The Effects of Intravenous Fluid Viscosity on the Accuracy of Intravenous Infusion Flow Regulators

Intravenous infusion flow regulators (IIFRs) are widely used devices but it is unknown how much the difference between the IIFR scale and the actual flow rate depends on the viscosity of the intravenous (IV) fluid. This study evaluated the effects of viscosity on the flow rate of five IV fluids (0.9% normal saline, Hartmann’s solution, plasma solution-A, 6% hetastarch, and 5% albumin) when using IIFRs. The viscosity of crystalloids was 1.07–1.12 mPa·s, and the viscosities of 6% hetastarch and 5% albumin were 2.59 times and 1.74 times that of normal saline, respectively. When the IIFR scales were preset to 20, 100, and 250 mL/hr, crystalloids were delivered at the preset flow rate within a difference of less than 10%, while 6% hetastarch was delivered at approximately 40% of the preset flow rates and 5% albumin was approximately 80% transmitted. When delivering colloids, IIFRs should be used with caution.

Development and Evaluation of Hyaluronic Acid-Based Hybrid Bio-Ink for Tissue Regeneration

BACKGROUND: Bioprinting has recently appeared as a powerful tool for building complex tissue and organ structures. However, the application of bioprinting to regenerative medicine has limitations, due to the restricted choices of bio-ink for cytocompatible cell encapsulation and the integrity of the fabricated structures. METHODS: In this study, we developed hybrid bio-inks based on acrylated hyaluronic acid (HA) for immobilizing bioactive peptides and tyramine-conjugated hyaluronic acids for fast gelation. RESULTS: Conventional acrylated HA-based hydrogels have a gelation time of more than 30 min, whereas hybrid bioink has been rapidly gelated within 200 s. Fibroblast cells cultured in this hybrid bio-ink up to 7 days showed < 90% viability. As a guidance cue for stem cell differentiation, we immobilized four different bio-active peptides: BMP-7-derived peptides (BMP-7D) and osteopontin for osteogenesis, and substance-P (SP) and Ac-SDKP (SDKP) for angiogenesis. Mesenchymal stem cells cultured in these hybrid bio-inks showed the highest angiogenic and osteogenic activity cultured in bio-ink immobilized with a SP or BMP-7D peptide. This bio-ink was loaded in a three-dimensional (3D) bioprinting device showing reproducible printing features. CONCLUSION: We have developed bio-inks that combine biochemical and mechanical cues. Biochemical cues were able to regulate differentiation of cells, and mechanical cues enabled printing structuring. This multi-functional bio-ink can be used for complex tissue engineering and regenerative medicine.

Effect of bFGF and fibroblasts combined with hyaluronic acid-based hydrogels on soft tissue augmentation: an experimental study in rats / 대한악안면성형재건외과학회지

BACKGROUND@#Hyaluronic acid (HA) has been applied as a primary biomaterial for temporary soft tissue augmentation and as a carrier for cells and the delivery of growth factors to promote tissue regeneration. Although HA derivatives are the most versatile soft tissue fillers on the market, they are resorbed early, within 3 to 12 months. To overcome their short duration, they can be combined with cells or growth factors. The purpose of this study was to investigate the stimulating effects of human fibroblasts and basic fibroblast growth factors (bFGF) on collagen synthesis during soft tissue augmentation by HA hydrogels and to compare these with the effects of a commercial HA derivative (Restylane®).@*METHODS@#The hydrogel group included four conditions. The first condition consisted of hydrogel (H) alone as a negative control, and the other three conditions were bFGF-containing hydrogel (HB), human fibroblast-containing hydrogel (HF), and human fibroblast/bFGF-containing hydrogel (HBF). In the Restylane® group (HGF), the hydrogel was replaced with Restylane® (R, RB, RF, RBF). The gels were implanted subdermally into the back of each nude mouse at four separate sites. Twelve nude mice were used for the hydrogel (n = 6) and Restylane® groups (n = 6). The specimens were harvested 8 weeks after implantation and assessed histomorphometrically, and collagen synthesis was evaluated by RT-PCR.@*RESULTS@#The hydrogel group showed good biocompatibility with the surrounding tissues and stimulated the formation of a fibrous matrix. HBF and HF showed significantly higher soft tissue synthesis compared to H (p < 0.05), and human collagen type I was well expressed in HB, HF, and HBF; HBF showed the strongest expression. The Restylane® filler was surrounded by a fibrous capsule without any soft tissue infiltration from the neighboring tissue, and collagen synthesis within the Restylane® filler could not be observed, even though no inflammatory reactions were observed.@*CONCLUSION@#This study revealed that HA-based hydrogel alone or hydrogel combined with fibroblasts and/or bFGF can be effectively used for soft tissue augmentation.

Fabrication of Microchannels and Evaluation of Guided Vascularization in Biomimetic Hydrogels

BACKGROUND: The fabrication of microchannels in hydrogel can facilitate the perfusion of nutrients and oxygen, which leads to guidance cues for vasculogenesis. Microchannel patterning in biomimetic hydrogels is a challenging issue for tissue regeneration because of the inherent low formability of hydrogels in a complex configuration. We fabricated microchannels using wire network molding and immobilized the angiogenic factors in the hydrogel and evaluated the vasculogenesis in vitro and in vivo. METHODS: Microchannels were fabricated in a hyaluronic acid-based biomimetic hydrogel by using “wire network molding” technology. Substance P was immobilized in acrylated hyaluronic acid for angiogenic cues using Michael type addition reaction. In vitro and in vivo angiogenic activities of hydrogel with microchannels were evaluated. RESULTS: In vitro cell culture experiment shows that cell viability in two experimental biomimetic hydrogels (with microchannels and microchannels + SP) was higher than that of a biomimetic hydrogel without microchannels (bulk group). Evaluation on differentiation of human mesenchymal stem cells (hMSCs) in biomimetic hydrogels with fabricated microchannels shows that the differentiation of hMSC into endothelial cells was significantly increased compared with that of the bulk group. In vivo angiogenesis analysis shows that thin blood vessels of approximately 25–30 µm in diameter were observed in the microchannel group and microchannel + SP group, whereas not seen in the bulk group. CONCLUSION: The strategy of fabricating microchannels in a biomimetic hydrogel and simultaneously providing a chemical cue for angiogenesis is a promising formula for large-scale tissue regeneration.

Comparison of Angiogenic Activities of Three Neuropeptides, Substance P, Secretoneurin, and Neuropeptide Y Using Myocardial Infarction

BACKGROUND: The interplay between neurogenesis and angiogenesis is crucial during the development mediated by neuro-angiogenic morphogens. In particular, the angiogenic activity of neuropeptides and their role in tissue regeneration have long been investigated for better understanding of their biological mechanisms and further applications. However, there have been few studies for direct comparison of angiogenic activities of neuropeptides for in vitro and in vivo models. In this study, we report that direct comparison of the angiogenic activities of neuropeptide Y, secretoneurin, and substance P (SP) immobilized on hydrogels in in vitro and in vivo experiments. METHODS: A hyaluronic acid-based hydrogel is prepared by utilizing acrylated hyaluronic acid and thiolated peptides as a crosslinker and angiogenic factors, respectively. Angiogenic activities of three neuropeptides are evaluated not only by in vitro angiogenic and gene expression assays, but also by an in vivo chronic myocardial infarction model. RESULTS: The comparison of in vitro angiogenic activities of three peptides demonstrates that the SP-immobilized hydrogel shows a higher degree of cell network formation and angiogenic-specific genes than those of the other peptides and the control case. In addition, a three-dimensional angiogenic assay illustrates that more sprouting is observable in the SP group. Evaluation of regenerative activity in the chronic myocardial infarction model reveals that all three peptideimmobilized hydrogels induce increased cardiac function as well as structural regeneration. Among all the cases, the SP group provided the highest regenerative activity both in vitro and in vivo. CONCLUSION: In our comparison study, the SP-immobilized hydrogel shows the highest angiogenic activity and tissue regeneration among the test groups. This result suggests that nerve regeneration factors help angiogenesis in damaged tissues, which also highlights the importance of the neuro-angiogenic peptides as an element of tissue regeneration.

Comparative Study of BMP-2 Alone and Combined with VEGF Carried by Hydrogel for Maxillary Alveolar Bone Regeneration

The effect of vascular endothelial growth factor (VEGF) combined with bone morphogenetic protein-2 (BMP-2) for bone regeneration is still controversial as to whether or not VEGF has a synergistic or additive effect. This study attempted to evaluate the synergistic effect of VEGF and BMP-2 compared to BMP-2 alone for maxillary alveolar bone regeneration using collagen sponge/hydrogel complex sheets in a canine model. After mixing BMP-2 and VEGF with a hyaluronic acid-based hydrogel (HAH), the collagen sponge/hydrogel complex was transplanted into maxillary alveolar bone defects (n=14) after the extraction of canine upper first molars on both sides. Bone regeneration was evaluated in three groups (control group without growth factors, experimental groups I and II with BMP-2 alone and BMP-2 and VEGF, respectively) using micro-computed tomography and histological staining. The total amount of new bone formations and bone mineral density were significantly higher in the group with BMP-2 only and the group with BMP-2 combined with VEGF than it in the control group. The area with positive staining of von Willebrand factor bone defect was significantly greater in the group with BMP-2 only and with dual growth factors than the control. BMP-2 released from the HAH promoted new bone formation. However, the combination of BMP-2 and VEGF did not show a synergistic or additive effect on bone regeneration at canine maxillary alveolar bone defects.