A comparative study of polyethylene glycol hydrogels derivatized with the RGD peptide and the cell-binding domain of fibronectin

Engineering Three-Dimensional Vascularized Cardiac Tissues

Heart disease is one of the largest burdens to human health worldwide and has very limited therapeutic options. Engineered three-dimensional (3D) vascularized cardiac tissues have shown promise in rescuing cardiac function in diseased hearts and may serve as a whole organ replacement in the future. One of the major obstacles in reconstructing these thick myocardial tissues to a clinically applicable scale is the integration of functional vascular networks capable of providing oxygen and nutrients throughout whole engineered constructs. Without perfusion of oxygen and nutrient flow throughout the entire engineered tissue not only is tissue viability compromised, but also overall tissue functionality is lost. There are many supporting technologies and approaches that have been developed to create vascular networks such as 3D bioprinting, co-culturing hydrogels, and incorporation of soluble angiogenic factors. In this state-of-the-art review, we discuss some of the most current engineered vascular cardiac tissues reported in the literature and future directions in the field. Impact statement The field of cardiac tissue engineering is rapidly evolving and is now closer than ever to having engineered tissue models capable of predicting preclinical responses to therapeutics, modeling diseases, and being used as a means of rescuing cardiac function following injuries to the native myocardium. However, a major obstacle of engineering thick cardiac tissue remains to be the integration of functional vasculature. In this review, we highlight seminal and recently published works that have influenced and pushed the field of cardiac tissue engineering toward achieving vascularized functional tissues.

Responsive Hybrid (Poly)peptide-Polymer Conjugates

(Poly)peptide-polymer conjugates continue to garner significant interest in the production of functional materials given their composition of natural and synthetic building blocks that confer select and synergistic properties. Owing to opportunities to design predefined architectures and structures with different morphologies, these hybrid conjugates enable new approaches for producing micro- or nanomaterials. Their modular design enables the incorporation of multiple responsive properties into a single conjugate. This review presents recent advances in (poly)peptide-polymer conjugates for drug-delivery applications, with a specific focus on the utility of the (poly)peptide component in the assembly of particles and nanogels, as well as the role of the peptide in triggered drug release.

Enhanced articular cartilage by human mesenchymal stem cells in enzymatically mediated transiently RGDS-functionalized collagen-mimetic hydrogels

Recapitulation of the articular cartilage microenvironment for regenerative medicine applications faces significant challenges due to the complex and dynamic biochemical and biomechanical nature of native tissue. Towards the goal of biomaterial designs that enable the temporal presentation of bioactive sequences, recombinant bacterial collagens such as Streptococcal collagen-like 2 (Scl2) proteins can be employed to incorporate multiple specific bioactive and biodegradable peptide motifs into a single construct. Here, we first modified the backbone of Scl2 with glycosaminoglycan-binding peptides and cross-linked the modified Scl2 into hydrogels via matrix metalloproteinase 7 (MMP7)-cleavable or non-cleavable scrambled peptides. The cross-linkers were further functionalized with a tethered RGDS peptide creating a system whereby the release from an MMP7-cleavable hydrogel could be compared to a system where release is not possible. The release of the RGDS peptide from the degradable hydrogels led to significantly enhanced expression of collagen type II (3.9-fold increase), aggrecan (7.6-fold increase), and SOX9 (5.2-fold increase) by human mesenchymal stem cells (hMSCs) undergoing chondrogenesis, as well as greater extracellular matrix accumulation compared to non-degradable hydrogels (collagen type II; 3.2-fold increase, aggrecan; 4-fold increase, SOX9; 2.8-fold increase). Hydrogels containing a low concentration of the RGDS peptide displayed significantly decreased collagen type I and X gene expression profiles, suggesting a major advantage over either hydrogels functionalized with a higher RGDS peptide concentration, or non-degradable hydrogels, in promoting an articular cartilage phenotype. These highly versatile Scl2 hydrogels can be further manipulated to improve specific elements of the chondrogenic response by hMSCs, through the introduction of additional bioactive and/or biodegradable motifs. As such, these hydrogels have the possibility to be used for other applications in tissue engineering.

Statement of Significance

Recapitulating aspects of the native tissue biochemical microenvironment faces significant challenges in regenerative medicine and tissue engineering due to the complex and dynamic nature of the tissue. The ability to take advantage of, mimic, and modulate cell-mediated processes within novel naturally-derived hydrogels is of great interest in the field of biomaterials to generate constructs that more closely resemble the biochemical microenvironment and functions of native biological tissues such as articular cartilage. Towards this goal, the temporal presentation of bioactive sequences such as RGDS on the chondrogenic differentiation of human mesenchymal stem cells is considered important as it has been shown to influence the chondrogenic phenotype. Here, a novel and versatile platform to recreate a high degree of biological complexity is proposed, which could also be applicable to other tissue engineering and regenerative medicine applications.

A gene expression-based comparison of cell adhesion to extracellular matrix and RGD-terminated monolayers

This work uses global gene expression analysis to compare the extent to which model substrates presenting peptide adhesion motifs mimic the use of conventional extracellular matrix protein coated substrates for cell culture. We compared the transcriptional activities of genes in cells that were cultured on matrix-coated substrates with those cultured on self-assembled monolayers presenting either a linear or cyclic RGD peptide. Cells adherent to cyclic RGD were most similar to those cultured on native ECM, while cells cultured on monolayers presenting the linear RGD peptide had transcriptional activities that were more similar to cells cultured on the uncoated substrates. This study suggests that biomaterials presenting the cyclic RGD peptide are substantially better mimics of extracellular matrix than are uncoated materials or materials presenting the common linear RGD peptide.

Proteolysis of decellularized extracellular matrices results in loss of fibronectin and cell binding activity

Excessive inflammation in the chronic wound bed is believed to result in increased fibronectin (FN) proteolysis and poor tissue repair. However, FN fragments can prime the immune response and result in higher protease levels. The reciprocity between FN proteolysis and inflammation makes it challenging to determine the specific contribution of FN proteolysis in the extracellular matrix (ECM) on tissue responses. We studied the impact of proteolysis of decellularized extracellular matrices (dECMs) obtained from NIH 3T3 mouse fibroblasts on FN level and activity. The dECMs were treated with α chymotrypsin and proteolysis was stopped at different time points. The protease solution was obtained, the remaining dECM was scrapped and examined by immunoblotting and Bicinchoninic Acid assays. Fibronectin was 9.4 ± 1.8% of the total protein content in the dECM but was more susceptible to proteolysis. After 15 min of protease treatment there was a 67.6% and 11.1% decrease in FN and total protein, respectively, in the dECMs. Fibronectin fragments were present both in the proteolysis solution and in the dECM. Cell adhesion, spreading and actin extensions on dECMs decreased with increasing proteolysis time. Interestingly, the solutions obtained after proteolysis of the dECMs supported cell adhesion and spreading in a time dependent manner, thus demonstrating the presence of FN cell binding activity in the protease solution of dECMs. This study demonstrates the susceptibility of FN in the ECM to proteolysis and the resulting loss of cell adhesion due to the decrease of FN activity and places weight on bioengineering strategies to stabilize FN against proteolysis.

Injectable hydrogels based on poly(ethylene glycol) and derivatives as functional biomaterials

The design criteria for injectable, in situ-gelling hydrogels are reviewed in conjunction with highlights on recent progress in the preparation of injectable PEG and PEG-analogue poly(oligoethylene glycol methacrylate) (POEGMA) hydrogels.

QHREDGS enhances tube formation, metabolism and survival of endothelial cells in collagen-chitosan hydrogels

Cell survival in complex, vascularized tissues, has been implicated as a major bottleneck in advancement of therapies based on cardiac tissue engineering. This limitation motivates the search for small, inexpensive molecules that would simultaneously be cardio-protective and vasculogenic. Here, we present peptide sequence QHREDGS, based upon the fibrinogen-like domain of angiopoietin-1, as a prime candidate molecule. We demonstrated previously that QHREDGS improved cardiomyocyte metabolism and mitigated serum starved apoptosis. In this paper we further demonstrate the potency of QHREDGS in its ability to enhance endothelial cell survival, metabolism and tube formation. When endothelial cells were exposed to the soluble form of QHREDGS, improvements in endothelial cell barrier functionality, nitric oxide production and cell metabolism (ATP levels) in serum starved conditions were found. The functionality of the peptide was then examined when conjugated to collagen-chitosan hydrogel, a potential carrier for in vivo application. The presence of the peptide in the hydrogel mitigated paclitaxel induced apoptosis of endothelial cells in a dose dependent manner. Furthermore, the peptide modified hydrogels stimulated tube-like structure formation of encapsulated endothelial cells. When integrin αvβ3 or α5β1 were antibody blocked during cell encapsulation in peptide modified hydrogels, tube formation was abolished. Therefore, the dual protective nature of the novel peptide QHREDGS may position this peptide as an appealing augmentation for collagen-chitosan hydrogels that could be used for biomaterial delivered cell therapies in the settings of myocardial infarction.