PURPOSE: Cranioplasties are crucial for ensuring cerebral protection, restoring neurological function, and improving psychosocial well-being. However, currently available cranioplasty materials have significant drawbacks. Consequently, there is a clinical need for regenerative bone biomaterials that emulate tissue-specific extracellular matrix (ECM) properties and regulate progenitor cell fate. Nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) promotes in vitro osteogenic differentiation and in vivo skull regeneration without exogenous growth factors and ex-vivo progenitor cell seeding, offering a promising “materials-only” solution for osseous defect reconstructions. However, further refinement of the material is imperative to enhance safety and regenerative potential for clinical translation. A pertinent challenge during early bone healing is ensuring underlying structures’ protection while maintaining optimal intracranial pressure to support neurological function. In this work, we investigated how the regenerative capacity of MC-GAG may be influenced by its fixation and overlay with a clinically available resorbable poly(D,L-lactide) (PDLLA) implant intended for cerebral protection.
METHODS: A 14-mm full-thickness, extradural defect was created in each New Zealand white rabbit. Animals were divided into four groups: 1) defect without reconstruction, 2) defect with PDLLA implant, 3) MC-GAG scaffold only, and 4) MC-GAG with PDLLA implant. Initial bone healing assessment was conducted on explanted skulls at three months using microcomputed tomography (microCT) scanning, histology, and reference point indentation. For a comprehensive understanding of long-term effects, in vivo microCT imaging was performed at three, six, and nine months, with further examination of the biomechanical properties of explanted skulls at nine months.
RESULTS: At three months, the explanted skulls revealed that MC-GAG significantly enhanced mineralization compared to the defect and PDLLA only, with even greater mineralization observed for the MC-GAG-PDLLA combination scaffold. Histological analysis of the interface between the reconstruction and native bone indicated that MC-GAG promoted the development of an intricate network of trabecular mineralized content, whereas the untreated defect primarily featured fibrous, non-mineralized tissue. MC-GAG-PDLLA demonstrated enhanced structural organization more closely representative of nearby native bone. Biomechanical assessment of the treated skulls demonstrated enhanced toughness and resistance to microfracture of both MC-GAG alone and MC-GAG-PDLLA compared to the empty and PDLLA-treated defects, with significantly greater measures of stiffness for MC-GAG-PDLLA. While no difference in regenerated bone mass was detected by in vivo CT between the treatment groups after three months, MC-GAG-PDLLA exhibited the highest bone mass at six months, and both MC-GAG-containing scaffolds demonstrated enhanced bone regeneration compared to the empty and PDLLA-treated defects at nine months. By nine months, PDLLA implants were completely resorbed, and analyses of the mechanical properties of explanted skulls at nine months revealed that both strength and stiffness were greatest and most similar to the native bone for MC-GAG-PDLLA.
CONCLUSION: Together, these results demonstrate that reconstructing a cranial defect with an MC-GAG scaffold fixated with PDLLA implants significantly enhanced long-term mineralization and bone regeneration compared to a scaffold consisting of either MC-GAG or PDLLA alone.