State-of-Art of Standard and Innovative Materials Used in Cranioplasty

Abstract

Cranioplasty is the surgical technology employed to repair a traumatic head injury, cerebrovascular disease, oncology resection and congenital anomalies. Actually, different bone substitutes are used, either derived from biological products such as hydroxyapatite and demineralized bone matrix or synthetic ones such as sulfate or phosphate ceramics and polymer-based substitutes. Considering that the choice of the best material for cranioplasty is controversial, linked to the best operation procedure, the intent of this review was to report the outcome of research conducted on materials used for such applications, comparing the most used materials. The most interesting challenge is to preserve the mechanical properties while improving the bioactivity, porosity, biocompatibility, antibacterial properties, lowering thickness and costs. Among polymer materials, polymethylmethacrylate and polyetheretherketone are the most motivating, due to their biocompatibility, rigidity and toughness. Other biomaterials, with ecofriendly attributes, such as polycaprolactone and polylactic acid have been investigated, due to their microstructure that mimic the trabecular bone, encouraging vascularization and cell-cell communications. Taking into consideration that each material must be selected for specific clinical use, the main limitation remains the defects and the lack of vascularization, consequently porous synthetic substitutes could be an interesting way to support a faster and wider vascularization, with the aim to improve patient prognosis.

Keywords: biomaterials; cranial defect; cranioplasty; neurosurgery; polycaprolactone (PCL); polyethereketoneketone (PEKK); polyetheretherketone (PEEK); polyglycolide (PGA); polylactic acid (PLA); polymers; polymethylmethacrylate (PMMA); skull reconstruction; synthetic cranioplasty.

Figure 1

Example of causes that require cranioplasty (authors personal database images): (1a) axial computerized tomography (CT) scan of tumor involving cranial bone; (1b) 3D-CT scan of tumor involving cranial bone; (2) 3D-CT scan of depressed skull fracture; (3) surgical exposition of complex depressed skull fracture.

Figure 2

Bone substitutes categories.

Figure 3

Chemical formulas of resorbable biodegradable polymers most commonly used in medicine: polyglycolic acid (PGA), polylactic acid (PLA) and polycaprolactone (PCL).

Figure 4

Cranioplasty in PMMA with titanium fixation plates and screws.

Figure 5

(1) PMMA cranioplasty fractures; (2a) 3D and (2b) axial CT-scan of PMMA cranioplasty displacement.

Figure 6

PEEK and PEKK chemical formulas.

Figure 7

(a) Phantom model for virtual craniotomy; (b) 3D HR CT-scan of Phantom; (c) stealth navigation station; (d) post-operative axial CT-scan.