3D-printed porous Ti6Al4V scaffolds for long bone repair in animal models: a systematic review

Biomechanical Properties of Novel Porous Scaffold Core and Hollow Lateral Hole Pedicle Screws: A Comparative Study in Bama Pigs

OBJECTIVE

Screw loosening is a common complication of internal fixation of pedicle screw. Therefore, the development of a pedicle screw with low loosening rate and high biosafety is of great clinical significance. This study aimed to investigate whether the application of a porous scaffold structure can improve the stability of pedicle screws by comparing the biomechanical properties of novel porous scaffold core pedicle screws (PSCPSs) with those of hollow lateral hole pedicle screws (HLHPSs) in a porcine lumbar spine.

METHODS

Thirty-two pedicle screws of both types were implanted bilaterally into the L1-4 vertebrae of four Bama pigs, with our newly designed PSCPSs on the right and HLHPSs on the left. All the Bama pigs were sacrificed 16 weeks postoperatively, and the lumbar spine was freed into individual vertebrae. Biomechanical properties of both the pedicle screws were evaluated using pull-out tests, as well as cyclic bending and pull-out tests, while the mechanical properties were assessed using three-point bending tests. The data generated were statistically analyzed using paired-sample t-tests and two independent sample t-tests.

RESULTS

We found that the maximal pull-out forces before and after cyclic bending of the PSCPSs (1161.50 ± 337.98 N and 1075.25 ± 223.33 N) were significantly higher than those of the HLHPSs (948.38 ± 194.32 N and 807.13 ± 242.75 N) (p < 0.05, p < 0.05). In 800 cycles of the bending tests, neither PSCPS nor HLHPS showed loosening or visible detachment, but their maximal pull-out forces after cyclic bending tests decreased compared to those in cycles without cyclic bending tests (7.43% and 14.89%, respectively), with no statistical significance (p > 0.05 and p > 0.05, respectively). Additionally, both screws buckled rather than broke in the three-point bending tests, with no statistically significant differences between the maximal bending load and modulus of elasticity of the two screws (p > 0.05 and p > 0.05, respectively).

CONCLUSIONS

Compared with the HLHPSs, the PSCPSs have greater pull-out resistance and better fatigue tolerance with appropriate mechanical properties. Therefore, PSCPSs theoretically have significant potential for clinical applications in reducing the incidence of loosening after pedicle screw implantation.

Study on the mechanism of magnesium calcium alloys/mineralized collagen composites mediating macrophage polarization to promote bone repair

Magnesium-based composites are a focal point in biomaterials research. However, the rapid degradation rate of magnesium alloys does not align with the healing time of bone tissue. Additionally, the host reaction caused by magnesium implantation hampers its full osteogenic potential. To maintain an appropriate microenvironment, it is important to enhance both corrosion resistance and osteogenic activity of the magnesium matrix. In this study, a composite scaffold composed of mineralized collagen and magnesium alloy was utilized to investigate the regulatory effect of mineralized collagen on mouse macrophages and evaluate its impact on mouse bone marrow mesenchymal stem cells in terms of osteogenesis, immune response, and macrophage-induced osteogenic differentiation. This experiment examined the biocompatibility of mouse bone marrow mesenchymal stem cells and macrophage-induced osteogenic differentiation in vitro, and examined the expression levels of relevant pathways proteins. Magnesium calcium alloys/mineralized collagen exhibited extensive spreading, facilitated by broad and abundant pseudopodia that firmly adhered them to the material surface and promoted growth and pseudopodia formation. The findings revealed that magnesium calcium alloy/mineralized collagen scaffold materials induced osteogenic differentiation mainly through M2 polarization of macrophages. This effect was mainly mediated by promoting the integrin α2β1-FAK-ERK1/2 signaling pathways and inhibiting the RANK signaling pathways.

Surface modification of additive manufactured Ti6Al4V scaffolds with gelatin/alginate- IGF-1 carrier: An effective approach for healing bone defects

The study investigates the potential of porous scaffolds with Gel/Alg-IGF-1 coatings as a viable candidate for orthopaedic implants. The scaffolds are composed of additively manufactured Ti6Al4V lattices, which were treated in an alkali solution to obtain the anatase and rutile phases. The treated surface exhibited hydrophilicity of <11.5°. A biopolymer carrier containing Insulin-like growth factor 1 was coated on the samples using immersion treatment. This study showed that the surface-modified porous Ti6Al4V scaffolds increased cell viability and proliferation, indicating potential for bone regeneration. The results demonstrate that surface modifications can enhance the osteoconduction and osteoinduction of Ti6Al4V implants, leading to improved bone regeneration and faster recovery. The porous Ti6Al4V scaffolds modified with surface coating of Gel/Alg-IGF-1 exhibited a noteworthy increase in cell viability (from 80.7 to 104.1%viability) and proliferation. These results suggest that the surface modified scaffolds have potential for use in treating bone defects.

Bio-functional hydroxyapatite-coated 3D porous polyetherketoneketone scaffold for enhanced osteogenesis and osteointegration in orthopedic applications

Polyetherketoneketone (PEKK), a high-performance thermoplastic special engineering material, maintains bone-like mechanical properties and has received considerable attention in the biomedical field. The 3D printing technique enables the production of porous scaffolds with a honeycomb structure featuring precisely controlled pore size, porosity and interconnectivity, which holds significant potential for applications in tissue engineering. The ideal pore architecture of porous PEKK scaffolds has yet to be elucidated. Porous PEKK scaffolds with five pore sizes P200 (225 ± 9.8 μm), P400 (411 ± 22.1 μm), P600 (596 ± 23.4 μm), P800 (786 ± 24.2 μm) and P1000 (993 ± 26.0 μm) were produced by a 3D printer. Subsequently, the optimum pore size, the P600, for mechanical properties and osteogenesis was selected based on in vitro experiments. To improve the interfacial bioactivity of porous PEKK scaffolds, hydroxyapatite (HAp) crystals were generated via in situ biomimetic mineralization induced by the phase-transited lysozyme coating. Herein, a micro/nanostructured surface showing HAp crystals on PEKK scaffold was developed. In vitro and in vivo experiments confirmed that the porous PEKK-HAp scaffolds exhibited highly interconnected pores and functional surface structures that were favorable for biocompatibility and osteoinductivity, which boosted bone regeneration. Therefore, this work not only demonstrates that the pore structure of the P600 scaffold is suitable for PEKK orthopedic implants but also sheds light on a synergistic approach involving 3D printing and biomimetic mineralization, which has the potential to yield customized 3D PEKK-HAp scaffolds with enhanced osteoinductivity and osteogenesis, offering a promising strategy for bone tissue engineering.

"Metal-bone" scaffold for accelerated peri-implant endosseous healing

Restoring bone defects caused by conditions such as tumors, trauma, or inflammation is a significant clinical challenge. Currently, there is a need for the development of bone tissue engineering scaffolds that meet clinical standards to promote bone regeneration in these defects. In this study, we combined the porous Ti6Al4V scaffold in bone tissue engineering with advanced bone grafting techniques to create a novel "metal-bone" scaffold for enhanced bone regeneration. Utilizing 3D printing technology, we fabricated a porous Ti6Al4V scaffold with an average pore size of 789 ± 22.69 μm. The characterization and biocompatibility of the scaffold were validated through in vitro experiments. Subsequently, the scaffold was implanted into the distal femurs of experimental animals, removed after 3 months, and transformed into a "metal-bone" scaffold. When this "metal-bone" scaffold was re-implanted into bone defects in the animals, the results demonstrated that, in comparison to a plain porous Ti6Al4V scaffold, the scaffold containing bone tissue achieved accelerated early-stage bone regeneration. The experimental group exhibited more bone tissue generation in the early stages at the defect site, resulting in superior bone integration. In conclusion, the "metal-bone" scaffold, containing bone tissue, proves to be an effective bone-promoting scaffold with promising clinical applications.

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.

Study of the Effect of Anodic Oxidation on the Corrosion Properties of the Ti6Al4V Implant Produced from SLM

Additive technologies allowed for the development of medicine and implantology, enabling the production of personalized and highly porous implants. Although implants of this type are used clinically, they are usually only heat treated. Surface modification using electrochemical methods can significantly improve the biocompatibility of biomaterials used for implants, including printed ones. The study examined the effect of anodizing oxidation on the biocompatibility of a porous implant made of Ti6Al4V by the SLM method. The study used a proprietary spinal implant intended for the treatment of discopathy in the c4–c5 section. As part of the work, the manufactured implant was assessed in terms of compliance with the requirements for implants (structure testing—metallography) and the accuracy of the pores produced (pore size and porosity). The samples were subjected to surface modification using anodic oxidation. The research was carried out for 6 weeks in in vitro conditions. Surface topographies and corrosion properties (corrosion potential, ion release) were compared for unmodified and anodically oxidized samples. The tests showed no effect of anodic oxidation on the surface topography and improved corrosion properties. Anodic oxidation stabilized the corrosion potential and limited the release of ions to the environment.

Construction of Vascularized Tissue Engineered Bone with nHA-Coated BCP Bioceramics Loaded with Peripheral Blood-Derived MSC and EPC to Repair Large Segmental Femoral Bone Defect

The regenerative repair of segmental bone defect (SBD) is an urgent problem in the field of orthopedics. Rapid induction of angiogenesis and osteoinductivity after implantation of scaffold is critical. In this study, a unique tissue engineering strategy with mixture of peripheral blood-derived mesenchymal stem cells (PBMSC) and endothelial progenitor cells (PBEPC) was applied in a 3D-printed biphasic calcium phosphate (BCP) scaffold with highly bioactive nano hydroxyapatite (nHA) coating (nHA/BCP) to construct a novel vascularized tissue engineered bone (VTEB) for rabbit femoral SBD repair. The 2D coculture of PBMSC and PBEPC showed that they could promote the osteogenic or angiogenic differentiation of the cells from each other, especially in the group of PBEPC/PBMSC = 75:25. Besides, the 3D coculture results exhibited that the nHA coating could further promote PBEPC/PBMSC adhesion, proliferation, and osteogenic and angiogenic differentiation on the BCP scaffold. In vivo experiments showed that among the four groups (BCP, BCP-PBEPC/PBMSC, nHA/BCP, and nHA/BCP-PBEPC/PBMSC), the nHA/BCP-PBEPC/PBMSC group induced the best formation of blood vessels and new bone and, thus, the good repair of SBD. It revealed the synergistic effect of nHA and PBEPC/PBMSC on the angiogenesis and osteogenesis of the BCP scaffold. Therefore, the construction of VTEB in this study could provide a possibility for the regenerative repair of SBD.

Coating of manganese functional polyetheretherketone implants for osseous interface integration

Polyetheretherketone (PEEK) has been used extensively in biomedical engineering and it is highly desirable for PEEK implant to possess the ability to promote cell growth and significant osteogenic properties and consequently stimulate bone regeneration. In this study, a manganese modified PEEK implant (PEEK-PDA-Mn) was fabricated via polydopamine chemical treatment. The results showed that manganese was successfully immobilized on PEEK surface, and the surface roughness and hydrophilicity significantly improved after surface modification. Cell experiments in vitro demonstrated that the PEEK-PDA-Mn possesses superior cytocompatibility in cell adhesion and spread. Moreover, the osteogenic properties of PEEK-PDA-Mn were proved by the increased expression of osteogenic genes, alkaline phosphatase (ALP), and mineralization in vitro. Further rat femoral condyle defect model was utilized to assess bone formation ability of different PEEK implants in vivo. The results revealed that the PEEK-PDA-Mn group promoted bone tissue regeneration in defect area. Taken together, the simple immersing method can modify the surface of PEEK, giving outstanding biocompatibility and enhanced bone tissue regeneration ability to the modified PEEK, which could be applied as an orthopedic implant in clinical.

Application of Biocompatible Scaffolds in Stem-Cell-Based Dental Tissue Engineering

Tissue engineering as an important field in regenerative medicine is a promising therapeutic approach to replace or regenerate injured tissues. It consists of three vital steps including the selection of suitable cells, formation of 3d scaffolds, and adding growth factors. Mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs) are mentioned as two main sources for this approach that have been used for the treatment of various types of disorders. However, the main focus of literature in the field of dental tissue engineering is on utilizing MSCs. On the other hand, biocompatible scaffolds play a notable role in this regenerative process which is mentioned to be harmless with acceptable osteoinductivity. Their ability in inhibiting inflammatory responses also makes them powerful tools. Indeed, stem cell functions should be supported by biomaterials acting as scaffolds incorporated with biological signals. Naturally derived polymeric scaffolds and synthetically engineered polymeric/ceramic scaffolds are two main types of scaffolds regarding their materials that are defined further in this review. Various strategies of tissue bioengineering can affect the regeneration of dentin-pulp complex, periodontium regeneration, and whole teeth bioengineering. In this regard, in vivo/ex vivo experimental models have been developed recently in order to perform preclinical studies of dental tissue engineering which make it more transferable to be used for clinic uses. This review summarizes dental tissue engineering through its different components. Also, strategies of tissue bioengineering and experimental models are introduced in order to provide a perspective of the potential roles of dental tissue engineering to be used for clinical aims.

Continuously released Zn2+ in 3D-printed PLGA/β-TCP/Zn scaffolds for bone defect repair by improving osteoinductive and anti-inflammatory properties

Long-term nonunion of bone defects has always been a major problem in orthopedic treatment. Artificial bone graft materials such as Poly (lactic-co-glycolic acid)/β-tricalcium phosphate (PLGA/β-TCP) scaffolds are expected to solve this problem due to their suitable degradation rate and good osteoconductivity. However, insufficient mechanical properties, lack of osteoinductivity and infections after implanted limit its large-scale clinical application. Hence, we proposed a novel bone repair bioscaffold by adding zinc submicron particles to PLGA/β-TCP using low temperature rapid prototyping 3D printing technology. We first screened the scaffolds with 1 wt% Zn that had good biocompatibility and could stably release a safe dose of zinc ions within 16 weeks to ensure long-term non-toxicity. As designed, the scaffold had a multi-level porous structure of biomimetic cancellous bone, and the Young's modulus (63.41 ± 1.89 MPa) and compressive strength (2.887 ± 0.025 MPa) of the scaffold were close to those of cancellous bone. In addition, after a series of in vitro and in vivo experiments, the scaffolds proved to have no adverse effects on the viability of BMSCs and promoted their adhesion and osteogenic differentiation, as well as exhibiting higher osteogenic and anti-inflammatory properties than PLGA/β-TCP scaffold without zinc particles. We also found that this osteogenic and anti-inflammatory effect might be related to Wnt/β-catenin, P38 MAPK and NFkB pathways. This study lay a foundation for the follow-up study of bone regeneration mechanism of Zn-containing biomaterials. We envision that this scaffold may become a new strategy for clinical treatment of bone defects.

The Promotion of Mechanical Properties by Bone Ingrowth in Additive-Manufactured Titanium Scaffolds

Although the initial mechanical properties of additive-manufactured (AM) metal scaffolds have been thoroughly studied and have become a cornerstone in the design of porous orthopaedic implants, the potential promotion of the mechanical properties of the scaffolds by bone ingrowth has barely been studied. In this study, the promotion of bone ingrowth on the mechanical properties of AM titanium alloy scaffolds was investigated through in vivo experiments and numerical simulation. On one hand, the osseointegration characteristics of scaffolds with architectures of body-centred cubic (BCC) and diamond were compared through animal experiments in which the mechanical properties of both scaffolds were not enhanced by the four-week implantation. On the other hand, the influences of the type and morphology of bone tissue in the BCC scaffolds on its mechanical properties were investigated by the finite element model of osseointegrated scaffolds, which was calibrated by the results of biomechanical testing. Significant promotion of the mechanical properties of AM metal scaffolds was only found when cortical bone filled the pores in the scaffolds. This paper provides a numerical prediction method to investigate the effect of bone ingrowth on the mechanical properties of AM porous implants, which might be valuable for the design of porous implants.

Influence of different fixation modes on biomechanical conduction of 3D printed prostheses for treating critical diaphyseal defects of lower limbs: A finite element study

Background

Applying 3D printed prostheses to repair diaphyseal defects of lower limbs has been clinically conducted in orthopedics. However, there is still no unified reference standard for which the prosthesis design and fixation mode are more conducive to appropriate biomechanical conduction.

Methods

We built five different types of prosthesis designs and fixation modes, from Mode I to Mode V. Finite element analysis (FEA) was used to study and compare the mechanical environments of overall bone-prosthesis structure, and the maximum stress concentration were recorded. Additionally, by comparing the maximum von Mises stress of bone, intramedullary (IM) nail, screw, and prosthesis with their intrinsic yield strength, the risk of fixation failure was further clarified.

Results

In the modes in which the prosthesis was fixed by an interlocking IM nail (Mode I and Mode IV), the stress mainly concentrated at the distal bone-prosthesis interface and the middle-distal region of nail. When a prosthesis with integrally printed IM nail and lateral wings was implanted (Mode II), the stress mainly concentrated at the bone-prosthesis junctional region. For cases with partially lateral defects, the prosthesis with integrally printed wings mainly played a role in reconstructing the structural integrity of bone, but had a weak role in sharing the stress conduction (Mode V). The maximum von Mises stress of both the proximal and distal tibia appeared in Mode III, which were 18.5 and 47.1 MPa. The maximum peak stress shared by the prosthesis, screws and IM nails appeared in Mode II, III and I, which were 51.8, 87.2, and 101.8 MPa, respectively. These peak stresses were all lower than the yield strength of the materials themselves. Thus, the bending and breakage of both bone and implants were unlikely to happen.

Conclusion

For the application of 3D printed prostheses to repair diaphyseal defects, different fixation modes will lead to the change of biomechanical environment. Interlocking IM nail fixation is beneficial to uniform stress conduction, and conducive to new bone regeneration in the view of biomechanical point. All five modes we established have reliable biomechanical safety.