Improving bone defect healing using magnesium phosphate granules with tailored degradation characteristics

OBJECTIVES

Dental implant placement frequently requires preceding bone augmentation, for example, with hydroxyapatite (HA) or β-tricalcium phosphate (β-TCP) granules. However, HA is degraded very slowly in vivo and for β-TCP inconsistent degradation profiles from too rapid to rather slow are reported. To shorten the healing time before implant placement, rapidly resorbing synthetic materials are of great interest. In this study, we investigated the potential of magnesium phosphates in granular form as bone replacement materials.

METHODS

Spherical granules of four different materials were prepared via an emulsion process and investigated in trabecular bone defects in sheep: struvite (MgNH4PO4·6H2O), K-struvite (MgKPO4·6H2O), farringtonite (Mg3(PO4)2) and β-TCP.

RESULTS

All materials except K-struvite exhibited promising support of bone regeneration, biomechanical properties and degradation. Struvite and β-TCP granules degraded at a similar rate, with a relative granules area of 29% and 30% of the defect area 4 months after implantation, respectively, whereas 18% was found for farringtonite. Only the K-struvite granules degraded too rapidly, with a relative granules area of 2% remaining, resulting in initial fibrous tissue formation and intermediate impairment of biomechanical properties.

SIGNIFICANCE

We demonstrated that the magnesium phosphates struvite and farringtonite have a comparable or even improved degradation behavior in vivo compared to β-TCP. This emphasizes that magnesium phosphates may be a promising alternative to established calcium phosphate bone substitute materials.

Biological Activity In Vitro, Absorption, BBB Penetration, and Tolerability of Nanoformulation of BT44:RET Agonist with Disease-Modifying Potential for the Treatment of Neurodegeneration

BT44 is a novel, second-generation glial cell line-derived neurotropic factor mimetic with improved biological activity and is a lead compound for the treatment of neurodegenerative disorders. Like many other small molecules, it suffers from intrinsic poor aqueous solubility, posing significant hurdles at various levels for its preclinical development and clinical translation. Herein, we report a poly(2-oxazoline)s (POx)-based BT44 micellar nanoformulation with an ultrahigh drug-loading capacity of 47 wt %. The BT44 nanoformulation was comprehensively characterized by 1H NMR spectroscopy, differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), dynamic light scattering (DLS), and cryo-transmission/scanning electron microscopy (cryo-TEM/SEM). The DSC, XRD, and redispersion studies collectively confirmed that the BT44 formulation can be stored as a lyophilized powder and can be redispersed upon need. The DLS suggested that the redispersed formulation is suitable for parenteral administration (Dh ≈ 70 nm). The cryo-TEM measurements showed the presence of wormlike structures in both the plain polymer and the BT44 formulation. The BT44 formulation retained biological activity in immortalized cells and in cultured dopamine neurons. The micellar nanoformulation of BT44 exhibited improved absorption (after subcutaneous injection) and blood-brain barrier (BBB) penetration, and no acute toxic effects in mice were observed. In conclusion, herein, we have developed an ultrahigh BT44-loaded aqueous injectable nanoformulation, which can be used to pave the way for its preclinical and clinical development for the management of neurodegenerative disorders.

Primary Glial Cell and Glioblastoma Morphology in Cocultures Depends on Scaffold Design and Hydrogel Composition

3D cell cultures better replicate the in vivo environment compared to 2D models. Glioblastoma multiforme, a malignant brain tumor, highly profits from its cellular environment. Here, the U87 glioblastoma cell line in the presence/absence of primary astrocytes is studied. Thiolated hyaluronic acid (HA-SH) hydrogel reinforced with microfiber scaffolds is compared to Matrigel. Hyaluronic acid is a major extracellular matrix (ECM) component in the brain. Poly(ɛ-caprolactone) (PCL) scaffolds are written by meltelectrowriting in a box and triangular shaped design with pore sizes of 200 µm. Scaffolds are composed of 10-layers of PCL microfibers. It is found that scaffold design has an impact on cellular morphology in the absence of hydrogel. Moreover, the used hydrogels have profound influences on cellular morphology resulting in spheroid formation in HA-SH for both the tumor-derived cell line and astrocytes, while cell viability is high. Although cocultures of U87 and astrocytes exhibit cell-cell interactions, polynucleated spheroid formation is still present for U87 cells in HA-SH. Locally restricted ECM production or inability to secrete ECM proteins may underlie the observed cell morphologies. Thus, the 3D reinforced PCL-HA-SH composite with glioma-like cells and astrocytes constitutes a reproducible system to further investigate the impact of hydrogel modifications on cellular behavior and development.

Exploring the potential of magnesium oxychloride, an amorphous magnesium phosphate, and newberyite as possible bone cement candidates

Magnesium phosphate-based bone cements, particularly struvite (MgNH4PO4∙6H2O)-forming cements, have attracted increased scientific interest in recent years because they exhibit similar biocompatibility to hydroxyapatite while degrading much more rapidly in vivo. However, other magnesium-based minerals which might be promising are, to date, little studied. Therefore, in this study, we investigated three magnesium-based bone cements: a magnesium oxychloride cement (Mg3(OH)5Cl∙4H2O), an amorphous magnesium phosphate cement based on Mg3(PO4)2, MgO, and NaH2PO4, and a newberyite cement (MgHPO4·3H2O). Because it is not sufficiently clear from the literature to what extent these cements are suitable for clinical use, all of them were characterized and optimized regarding setting time, setting temperature, compressive strength and passive degradation in phosphate-buffered saline. Because the in vitro properties of the newberyite cement were most promising, it was orthotopically implanted into a partially weight-bearing tibial bone defect in sheep. The cement exhibited excellent biocompatibility and degraded more rapidly compared to a hydroxyapatite reference cement; after 4 months, 18% of the cement was degraded. We conclude that the newberyite cement was the most promising candidate of the investigated cements and has clear advantages over calcium phosphate cements, especially in terms of setting time and degradation behavior.

Adjusting Degree of Modification and Composition of gelAGE-Based Hydrogels Improves Long-Term Survival and Function of Primary Human Fibroblasts and Endothelial Cells in 3D Cultures

This study aimed to develop a suitable hydrogel-based 3D platform to support long-term culture of primary endothelial cells (ECs) and fibroblasts. Two hydrogel systems based on allyl-modified gelatin (gelAGE), G_1MM and G_2LH, were cross-linked via thiol-ene click reaction with a four-arm thiolated polyethylene glycol (PEG-4-SH). Compared to G_1MM, the G_2LH hydrogel was characterized by the lower polymer content and cross-linking density with a softer matrix and homogeneous and open porosity. Cell viability in both hydrogels was comparable, although the G_2LH-based platform supported better F-actin organization, cell-cell interactions, and collagen and fibronectin production. In co-cultures, early morphogenesis leading to tubular-like structures was observed within 2 weeks. Migration of fibroblasts out of spheroids embedded in the G_2LH hydrogels started after 5 days of incubation. Taken together, the results demonstrated that the G_2LH hydrogel fulfilled the demands of both ECs and fibroblasts to enable long-term culture and matrix remodeling.

Design of Nanohydrogels for Targeted Intracellular Drug Transport to the Trans-Golgi Network

Nanohydrogels combine advantages of hydrogels and nanoparticles. In particular, they represent promising drug delivery systems. Nanogel synthesis by oxidative condensation of polyglycidol prepolymers, that are modified with thiol groups, results in crosslinking by disulfide bonds. Hereby, biomolecules like the antidiabetic peptide RS1-reg, derived from the regulatory protein RS1 of the Na⁺ -D-glucose cotransporter SGLT1, can be covalently bound by cysteine residues to the nanogel in a hydrophilic, stabilizing environment. After oral uptake, the acid-stable nanogels protect their loading during gastric passage from proteolytic degradation. Under alkaline conditions in small intestine the nanohydrogels become mucoadhesive, pass the intestinal mucosa and are taken up into small intestinal enterocytes by endocytosis. Using Caco-2 cells as a model for small intestinal enterocytes, by confocal laser scanning microscopy and structured illumination microscopy, the colocalization of fluorescent-labeled RS1-reg with markers of endosomes, lysosomes, and trans-Golgi-network after uptake with polyglycidol-based nanogels formed by precipitation polymerization is demonstrated. This indicates that RS1-reg follows the endosomal pathway. In the following, the design of bespoken nanohydrogels for specific targeting of RS1-reg to its site of action at the trans-Golgi network is described that might also represent a way of targeted transport for other drugs to their targets at the Golgi apparatus.

Physicochemical degradation of calcium magnesium phosphate (stanfieldite) based bone replacement materials and the effect on their cytocompatibility

Regenerative bone implants should be completely replaced by new bone within a period of time corresponding to the growth rate of native bone. To meet this requirement, suitable biomaterials must be biodegradable and promote osteogenesis. The combination of slowly degrading but osteoconductive calcium phosphates (CPs) with rapidly degrading and mechanically more resilient magnesium phosphates represents a promising material class for this purpose. In order to create the best possible conditions for optimal implant integration, microporous calcium magnesium phosphate (CMP) cements were processed using 3D powder printing. This technique enables the production of a defect-adapted implant with an optimal fit and a high degree of open porosity to promote bone ingrowth. Four different compositions of 3D printed CMP ceramics were investigated with regard to essential properties of bone implants, including chemical composition, porosity, microstructure, mechanical strength, and cytocompatibility. The ceramics consisted of farringtonite (Mg₃(PO₄)₂) and stanfieldite (Ca₄Mg₅(PO₄)₆), with either struvite (NH₄MgPO₄·6H₂O) or newberyite (MgHPO₄·3H₂O) and brushite (CaHPO₄·2H₂O) as additional phases. The CMP materials showed open porosities between 13 and 28% and compressive strengths between 11 and 17 MPa, which was significantly higher, as compared with clinically established CP. The cytocompatibility was evaluated with the human fetal osteoblast cell line hFOB 1.19 and was proven to be equal or to even exceed that of tricalcium phosphate. Furthermore, a release of 4-8 mg magnesium and phosphate ions per mg scaffold material could be determined for CMPs over a period of 21 d. In the case of struvite containing CMPs the chemical dissolution of the cement matrix was combined with a physical degradation, which resulted in a mass loss of up to 3.1 wt%. In addition to its beneficial physical and biological properties, the proven continuous chemical degradation and bioactivity in the form of CP precipitation indicate an enhanced bone regeneration potential of CMPs.

Real-Time Measurement of Cell Mechanics as a Clinically Relevant Readout of an In Vitro Lung Fibrosis Model Established on a Bioinspired Basement Membrane

Lung fibrosis, one of the major post-COVID complications, is a progressive and ultimately fatal disease without a cure. Here, an organ- and disease-specific in vitro mini-lung fibrosis model equipped with noninvasive real-time monitoring of cell mechanics is introduced as a functional readout. To establish an intricate multiculture model under physiologic conditions, a biomimetic ultrathin basement (biphasic elastic thin for air-liquid culture conditions, BETA) membrane (<1 µm) is developed with unique properties, including biocompatibility, permeability, and high elasticity (<10 kPa) for cell culturing under air-liquid interface and cyclic mechanical stretch conditions. The human-based triple coculture fibrosis model, which includes epithelial and endothelial cell lines combined with primary fibroblasts from idiopathic pulmonary fibrosis patients established on the BETA membrane, is integrated into a millifluidic bioreactor system (cyclic in vitro cell-stretch, CIVIC) with dose-controlled aerosolized drug delivery, mimicking inhalation therapy. The real-time measurement of cell/tissue stiffness (and compliance) is shown as a clinical biomarker of the progression/attenuation of fibrosis upon drug treatment, which is confirmed for inhaled Nintedanib-an antifibrosis drug. The mini-lung fibrosis model allows the combined longitudinal testing of pharmacodynamics and pharmacokinetics of drugs, which is expected to enhance the predictive capacity of preclinical models and hence facilitate the development of approved therapies for lung fibrosis.

Accelerated bone regeneration through rational design of magnesium phosphate cements

Results of several studies during past years suggested that magnesium phosphate cements (MPCs) not only show excellent biocompatibility and osteoconductivity, but they also provide improved regeneration capacity due to higher solubility compared to calcium phosphates. These findings also highlighted that chemical similarity of bone substitutes to the natural bone tissue is not a determinant factor in the success of regenerative strategies. The aim of this study was to further improve the degradation speed of MPCs for a fast bone ingrowth within a few months. We confirmed our hypothesis, that decreasing the powder-liquid ratio (PLR) of cement results in an increased content of highly soluble phases such as struvite (MgNH₄PO₄⋅6H₂O) as well as K-struvite (MgKPO₄⋅6H₂O). Promising compositions with a low PLR of 1 g ml^-1 were implanted in partially-loaded tibia defects in sheep. Both cements were partially degraded and replaced by bone tissue after 4 months. The degradation speed of the K-struvite cement was significantly higher compared to the struvite cement, initially resulting in the formation of a cell-rich resorption zone at the surface of some implants, as determined by histology. Overall, both MPCs investigated in this study seem to be promising as an alternative to the clinically well-established, but slowly degrading calcium phosphate cements, depending on defect size and desired degradation rate. Whereas the K-struvite cement might require further modification towards a slower resorption and reduced inflammatory response in vivo, the struvite cement appears promising for the treatment of bone defects due to its continuous degradation with simultaneous new bone formation. STATEMENT OF SIGNIFICANCE: Cold setting bone cements are used for the treatment of bone defects that exceed a critical size and cannot heal on their own. They are applied pasty into the bone defect and harden afterwards so that the shape adapts to the individual defect. Magnesium phosphates such as magnesium ammonium phosphate hexahydrate (struvite) belong to a new class of these cold setting bone cements. They degrade much faster than the clinically established calcium phosphates. In this study, a magnesium phosphate that has hardly been investigated so far was implanted into partially-loaded defects in sheeps: Potassium magnesium phosphate hexahydrate. This showed even faster resorption compared to the struvite cement: after 4 months, 63% of the cement was already degraded.

Preservation of the naïve features of mesenchymal stromal cells in vitro: Comparison of cell- and bone-derived decellularized extracellular matrix

The fate and behavior of bone marrow mesenchymal stem/stromal cells (BM-MSC) is bidirectionally influenced by their microenvironment, the stem cell niche, where a magnitude of biochemical and physical cues communicate in an extremely orchestrated way. It is known that simplified 2D in vitro systems for BM-MSC culture do not represent their naïve physiological environment. Here, we developed four different 2D cell-based decellularized matrices (dECM) and a 3D decellularized human trabecular-bone scaffold (dBone) to evaluate BM-MSC behavior. The obtained cell-derived matrices provided a reliable tool for cell shape-based analyses of typical features associated with osteogenic differentiation at high-throughput level. On the other hand, exploratory proteomics analysis identified native bone-specific proteins selectively expressed in dBone but not in dECM models. Together with its architectural complexity, the physico-chemical properties of dBone triggered the upregulation of stemness associated genes and niche-related protein expression, proving in vitro conservation of the naïve features of BM-MSC.

The Multiweek Thermal Stability of Medical-Grade Poly(ε-caprolactone) During Melt Electrowriting

Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that places unique constraints on the processing of thermally degradable polymers. With a single nozzle, MEW operates at low throughput and in this study, medical-grade poly(ε-caprolactone) (PCL) is heated for 25 d at three different temperatures (75, 85, and 95 °C), collecting daily samples. There is an initial increase in the fiber diameter and decrease in the jet speed over the first 5 d, then the MEW process remains stable for the 75 and 85 °C groups. When the collector speed is fixed to a value at least 10% above the jet speed, the diameter remains constant for 25 d at 75 °C and only increases with time for 85 and 95 °C. Fiber fusion at increased layer height is observed for 85 and 95 °C, while the surface morphology of single fibers remain similar for all temperatures. The properties of the prints are assessed with no observable changes in the degree of crystallinity or the Young's modulus, while the yield strength decreases in later phases only for 95 °C. After the initial 5-d period, the MEW processing of PCL at 75 °C is extraordinarily stable with overall fiber diameters averaging 13.5 ± 1.0 µm over the entire 25-d period.

Covalently Crosslinked Pig Gastric Mucin Hydrogels Prepared by Radical-based Chain-Growth and Thiol-ene Mechanisms

Mucin, a high molecular mass hydrophilic glycoprotein, is the main component of mucus that coats every wet epithelium in animals. It is thus intrinsically biocompatible, and with its protein backbone and the o-glycosidic bound oligosaccharides, it contains a plethora of functional groups which can be used for further chemical modifications. In this study we introduce and compare chain-growth and step-growth (thiol-ene) free-radical crosslinked hydrogels prepared from commercially available pig gastric mucin (PGM) as cost-efficient and easily accessible alternative to the more broadly applied bovine submaxillary gland mucin (BSM). For this, PGM was functionalized with photoreactive acrylate groups or allylether-moieties, respectively. Whereas homopolymerization of acrylate functionalized polymers was performed, for thiol-ene crosslinking, the allylether functionalized PGM was cross-linked with thiol-functionalized hyaluronic acid (HA). Morphology, mechanical properties, and cell compatibility of both kinds of PGM hydrogels are characterized and compared. Furthermore, the biocompatibility of these hydrogels could be evaluated in cell culture experiments. This article is protected by copyright. All rights reserved.

A thermogelling organic-inorganic hybrid hydrogel with excellent printability, shape fidelity and cytocompatibility for 3D bioprinting

Alginates are the most commonly used bioink in biofabrication, but their rheological profiles makes it very challenging to perform real 3D printing. In this study, an advanced hybrid hydrogel ink was developed, a mixture of thermogelling diblock copolymer, alginate and clay i.e. Laponite XLG. The reversible thermogelling and shear thinning properties of the diblock copolymer in the ink system improves handling and 3D printability significantly. Various three-dimensional constructs, including suspended filaments, were printed successfully with high shape fidelity and excellent stackability. Subsequent ionic crosslinking of alginate fixates the printed scaffolds, while the diblock copolymer is washed out of the structure, acting as a fugitive material on the (macro)molecular level. Finally, cell-laden printing and culture over 21 days demonstrated good cytocompatibility and feasibility of the novel hybrid hydrogels for 3D bioprinting. We believe that the developed material could be interesting for a wide range of bioprinting applications including tissue engineering and drug screening, potentially enabling also other biological bioinks such as collagen, hyaluronic acid, decellularized extracellular matrix or cellulose based bioinks.

Bioink Platform Utilizing Dual-Stage Crosslinking of Hyaluronic Acid Tailored for Chondrogenic Differentiation of Mesenchymal Stromal Cells

3D bioprinting often involves application of highly concentrated polymeric bioinks to enable fabrication of stable cell-hydrogel constructs, although poor cell survival, compromised stem cell differentiation, and an inhomogeneous distribution of newly produced extracellular matrix (ECM) are frequently observed. Therefore, this study presents a bioink platform using a new versatile dual-stage crosslinking approach based on thiolated hyaluronic acid (HA-SH), which not only provides stand-alone 3D printability but also facilitates effective chondrogenic differentiation of mesenchymal stromal cells. A range of HA-SH with different molecular weights is synthesized and crosslinked with acrylated (PEG-diacryl) and allylated (PEG-diallyl) polyethylene glycol in a two-step reaction scheme. The initial Michael addition is used to achieve ink printability, followed by UV-mediated thiol-ene reaction to stabilize the printed bioink for long-term cell culture. Bioinks with high molecular weight HA-SH (>200 kDa) require comparably low polymer content to facilitate bioprinting. This leads to superior quality of cartilaginous constructs which possess a coherent ECM and a strongly increased stiffness of long-term cultured constructs. The dual-stage system may serve as an example to design platforms using two independent crosslinking reactions at one functional group, which allows adjusting printability as well as material and biological properties of bioinks.

Bone regeneration capacity of newly developed spherical magnesium phosphate cement granules

OBJECTIVES

Magnesium phosphate-based cements begin to catch more attention as bone substitute materials and especially as alternatives for the more commonly used calcium phosphates. In bone substitutes for augmentation purposes, atraumatic materials with good biocompatibility and resorbability are favorable. In the current study, we describe the in vivo testing of novel bone augmentation materials in form of spherical granules based on a calcium-doped magnesium phosphate (CaMgP) cement.

MATERIALS AND METHODS

Granules with diameters between 500 and 710 μm were fabricated via the emulsification of CaMgP cement pastes in a lipophilic liquid. As basic material, two different CaMgP formulations were used. The obtained granules were implanted into drill hole defects at the distal femoral condyle of 27 New Zealand white rabbits for 6 and 12 weeks. After explantation, the femora were examined via X-ray diffraction analysis, histological staining, radiological examination, and EDX measurement.

RESULTS

Both granule types display excellent biocompatibility without any signs of inflammation and allow for proper bone healing without the interposition of connective tissue. CaMgP granules show a fast and continuous degradation and enable fully adequate bone regeneration.

CONCLUSIONS

Due to their biocompatibility, their degradation behavior, and their completely spherical morphology, these CaMgP granules present a promising bone substitute material for bone augmentation procedures, especially in sensitive areas.

CLINICAL RELEVANCE

The mostly insufficient local bone supply after tooth extractions complicates prosthetic dental restoration or makes it even impossible. Therefore, bone augmentation procedures are oftentimes inevitable. Spherical CaMgP granules may represent a valuable bone replacement material in many situations.

From Thermogelling Hydrogels toward Functional Bioinks: Controlled Modification and Cytocompatible Crosslinking

Hydrogels are key components in bioink formulations to ensure printability and stability in biofabrication. In this study, a well-known Diels-Alder two-step post-polymerization modification approach is introduced into thermogelling diblock copolymers, comprising poly(2-methyl-2-oxazoline) and thermoresponsive poly(2-n-propyl-2-oxazine). The diblock copolymers are partially hydrolyzed and subsequently modified by acid/amine coupling with furan and maleimide moieties. While the thermogelling and shear-thinning properties allow excellent printability, trigger-less cell-friendly Diels-Alder click-chemistry yields long-term shape-fidelity. The introduced platform enables easy incorporation of cell-binding moieties (RGD-peptide) for cellular interaction. The hydrogel is functionalized with RGD-peptides using thiol-maleimide chemistry and cell proliferation as well as morphology of fibroblasts seeded on top of the hydrogels confirm the cell adhesion facilitated by the peptides. Finally, bioink formulations are tested for biocompatibility by incorporating fibroblasts homogenously inside the polymer solution pre-printing. After the printing and crosslinking process good cytocompatibility is confirmed. The established bioink system combines a two-step approach by physical precursor gelation followed by an additional chemical stabilization, offering a broad versatility for further biomechanical adaptation or bioresponsive peptide modification.

Tuning the Thermogelation and Rheology of Poly(2-Oxazoline)/Poly(2-Oxazine)s Based Thermosensitive Hydrogels for 3D Bioprinting

As one kind of "smart" material, thermogelling polymers find applications in biofabrication, drug delivery and regenerative medicine. In this work, we report a thermosensitive poly(2-oxazoline)/poly(2-oxazine) based diblock copolymer comprising thermosensitive/moderately hydrophobic poly(2-N-propyl-2-oxazine) (pPrOzi) and thermosensitive/moderately hydrophilic poly(2-ethyl-2-oxazoline) (pEtOx). Hydrogels were only formed when block length exceeded certain length (≈100 repeat units). The tube inversion and rheological tests showed that the material has then a reversible sol-gel transition above 25 wt.% concentration. Rheological tests further revealed a gel strength around 3 kPa, high shear thinning property and rapid shear recovery after stress, which are highly desirable properties for extrusion based three-dimensional (3D) (bio) printing. Attributed to the rheology profile, well resolved printability and high stackability (with added laponite) was also possible. (Cryo) scanning electron microscopy exhibited a highly porous, interconnected, 3D network. The sol-state at lower temperatures (in ice bath) facilitated the homogeneous distribution of (fluorescently labelled) human adipose derived stem cells (hADSCs) in the hydrogel matrix. Post-printing live/dead assays revealed that the hADSCs encapsulated within the hydrogel remained viable (≈97%). This thermoreversible and (bio) printable hydrogel demonstrated promising properties for use in tissue engineering applications.

An Inverse Thermogelling Bioink Based on an ABA-Type Poly(2-oxazoline) Amphiphile

Hydrogels are key components in several biomedical research areas such as drug delivery, tissue engineering, and biofabrication. Here, a novel ABA-type triblock copolymer comprising poly(2-methyl-2-oxazoline) as the hydrophilic A blocks and poly(2-phenethyl-2-oxazoline) as the aromatic and hydrophobic B block is introduced. Above the critical micelle concentration, the polymer self-assembles into small spherical polymer micelles with a hydrodynamic radius of approx 8-8.5 nm. Interestingly, this specific combination of hydrophilic and hydrophobic aromatic moieties leads to rapid thermoresponsive inverse gelation at polymer concentrations above a critical gelation concentration (20 wt %) into a macroporous hydrogel of densely packed micelles. This hydrogel exhibited pronounced viscoelastic solid-like properties, as well as extensive shear-thinning, rapid structure recovery, and good strain resistance properties. Excellent 3D-printability of the hydrogel at lower temperature opens a wide range of different applications, for example, in the field of biofabrication. In preliminary bioprinting experiments using NIH 3T3 cells, excellent cell viabilities of more than 95% were achieved. The particularly interesting feature of this novel material is that it can be used as a printing support in hybrid bioink systems and sacrificial bioink due to rapid dissolution at physiological conditions.

A Bioinspired in vitro Lung Model to Study Particokinetics of Nano-/Microparticles Under Cyclic Stretch and Air-Liquid Interface Conditions

Evolution has endowed the lung with exceptional design providing a large surface area for gas exchange area (ca. 100 m²) in a relatively small tissue volume (ca. 6 L). This is possible due to a complex tissue architecture that has resulted in one of the most challenging organs to be recreated in the lab. The need for realistic and robust in vitro lung models becomes even more evident as causal therapies, especially for chronic respiratory diseases, are lacking. Here, we describe the Cyclic InVItroCell-stretch (CIVIC) “breathing” lung bioreactor for pulmonary epithelial cells at the air-liquid interface (ALI) experiencing cyclic stretch while monitoring stretch-related parameters (amplitude, frequency, and membrane elastic modulus) under real-time conditions. The previously described biomimetic copolymeric BETA membrane (5 μm thick, bioactive, porous, and elastic) was attempted to be improved for even more biomimetic permeability, elasticity (elastic modulus and stretchability), and bioactivity by changing its chemical composition. This biphasic membrane supports both the initial formation of a tight monolayer of pulmonary epithelial cells (A549 and 16HBE14o⁻) under submerged conditions and the subsequent cell-stretch experiments at the ALI without preconditioning of the membrane. The newly manufactured versions of the BETA membrane did not improve the characteristics of the previously determined optimum BETA membrane (9.35% PCL and 6.34% gelatin [w/v solvent]). Hence, the optimum BETA membrane was used to investigate quantitatively the role of physiologic cyclic mechanical stretch (10% linear stretch; 0.33 Hz: light exercise conditions) on size-dependent cellular uptake and transepithelial transport of nanoparticles (100 nm) and microparticles (1,000 nm) for alveolar epithelial cells (A549) under ALI conditions. Our results show that physiologic stretch enhances cellular uptake of 100 nm nanoparticles across the epithelial cell barrier, but the barrier becomes permeable for both nano- and micron-sized particles (100 and 1,000 nm). This suggests that currently used static in vitro assays may underestimate cellular uptake and transbarrier transport of nanoparticles in the lung.

Crosslinking of hydrophilic polymers using polyperoxides

Hydrogels that can mimic mechanical properties and functions of biological tissue have attracted great interest in tissue engineering and biofabrication. In these fields, new materials and approaches to prepare hydrogels without using toxic starting materials or materials that decompose into toxic compounds remain to be sought after. Here, we report the crosslinking of commercial, unfunctionalized hydrophilic poly(2-ethyl-2-oxazoline) using peroxide copolymers in their melt. The influence of temperature, peroxide copolymer concentration, and duration of the crosslinking process has been investigated. The method allows to create hydrogels from unfunctionalized polymers in their melt and to control the mechanical properties of the resulting materials. The design of hydrogels with a suitable mechanical performance is of crucial importance in many existing and potential applications of soft materials, including medical applications.

Hyaluronic Acid-Based Bioink Composition Enabling 3D Bioprinting and Improving Quality of Deposited Cartilaginous Extracellular Matrix

In 3D bioprinting, bioinks with high concentrations of polymeric materials are frequently used to enable fabrication of 3D cell-hydrogel constructs with sufficient stability. However, this is often associated with restricted cell bioactivity and an inhomogeneous distribution of newly produced extracellular matrix (ECM). Therefore, this study investigates bioink compositions based on hyaluronic acid (HA), an attractive material for cartilage regeneration, which allow for reduction of polymer content. Thiolated HA and allyl-modified poly(glycidol) in varying concentrations are UV-crosslinked. To adapt bioinks to poly(ε-caprolactone) (PCL)-supported 3D bioprinting, the gels are further supplemented with 1 wt% unmodified high molecular weight HA (hmHA) and chondrogenic differentiation of incorporated human mesenchymal stromal cells is assessed. Strikingly, addition of hmHA to gels with a low polymer content (3 wt%) results in distinct increase of construct quality with a homogeneous ECM distribution throughout the constructs, independent of the printing process. Improved ECM distribution in those constructs is associated with increased construct stiffness after chondrogenic differentiation, as compared to higher concentrated constructs (10 wt%), which only show pericellular matrix deposition. The study contributes to effective bioink development, demonstrating dual function of a supplement enabling PCL-supported bioprinting and at the same time improving biological properties of the resulting constructs.

Inverse Thermogelation of Aqueous Triblock Copolymer Solutions into Macroporous Shear-Thinning 3D Printable Inks

Amphiphilic block copolymers that undergo (reversible) physical gelation in aqueous media are of great interest in different areas including drug delivery, tissue engineering, regenerative medicine, and biofabrication. We investigated a small library of ABA-type triblock copolymers comprising poly(2-methyl-2-oxazoline) as the hydrophilic shell A and different aromatic poly(2-oxazoline)s and poly(2-oxazine)s cores B in an aqueous solution at different concentrations and temperatures. Interestingly, aqueous solutions of poly(2-methyl-2-oxazoline)-block-poly(2-phenyl-2-oxazine)-block-poly(2-methyl-2-oxazoline) (PMeOx-b-PPheOzi-b-PMeOx) undergo inverse thermogelation below a critical temperature by forming a reversible nanoscale wormlike network. The viscoelastic properties of the resulting gel can be conveniently tailored by the concentration and the polymer composition. Storage moduli of up to 110 kPa could be obtained while the material retains shear-thinning and rapid self-healing properties. We demonstrate three-dimensional (3D) printing of excellently defined and shape-persistent 24-layered scaffolds at different aqueous concentrations to highlight its application potential, e.g., in the research area of biofabrication. A macroporous microstructure, which is stable throughout the printing process, could be confirmed via cryo-scanning electron microscopy (SEM) analysis. The absence of cytotoxicity even at very high concentrations opens a wide range of different applications for this first-in-class material in the field of biomaterials.

Emotional adjustment and perceived locus of control in heart transplant patients

Orthotopic heart transplantation has been established as a routine clinical operation. In this study, we were interested in: (a) how patients cope emotionally with the situation pre- and postsurgically, especially with regard to anxiety and depression; and (b) whether the patient's perceived locus of control is related to emotional adjustment before and after heart transplantation. Twenty patients who were on the waiting list for heart transplantation with highest priority provided complete psychological questionnaires presurgically and 20 days after surgery when intensive care was no longer required. During the waiting period, patients rated high on depression, state and trait anxiety in comparison with healthy references while ratings on perceived locus of control scales were within the norm ranges. After surgery, heart transplant patients experienced significantly less state/trait anxiety and depression reaching levels which were no longer statistically different from health references. While postsurgical ratings of anxiety (state and trait) and depression were not significantly correlated with presurgical ratings, both were closely related to ratings of locus of control. Belief in powerful others was positively correlated with pre- and postsurgical anxiety and depression. Chance control orientation was related only to presurgical emotional disturbances. It can be concluded that emotional adjustment after heart transplantation is more likely to be predicted by presurgical ratings of locus of control than by presurgical emotional adjustment.