A synthetic elastomer based on acrylated polypropylene glycol triol with tunable modulus for tissue engineering applications

Incorporation of Cell-Adhesive Proteins in 3D-Printed Lipoic Acid-Maleic Acid-Poly(Propylene Glycol)-Based Tough Gel Ink for Cell-Supportive Microenvironment

In extrusion-based 3D printing, the use of synthetic polymeric hydrogels can facilitate fabrication of cellularized and implanted scaffolds with sufficient mechanical properties to maintain the structural integrity and physical stress within the in vivo conditions. However, synthetic hydrogels face challenges due to their poor properties of cellular adhesion, bioactivity, and biofunctionality. New compositions of hydrogel inks have been designed to address this limitation. A viscous poly(maleate-propylene oxide)-lipoate-poly(ethylene oxide) (MPLE) hydrogel is recently developed that shows high-resolution printability, drug-controlled release, excellent mechanical properties with adhesiveness, and biocompatibility. In this study, the authors demonstrate that the incorporation of cell-adhesive proteins like gelatin and albumin within the MPLE gel allows printing of biologically functional 3D scaffolds with rapid cell spreading (within 7 days) and high cell proliferation (twofold increase) as compared with MPLE gel only. Addition of proteins (10% w/v) supports the formation of interconnected cell clusters (≈1.6-fold increase in cell areas after 7-day) and spreading of cells in the printed scaffolds without additional growth factors. In in vivo studies, the protein-loaded scaffolds showed excellent biocompatibility and increased angiogenesis without inflammatory response after 4-week implantation in mice, thus demonstrating the promise to contribute to the printable tough hydrogel inks for tissue engineering.

Quantitative analysis of polypropylene glycol polymers by liquid chromatography tandem mass spectrometry based on collision induced dissociation technique

Polypropylene glycol (PPG) is a commonly used synthetic polymer in many fields. Investigating the toxicity and pharmacokinetic behavior of PPG polymers is necessary and important for evaluating their safety in medicine and daily cosmetics. In this study, PPG425, PPG1K and PPG2K were selected as the target polymers for cytotoxicity and cellular pharmacokinetics study of PPG polymers. Structural diversity and polydisperse molecular weights (MWs) are significant challenges for quantification of PPG polymers by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Collision induced dissociation in source or collision cell generated a series of PPG-related product ions at m/z 59.0, 117.1, 175.1, 233.2, 291.2, 349.3, 407.2, 465.3 and 523.5 corresponding to fragments containing 1, 2, 3, 4, 5, 6, 7, 8, 9 repeating propylene oxide subunits. PPG425 was determined by the sum of the MRM acquisitions used the transitions [M+H]⁺¹ precursor ions → product ions. PPG1K and PPG2K were determined by the MRM acquisitions used the transitions [M+H]⁺¹ precursor ions → product ions at m/z 233.2(four subunits)→59.0(one subunit). Based on the collision induced disassociation technique and structural specific product ions, pharmacokinetic studies of PEG425, PPG1K and PPG2K were successfully conducted in McF-7 cells. The experimental results revealed that PPG polymers are not biologically inert and they can enter into McF-7 cells. The safety of PPG polymers should be considered when they are used as pharmaceutical or cosmetic excipients.

Delivery vehicle of muscle-derived irisin based on silk/calcium silicate/sodium alginate composite scaffold for bone regeneration

Background

Irisin is a cytokine produced by skeletal muscle and usually plays a pivotal role in inducing fat browning and regulating energy expenditure. In recent years, it was found that irisin might be the molecular entity responsible for muscle–bone connectivity and is useful in osteogenesis induction.

Materials and methods

To study its effect on bone regeneration, we developed silk/calcium silicate/sodium alginate (SCS) composite scaffold based on an interpenetrating network hydrogel containing silk fibroin, calcium silicate, sodium alginate. Then we loaded irisin on the SCS before coating it with polyvinyl alcohol (PVA). The SCS/P scaffold was physically characterized and some in vitro and in vivo experiments were carried out to evaluate the scaffold effect on bone regeneration.

Results

The SCS/P scaffold was showed a porous sponge structure pursuant to scanning electron microscopy analysis. The release kinetics assay demonstrated that irisin was stably released from the irisin-loaded hybrid system (i/SCS/P system) to 50% within 7 days. Moreover, osteoinductive studies using bone marrow stem cells (BMSCs) in vitro exhibited the i/SCS/P system improved the activity of alkaline phosphatase (ALP) and enhanced the expression levels of a series of osteogenic markers containing Runx-2, ALP, BMP2, Osterix, OCN, and OPN. Alizarin red staining also demonstrated the promotion of osteogenesis induced by i/SCS/P scaffolds. In addition, in vivo studies showed that increased bone regeneration with better mineralization and higher quality was found during the repair of rat calvarial defects through utilizing the i/SCS/P system.

Conclusion

These data provided strong evidence that the composite i/SCS/P would be a promising substitute for bone tissue engineering.

Biodegradable star-shaped polycyclic ester elastomers: Preparation, degradability, protein release, and biocompatibility in vitro

Effective local delivery methods for sustained and stable release of protein drugs are urgently needed. Biodegradable elastomers based on star-shaped polycyclic esters have received attention for their drug-loading and drug-release kinetics. However, the long degradation periods resulting from their strong lipophilicity greatly hinder their application. In this study, we synthesized new cross-linked elastomers based on methyl-acrylic-star-poly(ϵ-caprolactone- co-d,l-lactide) cyclic ester and methyl-bi-acrylic-poly(ϵ-caprolactone-b-poly(ethylene glycol)-b-ϵ-caprolactone) with different molecular weights; determined their physical, thermal, and morphological characteristics; and studied their in vitro degradation and release of bovine serum albumin and recombinant human interleukin 2. Elastomer hydrophilicity improved with the introduction of methyl-bi-acrylic-poly(ϵ-caprolactone-b-poly(ethylene glycol)-b-ϵ-caprolactone), and a shorter degradation period (~25 weeks) was achieved. Additionally, the degradation rate could be adjusted by varying the composition of methyl-bi-acrylic-poly(ϵ-caprolactone-b-poly(ethylene glycol)-b-ϵ-caprolactone) to directly influence the degree of swelling, cross-linking density, and sol content of the elastomer. The controlled rate of bovine serum albumin and recombinant human interleukin 2 release increased with a larger degree of swelling, higher sol content, and lower cross-link density of the elastomers. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis showed good biocompatibility. These results suggest that these new elastomers are potential candidates for carrier materials in controlled, implantable delivery systems for protein drugs and other biomedical applications.

Degradation-mediated cellular traction directs stem cell fate in covalently crosslinked three-dimensional hydrogels

Although cell-matrix adhesive interactions are known to regulate stem cell differentiation, the underlying mechanisms, in particular for direct three-dimensional encapsulation within hydrogels, are poorly understood. Here, we demonstrate that in covalently crosslinked hyaluronic acid (HA) hydrogels, the differentiation of human mesenchymal stem cells (hMSCs) is directed by the generation of degradation-mediated cellular traction, independently of cell morphology or matrix mechanics. hMSCs within HA hydrogels of equivalent elastic moduli that permit (restrict) cell-mediated degradation exhibited high (low) degrees of cell spreading and high (low) tractions, and favoured osteogenesis (adipogenesis). Moreover, switching the permissive hydrogel to a restrictive state through delayed secondary crosslinking reduced further hydrogel degradation, suppressed traction, and caused a switch from osteogenesis to adipogenesis in the absence of changes to the extended cellular morphology. Furthermore, inhibiting tension-mediated signalling in the permissive environment mirrored the effects of delayed secondary crosslinking, whereas upregulating tension induced osteogenesis even in the restrictive environment.

Tailored integrin-extracellular matrix interactions to direct human mesenchymal stem cell differentiation

Integrins provide the primary link between mesenchymal stem cells (MSCs) and their surrounding extracellular matrix (ECM), with different integrin pairs having specificity for different ECM molecules or peptide sequences contained within them. It is widely acknowledged that the type of ECM present can influence MSC differentiation; however, it is yet to be determined how specific integrin-ECM interactions may alter this or how they change during differentiation. We determined that human bone marrow-derived mesenchymal stem cells (hMSCs) express a broad range of integrins in their undifferentiated state and show a dramatic, but transient, increase in the level of α5 integrin on day 7 of osteogenesis and an increase in α6 integrin expression throughout adipogenesis. We used a nonfouling polystyrene-block-poly(ethylene oxide)-copolymer (PS-PEO) surface to present short peptides with defined integrin-binding capabilities (RGD, IKVAV, YIGSR, and RETTAWA) to hMSCs and investigate the effects of such specific integrin-ECM contacts on differentiation. hMSCs cultured on these peptides displayed different morphologies and had varying abilities to differentiate along the osteogenic and adipogenic lineages. The peptide sequences most conducive to differentiation (IKVAV for osteogenesis and RETTAWA and IKVAV for adipogenesis) were not necessarily those that were bound by those integrin subunits seen to increase during differentiation. Additionally, we also determined that presentation of RGD, which is bound by multiple integrins, was required to support long-term viability of hMSCs. Overall we confirm that integrin-ECM contacts change throughout hMSC differentiation and show that surfaces presenting defined peptide sequences can be used to target specific integrins and ultimately influence hMSC differentiation. This platform also provides information for the development of biomaterials capable of directing hMSC differentiation for use in tissue engineering therapies.

Effect of geometric challenges on cell migration

Cellular infiltration and colonization of three-dimensional (3D) porous scaffolds is influenced by many factors. One of the major factors is the internal architecture presented to the cells. In this work, we have developed and validated a microfluidic device that presents a multitude of geometric challenges to cells, mimicking the architectural aspects and characteristics of 3D porous scaffolds in a two-dimensional arrangement. This device has been utilized to investigate the influence of varying channel widths, degrees of channel tortuosity, the presence of contractions or expansions, and channel junctions on the migration of NIH 3T3 mouse fibroblasts and human bone marrow-derived mesenchymal stromal cell (hMSCs). These two cell types were observed to have vastly different migration characteristics; 3T3 fibroblasts migrate as a collective cell front, whereas hMSCs migrate as single cells. This resulted in 3T3 fibroblasts displaying significant differences in migration depending on the type of geometrical constraint, whereas hMSCs were only influenced by channel width when it approached that of the length scale of a single cell. The differences in migration characteristics were shown to be related to the expression of the intercellular junction protein N-cadherin. We observed that 3T3 fibroblasts express higher levels of N-cadherin than hMSCs and that N-cadherin inhibition modified the migration characteristics of the 3T3 fibroblasts, so that they were then similar to that of hMSCs. The results of this study both confirm the utility of the device and highlight that differences in migration characteristics of different cell types can be deterministic of how they may respond to geometric constraints within porous tissue engineering constructs.