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Preparation and printability of ultrashort self-assembling peptide nanoparticles
clear that the run with 50% ethanol performed the best. factors is the diffusion gradient that emerges as a result
As such, the subsequent experiments were all performed of the nanofibrous network that hinders the ability of the
using an optimized ethanol concentration of 50% for the species to migrate to the center of the hydrogel . This
[37]
side streams at each junction. Following the optimization means that the therapeutic molecules or specific factors
of the ethanol concentration, the flow rate ratio of the needed for cell growth are not evenly distributed within
peptide to ethanol solutions for the production of peptide the sample. By producing peptide NPs modified to have
NPs was also optimized using the same criteria described these specific molecules attached to their surface and
[38]
for the ethanol optimizations. In the experiments with by distributing these NPs throughout the hydrogel, we
lower peptide to ethanol flow rate ratios – such as 1:1 or 1:5, can overcome the diffusion gradient and allow for a slow,
we observed that significantly more of the peptide formed controlled release of these therapeutics/specific factors to
a fiber network in the background (Figure 3A and B). Our the surrounding cells. The previous reports on the controlled
results from several trials of these experiments suggest release of NPs within a peptide hydrogel have focused on
that as the flow rate of the ethanol increases relative to AgNPs used for antimicrobial applications. The use
[25]
that of the peptide, more peptide NPs form. As such, the of peptide NPs allows for the introduction of a scaffold
flow rate ratio of peptide to ethanol of 1:10 was used in and carriers comprised only a single foreign material to
all of the following experiments. the body of the host, thus minimizing the likelihood of
Characterization of the NPs using DLS revealed that any adverse effects. This series of experiments serves as
the average size of both the CH-01 and CH-02 NPs a proof of principle study of the ability to produce and
was around 73.0 nm. The size distribution plot shown print NPs from ultrashort self-assembling peptides into
in Figure 4 suggests a homogenous batch of NPs, and peptide-based hydrogels. Perhaps, the best way to ensure
the average size of the NPs from the DLS results is
consistent with the measured sizes of the NPs seen in a uniform distribution of NPs within each sample is
the SEM images in Figure 5. The similar average size to automate the process through the use of 3D printing
for NPs produced from both peptides is due to the fact technology. Although future experiments are needed to
that similar parameters were used during their production further confirm and optimize the homogenous distribution
with the microfluidic flow-focusing chip. As such, the of NPs within the hydrogel samples, this paves the way
original peptide solutions were subject to very similar for an exciting future where we can possibly make use of
forces and pressure from the ethanol side stream, thus this system for applications in medicine. One interesting
resulting in similar behavior. On close examination of area to work toward is the ability to reprogram stem
the SEM images of the hydrogels in Figure 5, we can cells through careful control of the ratio of each of the
draw comparisons between the size, morphology, and Yamanaka factors attached to 3D-printed peptide NPs
[39]
relative distribution of the NPs within each printed versus embedded within a hydrogel scaffold .
manually prepared hydrogel sample. As the images Acknowledgments
are quite similar, the results suggest that the NPs are
capable of withstanding the stress associated with the The authors acknowledge Ms. Zainab Khan for her
printing process. A comparison of the manually prepared valuable contributions to the design of the 3D printing
and 3D-printed samples without the addition of NPs to system used for these studies. We also thank Ms. Kholoud
those made with NPs provides confirmation that the NPs Seferji for her help in obtaining the DLS measurements.
observed in SEM are only present in the samples with the The research reported in this publication was supported
NPs added. The samples prepared with the addition of the by funding from King Abdullah University of Science
NPs in ethanol solution serve as a reference to ensure that and Technology.
the general morphology of the NPs is not affected by the
lyophilizing process. Authors’ Contributions

5. Conclusion C.A.E.H. developed the concept of ultrashort self-
assembling peptides and supervised the project, S.G.
The discovery and characterization of biomaterials suitable wrote the manuscript, H.H.S. and S.H. optimized the
for use in medicine are an area of keen interest in the NP preparation method, S.G. fabricated the NPs, H.H.S.
world of research. For tissue engineering, peptide-based and S.G. did the SEM imaging, K.K. printed the samples
hydrogels have emerged as an excellent material to serve
as a scaffold that is biocompatible, biodegradable, and together with S.G., and H.H.S. helped with the SEM
promotes cell proliferation and migration as it mimics the sample preparation.
natural extracellular matrix. One of the biggest challenges Conflicts of Interest
with using these peptide hydrogels in conjunction with
specific therapeutic molecules or growth/differentiation The authors declare that they have no conflicts of interest.

114 International Journal of Bioprinting (2019)–Volume 5, Issue 2