating provides significant potential for clinical applications of Zn alloys implants.

Computer-aided design and 3D printing for a stable construction of segmental bone defect model in Beagles: a short term observation

OBJECTIVE

Segmental bone defect animal studies require stable fixation which is a continuous experimental challenge. Large animal models are comparable to the human bone, but with obvious drawbacks of housing and costs. Our study aims to utilize CAD and 3D printing in the construction of a stable and reproducible segmental bone defect animal mode.

METHODS

CAD-aided 3D printed surgical instruments were incorporated into the construction of the animal model through preoperative surgical emulation. 20 3D printed femurs were divided into either experimental group using 3D surgical instruments or control group. In Vitro surgical time and accuracy of fixation were analysed and compared between the two groups. A mature surgical plan using the surgical instruments was then utilized in the construction of 3 segmental bone defect Beagle models in vivo. The Beagles were postoperatively assessed through limb function and imaging at 1, 2 and 3 months postoperatively.

RESULTS

In vitro experiments showed a significant reduction in surgical time from 40.6 ± 14.1 (23-68 min) to 26 ± 4.6 (19-36 min) (n = 10, p < 0.05) and the accuracy of intramedullary fixation placement increased from 71.6 ± 23.6 (33.3-100) % to 98.3 ± 5.37 (83-100) %, (n = 30, p < 0.05) with the use of CAD and 3D printed instruments. All Beagles were load-bearing within 1 week, and postoperative radiographs showed no evidence of implant failure.

CONCLUSION

Incorporation of CAD and 3D printing significantly increases stability, while reducing the surgical time in the construction of the animal model, significantly affecting the success of the segmental bone defect model in Beagles.

A Standardized Rat Model to Study Peri-implantitis of Transmucosal Osseointegrated Implants

With the high incidence rate, distinctive implant characteristic and unique infection pattern, peri-implantitis (PI) requires a specially designed implant animal model for the researches on the pathogenesis and treatments. Previous small-animal PI models exhibit variability in implant site selection, design, and surgical procedures resulting in unnecessary tissue damage and less effectivity. Herein, a quantitative-analysis-based standardized rat model for transmucosal PI-related research was proposed. After dissecting the anatomic structures of the rat maxilla, we determined that placing the implant anterior to the molars in the rat maxilla streamlined the experimental period and enhanced animal welfare. We standardized the model by controlling the rat strain, gender, and size. The customized implant and a series of matched surgical instruments were appropriately designed. A clear, step-by-step surgical process was established. These designs ensured the success rate, stability, and replicability of the model. Each validation method confirmed the successful construction of the model. This study proposed a quantitative-analysis-based standardized transmucosal PI rat model with improved animal welfare and reliable procedures. This model could provide efficient in vivo insights to study the pathogenesis and treatments of PI and preliminary screening data for further large-animal and clinical trials.

Finite element method-based simulation on bone fracture fixation configuration factors for biodegradable embossed locking compression plate

As an evolution, biodegradable implants need to maximize mechanical performance thereby may lead to confusion in selection of the biodegradable material and implant design to the fracture site. This requires selecting a unique fixation configuration to fit within the fractured bone, factors of which can be bone-plate clearance, interfragmentary gap, alteration in screw fixation position and variation in the number of screws whose configuration optimization can re-maximize the mechanical performance of the biodegradable implant. Therefore, these factors have been optimized based on the induced minimum stress using the finite element method-based simulation for which biodegradable embossed locking plates (BELCP) via screws made of Mg-alloy have been fitted over two fragments of femur body (as hollow cylindrical cortical bone). An average human weight of 62 kg is applied to one segment of the femur for all different configurations of each factor, where another segment is assumed to be fixed. By this simulation, the most optimal fixation configuration was found at a minimum induced stress value of 41.96 MPa which is approximately 85%, 18%, 6% and 48% respectively less than all maximum stress induced configurations in each of the factor. This optimized configuration was at the minimum clearance between bone and plate with a 3 mm interfragmentary gap using 8 screws where the locking screw begins to apply from the center of the BELCP. Overall, BELCP may be a better biodegradable implant plate for bone fracture fixation with these optimized fixation configurations as the improved mechanical performance after experimental validation.

Feasibility Insights of the Green-Assisted Calcium-Phosphate Coating on Biodegradable Zinc Alloys for Biomedical Application: In Vitro and In Vivo Studies

In the field of bone tissue engineering, recently developed Zn alloy scaffolds are considered potential candidates for biodegradable implants for bone regeneration and defect reconstruction. However, the clinical success of these alloys is limited due to their insufficient surface bioactivities. Further, the higher concentration of Zn2+ produced during degradation promotes antibacterial activity, but deteriorates osteogenic properties. This study fabricated an Azadirachta indica (neem)-assisted brushite-hydroxyapatite (HAp) coating on the recently developed Zn-2Cu-0.5Mg alloy to tackle the above dilemma. The microstructure, degradation behavior, antibacterial activity, and hemocompatibility, along with in vitro and in vivo cytocompatibility of the coated alloys, are systematically investigated. Microstructural analysis reveals flower-like morphology with uniformly grown flakes for neem-assisted deposition. The neem-assisted deposition significantly improves the adhesion strength from 12.7 to 18.8 MPa, enhancing the mechanical integrity. The potentiodynamic polarization study shows that the neem-assisted deposition decreases the degradation rate, with the lowest degradation rate of 0.027 mm/yr for the ZHN2 sample. In addition, the biomineralization process shows the apatite formation on the deposited coating after 21 days of immersion. In vitro cytotoxicity assay exhibits the maximum cell viability of 117% for neem-assisted coated alloy in 30% extract after 5d and the improved cytocompatibility which is due to the controlled release of Zn2+ ions. Meanwhile, neem-assisted coated alloy increases the ZOI by 32 and 24% for Gram-positive and Gram-negative bacteria, respectively. Acceptable hemolysis (<5%) and anticoagulation parameters demonstrate a promising hemocompatibility of the coated alloy. In vivo implantation illustrates a slight inflammatory response and vascularization after 2 weeks of subcutaneous implantation, and neo-bone formation in the defect areas of the rat femur. Micro-CT and histology studies demonstrate better osseointegration with satisfactory biosafety response for the neem-assisted coated alloy as compared to that without neem-assisted deposition. Hence, this neem-assisted brushite-Hap coating strategy elucidates a new perspective on the surface modification of biodegradable implants for the treatment of bone defects.

Lithium-Doped Titanium Dioxide-Based Multilayer Hierarchical Structure for Accelerating Nerve-Induced Bone Regeneration

Despite considerable advances in artificial bone tissues, the absence of neural network reconstruction in their design often leads to delayed or ineffective bone healing. Hence, we propose a multilayer hierarchical lithium (Li)-doped titanium dioxide structure, constructed through microarc oxidation combined with alkaline heat treatment. This structure can induce the sustained release of Li ions, mimicking the environment of neurogenic osteogenesis characterized by high brain-derived neurotrophic factor (BDNF) expression. During in vitro experiments, the structure enhanced the differentiation of Schwann cells (SCs) and the growth of human umbilical vein endothelial cells (HUVECs) and mouse embryo osteoblast progenitor cells (MC3T3-E1). Additionally, in a coculture system, the SC-conditioned media markedly increased alkaline phosphatase expression and the formation of calcium nodules, demonstrating the excellent potential of the material for nerve-induced bone regeneration. In an in vivo experiment based on a rat distal femoral lesion model, the structure substantially enhanced bone healing by increasing the density of the neural network in the tissue around the implant. In conclusion, this study elucidates the neuromodulatory pathways involved in bone regeneration, providing a promising method for addressing bone deformities.

Patient-specific implants made of 3D printed bioresorbable polymers at the point-of-care: material, technology, and scope of surgical application

BACKGROUND

Bioresorbable patient-specific additive-manufactured bone grafts, meshes, and plates are emerging as a promising alternative that can overcome the challenges associated with conventional off-the-shelf implants. The fabrication of patient-specific implants (PSIs) directly at the point-of-care (POC), such as hospitals, clinics, and surgical centers, allows for more flexible, faster, and more efficient processes, reducing the need for outsourcing to external manufacturers. We want to emphasize the potential advantages of producing bioresorbable polymer implants for cranio-maxillofacial surgery at the POC by highlighting its surgical applications, benefits, and limitations.

METHODS

This study describes the workflow of designing and fabricating degradable polymeric PSIs using three-dimensional (3D) printing technology. The cortical bone was segmented from the patient's computed tomography data using Materialise Mimics software, and the PSIs were designed created using Geomagic Freeform and nTopology software. The implants were finally printed via Arburg Plastic Freeforming (APF) of medical-grade poly (L-lactide-co-D, L-lactide) with 30% β-tricalcium phosphate and evaluated for fit.

RESULTS

3D printed implants using APF technology showed surfaces with highly uniform and well-connected droplets with minimal gap formation between the printed paths. For the plates and meshes, a wall thickness down to 0.8 mm could be achieved. In this study, we successfully printed plates for osteosynthesis, implants for orbital floor fractures, meshes for alveolar bone regeneration, and bone scaffolds with interconnected channels.

CONCLUSIONS

This study shows the feasibility of using 3D printing to create degradable polymeric PSIs seamlessly integrated into virtual surgical planning workflows. Implementing POC 3D printing of biodegradable PSI can potentially improve therapeutic outcomes, but regulatory compliance must be addressed.

In vitro and in vivo studies on biodegradable Zn porous scaffolds with a drug-loaded coating for the treatment of infected bone defect

Additively manufactured biodegradable zinc (Zn) scaffolds have great potential to repair infected bone defects due to their osteogenic and antibacterial properties. However, the enhancement of antibacterial properties depends on a high concentration of dissolved Zn2+, which in return deteriorates osteogenic activity. In this study, a vancomycin (Van)-loaded polydopamine (PDA) coating was prepared on pure Zn porous scaffolds to solve the above dilemma. Compared with pure Zn scaffolds according to comprehensive in vitro tests, the PDA coating resulted in a slow degradation and inhibited the excessive release of Zn2+ at the early stage, thus improving cytocompatibility and osteogenic activity. Meanwhile, the addition of Van drug substantially suppressed the attachment and proliferation of S. aureus and E. coli bacterial. Furthermore, in vivo implantation confirmed the simultaneously improved osteogenic and antibacterial functions by using the pure Zn scaffolds with Van-loaded PDA coating. Therefore, it is promising to employ biodegradable Zn porous scaffolds with the proposed drug-loaded coating for the treatment of infected bone defects.

Metallic Materials for Bone Repair

Repair of large bone defects caused by trauma or disease poses significant clinical challenges. Extensive research has focused on metallic materials for bone repair because of their favorable mechanical properties, biocompatibility, and manufacturing processes. Traditional metallic materials, such as stainless steel and titanium alloys, are widely used in clinics. Biodegradable metallic materials, such as iron, magnesium, and zinc alloys, are promising candidates for bone repair because of their ability to degrade over time. Emerging metallic materials, such as porous tantalum and bismuth alloys, have gained attention as bone implants owing to their bone affinity and multifunctionality. However, these metallic materials encounter many practical difficulties that require urgent improvement. This article systematically reviews and analyzes the metallic materials used for bone repair, providing a comprehensive overview of their morphology, mechanical properties, biocompatibility, and in vivo implantation. Furthermore, the strategies and efforts made to address the short-comings of metallic materials are summarized. Finally, the perspectives for the development of metallic materials to guide future research and advancements in clinical practice are identified.

The effect of pore size on the mechanical properties, biodegradation and osteogenic effects of additively manufactured magnesium scaffolds after high temperature oxidation: An in vitro and in vivo study

The effects of pore size in additively manufactured biodegradable porous magnesium on the mechanical properties and biodegradation of the scaffolds as well as new bone formation have rarely been reported. In this work, we found that high temperature oxidation improves the corrosion resistance of magnesium scaffold. And the effects of pore size on the mechanical characteristics and biodegradation of scaffolds, as well as new bone formation, were investigated using magnesium scaffolds with three different pore sizes, namely, 500, 800, and 1400 μm (P500, P800, and P1400). We discovered that the mechanical characteristics of the P500 group were much better than those of the other two groups. In vitro and in vivo investigations showed that WE43 magnesium alloy scaffolds supported the survival of mesenchymal stem cells and did not cause any local toxicity. Due to their larger specific surface area, the scaffolds in the P500 group released more magnesium ions within reasonable range and improved the osteogenic differentiation of bone mesenchymal stem cells compared with the other two scaffolds. In a rabbit femoral condyle defect model, the P500 group demonstrated unique performance in promoting new bone formation, indicating its great potential for use in bone defect regeneration therapy.

In vitro and in vivo degradation behavior of Mg-0.45Zn-0.45Ca (ZX00) screws for orthopedic applications

Magnesium (Mg) alloys have become a potential material for orthopedic implants due to their unnecessary implant removal, biocompatibility, and mechanical integrity until fracture healing. This study examined the in vitro and in vivo degradation of an Mg fixation screw composed of Mg-0.45Zn-0.45Ca (ZX00, in wt.%). With ZX00 human-sized implants, in vitro immersion tests up to 28 days under physiological conditions, along with electrochemical measurements were performed for the first time. In addition, ZX00 screws were implanted in the diaphysis of sheep for 6, 12, and 24 weeks to assess the degradation and biocompatibility of the screws in vivo. Using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), micro-computed tomography (μCT), X-ray photoelectron spectroscopy (XPS), and histology, the surface and cross-sectional morphologies of the corrosion layers formed, as well as the bone-corrosion-layer-implant interfaces, were analyzed. Our findings from in vivo testing demonstrated that ZX00 alloy promotes bone healing and the formation of new bone in direct contact with the corrosion products. In addition, the same elemental composition of corrosion products was observed for in vitro and in vivo experiments; however, their elemental distribution and thicknesses differ depending on the implant location. Our findings suggest that the corrosion resistance was microstructure-dependent. The head zone was the least corrosion-resistant, indicating that the production procedure could impact the corrosion performance of the implant. In spite of this, the formation of new bone and no adverse effects on the surrounding tissues demonstrated that the ZX00 is a suitable Mg-based alloy for temporary bone implants.

Physiomimetic biocompatibility evaluation of directly printed degradable porous iron implants using various cell types

Additively manufactured (AM) degradable porous metallic biomaterials offer unique opportunities for satisfying the design requirements of an ideal bone substitute. Among the currently available biodegradable metals, iron has the highest elastic modulus, meaning that it would benefit the most from porous design. Given the successful preclinical applications of such biomaterials for the treatment of cardiovascular diseases, the moderate compatibility of AM porous iron with osteoblast-like cells, reported in earlier studies, has been surprising. This may be because, as opposed to static in vitro conditions, the biodegradation products of iron in vivo are transported away and excreted. To better mimic the in situ situations of biodegradable biomaterials after implantation, we compared the biodegradation behavior and cytocompatibility of AM porous iron under static conditions to the conditions with dynamic in situ-like fluid flow perfusion in a bioreactor. Furthermore, the compatibility of these scaffolds with four different cell types was evaluated to better understand the implications of these implants for the complex process of natural wound healing. These included endothelial cells, L929 fibroblasts, RAW264.7 macrophage-like cells, and osteoblastic MG-63 cells. The biodegradation rate of the scaffolds was significantly increased in the perfusion bioreactor as compared to static immersion. Under either condition, the compatibility with L929 cells was the best. Moreover, the compatibility with all the cell types was much enhanced under physiomimetic dynamic flow conditions as compared to static biodegradation. Our study highlights the importance of physiomimetic culture conditions and cell type selection when evaluating the cytocompatibility of degradable biomaterials in vitro. STATEMENT OF SIGNIFICANCE: Additively manufactured (AM) degradable porous metals offer unique opportunities for the treatment of large bony defects. Despite the successful preclinical applications of biodegradable iron in the cardiovascular field, the moderate compatibility of AM porous iron with osteoblast-like cells was reported. To better mimic the in vivo condition, we compared the biodegradation behavior and cytocompatibility of AM porous iron under static condition to dynamic perfusion. Furthermore, the compatibility of these scaffolds with various cell types was evaluated to better simulate the process of natural wound healing. Our study suggests that AM porous iron holds great promise for orthopedic applications, while also highlighting the importance of physio-mimetic culture conditions and cell type selection when evaluating the cytocompatibility of degradable biomaterials in vitro.

A drug-loaded composite coating to improve osteogenic and antibacterial properties of Zn-1Mg porous scaffolds as biodegradable bone implants

Zinc (Zn) alloy porous scaffolds produced by additive manufacturing own customizable structures and biodegradable functions, having a great application potential for repairing bone defect. In this work, a hydroxyapatite (HA)/polydopamine (PDA) composite coating was constructed on the surface of Zn-1Mg porous scaffolds fabricated by laser powder bed fusion, and was loaded with a bioactive factor BMP2 and an antibacterial drug vancomycin. The microstructure, degradation behavior, biocompatibility, antibacterial performance and osteogenic activities were systematically investigated. Compared with as-built Zn-1Mg scaffolds, the rapid increase of Zn²⁺, which resulted to the deteriorated cell viability and osteogenic differentiation, was inhibited due to the physical barrier of the composite coating. In vitro cellular and bacterial assay indicated that the loaded BMP2 and vancomycin considerably enhanced the cytocompatibility and antibacterial performance. Significantly improved osteogenic and antibacterial functions were also observed according to in vivo implantation in the lateral femoral condyle of rats. The design, influence and mechanism of the composite coating were discussed accordingly. It was concluded that the additively manufactured Zn-1Mg porous scaffolds together with the composite coating could modulate biodegradable performance and contribute to effective promotion of bone recovery and antibacterial function.

Evolution from Bioinert to Bioresorbable: In Vivo Comparative Study of Additively Manufactured Metal Bone Scaffolds

Additively manufactured scaffolds offer significant potential for treating bone defects, owing to their porous, customizable architecture and functionalization capabilities. Although various biomaterials have been investigated, metals - the most successful orthopedic material - have yet to yield satisfactory results. Conventional bio-inert metals, such as titanium (Ti) and its alloys, are widely used for fixation devices and reconstructive implants, but their non-bioresorbable nature and the mechanical property mismatch with human bones limit their application as porous scaffolds for bone regeneration. Advancements in additive manufacturing have facilitated the use of bioresorbable metals, including magnesium (Mg), zinc (Zn), and their alloys, as porous scaffolds via Laser Powder Bed Fusion (L-PBF) technology. This in vivo study presents a comprehensive, side-by-side comparative analysis of the interactions between bone regeneration and additively manufactured bio-inert/bioresorbable metal scaffolds, as well as their therapeutic outcomes. The research offers an in-depth understanding of the metal scaffold-assisted bone healing process, illustrating that Mg and Zn scaffolds contribute to the bone healing process in distinct ways, but ultimately deliver superior therapeutic outcomes compared to Ti scaffolds. These findings suggest that bioresorbable metal scaffolds hold considerable promise for the clinical treatment of bone defects in the near future.

Noninvasive and Microinvasive Nanoscale Drug Delivery Platforms for Hard Tissue Engineering

Bone tissue plays a crucial role in protecting internal organs and providing structural support and locomotion of the body. Treatment of hard tissue defects and medical conditions due to physical injuries, genetic disorders, aging, metabolic syndromes, and infections is more often a complex and drawn out process. Presently, dealing with hard-tissue-based clinical problems is still mostly conducted via surgical interventions. However, advances in nanotechnology over the last decades have led to shifting trends in clinical practice toward noninvasive and microinvasive methods. In this review article, recent advances in the development of nanoscale platforms for bone tissue engineering have been reviewed and critically discussed to provide a comprehensive understanding of the advantages and disadvantages of noninvasive and microinvasive methods for treating medical conditions related to hard tissue regeneration and repair.

Biofabrication of functional bone tissue: defining tissue-engineered scaffolds from nature

Damage to bone leads to pain and loss of movement in the musculoskeletal system. Although bone can regenerate, sometimes it is damaged beyond its innate capacity. Research interest is increasingly turning to tissue engineering (TE) processes to provide a clinical solution for bone defects. Despite the increasing biomimicry of tissue-engineered scaffolds, significant gaps remain in creating the complex bone substitutes, which include the biochemical and physical conditions required to recapitulate bone cells' natural growth, differentiation and maturation. Combining advanced biomaterials with new additive manufacturing technologies allows the development of 3D tissue, capable of forming cell aggregates and organoids based on natural and stimulated cues. Here, we provide an overview of the structure and mechanical properties of natural bone, the role of bone cells, the remodelling process, cytokines and signalling pathways, causes of bone defects and typical treatments and new TE strategies. We highlight processes of selecting biomaterials, cells and growth factors. Finally, we discuss innovative tissue-engineered models that have physiological and anatomical relevance for cancer treatments, injectable stimuli gels, and other therapeutic drug delivery systems. We also review current challenges and prospects of bone TE. Overall, this review serves as guide to understand and develop better tissue-engineered bone designs.

Electrospun core-sheath PCL nanofibers loaded with nHA and simvastatin and their potential bone regeneration applications

Introduction: Drugs and biocompatible nanoparticles have raised significant potential in advancing the bone regeneration. Electrospinning technology enables the full realization of the value of drugs and nanoparticles. Methods: In this study, we have successfully fabricated core-sheath nanofibers solely composed of polycaprolactone (PCL) polymer. Simvastatin (SIM) was confined to the core of the nanofibers while nanohydroxyapatite (nHA) was loaded on the nanofiber surface. Results: All the prepared nanofibers exhibited a cylindrical micromorphology, and the core-sheath structure was exploited using a Transmission Electron Microscope. X-ray pattern results indicated that SIM was in an amorphous state within nanofibers, while Fourier Transform InfraRed spectroscopy showed excellent chemical compatibility among SIM, nHA, and PCL. The actual loading of nHA within the nanofiber was determined by a thermogravimetric test due to the high melting point of nHA. Core-sheath nanofibers could release SIM for 672 h, which was attributed to the core-sheath structure. Furthermore, nanofibers loaded with SIM or nHA had a positive impact on cell proliferation, with the core-sheath nanofibers displaying the most favorable cell proliferation behavior. Discussion: Such a synergistic facilitation strategy based on materials and nanostructure may encourage researchers to exploit new biomedical materials in future.

miR-218-5p-Modified Bone Marrow Mesenchymal Stem Cells Mediate the Healing Effect of EphrinB2-EphB4 Signals on Alveolar Bone Defect

Abnormally expressed miR-218-5p involves in alveolar bone defect. We intend to investigate whether miR-218-5p-modified bone marrow mesenchymal stem cells (BMSCs) mediates the healing effects of EphrinB2-EphB4 signals on the alveolar bone defect. Fifty germ-free rats (6-month-old) were utilized in this study. The grouping was set up as follows: blank group, model group, miR-218-5p group, EphrinB2-EphB4 antagonist group, and positive control group (10 rats in each group). HE staining was employed to quantify bone resorption lacunae number. And the following indicators were monitored: miR-218-5p expression, differentiation status of osteoblasts, concentrations of TNF-α/IL-10/ IL-8, and EphrinB2 and EphB4 expression. As shown in HE staining, massive infiltration of inflammatory cells was denoted at the alveolar bone defective sites in rats from model group. However, infiltration of inflammatory cells in lesions was moderate in rats from EphrinB2-EphB4 antagonist group and positive control group, which was accompanied by formation of small bone islands. Furthermore, lesser infiltration of inflammatory cells was denoted at the alveolar bone defective sites in rats from the miR-218-5p group, which also exhibited a larger number of newly formed bone trabeculae growing toward the center of lesions. On the 3rd day of culture, absorption lacunae were rare in the model group, while remaining undetectable in other groups. On the 7th day of culture, bone resorption lacunae number in samples from model group was significantly higher in comparison with that in other groups. Meanwhile, it was reduced significantly in miR-218-5p group. However, it was increased in EphrinB2-EphB4 antagonist group and positive control group (P <0.05). An elevation of the intracellular miR-218-5p level was denoted in the modified BMSCs in comparison with those unmodified BMSCs (P < 0.05). In comparison with blank group, other groups exhibited significantly elevated ALP levels, among which model group showed highest level. However, decline of ALP levels was denoted in positive control group, EphrinB2-EphB4 antagonist group and miR-218-5p group, with lowest ALP level in miR-218-5p group (P <0.05). Except blank group, rats in other groups exhibited a significant elevation of TNF-α, IL-10 and IL-8 in the serum, among which those in the model group displayed the most remarkable increase of these cytokines. Rats in miR-218-5p group, EphrinB2-EphB4 antagonist group and positive control group exhibited significantly reduced levels of IL-8, IL-10 and TNF-α in the serum, with miR-218-5p group showing lowest levels (P < 0.05). In comparison with the blank group, other groups showed significantly enhanced protein expression of EphrinB2 and EphB4, among which the model group displayed the most remarkable enrichment of these proteins. In comparison with the model group, samples from the miR-218-5p group, EphrinB2-EphB4 antagonist group and positive control group exhibited significantly weakened expression of EphrinB2 and EphB4, among which the miR-218-5p group displayed the most remarkable decrease of these proteins (P <0.05). miR-218-5p-modified BMSCs can modulate the EphrinB2-EphB4 signal transduction pathway to produce two-way transmission, which included their inhibition of the osteoclast generation and their enhancement of the osteoclast differentiation. In this way, they aided in alleviating inflammatory response in alveolar bone defective lesions, thereby accelerating the healing process of alveolar bone defect. The function of miR-218-5p-modified BMSCs is mainly achieved in the healing process of the alveolar bone defect.

Black phosphorous-based biomaterials for bone defect regeneration: a systematic review and meta-analysis

Critical-sized bone defects are always difficult to treat, and they are associated with a significant burden of disease in clinical practice. In recent decades, due to the fast development of biomaterials and tissue engineering, many bioinspired materials have been developed to treat large bone defects. Due to the excellent osteoblastic ability of black phosphorous (BP), many BP-based biomaterials have been developed to treat bone defects. Therefore, there are abundant studies as well as a tremendous amount of research data. It is urgent to conduct evidence-based research to translate these research data and results into validated scientific evidence. Therefore, in our present study, a qualitative systematic review and a quantitative meta-analysis were performed. Eighteen studies were included in a systematic review, while twelve studies were included in the meta-analysis. Our results showed that the overall quality of experimental methods and reports of biomaterials studies was still low, which needs to be improved in future studies. Besides, we also proved the excellent osteoblastic ability of BP-based biomaterials. But we did not find a significant effect of near-infrared (NIR) laser in BP-based biomaterials for treating bone defects. However, the quality of the evidence presented by included studies was very low. Therefore, to accelerate the clinical translation of BP-based biomaterials, it is urgent to improve the quality of the study method and reporting in future animal studies. More evidence-based studies should be conducted to enhance the quality and clinical translation of BP-based biomaterials.

Plain metallic biomaterials: opportunities and challenges

The 'plainification of materials' has been conceptualized to promote the sustainable development of materials. This perspective, for the first time in the field of biomaterials, proposes and defines 'plain metallic biomaterials (PMBs)' with demonstrated research and application case studies of pure titanium with high strength and toughness, and biodegradable, fine-grained and high-purity magnesium. Then, after discussing the features, benefits and opportunities of PMBs, the challenges are analyzed from both technical and regulatory aspects. Regulatory perspectives on PMB-based medical devices are also provided for the benefit of future research, development and commercialization.

Advancing medical device regulatory reforms for innovation, translation and industry development in China

The blossoming Chinese medical device market calls for a science-based regulatory system in China. Consistent efforts have been made to advance the medical device regulatory reforms for innovation, translation and industry development. In this article, we report both the latest regulatory requirements which aim to ensure safety and efficacy for patients while encouraging innovation of the medical device industry, and the key programs on medical devices covered in the Regulatory Science Action Plan (RSAP) of the National Medical Products Administration of China (NMPA). The main features of the revised regulations are first elucidated before the opportunities for translational research are interpreted, including those for additive manufacturing and customized devices, drug–device combination products, artificial intelligence-powered software and surgical robots, and nanomaterials for medical devices. Finally, a regulatory perspective is provided to researchers who expect to translate their technologies in the Chinese medical device market. Important issues including early attention to critical market and clinical needs, understanding the true principle and spirit underlying the changing regulations and standards, and protecting intellectual property rights with comprehensive measures, are discussed. These developments warrant further investigations into the distinct role of regulatory science in shaping medical devices research and development.

Surgical Classification for Preclinical Rat Femoral Bone Defect Model: Standardization Based on Systematic Review, Anatomical Analysis and Virtual Surgery

Though surgical techniques profoundly influence in vivo experiments, significant heterogeneity exists in current surgeries for inducing rat femoral bone defects. Such variations reduce the reproducibility and comparability of preclinical studies, and are detrimental to clinical translation. The purposes of this study were: (1) to conduct a systematic review of rat femoral defect models, summarizing and analyzing the surgical techniques; (2) to analyze surgical design and potential pitfalls via 3D anatomy and virtual surgeries for fostering future precision research; and (3) to establish a surgical classification system, for improving the reproducibility and comparability among studies, avoiding unnecessary repetitive experiments. The online database PubMed was searched to identify studies from January 2000 to June 2022 using keywords, including rat, femur, bone defect. Eligible publications were included for a review of surgical methods. Anatomical analysis and virtual surgeries were conducted based on micro-CT reconstruction of the rat femur for further investigation and establishment of a classification system. A total of 545 publications were included, revealing marked heterogeneity in surgical methods. Four major surgical designs were reported for inducing defects from the proximal to distal femur: bone tunnel, cortical window, segmental defect, and wedge-shaped defect. Anatomical analysis revealed potential pitfalls hindering efficient clinical translation. A classification system was established according to the anatomical region, surgical design, and fixation devices. This systematic review in combination with 3D analysis and virtual surgery provides a general overview of current surgical approaches to inducing femoral defects in rats, and establishes a surgical classification facilitating preclinical research of quality and translational value.

García A, G. Mikos A, M. Anderson J, Zhang X. Evidence-based biomaterials research

The fast development of biomaterials science and engineering has generated significant number of studies and publications as well as tremendous amount of research data. A methodology is needed to translate such research data and results to validated scientific evidence. This article for the first time proposes the concept and methodology of evidence-based biomaterials research, which is to use evidence-based research approach represented by systematic reviews to generate evidence for answering scientific questions related to biomaterials. After briefly introducing the advancement of biomaterials since 1950s, the scientific and engineering nature of biomaterials are discussed along with the roadmap of biomaterials translation from basic research to commercialized medical products, and the needs of scientific evidence. Key information of the evidence-based approach such as its origination from evidence-based medicine, levels of evidence, systematic review and meta-analysis, differences between systematic and narrative reviews is then highlighted. Applications with a step-by-step procedure of conducting evidence-based biomaterials research, three examples of biomaterials research using evidence-based approach to generate scientific evidence, and opportunities and challenges of evidence-based biomaterials research are presented. With its notable impact on the practice of medicine, the evidence-based approach is also expected to make influential contributions to the biomaterials field.

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Evidence-based biomaterials research (EBBR) is very important for biomaterials.

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Authors for the first time propose the concept, practice and methodology of EBBR.

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EBBR uses an evidence-based approach of systematic review and meta-analysis.

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Key elements of an evidence-based approach are discussed.

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Procedures and examples of evidence-based biomaterials research are illustrated.

Advances in Translational 3D Printing for Cartilage, Bone, and Osteochondral Tissue Engineering

The regeneration of 3D tissue constructs with clinically relevant sizes, structures, and hierarchical organizations for translational tissue engineering remains challenging. 3D printing, an additive manufacturing technique, has revolutionized the field of tissue engineering by fabricating biomimetic tissue constructs with precisely controlled composition, spatial distribution, and architecture that can replicate both biological and functional native tissues. Therefore, 3D printing is gaining increasing attention as a viable option to advance personalized therapy for various diseases by regenerating the desired tissues. This review outlines the recently developed 3D printing techniques for clinical translation and specifically summarizes the applications of these approaches for the regeneration of cartilage, bone, and osteochondral tissues. The current challenges and future perspectives of 3D printing technology are also discussed.

Bone Engineering Scaffolds With Exosomes: A Promising Strategy for Bone Defects Repair

The treatment of bone defects is still an intractable clinical problem, despite the fact that numerous treatments are currently available. In recent decades, bone engineering scaffolds have become a promising tool to fill in the defect sites and remedy the deficiencies of bone grafts. By virtue of bone formation, vascular growth, and inflammation modulation, the combination of bone engineering scaffolds with cell-based and cell-free therapy is widely used in bone defect repair. As a key element of cell-free therapy, exosomes with bioactive molecules overcome the deficiencies of cell-based therapy and promote bone tissue regeneration via the potential of osteogenesis, angiogenesis, and inflammation modulation. Hence, this review aimed at overviewing the bone defect microenvironment and healing mechanism, summarizing current advances in bone engineering scaffolds and exosomes in bone defects to probe for future applications.

Preparation of BMP-2/PDA-BCP Bioceramic Scaffold by DLP 3D Printing and its Ability for Inducing Continuous Bone Formation

Digital light processing (DLP)-based 3D printing is suitable to fabricate bone scaffolds with small size and high precision. However, the published literature mainly deals with the fabrication procedure and parameters of DLP printed bioceramic scaffold, but lacks the subsequent systematic biological evaluations for bone regeneration application. In this work, a biphasic calcium phosphate (BCP) macroporous scaffold was constructed by DLP-based 3D printing technique. Furthermore, bone morphogenetic protein-2 (BMP-2) was facilely incorporated into this scaffold through a facile polydopamine (PDA) modification process. The resultant scaffold presents an interconnected porous structure with pore size of ∼570 μm, compressive strength (∼3.6 MPa), and the self-assembly Ca-P/PDA nanocoating exhibited excellent sustained-release property for BMP-2. Notably, this BMP-2/PDA-BCP scaffold presents favorable effects on the adhesion, proliferation, osteogenic differentiation, and mineralization of bone marrow stromal cells (BMSCs). Furthermore, in vivo experiments conducted on rats demonstrated that the scaffolds could induce cell layer aggregation adjacent to the scaffolds and continuous new bone generation within the scaffold. Collectively, this work demonstrated that the BMP-2/PDA-BCP scaffold is of immense potential to treat small craniofacial bone defects in demand of high accuracy.

Improved Mechanical Properties and Bioactivity of Silicate Based Bioceramics Reinforced Poly(ether-ether-ketone) Nanocomposites for Prosthetic Dental Implantology

Polyether-ether-ketone (PEEK) biomaterial has been increasingly employed for orthopedic, trauma, spinal, and dental implants due to its biocompatibility and in vivo stability. However, a lack of bioactivity and binding ability to natural bone tissue has significantly limited PEEK for many challenging dental implant applications. In this work, nanocomposites based on PEEK reinforced with bioactive silicate-based bioceramics (forsterite or bioglass) as nanofillers were prepared using high energy ball milling followed by melt blending and compression molding. The influence of nanofillers type and content (10, 20 and 30 wt.%) on the crystalline structure, morphology, surface roughness, hydrophilicity, microhardness, elastic compression modulus, and flexural strength of the nanocomposites was investigated. The scanning electron microscopy images of the nanocomposites with low nanofillers content showed a homogenous surface with uniform dispersion within the PEEK matrix with no agglomerates. All nanocomposites showed an increased surface roughness compared to pristine PEEK. It was found that the incorporation of 20 wt.% forsterite was the most effective in the nanocomposite formulation compared with bioglass-based nanocomposites; it has significantly improved the elastic modulus, flexural strength, and microhardness. In vitro bioactivity evaluation, which used biomimetic simulated body fluid indicated the ability of PEEK nanocomposites loaded with forsterite or bioglass nanofillers to precipitate calcium and phosphate bone minerals on its surface. These nanocomposites are expected to be used in long-term load-bearing implant applications and could be recommended as a promising alternative to titanium and zirconia when used as a dental implant material.

Regulatory perspectives of combination products

Combination products with a wide range of clinical applications represent a unique class of medical products that are composed of more than a singular medical device or drug/biological product. The product research and development, clinical translation as well as regulatory evaluation of combination products are complex and challenging. This review firstly introduced the origin, definition and designation of combination products. Key areas of systematic regulatory review on the safety and efficacy of device-led/supervised combination products were then presented. Preclinical and clinical evaluation of combination products was discussed. Lastly, the research prospect of regulatory science for combination products was described. New tools of computational modeling and simulation, novel technologies such as artificial intelligence, needs of developing new standards, evidence-based research methods, new approaches including the designation of innovative or breakthrough medical products have been developed and could be used to assess the safety, efficacy, quality and performance of combination products. Taken together, the fast development of combination products with great potentials in healthcare provides new opportunities for the advancement of regulatory review as well as regulatory science.

Processing optimization, mechanical properties, corrosion behavior and cytocompatibility of additively manufactured Zn-0.7Li biodegradable metals

Biodegradable Zn-Li alloys exhibit superior mechanical performance and favorable osteogenic capability for load-bearing bone devices. Additive manufacturing (AM) endows freedom for the fabrication of bone implants of personalized structure to satisfy patient-specific needs. In this paper, AM of Zn-Li alloys was attempted for the first-time using laser powder bed fusion (LPBF), and the fabricated samples exhibited good fusion quality and high dimensional accuracy. The processing optimization, mechanical properties, in vitro corrosion behavior and cytocompatibility were investigated by using Zn-0.7Li bulk and porous samples. The ultimate tensile strength and elastic modulus of bulk samples respectively reached 416.5 MPa and 83.3 GPa, and both were the highest among various additively manufactured Zn alloys reported so far. Porous samples achieved compressive strength (18.2 MPa) and elastic modulus (298.0 MPa), which were comparable to those of cancellous bone. Porous samples exhibited a higher corrosion rate and alleviated the problem of slow degradation of Zn-Li alloys. Nevertheless, osteoblastic cells showed a more spreading and healthier morphology when adhering to the porous samples compared to the bulk samples, thus a better cytocompatibility was confirmed. This work shows tremendous potential to precisely design and modulate biodegradable Zn alloys to fulfill clinical needs by using AM technology. STATEMENT OF SIGNIFICANCE: This paper firstly studied processing optimization during laser powder bed fusion of Zn-Li alloy. Bulk and porous Zn-0.7Li samples in customized design were obtained with high formation quality. The tensile strength of bulk samples reached 416.5 MPa, while the compressive strength and modulus of porous samples reduced to 18.2 MPa and 298.0 MPa, comparable to those of bone. The weight loss of porous samples was roughly 5 times that of bulk samples; osteoblastic cells showed a more spreading and healthier morphology at porous samples, indicating improved biodegradation rate and cytocompatibility. This work shows tremendous potential to precisely design and modulate biodegradable Zn alloy porous scaffolds to fulfill clinical needs by using additive manufacturing technology.

A Systematic Review and Network Meta-Analysis of Biomedical Mg Alloy and Surface Coatings in Orthopedic Application

Magnesium alloys have great application prospects as ideal bone implant materials. However, their poor corrosion resistance limits their clinical orthopedic application. Surface modification promotes the corrosion resistance of magnesium. Conversion coatings, such as calcium phosphate (Ca-P) coating, microarc oxidation (MAO) treatment, and fluoride (FLU) treatment, have been extensively investigated in in vivo studies. This systematic review and network meta-analysis compared the influence of different conversion coatings on bone repair, material properties, and systemic host response in orthopedic applications. Using the PICOS model, the inclusion criteria for biodegradable magnesium and its alloys were determined for in vivo studies. Four databases were used. The standard and weight mean differences with 95% confidence intervals were used to analyze new bone formation and degradation rate. Network structure and forest plots were created, and ranking probabilities were estimated. The risk of bias and quality of evidence were assessed using SYRCLE, CERQual, and GRADE tools. In the qualitative analysis, 43 studies were selected, and the evaluation of each outcome indicator was not entirely consistent from article to article. In the quantitative analysis, 21 articles were subjected to network meta-analysis, with 16 articles on implant degradation and 8 articles for new bone formation. Additionally, SUCRA indicated that Ca-P coating exhibited the highest corrosion resistance, followed by FLU treatment. MAO demonstrated the best capability for new bone formation, followed by Ca-P coating. Ca-P coating exhibited the highest overall performance. To conclude, coated Mg can promote better new bone formation than bare Mg and has considerable biocompatibility. Ca-P-coated Mg and MAO-coated Mg have the greatest potential to significantly promote corrosion resistance and bone regeneration, respectively. The findings of this study will provide a theoretical basis for the investigation of composite coatings and guidance for the orthopedic application of Mg bone implants.

Biodegradable iron-silicon implants produced by additive manufacturing

Due to many negative and undesirable side effects from the use of permanent implants, the development of temporary implants based on biocompatible and biodegradable materials is a promising area of modern medicine. In the presented study, we have investigated complex-shaped iron-silicon (Fe-Si) scaffolds that can be used as potential biodegradable framework structures for creating solid implants for bone grafting. Since iron and silicon are biocompatible materials, and their alloy should also have biocompatibility. It has been demonstrated that cells UC-MSC and 3T3 were attached to, spread, and proliferated on the Fe-Si scaffolds' surface. Most of UC-MSC and 3T3 remained viable, only single dead cells were observed. According to the results of biological testing, the scaffolds have shown that deposition of calcium phosphate particles occurs on day one in the scaffold at the defect site that can be used as a primary marker of osteodifferentiation. These results demonstrate that the 3D-printed porous iron-silicon (Fe-Si) alloy scaffolds are promising structures for bone grafting and regeneration.

Regulatory considerations for animal studies of biomaterial products

Animal studies play a vital role in validating the concept, feasibility, safety, performance and efficacy of biomaterials products during their bench-to-clinic translation. This article aims to share regulatory considerations for animal studies of biomaterial products. After briefly emphasizing the importance of animal studies, issues of animal studies during biomaterial products' translation are discussed. Animal studies with unclear purposes, flawed design and poor reporting quality could significantly reduce the translation efficiency and create regulatory challenges. Regulatory perspectives on the purpose, principle, quality and regulatory science of animal studies are also presented. Animal studies should have clear purposes, follow principles of 3R+DQ (replacement, reduction, refinement, design and quality) and execute under an efficiently operating quality management system. With the advancement of regulatory science, National Medical Products Administration of China has been developing a series of standards and guidance documents on animal studies of medical devices. Case studies of making decisions on whether to conduct animal studies are provided in the end with drug-eluting stents as examples. In summary, animal studies of biomaterial products should pay close attention to the rationale, design and quality in order to achieve their purposes.

Meta-analysis of cellular toxicity for graphene via data-mining the literature and machine learning

Since graphene is currently incorporated into various consumer products and used in a variety of applications, determining the relationships between the physicochemical properties of graphene and its toxicity is critical for conducting environmental and health risk analyses. Data from the literature suggest that exposure to graphene may result in cytotoxicity. However, existing graphene toxicity data are complex and heterogeneous, making it difficult to conduct risk assessments. Here, we conducted a meta-analysis of published data on the cytotoxicity of graphene based on 792 publications, including 986 cell viability data points, 762 half maximal inhibitory concentration (IC₅₀) data points, and 100 lactate dehydrogenase (LDH) release data points. Models to predict graphene cytotoxicity were then developed based on cell viability, IC₅₀, and LDH release as toxicity endpoints using random forests learning algorithms. The most influential attributes influencing graphene cytotoxicity were revealed to be exposure dose and detection method for cell viability, diameter and surface modification for IC₅₀, and detection method and organ source for LDH release. The meta-analysis produced three sets of key attributes for the three abovementioned toxicity endpoints that can be used in future studies of graphene toxicity. The findings indicate that rigorous data mining protocols can be combined with suitable machine learning tools to develop models with good predictive power and accuracy. The results also provide guidance for the design of safe graphene materials.

Hydroxyapatite Obtained via the Wet Precipitation Method and PVP/PVA Matrix as Components of Polymer-Ceramic Composites for Biomedical Applications

The aspect of drug delivery is significant in many biomedical subareas including tissue engineering. Many studies are being performed to develop composites with application potential for bone tissue regeneration which at the same provide adequate conditions for osteointegration and deliver the active substance conducive to the healing process. Hydroxyapatite shows a great potential in this field due to its osteoinductive and osteoconductive properties. In the paper, hydroxyapatite synthesis via the wet precipitation method and its further use as a ceramic phase of polymer-ceramic composites based on PVP/PVA have been presented. Firstly, the sedimentation rate of hydroxyapatite in PVP solutions has been determined, which allowed us to select a 15% PVP solution (sedimentation rate was 0.0292 mm/min) as adequate for preparation of homogenous reaction mixture treated subsequently with UV radiation. Both FT-IR spectroscopy and EDS analysis allowed us to confirm the presence of both polymer and ceramic phase in composites. Materials containing hydroxyapatite showed corrugated and well-developed surface. Composites exhibited swelling properties (hydroxyapatite reduced this property by 25%) in simulated physiological fluids, which make them useful in drug delivery (swelling proceeds parallel to the drug release). The short synthesis time, possibility of preparation of composites with desired shapes and sizes and determined physicochemical properties make the composites very promising for biomedical purposes.

Zn-0.8Mg-0.2Sr (wt.%) Absorbable Screws-An In-Vivo Biocompatibility and Degradation Pilot Study on a Rabbit Model

In this pilot study, we investigated the biocompatibility and degradation rate of an extruded Zn-0.8Mg-0.2Sr (wt.%) alloy on a rabbit model. An alloy screw was implanted into one of the tibiae of New Zealand White rabbits. After 120 days, the animals were euthanized. Evaluation included clinical assessment, microCT, histological examination of implants, analyses of the adjacent bone, and assessment of zinc, magnesium, and strontium in vital organs (liver, kidneys, brain). The bone sections with the implanted screw were examined via scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). This method showed that the implant was covered by a thin layer of phosphate-based solid corrosion products with a thickness ranging between 4 and 5 µm. Only negligible changes of the implant volume and area were observed. The degradation was not connected with gas evolution. The screws were fibrointegrated, partially osseointegrated histologically. We observed no inflammatory reaction or bone resorption. Periosteal apposition and formation of new bone with a regular structure were frequently observed near the implant surface. The histological evaluation of the liver, kidneys, and brain showed no toxic changes. The levels of Zn, Mg, and Sr after 120 days in the liver, kidneys, and brain did not exceed the reference values for these elements. The alloy was safe, biocompatible, and well-tolerated.