TABLE 2.
Fabrication techniques of scaffolds in osteochondral tissue engineering.
| Techniques | Processes | The pros and cons |
|---|---|---|
| Lyophilization | The mixture is cooled by freeze-drying to eliminate the solvent and water, forming macropores and micropores in the scaffold structure | • The pore size and porosity can be modified by solution characteristics (e.g., concentration and viscosity), quenching rate and freezing temperature (Tf). Raeisdasteh Hokmabad et al. (2017) |
| • The use of organic solvents; instability of the emulsion | ||
| Freeze casting | The manufacturing technique includes the controlled solidification process, the sublimation of solvents under reduced pressure and subsequent densification | • The applicability to various materials; changeable micro- and macrostructures of obtained scaffolds |
| Gas foaming | The raw materials are kept under a high carbon dioxide pressure to produce porous structures | • The uniformity of cell infiltration should be improved. Salonius et al. (2019) |
| Microfluidic foaming | The foam is generated via microfluidics under highly controlled and reproducible conditions | • Homogeneous pore monodispersity and interconnection; abundant cell infiltration; versatility. Costantini et al. (2016) |
| • There is still room to expand the range of applicable biomaterials | ||
| Sol-gel process | The sol-gel method can result in oxides or hybrid materials in soft conditions | • Combined with other techniques, such as 3D printing, this approach can open a new way for the design of biocompatible hydrogels by promoting cross-linking. Valot et al. (2019); Tourné-Péteilh et al. (2019); Raucci et al. (2018) |
| Solvent casting | The polymer solution is first combined with necessary particles and then poured onto pre-designed molds | • Addition of functional elements such as drugs and growth factors |
| • The potential toxicity of organic solvents | ||
| Melt molding | The mixture of powdered polymers and porogen is loaded into pre-designed molds and annealed at an elevated pressure | • Porous scaffolds with desired morphological features |
| • The difficulty of later particulate leaching; high processing temperature; inapplicability of organic solvents | ||
| Compression molding | The mixture is pressed into molds under heat and pressure to obtain the required structures. Sempertegui et al. (2018); Zhang et al. (2016) | • High-pressure molding can compact the stacking structure and optimize mechanical performance |
| Particulate leaching | The preliminarily obtained scaffolds are treated and soaked to leach out particles | • Porous structures adjusted by the added porogen as required |
| • The technical demands for better control of pore morphology and interconnection; extra time consumption | ||
| Phase separation process | The polymer solution is quenched under the freezing point (Tk) and separated into a polymer-rich phase and a polymer-poor phase which will solidify and crystallize respectively. Crystals are removed subsequently | • The scaffold structure can be tunable on account of processing parameters such as quenching temperature and rate |
| • The improvement and integration of techniques is needed to optimize the probably unfavorable pore structure | ||
| Electrospinning | Under a strong electric field, a polymer solution, emulsion or melt is extruded through a spinneret to produce fibre and deposit on an appropriate collector | • Structures resembling the native ECM; encapsulation of bioactive elements |
| • Poor control over architectures restricted by environmental parameters; difficulty in producing 3D structures; limited cell passage and substance exchange related to pore size; environmental safety issues | ||
| Additive manufacturing (AM) | The electrohydrodynamic technique, also known as rapid prototyping or solid freeform fabrication, is classified into seven processes: vat photopolymerization, material jetting, material extrusion, powder bed fusion, directed energy deposition, sheet lamination and binder jetting. Tang et al. (2016); Gibbs et al. (2014) | • Better control over architectures; flexibility to scale-up customisation; standardisation and repeatability of manufacturing |
| • Narrow range of suitable materials, time-consuming layer-by-layer processing and high costs |