Table 3.

The strengths and weaknesses of 3D-printed PEEK-based scaffolds.

Scaffold	Strengths	Weaknesses
FFF-printed PEEK	Ease of fabrication. No additional processing steps are needed.	The printed scaffolds are bioinert and nondegradable. No micropores formed on the filaments of printed scaffolds for osteoblastic adhesion. The macro-pores formed between the filaments created by printing are far too large for bone cell adhesion
SHPEEK	Sulfonation of FFF-printed PEEK creates micropores on the filaments for bone cell adhesion	Sulfuric acid residuals can damage bone cells and reduce their viability greatly. After sulfonation, the scaffolds must be rinsed in water several times to remove the residuals until they are contamination-free. So, it is a tedious process.
SLS-printed PEEK-PGA	Degradable scaffolds due to the dissolution of PGA. SLS process creates rough surface needed for bone cell adhesion	High-temperature laser beam used for sintering polymer powders would degrade their properties. Raw polymer powders trap inside the fine voids of scaffolds due to printing are difficult to remove and may induce inflammation [228].
SLS-printed PEEK-PGA/nHA	nHA and rough surface finish are beneficial for bone cell adhesion. nHA neutralizes autocatalytic effect of acidic PGA byproduct, thus reducing inflammation of wounds	As above
SLS-printed PEEK-PGA/GO	GO sheets with high stiffness and strength increase the compressive strength/stiffness of resulting nanocomposite scaffolds. GO promotes bone cell adhesion and growth	GO sheets must be firmly attached in the matrix of composite scaffold. Otherwise, stand-alone or delaminated GO may induce cytotoxicity to human cells [76]