In vivo characterization of 3D-printed polycaprolactone-hydroxyapatite scaffolds with Voronoi design to advance the concept of scaffold-guided bone regeneration

Fabrication Strategies for Bioceramic Scaffolds in Bone Tissue Engineering with Generative Design Applications

The aim of this study is to provide an overview of the current state-of-the-art in the fabrication of bioceramic scaffolds for bone tissue engineering, with an emphasis on the use of three-dimensional (3D) technologies coupled with generative design principles. The field of modern medicine has witnessed remarkable advancements and continuous innovation in recent decades, driven by a relentless desire to improve patient outcomes and quality of life. Central to this progress is the field of tissue engineering, which holds immense promise for regenerative medicine applications. Scaffolds are integral to tissue engineering and serve as 3D frameworks that support cell attachment, proliferation, and differentiation. A wide array of materials has been explored for the fabrication of scaffolds, including bioceramics (i.e., hydroxyapatite, beta-tricalcium phosphate, bioglasses) and bioceramic-polymer composites, each offering unique properties and functionalities tailored to specific applications. Several fabrication methods, such as thermal-induced phase separation, electrospinning, freeze-drying, gas foaming, particle leaching/solvent casting, fused deposition modeling, 3D printing, stereolithography and selective laser sintering, will be introduced and thoroughly analyzed and discussed from the point of view of their unique characteristics, which have proven invaluable for obtaining bioceramic scaffolds. Moreover, by highlighting the important role of generative design in scaffold optimization, this review seeks to pave the way for the development of innovative strategies and personalized solutions to address significant gaps in the current literature, mainly related to complex bone defects in bone tissue engineering.

An innovative intramedullary bone graft harvesting concept as a fundamental component of scaffold-guided bone regeneration: A preclinical in vivo validation

Background

The deployment of bone grafts (BGs) is critical to the success of scaffold-guided bone regeneration (SGBR) of large bone defects. It is thus critical to provide harvesting devices that maximize osteogenic capacity of the autograft while also minimizing graft damage during collection. As an alternative to the Reamer-Irrigator-Aspirator 2 (RIA 2) system - the gold standard for large-volume graft harvesting used in orthopaedic clinics today - a novel intramedullary BG harvesting concept has been preclinically introduced and referred to as the ARA (aspirator + reaming-aspiration) concept. The ARA concept uses aspiration of the intramedullary content, followed by medullary reaming-aspiration of the endosteal bone. This concept allows greater customization of BG harvesting conditions vis-à-vis the RIA 2 system. Following its successful in vitro validation, we hypothesized that an ARA concept-collected BG would have comparable in vivo osteogenic capacity compared to the RIA 2 system-collected BG.

Methods

We used 3D-printed, medical-grade polycaprolactone-hydroxyapatite (mPCL-HA, wt 96 %:4 %) scaffolds with a Voronoi design, loaded with or without different sheep-harvested BGs and tested them in an ectopic bone formation rat model for up to 8 weeks.

Results

Active bone regeneration was observed throughout the scaffold-BG constructs, particularly on the surface of the bone chips with endochondral bone formation, and highly vascularized tissue formed within the fully interconnected pore architecture. There were no differences between the BGs derived from the RIA 2 system and the ARA concept in new bone volume formation and in compression tests (Young's modulus, p = 0.74; yield strength, p = 0.50). These results highlight that the osteogenic capacities of the mPCL-HA Voronoi scaffold loaded with BGs from the ARA concept and the RIA 2 system are equivalent.

Conclusion

In conclusion, the ARA concept offers a promising alternative to the RIA 2 system for harvesting BGs to be clinically integrated into SGBR strategies.

The translational potential of this article

Our results show that biodegradable composite scaffolds loaded with BGs from the novel intramedullary harvesting concept and the RIA 2 system have equivalent osteogenic capacity. Thus, the innovative, highly intuitive intramedullary harvesting concept offers a promising alternative to the RIA 2 system for harvesting bone grafts, which are an important component for the routine translation of SGBR concepts into clinical practice.

In vivo study to assess fat embolism resulting from the Reamer-Irrigator-Aspirator 2 system compared to a novel aspirator-based concept for intramedullary bone graft harvesting

INTRODUCTION

Fat embolism (FE) following intramedullary (IM) reaming can cause severe pulmonary complications and sudden death. Recently, a new harvesting concept was introduced in which a novel aspirator is used first for bone marrow (BM) aspiration and then for subsequent aspiration of morselized endosteal bone during sequential reaming (A + R + A). In contrast to the established Reamer-Irrigator-Aspirator (RIA) 2 system, the new A + R + A concept allows for the evacuation of fatty BM prior to reaming. In this study, we hypothesized that the risk of FE, associated coagulopathic reactions and pulmonary FE would be comparable between the RIA 2 system and the A + R + A concept.

MATERIALS AND METHODS

Intramedullary bone graft was harvested from intact femora of 16 Merino sheep (age: 1-2 years) with either the RIA 2 system (n = 8) or the A + R + A concept (n = 8). Fat intravasation was monitored with the Gurd test, coagulopathic response with D-dimer blood level concentration and pulmonary FE with histological evaluation of the lungs.

RESULTS

The total number and average size of intravasated fat particles was similar between groups (p = 0.13 and p = 0.98, respectively). D-dimer concentration did not significantly increase within 4 h after completion of surgery (RIA 2: p = 0.82; A + R + A: p = 0.23), with an interaction effect similar between groups (p = 0.65). The average lung area covered with fat globules was similar between groups (p = 0.17).

CONCLUSIONS

The use of the RIA 2 system and the novel A + R + A harvesting concept which consists of BM evacuation followed by sequential IM reaming and aspiration of endosteal bone, resulted in only minor fat intravasation, coagulopathic reactions and pulmonary FE, with no significant differences between the groups. Our results, therefore, suggest that both the RIA 2 system and the new A + R + A concept are comparable technologies in terms of FE-related complications.