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International Journal of Bioprinting Nanoclay biopolymer inks for 3D printing

ionize, the electrostatic repulsive forces between system and may restrict hydrogel swelling, as confirmed by other
components increased, and the fluids were encouraged to researchers. 25,40,55,57
enter into the semi-interpenetrating biopolymer-based In summary, according to swelling data, the novel
network. 39,44 alginate–salecan-based 3D constructs exhibited pH
Depending on the pH, the analyzed samples reach sensitivity and adjustable swelling degree achieved with
constant weight in different times. Thus, the maximum modification of the nanocomposite system’s constituent
degree of swelling occurs at pH = 2 in about 6 h, while for parts. These findings may enable the development of useful
experiments conducted at higher pH levels, the swelling materials with a variety of operating pHs, depending on
degree reached its maximum in about 48 h and 72 h for the foreseen application.
pH 5.5 and 7.4, respectively. On the other hand, samples The samples’ degradation was assessed by incubating
maintained in media at neutral pH swell enormously and the specimens in distilled water or PBS at 37°C for 7 days.
disintegrate after 72 h, producing relatively loose hydrogel After this period, it was found that all the samples stored in
structures that were unable to be weighed. Samples held water degraded with a loss of ~3%wt. The samples retained
in deionized water (pH = 5.5) retained their shape for their inflated shape extremely well, being particularly stable
a longer period of time. After around 3 weeks, the 3D at pH of 5.5. On the other hand, the composite samples
constructs began to disintegrate. The nanocomposite with high silicate content (AV2C3 and AV2C4) kept in
samples disintegrated in a percentage of ~80–90%wt. as PBS began to disintegrate, with little pieces detaching from
opposed to the pristine polysaccharide samples, which the sample. After 5 days, the samples completely degraded
retain their shape in a proportion of ~95%wt. Herein, and appeared as discrete delaminated layers in the PBS.
we assume that the increased porosity in the presence of In contrast, the samples with minimal silicate content
clay (revealed further through CT analyses) enhances the (AV2C1 and AV2C2), as well as the non-compounded
scaffold’s contact surface with the incubation medium and biopolymeric sample AV2, are well maintained in PBS and
boosts the degradability of the samples, as stated by other do not degrade over the 7-day study more than ~10%wt.
research groups. 56 As previously noted by other researchers, this behavior
The hydrogel’s ability to swell is significantly could be related to the increased level of clay dispersion
influenced by both the matrix composition and its surface and intercalation within biopolymeric matrix at low clay
hydrophilicity. When salecan biopolymer was added to content. 58,59 Another point worth noticing is that round-
the alginate matrix, the 3D polysaccharide constructs shaped samples retained their shape better than square-
had varying degrees of hydrophilicity. Thus, at low pH, shaped samples, which is most likely owing to the more
the ESD increased in the presence of salecan and as the compact structure.
amount of salecan in the biopolymeric matrix was greater. In summary, all samples incubated in water are stable
These findings, supported also by salecan retention tests, for up to 7 days, but only samples with low silicate content
demonstrated that higher alginate concentrations resulted are highly stable in PBS, and the high content of inorganic
in more crosslinking sites, which in turn produced a more partner leads to full deterioration of the 3D-printed
restricted semi-interpenetrating network. Consequently, constructs. These findings could be useful for tailoring the
larger amounts of salecan resulted in a decrease in network degradation of a material in a certain environment based
packing and higher ESD. Moreover, salecan structure which on the planned application.
is rich in OH groups favored increased fluid retention at
higher concentrations. 27,32
3.5. Mechanical behavior of the 3D-printed
When compared to the associated biopolymeric matrix, constructs
all nanocomposite samples presented ESD changes. In each As substrates for tissue regeneration and repair, 3D
case, adding clay to the alginate–salecan matrix as well as hydrogel-based constructs are of great interest because
the increasing clay concentration reduced the swelling’s of their tissue-like composition with linked porosity and
intensity. It is quite likely that this behavior is related to the the potential for tailored fabrication. The generally poor
chemical composition of the resulting nanocomposites, mechanical strength of 3D hydrogel-printed materials
given that clay was added to the system and did not is a typical drawback, limiting their utility in various
retain as much water as the substituted polysaccharide. clinical applications. In this regard, in our study, we
Furthermore, the physical interactions between the developed composite inks that outperform hydrogels
biopolymer and the clay, involving hydrogen bonds, as made solely from alginate or alginate–salecan, in terms
well as the increase in matrix crystallinity, as revealed by of final mechanical quality and structural integrity of the
XRD studies, could result in lesser molecular flexibility 3D-printed structures.

Volume 10 Issue 1 (2024) 186 https://doi.org/10.36922/ijb.0967