Development and Evaluation of Biodegradable Core-Shell Microfibrous and Nanofibrous Scaffolds for Tissue Engineering Applications.

Tissue engineering scaffolds as three-dimensional substrates may serve as ideal templates for tissue regeneration by simulating the structure of the extracellular matrix (ECM). Many biodegradable synthetic polymers, either hydrophobic, like Poly-ε-caprolactone (PCL), or hydrophilic, like Poly(Vinyl Alcohol) (PVA), are widely used as candidate bioactive materials for fabricating tissue engineering scaffolds. However, a combination of good cytocompatibility of hydrophilic polymers with good biomechanical performance of hydrophobic polymers could be beneficial for the in vivo performance of the scaffolds. In this study, we aimed to fabricate biodegradable fibrous scaffolds by combining the properties of hydrophobic PCL with those of hydrophilic PVA and evaluate their properties in comparison with pristine PCL scaffolds. Therefore, single-layered PCL scaffolds, sequential tri-layered (PVA/PCL/PVA), and core-shell (PVA as shell and PCL as core) composite scaffolds were developed utilizing the electrospinning technique. The material structural and biomechanical properties of the electrospun scaffolds, before and after their hydrolytic degradation over a seven-month period following storage in phosphate-buffered saline (PBS) at 37 °C, were comprehensively compared. In addition, human embryonic kidney cells (HEK-293) were cultured on the scaffolds to investigate potential cell attachment, infiltration, and proliferation. The results demonstrated the long-term efficacy of core-shell biodegradable fibrous scaffolds in comparison to single-layers PCL and tri-layers PVA/PCL/PVA, not only due to its superior morphological characteristics and mechanical properties, but also due to its ability to promote homogeneous cell distribution and proliferation, without any external chemical or physical stimuli.

A novel polymeric fibrous microstructured biodegradable small-caliber tubular scaffold for cardiovascular tissue engineering.

Increasing morbidity of cardiovascular diseases in modern society has made it crucial to develop artificial small-caliber cardiovascular grafts for surgical intervention of diseased natural arteries, as alternatives to the gold standard autologous implants. Synthetic small-caliber grafts are still not in use due to increased risk of restenosis, lack of lumen re-endothelialization and mechanical mismatch, leading sometimes either to graft failure or to unsuccessful remodeling and pathology of the distal parts of the anastomosed healthy vascular tissues. In this work, we aimed to synthesize small-caliber polymeric (polycaprolactone) tissue-engineered vascular scaffolds that mimic the structure and biomechanics of natural vessels. Electrospinning was implemented to prepare microstructured polymeric membranes with controlled axis-parallel fiber alignment. Consequently, we designed small-caliber multilayer anisotropic biodegradable nanofibrous tubular scaffolds, giving attention to their radial compliance. Polycaprolactone scaffold morphology and mechanical properties were assessed, quantified, and compared with those of native vessels and commercial synthetic grafts. Results showed a highly hydrophobic scaffold material with a three-layered tubular morphology, 4-mm internal diameter/0.25 ± 0.09-mm thickness, consisting of predominantly axially aligned thin (1.156 ± 0.447 µm), homogeneous and continuous microfibers, with adequate (17.702 ± 5.369 µm) pore size, potentially able to promote cell infiltration in vivo. In vitro accelerated degradation showed a 5% mass loss within 17-25 weeks. Mechanical anisotropy was attained as a result, almost one order of magnitude difference of the elastic modulus (18 ± 3 MPa axially/1 ± 0.3 MPa circumferentially), like that of natural arterial walls. Furthermore, a desirable radial compliance (5.04 ± 0.82%, within the physiological pressure range) as well as cyclic stability of the tubular scaffold was achieved. Finally, cytotoxicity evaluation of the polymeric scaffolds revealed that the materials were nontoxic and did not release substances harmful to living cells (over 80% cell viability achieved).

A Quantitative Systematic Literature Review of Combination Punishment Literature: Progress Over the Last Decade.

This review evaluated single-case experimental design research that examined challenging behavior interventions utilizing punishment elements. Thirty articles published between 2013 and 2022 met study inclusion criteria. Study quality was also assessed. Through multiple levels of analysis (e.g., descriptive statistics, non-parametric statistics), we examined (a) participant and study trends, (b) differential outcomes related to temporal reinforcement approaches (antecedent, consequent, or combined reinforcement) applied alongside punishment element(s), (c) differential outcomes related to the punishment type (negative, positive) applied alongside reinforcement, and (d) effect sizes associated with study rigor across peer-reviewed and gray literature. Our results may tentatively suggest that, for certain situations, concurrently applying punishment with antecedent reinforcement approaches may coincide with significantly larger effect sizes compared to combined temporal reinforcement approaches, while positive punishment applied concurrently with reinforcement may coincide with larger but non-significant intervention effects. Most featured articles met rigor criteria, but larger effects were seen in peer-reviewed literature.

Laser-assisted bioprinting of targeted cartilaginous spheroids for high density bottom-up tissue engineering.

Multicellular spheroids such as microtissues and organoids have demonstrated great potential for tissue engineering applications in recent years as these 3D cellular units enable improved cell-cell and cell-matrix interactions. Current bioprinting processes that use multicellular spheroids as building blocks have demonstrated limited control on post printing distribution of cell spheroids or moderate throughput and printing efficiency. In this work, we presented a laser-assisted bioprinting approach able to transfer multicellular spheroids as building blocks for larger tissue structures. Cartilaginous multicellular spheroids formed by human periosteum derived cells (hPDCs) were successfully bioprinted possessing high viability and the capacity to undergo chondrogenic differentiation post printing. Smaller hPDC spheroids with diameters ranging from ∼100 to 150µm were successfully bioprinted through the use of laser-induced forward transfer method (LIFT) however larger spheroids constituted a challenge. For this reason a novel alternative approach was developed termed as laser induced propulsion of mesoscopic objects (LIPMO) whereby we were able to bioprint spheroids of up to 300µm. Moreover, we combined the bioprinting process with computer aided image analysis demonstrating the capacity to 'target and shoot', through automated selection, multiple large spheroids in a single sequence. By taking advantage of target and shoot system, multilayered constructs containing high density cell spheroids were fabricated.

Dually crosslinked injectable alginate-based graft copolymer thermoresponsive hydrogels as 3D printing bioinks for cell spheroid growth and release.

In this work a dual crosslinked network based on sodium alginate graft copolymer, bearing poly(N-isopropylacrylamide-co-N-tert-butylacrylamide) P(NIPAM-co-NtBAM) side chains was developed and examined as a shear thinning soft gelating bioink. The copolymer was found to undergo a two-step gelation mechanism; in the first step a three-dimensional (3D) network is formed through ionic interactions between the negatively ionized carboxylic groups of the alginate backbone and the positive charges of Ca2+ divalent cations, according to the "egg-box" mechanism. The second gelation step occurs upon heating which triggers the hydrophobic association of the thermoresponsive P(NIPAM-co-NtBAM) side chains, increasing the network crosslinking density in a highly cooperative manner. Interestingly, the dual crosslinking mechanism resulted in a five-to-eight-fold improvement of the storage modulus implying reinforced hydrophobic crosslinking above the critical thermo-gelation temperature which is further boosted by the ionic crosslinking of the alginate backbone. The proposed bioink could form arbitrary geometries under mild 3D printing conditions. Last, it is demonstrated that the proposed developed bioink can be further utilized as bioprinting ink and showcased its ability to promote human periosteum derived cells (hPDCs) growth in 3D and their capacity to form 3D spheroids. In conclusion, the bioink, owing its ability to reverse thermally the crosslinking of its polymer network, can be further utilized for the facile recovery of the cell spheroids, implying its promising potential use as cell spheroid-forming template bionk for applications in 3D biofabrication.