Elastin-like Polypeptide-Based Bioink: A Promising Alternative for 3D Bioprinting.

Three-dimensional (3D) bioprinting offers a great alternative to traditional techniques in tissue reconstruction, based on seeding cells manually into a scaffold, to better reproduce organs' complexity. When a suitable bioink is engineered with appropriate physicochemical properties, such a process can advantageously provide a spatial control of the patterning that improves tissue reconstruction. The design of an adequate bioink must fulfill a long list of criteria including biocompatibility, printability, and stability. In this context, we have developed a bioink containing a precisely controlled recombinant biopolymer, namely, elastin-like polypeptide (ELP). This material was further chemoselectively modified with cross-linkable moieties to provide a 3D network through photopolymerization. ELP chains were additionally either functionalized with a peptide sequence Gly-Arg-Gly-Asp-Ser (GRGDS) or combined with collagen I to enable cell adhesion. Our ELP-based bioinks were found to be printable, while providing excellent mechanical properties such as stiffness and elasticity in their cross-linked form. Besides, they were demonstrated to be biocompatible, showing viability and adhesion of dermal normal human fibroblasts (NHF). Expressions of specific extracellular matrix (ECM) protein markers as pro-collagen I, elastin, fibrillin, and fibronectin were revealed within the 3D network containing cells after only 18 days of culture, showing the great potential of ELP-based bioinks for tissue engineering.

Engineering Shape to Overcome Contraction: The Role of Polymer-Collagen Hybrids in Advanced Dermal Substitutes.

Collagen gels are the standard dermal equivalents par excellence, however the problem of rapid cell-mediated contraction remains unresolved. Therefore, the development of hybrid constructs (HCs) based on collagen and polymeric scaffolds is proposed to address the mechanical instability that usually limits the formation of new, functional tissue. Equally important, these synthetic structures should be temporary (degradable) while ensuring that cells are well-adapted to the new extracellular environment. In this study, we screened a library of scaffolds made of various polymers, including homopolymers of polycaprolactone (PCL) and poly D,L-lactide (PLA50), their blends (PCL/PLA50), and copolymers (poly(D,L-lactide-co-caprolactone), PCLLA50) to prepare HCs in a layer-by-layer fashion. The properties of polymers and copolymers along with their processability by electrospinning and 3D-printing were evaluated. Then, we assessed the HCs resistance toward cell-mediated contraction as well as the degradation of the polymeric scaffolds. Our results indicate that scaffolds with higher PLA50 content (e.g., PLA50 100%, PCL/PLA50 or PCLLA50, both at 50/50 caprolactone-to-D,L-lactide molar ratio) presented more drawbacks in terms of handleability and processing, while those with greater PCL presence showed structural steadiness and ease to use. All the scaffolds integrated well with the collagen gel to form the corresponding HCs. With few exceptions, the HCs demonstrated good resistance to cell-derived contraction over 3 weeks. Notably, HCs based on PCLLA50 90/10 (both versions, electrospun or 3D-printed) performed best, showing only a 5%-17% area reduction compared to the 93% observed in collagen-only gels. This copolymer displayed hydrolytic degradation depending on its shape, with up to 45% and 65% loss of molecular weight for the electrospun and 3D-printed forms, respectively, correlating with their progressive change in mechanical features. HCs containing PCLLA50 90/10 also exhibited a better fibroblast distribution, enhanced myofibroblastic differentiation, and a three-fold increase in cell proliferation (when the electrospun type was used) compared to collagen controls. These findings were instrumental in selecting a potential HC that might be used for future experiments in vivo.

Refining the Design of Diblock Elastin-Like Polypeptides for Self-Assembly into Nanoparticles.

Diblock copolymers based-on elastin-like polypeptide (ELP) have the potential to undergo specific phase transitions when thermally stimulated. This ability is especially suitable to form carriers, micellar structures for instance, for delivering active cargo molecules. Here, we report the design and study of an ELP diblock library based on ELP-[M1V3-i]-[I-j]. First, ELP-[M1V3-i]-[I-j] (i = 20, 40, 60; j = 20, 90) that showed a similar self-assembly propensity (unimer-to-aggregate transition) as their related monoblocks ELP-[M1V3-i] and ELP-[I-j]. By selectively oxidizing methionines of ELP-[M1V3-i] within the different diblocks structures, we have been able to access a thermal phase transition with three distinct regimes (unimers, micelles, aggregates) characteristic of well-defined ELP diblocks.