Two-dimensional nanosilicate particles (NS) have shown promise for the prolonged release of small-molecule therapeutics while minimizing burst release. When incorporated in a hydrogel, the high surface area and charge of NS enable electrostatic adsorption and/or intercalation of therapeutics, providing a lever to localize and control release. However, little is known about the physio-chemical interplay between the hydrogel, NS, and encapsulated small molecules. Here, we fabricated polyethylene glycol (PEG)-NS hydrogels for the release of model small molecules such as acridine orange (AO). We then elucidated the effect of NS concentration, NS/AO incubation time, and the ability of NS to freely associate with AO on hydrogel properties and AO release profiles. Overall, NS incorporation increased the hydrogel stiffness and decreased swelling and mesh size. When individual NS particles were embedded within the hydrogel, a 70-fold decrease in AO release was observed compared to PEG-only hydrogels, due to adsorption of AO onto NS surfaces. When NS was pre-incubated and complexed with AO prior to hydrogel encapsulation, a >9000-fold decrease in AO release was observed due to intercalation of AO between NS layers. Similar results were observed for other small molecules. Our results show the potential for use of these nanocomposite hydrogels for the tunable, long-term release of small molecules.

Pectin, a natural biopolymer mainly derived from citrus fruits and apple peels, shows excellent biodegradable and biocompatible properties. This study investigated the electrospinning of pectin-based nanofibers. The parameters, pectin:PEO (polyethylene oxide) ratio, surfactant concentration, voltage, and flow rate, were studied to optimize the electrospinning process for generating the pectin-based nanofibers. Oligochitosan, as a novel and nonionic cross-liker of pectin, was also researched. Nanofibers were characterized by using AFM, SEM, and FTIR spectroscopy. The results showed that oligochitosan was preferred over Ca 2+ because it cross-linked pectin molecules without negatively affecting the nanofiber morphology. Moreover, oligochitosan treatment produced a positive surface charge of nanofibers, determined by zeta potential measurement, which is desired for tissue engineering applications.

Nanocomposite hydrogels containing two-dimensional nanosilicates (NS) have emerged as a new technology for the prolonged delivery of biopharmaceuticals. However, little is known about the physical–chemical properties governing the interaction between NS and proteins and the release profiles of NS–protein complexes in comparison to traditional poly­(ethylene glycol) (PEG) hydrogel technologies. To fill this gap in knowledge, we fabricated a nanocomposite hydrogel composed of PEG and laponite and identified simple but effective experimental conditions to obtain sustained protein release, up to 23 times slower as compared to traditional PEG hydrogels, as determined by bulk release experiments and fluorescence correlation spectroscopy. Slowed protein release was attributed to the formation of NS–protein complexes, as NS–protein complex size was inversely correlated with protein diffusivity and release rates. While protein electrostatics, protein concentration, and incubation time were important variables to control protein–NS complex formation, we found that one of the most significant and less appreciated variable to obtain a sustained release of bioactive proteins was the buffer chosen for preparing the initial suspension of NS particles. The buffer was found to control the size of nanoparticles, the absorption potential, morphology, and stiffness of hydrogels. From these studies, we conclude that the PEG–laponite composite fabricated is a promising new platform for sustained delivery of positively charged protein therapeutics.

Platelet-rich plasma (PRP) is an autologous blood product that contains a variety of growth factors (GFs) that are released upon platelet activation. Despite some therapeutic potential of PRP in vitro, in vivo data are not convincing. Bolus injection of PRP is cleared rapidly from the body diminishing its therapeutic efficacy. This highlights a need for a delivery vehicle for a sustained release of PRP to improve its therapeutic effect. In this study, we used microfluidics to fabricate biodegradable PRP-loaded polyethylene glycol (PEG) microspheres. PRP was incorporated into the microspheres as a lyophilized PRP powder either as is (powder PRP) or first solubilized and pre-clotted to remove clots (liquid PRP). A high PRP loading of 10% w/v was achieved for both PRP preparations. We characterized the properties of the resulting PRP-loaded PEG microspheres including swelling, modulus, degradation, and protein release as a function of PRP loading and preparation. Overall, loading powder PRP into the PEG microspheres significantly affected the properties of microspheres, with the most pronounced effect noted in degradation. We further determined that microsphere degradation in the presence of powder PRP was affected by platelet aggregation and clotting. Platelet aggregation did not prevent but prolonged sustained PRP release from the microspheres. The delivery system developed and characterized herein could be useful for the loading and releasing of PRP to promote tissue regeneration and wound healing or to suppress tissue degeneration in osteoarthritis, and intervertebral disc degeneration.

Purpose: Bioprinting is an alternative method for constructing tissues/organs for transplantation. This study investigated the cross-linker influence and post-printing modification using oligochitosan and chitosan for stability improvement. Methods: Oligochitosan was tested as a novel cross-linker to replace Ca 2+ for pectin-based bio-ink. Oligochitosan (2 kD) and different molecular weight of chitosan were used to modify the bioprinted scaffold. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were used to characterize the scaffolds. Results: Oligochitosan failed to serve as a viable cross-linker. Successful post-printing modification was confirmed by FTIR and SEM analyses. Conclusion: Regarding post-modification, chitosan-treated scaffolds showed enhanced stability compared to untreated scaffolds. In particular, scaffolds modified with 150 kD chitosan exhibited the highest stability.

Microfluidic devices that combine an extracellular matrix environment, cells, and physiologically relevant perfusion, are advantageous as cell culture platforms. We developed a hydrogel-based, microfluidic cell culture platform by loading polyethylene glycol (PEG) hydrogel-encapsulated U87 glioblastoma cells into membrane-capped wells in polydimethyl siloxane (PDMS). The multilayer microfluidic cell culture system combines previously reported design features in a configuration that loads and biomimetically perfuses a 2D array of cell culture chambers. One dimension of the array is fed by a microfluidic concentration gradient generator (MCGG) while the orthogonal dimension provides loading channels that fill rows of cell culture chambers in a separate layer. In contrast to typical tree-like MCGG mixers, a fractional serial dilution of 1, ½, ¼, and 0 of the initial solute concentration is achieved by tailoring the input microchannel widths. Hydrogels are efficiently and reproducibly loaded in all wells and cells are evenly distributed throughout the hydrogel, maintaining > 90% viability for up to 4 days. In a drug screening assay, diffusion of temozolomide and carmustine to hydrogel-encapsulated U87 cells from the perfusion solution is measured, and dose–response curves are generated, demonstrating utility as an in vitro mimic of the glioblastoma microenvironment.

Hydrogels have been widely used for therapeutic delivery applications due to their tunability and biocompatibility, although delivery of small molecules is difficult due to high burst release and rapid diffusion from the device. Nanosilicate clays (nanoclays) have shown the adsorption potential of small molecules, offering a lever to prolong the release kinetics of hydrogel delivery devices. However, further characterization of small molecule–nanoclay interactions and their effect on molecule release is needed to allow for the custom design of tunable nanocomposite hydrogel delivery devices. Here, we have characterized the adsorption of small molecules onto three nanoclays, Laponite, montmorillonite, and halloysite, and monitored their release in various conditions. The layered structures of Laponite and montmorillonite led to cationic exchange of the small molecules into the interlayer space, whereas the small molecules were adsorbed onto the surface of the tubular halloysite. The addition of nanoclays to polyethylene glycol (PEG) hydrogels significantly slowed the release of small molecules, especially from Laponite (500-fold decrease) and montmorillonite (∼3000-fold decrease) composite gels. Cationic small molecules were shown to be released significantly slower from nanocomposite hydrogels than anionic ones. The incubation time of small molecules with nanoclays prior to hydrogel encapsulation also played a key role in determining their release rate, with montmorillonite showing near-immediate adsorption while halloysite exhibited a higher dependence on incubation time due to slower adsorption kinetics. Release buffer salt concentration and pH were shown to affect release kinetics due to modulation of nanoclay–small molecule interactions. These results show the potential for formation of a highly tunable nanocomposite hydrogel delivery device for a greatly prolonged release of small molecules compared to traditional hydrogels.

Hydrogel microspheres are sought for a variety of biomedical applications, including therapeutic and cellular delivery, sensors, and lubricants. Robust fabrication of hydrogel microspheres with uniform sizes and properties can be achieved using microfluidic systems that rely on droplet formation and subsequent gelation to form microspheres. Such systems work well when gelation is initiated after droplet formation but are not practical for timed gelation systems where gelation is initiated prior to droplet formation; premature gelation can lead to device blockage, variable microsphere diameter due to viscosity changes in the precursor solution, and limited numbers of microspheres produced in a single run. To enable microfluidic fabrication of microspheres from timed gelation hydrogel systems, an in situ mixing region is needed so that various hydrogel precursor components can be added separately. Here, we designed and evaluated three mixing devices for their effectiveness at mixing hydrogel precursor solutions prior to droplet formation and subsequent gelation. The serpentine geometry was found to be the most effective and was further improved with the inclusion of a pillar array to increase agitation. The optimized device was shown to fully mix precursor solutions and enable the fabrication of monodisperse polyethylene glycol microspheres, offering great potential for use with timed gelation hydrogel systems.