Three-Dimensional Printed Hydroxyapatite Bone Substitutes Designed by a Novel Periodic Minimal Surface Algorithm Are...

Current bone grafting practices rely heavily on autologous bone, which is considered the most effective option. However, the supply of autologous bone is limited, and its use can lead to donor site complications. Synthetic bone substitutes aim to mimic the natural bone microarchitecture to support bone regeneration. Natural bone is both lightweight and mechanically stable, adapting to biomechanical demands. Replicating this structure in synthetic materials is a major challenge. Additive manufacturing offers a way to create complex scaffold geometries. A key issue is how to balance mechanical strength with sufficient porosity for cell infiltration and tissue growth. Prior research has shown that triply periodic minimal surfaces (TPMS) can produce lightweight, stable structures. However, the impact of specific TPMS derivatives on osteoconductivity remains unclear. This gap motivated the development and testing of a new algorithm for scaffold design.

This study aimed to evaluate a novel algorithm called Adaptive Density Minimal Surfaces (ADMS) for designing synthetic bone scaffolds. The goal was to compare ADMS scaffolds with a well-established lattice microarchitecture in terms of mechanical strength and osteoconductivity. The researchers focused on how pore size and scaffold geometry influence bone ingrowth. They used hydroxyapatite as the scaffold material, which is known for its osteoconductive properties. The study tested whether ADMS could produce scaffolds that are both strong and conducive to bone regeneration. The research also sought to determine if ADMS could match or exceed the performance of lattice-based scaffolds. By using a rabbit calvaria defect model, the team assessed the in vivo performance of the scaffolds. The ultimate aim was to identify a scaffold design that is suitable for both weight-bearing and non-weight-bearing bone defects.

The researchers used the ADMS algorithm to generate scaffold designs with varying pore sizes. These designs were fabricated from hydroxyapatite using a lithography-based additive manufacturing process. The resulting scaffolds were compared with a standard orthogonal lattice microarchitecture. Mechanical testing was performed to measure compression strength. The scaffolds were implanted in a rabbit calvaria defect model to assess osteoconductivity. Bone ingrowth was evaluated using histological and radiographic methods. Pore diameters were measured to determine how they influenced tissue infiltration. The study also assessed the microarchitectural integrity of the scaffolds after implantation. The researchers compared the mechanical and biological performance of ADMS and lattice scaffolds to determine their relative advantages.

The in vivo results showed that ADMS scaffolds supported bone ingrowth when pore diameters were below 1.53 mm. At 1.76 mm, osteoconductivity significantly decreased. The most effective ADMS scaffolds were as osteoconductive as the lattice scaffolds in both noncritical and critical-size defects. However, ADMS scaffolds had higher compression strength and better microarchitectural integrity. The ADMS-based microarchitectures maintained their structural stability during the healing process. The lattice microarchitecture showed lower mechanical performance despite its high connectivity. The study found that ADMS scaffolds could achieve high osteoconductivity while maintaining mechanical stability. The pore size threshold of 1.53 mm was critical for supporting tissue infiltration. The results suggest that ADMS is a viable alternative to lattice-based designs for bone substitutes.

The study demonstrated that ADMS scaffolds can achieve high osteoconductivity comparable to lattice scaffolds. The mechanical performance of ADMS scaffolds was significantly better, with higher compression strength and microarchitectural integrity. The pore size threshold of 1.53 mm was identified as a key factor for osteoconduction. The researchers propose that ADMS scaffolds are suitable for both weight-bearing and non-weight-bearing bone defects. The ADMS algorithm allows for the design of lightweight, mechanically stable structures. The results support the use of ADMS-based scaffolds in clinical settings. The study highlights the importance of balancing pore size and mechanical strength in scaffold design. The authors suggest that further research could explore the long-term performance of ADMS scaffolds in different clinical applications.