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3D Printable PLA/BG Composite In Vitro Evaluation
degradation products are non-toxic and absorbable by simultaneous release of ions, such as calcium, sodium,
the organism [2,3] . Despite that, these materials display or magnesium, has a positive effect on proliferation,
some disadvantages for BTE applications, such as a low cell adhesion, and osteogenic differentiation (OD)
bioactivity, a hydrophobic surface, and a low degradation of mesenchymal stem cells (MSCs) [20,21] . In addition,
rate . Polyhydroxyalkanoates are now coming into studies have shown inhibition of antimicrobial
[4]
focus as promising alternatives. These pro-osteogenic growth, especially of resistant microorganisms such
biopolymers can be naturally produced by bacteria in as methicillin-resistant Staphylococcus aureus or
the bioreactor . However, the mass production of these methicillin-resistant Staphylococcus epidermidis [22,23] .
[5]
polymers still needs to be established . Finally, its weak alkaline nature has shown to reduce the
[6]
Mineral alternatives, such as tricalcium phosphates strong acidic effect of PLA’s degradation products .
[24]
and hydroxylapatite (and many others), with their bone- With these potential properties, composites could then
like composition and highly porous surfaces, improve also be used in the integrated tissue-organ printer, a
cell attachment and bone formation. Calcium release bioprinting strategy . Here, vascularized cell-loaded
[25]
during resorption has a stimulatory effect on bone bone constructs with tunable mechanical properties
regenerative cells . However, the printing properties are developed. They thus represent the next stage in
[7]
and low mechanical stability limit their application in BTE [26,27] .
BTE [8,9] . To generate a mechanical stability comparable The use of composites in 3D printing to create
to polymers, compact grid structures are necessary. complex structures is not yet routine. Even the production
Large pores in the scaffold walls, required for hematoma of the necessary filaments is a challenge. In most cases,
penetration, can thus be obtained only at the expense PLA and BG are available as a powder or fine granules,
of stability. In addition, due to the very high melting which are melted together. Usually, the mass is then
point of mineral components, melting and subsequent pressed into a mold or extruded through a nozzle. The
molding, as it occurs with polymers, are not possible. resulting frameworks are usually compact and have
In this case, a solvent or a binder is required. Only after amorphous internal structures [7,28,29] . PLA/BG composites
its volatilization or pyrolysis and subsequent sintering with up to 10% BG have already been produced, but the
connection between individual layers and single-strand printing results in terms of strand thickness and pore size
structures gain stability [10,11] . Complex, ultrafine internal are insufficient [30-32] .
structures, such as interconnected pores and fibers with It has been shown that a high BG fraction has
diameters of a few micrometers, important for cell a beneficial effect on bioactivity. However, as the
attachment and vascularization, are, in turn, very difficult proportion of mineral components increases, the stability
to obtain . of the material decreases . This increases the likelihood
[11]
[33]
Composites are increasingly reported in literature of strand breakage during the printing process and also
in the attempt to combine the beneficial properties reduces the mechanical stability of the printed products.
of polymer and mineral materials [12,13] . Incorporation This especially impedes the printing of ultrafine structures
of calcium phosphates in a composite can increase and limits the structure size.
wettability and roughness of the material that, in turn, Thus, the basis for the successful development
can lead to better cell adhesion and proliferation . of 3D-printed scaffolds for BTE is the production of a
[14]
The combination of PLA and bioglass (BG) is very composite filament that serves the highest possible BG
promising. PLA, commonly used in routine clinical content without compromising the printing requirements.
applications (suture material, material for resorbable Finally, it should be possible to print ultra-fine structures
screws, and bone anchors), is characterized by its with the material.
good biocompatibility, mechanical resistance, and In view of this requirement profile, our working
resorbability . In addition, it is widely used in 3D group developed a PLA/BG composite material with
[15]
printing . Even the finest structures down to the three different BG contents (5%, 10%, and 20%) which
[16]
nanometer range can be produced . However, PLA’s are suitable for high-resolution 3D printing. Despite
[1]
poor osteoconductive and osteoinductive properties, its the high proportion of BG, scaffolds with fine internal
hydrophobicity, which could inhibit cell adhesion and structures could be produced. The aim of this work was
tissue regeneration and the cytotoxic acidity induced by the in vitro characterization of the composite material. Its
its degradation products could limit its widespread use. stimulatory influence on MSCs behavior (cell adherence
These restrictions could be counteracted by the addition and viability, OD), as well as the immunostimulatory
of BG on its composition. Literature shows that the brittle and inflammatory potential were detailed investigated.
and very hard BG material forms a hydroxyapatite layer Therefore, 3D-printed mesh specimens with a diameter of
when in contact with physiological fluids that serve as 5 mm and varying BG concentrations were successfully
a basis for bone formation by osteogenic cells [17-19] . The fabricated and thoroughly tested.

66 International Journal of Bioprinting (2022)–Volume 8, Issue 4