Self-assembling peptide-enriched electrospun polycaprolactone scaffolds promote the h-osteoblast adhesion and modulate differentiation-associated gene expression

Hierarchically porous 3D-printed ceramic scaffolds for bone tissue engineering

Sacrificial templating offers the ability to create interconnected pores within 3D printed filaments and to control pore morphology. Beta-tricalcium phosphate (TCP) bone tissue engineering (BTE) scaffolds were fabricated with multiscale porosity: (i) macropores from direct ink writing (DIW, a material extrusion 3D printing technique), (ii) micropores from oil templating, and (iii) smaller micropores from partial sintering. The hierarchically porous scaffolds possessed a total porosity of 58-70 %, comprising 54-63 % interconnected open pores. The in vitro results demonstrated that scaffolds with macroporosity promoted human osteoblast growth more than scaffolds with only microporosity. The elongated pores from the capillary suspension filament microstructure induced greater cell spreading than the sphere-like pores from the emulsion. Overall, the hierarchically porous scaffold with capillary suspension TCP filaments provided a superior microenvironment for significantly higher cell viability and proliferation than the other scaffolds, including a poly(ε-caprolactone) (PCL) control, a material currently used clinically as porous BTE scaffolds. The cellular response was further enhanced when macropore size was in the range of 570-590 μm. Therefore, the hierarchically porous scaffolds in this study are promising as BTE scaffolds, and the reported process of DIW of oil-templated colloidal pastes is a feasible strategy with potential for further customization.

Peptide-Based Supramolecular Hydrogels as Drug Delivery Agents: Recent Advances

Supramolecular peptide hydrogels have many important applications in biomedicine, including drug delivery applications for the sustained release of therapeutic molecules. Targeted and selective drug administration is often preferential to systemic drug delivery, as it can allow reduced doses and can avoid the toxicity and side-effects caused by off-target binding. New discoveries are continually being reported in this rapidly developing field. In this review, we report the latest developments in supramolecular peptide-based hydrogels for drug delivery, focusing primarily on discoveries that have been reported in the last four years (2018-present). We address clinical points, such as peptide self-assembly and drug release, mechanical properties in drug delivery, peptide functionalization, bioadhesive properties and drug delivery enhancement strategies, drug release profiles, and different hydrogel matrices for anticancer drug loading and release.

Enhanced cell affinity and osteogenic differentiation of liquid crystal-based substrate via surface bio-functionalization

Regulation of cell-substrate interactions is an important factor for modulating cell behaviors. Tailoring the physical and chemical properties of the substrates to better mimic the extracellular matrix (ECM) of native tissue is a more effective strategy for enhancing the cell-substrate contact. In current work, we aim at improving surface bioactivity based on the liquid crystalline substrates for the enhancement in cell affinity and osteogenic differentiation. Polydopamine (PDOPA) adhesive coating was used as a reactive platform for the immobilization of chitooligosaccharide (COS) on the octyl hydroxypropyl cellulose ester (OPC) substrate to generate active OPC-PDOPA-COSs liquid crystalline substrates. Results demonstrated that PDOPA-coated OPC surfaces showed remarkably improved hydrophility and increased elastic modulus, leading to better initial cell attachment. Subsequent COS immobilization on the OPC-PDOPA layer could induce promotion of cell proliferation, polarization and cytoskeleton formation. Rat bone marrow mesenchymal stem cells (rBMSCs) seeded on the OPC-PDOPA-COSs showed higher alkaline phosphatase (ALP) activity, calcium deposition, and up-regulated bone-related genes expression, including BMP-2, RUNx-2, COL-I and OCN. In conclusion, surface biofunctionalization on the OPC-based liquid crystalline substrates could come into being the appropriate combination of surface chemistry and liquid crystalline characteristic that simulating in vivo ECM environment, resulting in a favorable support to enhance positive cell-substrate interactions.

Biomimetic peptide enriched nonwoven scaffolds promote calcium phosphate mineralisation

Cell-free translational strategies are needed to accelerate the repair of mineralised tissues, particularly large bone defects, using minimally invasive approaches. Regenerative bone scaffolds should ideally mimic aspects of the tissue's ECM over multiple length scales and enable surgical handling and fixation during implantation in vivo. Leveraging the knowledge gained with bioactive self-assembling peptides (SAPs) and SAP-enriched electrospun fibres, we presented a cell free approach for promoting mineralisation via apatite deposition and crystal growth, in vitro, of SAP-enriched nonwoven scaffolds. The nonwoven scaffold was made by electrospinning poly(ε-caprolactone) (PCL) in the presence of either peptide P₁₁-4 (Ac-QQRFEWEFEQQ-Am) or P₁₁-8 (Ac QQRFOWOFEQQ-Am), in light of the polymer's fibre forming capability and its hydrolytic degradability as well as the well-known apatite nucleating capability of SAPs. The 11-residue family of peptides (P₁₁-X) has the ability to self-assemble into β-sheet ordered structures at the nano-scale and to generate hydrogels at the macroscopic scale, some of which are capable of promoting biomineralisation due to their apatite-nucleating capability. Both variants of SAP-enriched nonwoven used in this study were proven to be biocompatible with murine fibroblasts and supported nucleation and growth of apatite minerals in simulated body fluid (SBF) in vitro. The fibrous nonwoven provided a structurally robust scaffold, with the capability to control SAP release behaviour. Up to 75% of P₁₁-4 and 45% of P₁₁-8 were retained in the fibres after 7 day incubation in aqueous solution at pH 7.4. The encapsulation of SAP in a nonwoven system with apatite-forming as well as localised and long-term SAP delivery capabilities is appealing as a potential means of achieving cost-effective bone repair therapy for critical size defects.

A structurally robust electrospun peptide-enriched scaffold, with controlled peptide release behaviour, supports nucleation and growth of hydroxyapatite minerals in vitro.

Peptide nanostructures on nanofibers for peripheral nerve regeneration

Self-assembled peptide nanofibrous scaffolds with designer sequences, similar to neurite growth promoting molecules enhance the differentiation of neural stem cells. However, self-assembled peptide nanofibrous scaffolds lack the required mechanical strength to suffice to bridge long critical-sized peripheral nerve defects. Hence, there is a demand for a potential neural substrate, which could be biomimetic coupled with bioactive nanostructures to regrow the denuded axons towards the distal end. In the present study, we developed designer self-assembling peptide-based aligned poly(lactic-co-glycolic acid) (PLGA) nanofibrous scaffolds by simple surface coating of peptides or coelectrospinning. Retention of secondary structures of peptides in peptide-coated and cospun fibers was confirmed by circular dichroism spectroscopy. The rod-like peptide nanostructures enhance the typical bipolar morphology of Schwann cells. Although the peptide-coated PLGA scaffolds exhibited significant increase in Schwann cell proliferation than pristine PLGA and PLGA-peptide cospun scaffolds (p < .05), peptide cospun scaffolds demonstrated better cellular infiltration and significantly higher gene expression of neural cell adhesion molecule, glial fibrillary acidic protein, and peripheral myelin protein22 compared to the pristine PLGA and PLGA-peptide-coated scaffolds. Our results demonstrate the positive effects of aligned peptide coelectrospun scaffolds with biomimetic cell recognition motifs towards functional proliferation of Schwann cells. These scaffolds could subsequently repair peripheral nerve defects by augmenting axonal regeneration and functional nerve recovery.

Biofunctionalization of TiO2 surfaces with self-assembling oligopeptides in different pH and Ionic Strength conditions: Charge effects and molecular organization

Self-assembling peptides (SAPs) were investigated by means of XPS and Angular Dependent NEXAFS spectroscopies, with the aim to probe the influence of pH and Ionic Strength conditions on the chemical structure and molecular organization of SAPs anchored on titania surfaces. XPS at the C1s, N1s, O1s core levels allowed to study surfaces and biomolecule/substrate interfaces. NEXAFS data allowed ascertaining that SAPs molecular structure is preserved upon grafting to the titania surface. Angular Dependent NEXAFS was used to investigate the influence of environmental conditions on the molecular organization behaviour. The objective of our study was to establish a set of methodologies for obtaining arrangements of well-organized biomolecules on scaffolds surfaces as a basic technology to develop and optimize cells adhesion and proliferation for tissue engineering applications.

Fabrication of nanofibrous electrospun scaffolds from a heterogeneous library of co- and self-assembling peptides

Self-assembling (SAPs) and co-assembling peptides (CAPs) are driving increasing enthusiasm as synthetic but biologically inspired biomaterials amenable of easy functionalization for regenerative medicine. On the other hand, electrospinning (ES) is a versatile technique useful for tailoring the nanostructures of various biomaterials into scaffolds resembling the extracellular matrices found in organs and tissues. The synergistic merging of these two approaches is a long-awaited advance in nanomedicine that has not been deeply documented so far. In the present work, we describe the successful ES of a library of diverse SAPs and CAPs into biomimetic nanofibrous mats. Our results suggest that suitable ES solutions are characterized by high concentrations of peptides, providing backbone physical chain entanglements, and by random coil/α-helical conformations while β-sheet aggregation may be detrimental to spinnability. The resulting peptide fibers feature interconnected seamless mats with nanofibers average diameters ranging from ∼100nm to ∼400nm. Also, peptide chemical nature and ES set up parameters play pivotal roles in determining the conformational transitions and morphological properties of the produced nanofibers. Far from being an exhaustive description of the just-opened novel field of ES-assembled peptides, this seminal work aims at shining a light on a still missing general theory for the production of electrospun peptidic biomaterials bringing together the spatial, biochemical and biomimetic of these two techniques into unique scaffolds for tissue engineering.

STATEMENT OF SIGNIFICANCE

Construction of peptide hydrogels has received considerable attention due to their potential as nanostructures amenable of easy functionalization and capable of creating microenvironments suited for culturing cells and triggering tissue regeneration. They display a superior biocompatibility unmatched by other known synthetic biomaterials so far. However, their applications are confined to body fillers because most of them do spontaneously form hydrogels, while effective tissue regeneration often requires well-defined fibrous scaffolds. In this work, we developed electrospun fibers of various peptides (cross-beta self-assembling, hierarchically assembling, functionalized, co-assembling) and we provided a deep understanding of the crucial phenomena to be taken into account when peptides fibers fabrication. These results open new venues for exploring novel regenerative applications of peptide nanofibrous scaffolds.

Self-assembling peptide nanostructures on aligned poly(lactide-co-glycolide) nanofibers for the functional regeneration of sciatic nerve

Aim: Regeneration of functional peripheral nerve tissue at critical-sized defect requires extracellular matrix analogs impregnated with appropriate biosignals to regulate the cell fate process and subsequent tissue progression. The aim of the study was to develop electrospun aligned nanofibers as architectural analogs integrated with RADA16-I-BMHP1 as biofunctional peptides. Materials & methods: Aligned poly(lactide-co-glycolide) (PLGA)-RADA16-I-BMHP1 nanofibers were fabricated and characterized for their in vitro potential using rat Schwann cell line and in vivo potential using a 10 mm sciatic nerve transection rat model. Results: PLGA-peptide scaffolds significantly promoted higher expression of genotypic markers and bipolar extension of Schwann cells. Further, PLGA-peptide treated animals promoted the native collagen organization, remyelination and showed significantly higher recovery of sensorimotor and motor function than PLGA-treated groups (p < 0.05). Conclusion: Our results demonstrate that self-assembling peptide nanostructures on aligned PLGA nanofibers provided better cell–matrix communication with significant functional restoration of the sciatic nerve.

Adhesion of mesenchymal stem cells to biomimetic polymers: A review

The mesenchymal stem cells (MSCs) are promising candidates for cell therapy due to the self-renewal, multi-potency, ethically approved state and suitability for autologous transplantation. However, key issue for isolation and manipulation of MSCs is adhesion in ex-vivo culture systems. Biomaterials engineered for mimicking natural extracellular matrix (ECM) conditions which support stem cell adhesion, proliferation and differentiation represent a main area of research in tissue engineering. Some of them successfully enhanced cells adhesion and proliferation because of their biocompatibility, biomimetic texture, and chemistry. However, it is still in its infancy, therefore intensification and optimization of in vitro, in vivo, and preclinical studies is needed to clarify efficacies as well as applicability of those bioengineered constructs. The aim of this review is to discuss mechanisms related to the in-vitro adhesion of MSCs, surfaces biochemical, biophysical, and other factors (of cell's natural and artificial micro-environment) which could affect it and a review of previous research attempting for its bio-chemo-optimization.

Electrospun poly(l-lactide)/zein nanofiber mats loaded with Rana chensinensis skin peptides for wound dressing

Electrospun nanofiber mats can display impressive performance as an ideal wound dressing. In this study, poly(l-lactide)(PLLA)/zein nanofiber mats loaded with Rana chensinensis skin peptides (RCSPs) were successfully produced by two different electrospinning techniques, blend and coaxial, with the goal of developing a wound dressing material. The nanofiber mats were investigated by environmental scanning electron microscope (ESEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), water contact angle, mechanical tests and cell viability. The resulting nanofiber mats exhibited smooth surfaces, tiny diameters and different cross-sectional shapes from pure PLLA and zein nanofibers. The FTIR result showed that PLLA, zein and RCSPs were well dispersed, without chemical interactions. Compared with coaxial nanofiber mats, blending zein-RCSPs with PLLA enhanced hydrophilicity but decreased mechanical properties. Adding RCSPs into the electrospun nanofibers significantly improved the mechanical properties of the mats. Cell viability studies with human foreskin fibroblasts demonstrated that cell growth on PLLA/zein-RCSPs nanofiber mats was significantly higher than that on PLLA/zein nanofiber mats. The results indicate that nanofiber mats containing RCSPs are potential candidates for wound dressing.

Inhibition of filamentous fungi by ketoconazole-functionalized electrospun nanofibers

Nanotechnology strategies have been used for delivery and controlled release of antimicrobial drugs. Electrospun nanofibers can be versatile vehicles to incorporate antimicrobials. In this work, poly-ε-caprolactone nanofibers functionalized with ketoconazole were produced by electrospinning and tested against filamentous fungi. Ketoconazole-free nanofibers were produced as controls. Functionalized nanofibers showed antifungal activity against Aspergillus flavus, A. carbonarius, A. niger, Aspergillus sp. A29, Fusarium oxysporum and Penicillium citrinum by agar diffusion test. Inhibitory zones ranging from 6 to 44mm were observed, this larger inhibition was against A. flavus. The nanofibers were incubated in different simulant solutions to evaluate the ketoconazole release, which was only detected in the solution containing 5% (v/v) Tween 20. Electron microscopy images showed the nanofibers with ketoconazole presented mean diameters of 526nm, and the degradation of the nanofiber structures could be observed by electron microscopy after incubation in simulant solution. Infrared and thermal analyses indicated that ketoconazole was dispersed without chemical interactions with the polycaprolactone matrix. These results suggest that polycaprolactone nanofibers incorporating ketoconazole may be an interesting alternative to control pathogenic fungi.

A structurally self-assembled peptide nano-architecture by one-step electrospinning

Peptide self-assembly during electrospinning while the solvent is evaporating and the fibres are forming.

Electrospun Scaffolds for Osteoblast Cells: Peptide-Induced Concentration-Dependent Improvements of Polycaprolactone

The design of hybrid poly-ε-caprolactone (PCL)-self-assembling peptides (SAPs) matrices represents a simple method for the surface functionalization of synthetic scaffolds, which is essential for cell compatibility. This study investigates the influence of increasing concentrations (2.5%, 5%, 10% and 15% w/w SAP compared to PCL) of three different SAPs on the physico-chemical/mechanical and biological properties of PCL fibers. We demonstrated that physico-chemical surface characteristics were slightly improved at increasing SAP concentrations: the fiber diameter increased; surface wettability increased with the first SAP addition (2.5%) and slightly less for the following ones; SAP-surface density increased but no change in the conformation was registered. These results could allow engineering matrices with structural characteristics and desired wettability according to the needs and the cell system used. The biological and mechanical characteristics of these scaffolds showed a particular trend at increasing SAP concentrations suggesting a prevailing correlation between cell behavior and mechanical features of the matrices. As compared with bare PCL, SAP enrichment increased the number of metabolic active h-osteoblast cells, fostered the expression of specific osteoblast-related mRNA transcripts, and guided calcium deposition, revealing the potential application of PCL-SAP scaffolds for the maintenance of osteoblast phenotype.

Decoration of PLGA electrospun nanofibers with designer self-assembling peptides: a “Nano-on-Nano” concept

A composite neural scaffold which combines the topographical features of electrospun nanofibrous scaffolds and bioactive as well as nanostructured features of designer self-assembling peptides (“Nano on Nano” approach).