A Mineralized Collagen-Polycaprolactone Composite Promotes Healing of a Porcine Mandibular Defect

Abstract

A tissue engineering approach to address craniofacial defects requires a biomaterial that balances macro-scale mechanical stiffness and strength with the micron-scale features that promote cell expansion and tissue biosynthesis. Such criteria are often in opposition, leading to suboptimal mechanical competence or bioactivity. We report the use of a multiscale composite biomaterial that integrates a polycaprolactone (PCL) reinforcement structure with a mineralized collagen-glycosaminoglycan scaffold to circumvent conventional tradeoffs between mechanics and bioactivity. The composite promotes activation of the canonical bone morphogenetic protein 2 (BMP-2) pathway and subsequent mineralization of adipose-derived stem cells in the absence of supplemental BMP-2 or osteogenic media. We subsequently examined new bone infill in the acellular composite, scaffold alone, or PCL support in 10 mm dia. ramus mandibular defects in Yorkshire pigs. We report an analytical approach to quantify radial, angular, and depth bone infill from micro-computed tomography data. The collagen-PCL composite showed improved overall infill, and significantly increased radial and angular bone infill versus the PCL cage alone. Bone infill was further enhanced in the composite for defects that penetrated the medullary cavity, suggesting recruitment of marrow-derived cells. These results indicate a multiscale mineralized collagen-PCL composite offers strategic advantages for regenerative repair of craniofacial bone defects.

Sequential sequestrations increase the incorporation and retention of multiple growth factors in mineralized collagen scaffolds

“…cell penetration, diffusive biotransport), all scaffold variants show sub-optimal mechanical performance. While beyond the scope of this project, we have described methods to increase the mechanical stability of a cell activity optimized scaffolds via the inclusion of 3D printed polymeric meshes 49,69 . Based on these results, we did not use extended mSBF treatments prior to sequestration in subsequent experiments and instead focused on repeated mSBF treatments during sequestration.…”

“…Our lab has developed a mineralized collagen-glycosaminoglycan scaffold capable of inducing osteogenesis without the addition of exogenous factors 47 , and these materials have been used to heal sub-critical injuries in vivo 48,49 . However, as we move into larger injury models, we may require biomolecular supplements to improve implant-bone integration, cell recruitment, and vascular remodeling.…”

Solvent-Free Approaches for the Processing of Scaffolds in Regenerative Medicine

“…SLS is a single-step process that offers products with higher resolution due to the laser precision (sub-millimeter region [65]), compared to other 3D-printing solvent-free processes such as FDM, as well as the ability to manufacture protruding regions without supporting materials. The main advantages of SLS for tissue engineering applications are related to the processability of a wide range of biomaterials, including ceramics, thermoplastic polymers [66][67][68][69], and composites [70][71][72][73][74][75][76][77][78], and the high customization degree. Namely, PCL sintered patient-specific external airway splints were implanted in infant patients suffering a life-threatening cardiopulmonary disease (tracheobronchomalacia), to prevent the collapse of the airways during respiration.…”

The inclusion of zinc into mineralized collagen scaffolds for craniofacial bone repair applications

“…pASCs were chosen as they have been shown to have robust and well defined osteogenic capabilities [41]; pASCs were also used to identify a dose range of zinc ions to be added into cell culture media (0.04 -0.08 mM) to enhance osteogenesis. Further, we have previously used a porcine mandibular defect model to evaluate the regenerative capacity of our mineralized collagen scaffolds [18,26,41]. Cells were expanded in T175 flasks (Fisher Scientific, Hampton, New Hampshire USA) until passage 6 and cultured in complete mesenchymal stem cell growth media (Low glucose DMEM + L-glutamine, 10% fetal bovine serum, 1% antibiotic-antimycotic) at 37°C and 5% CO 2 until confluent.…”

“…A portion of the calcium and phosphate ions incorporated into the mineralized scaffolds are released during culture and are believed to accelerate osteogenesis [16]. Craniofacial bones rely on intramembranous ossification processes, and the mineralized collagen scaffold has been previously shown to promote osteogenesis in vitro and also to enhance regenerative healing of craniofacial bone injuries (rabbit calvarial; sub-critical sized porcine mandible) [17][18][19]. However, as with most tissue engineering biomaterials, the need to enhance osteogenic capacity increases with the size and complexity of craniomaxillofacial trauma.…”