Silk fibroin as a functional biomaterial for drug and gene delivery

Silk is a natural polymer with unique physicochemical and mechanical properties which makes it a desirable biomaterial for biomedical and pharmaceutical applications. Silk fibroin (SF) has been widely used for preparation of drug delivery systems due to its biocompatibility, controllable degradability and tunable drug release properties. SF-based drug delivery systems can encapsulate and stabilize various small molecule drugs as well as large biological drugs such as proteins and DNA to enhance their shelf lives and control the release to enhance their circulation time in the blood and thus the duration of action. Understanding the properties of SF and the potential ways of manipulating its structure to modify its physicochemical and mechanical properties allows for preparation of modulated drug delivery systems with desirable efficacies. This review will discuss the properties of SF material and summarize the recent advances of SF-based drug and gene delivery systems. Furthermore, conjugation of the SF to other biomolecules or polymers for tissue-specific drug delivery will also be discussed

Silk fibroin as a functional biomaterial for tissue engineering

Tissue engineering (TE) is the approach to combine cells with scaffold materials and appropriate growth factors to regenerate or replace damaged or degenerated tissue or organs. The scaffold material as a template for tissue formation plays the most important role in TE. Among scaffold materials, silk fibroin (SF), a natural protein with outstanding mechanical properties, biodegradability, biocompatibility, and bioresorbability has attracted significant attention for TE applications. SF is commonly dissolved into an aqueous solution and can be easily reconstructed into different material formats, including films, mats, hydrogels, and sponges via various fabrication techniques. These include spin coating, electrospinning, freeze drying, physical, and chemical crosslinking techniques. Furthermore, to facilitate fabrication of more complex SF-based scaffolds with high precision techniques including micro-patterning and bio-printing have recently been explored. This review introduces the physicochemical and mechanical properties of SF and looks into a range of SF-based scaffolds that have been recently developed. The typical TE applications of SF-based scaffolds including bone, cartilage, ligament, tendon, skin, wound healing, and tympanic membrane, will be highlighted and discussed, followed by future prospects and challenges needing to be addressed

Designed antitumor peptide for targeted siRNA delivery into cancer spheroids

Antimicrobial/anticancer peptides (AMPs/ACPs) have shown promising results as new therapeutic agents in cancer therapy. Among them, the designed amphiphilic α-helical peptide G(IIKK)3I-NH2 (G3) displayed great affinity and specificity in targeting cancer cells. Here, we report new insights on how G3 penetrates cancer cells. G3 showed high specificity to HCT-116 colon cancer cells compared to the HDFs (human neonatal primary dermal fibroblasts) control. With high concentrations of peptide, a clear cancer cell membrane disruption was observed through SEM. Gene knockdown of the endocytic pathways demonstrated that an energy-dependent endocytic pathway is required for the uptake of the peptide. In addition, G3 can protect and selectively deliver siRNAs into cancer cells and successfully modulated their gene expression. Gene delivery was also tested in 3D cancer spheroids and showed deep penetration delivery into the cancer spheroids. Finally, the in vivo toxicity of G3 was evaluated on zebrafish embryos, showing an increasing toxicity effect with concentration. However, the toxicity of the peptide was attenuated when complexed with siRNA. In addition, negligible toxicity was observed at the concentration range for efficient gene delivery. The current results demonstrate that G3 is promising as an excellent agent for cancer therapy

Patterning the neuronal cells via inkjet printing of self-assembled peptides on silk scaffolds

The patterning of neuronal cells and guiding neurite growth are important for neuron tissue engineering and cell-based biosensors. In this paper, inkjet printing has been employed to pattern self-assembled I3QGK peptide nanofibers on silk substrates for guiding the growth of neuron-like PC12 cells. Atomic force microscopy (AFM) confirmed the dynamic self-assembly of I3QGK into nanofiber structures. The printed self-assembled peptide strongly adheres to regenerated silk fibroin (RSF) substrates through charge-charge interactions. It was observed that in the absence of I3QGK, PC12 cells exhibited poor attachment to RSF films, while for RSF surfaces coated or printed with peptide nanofibers, cellular attachment was significantly improved in terms of both cell density and morphology. AFM results revealed that peptide nanofibers can promote the generation of axons and terminal buttons of PC12 cells, indicating that I3QGK nanofibers not only promote cellular attachment but also facilitate differentiation into neuronal phenotypes. Inkjet printing allows complex patterning of peptide nanofibers onto RSF substrates, which enabled us to engineer cell alignment and provide an opportunity to direct axonal development in vitro. The live/dead assay showed that printed I3QGK patterns exhibit no cytotoxicity to PC12 cells demonstrating potential for future nerve tissue engineering applications

Cell guidance on peptide micropatterned silk fibroin scaffolds

Guiding neuronal cell growth is desirable for neural tissue engineering but is very challenging. In this work, a self-assembling ultra-short surfactant-like peptide I3K which possesses positively charged lysine head groups, and hydrophobic isoleucine tails, was chosen to investigate its potential for guiding neuronal cell growth. The peptides were able to self-assemble into nanofibrous structures and interact strongly with silk fibroin (SF) scaffolds, providing a niche for neural cell attachment and proliferation. SF is an excellent biomaterial for tissue engineering. However neuronal cells, such as rat PC12 cells, showed poor attachment on pure regenerated SF (RSF) scaffold surfaces. Patterning of I3K peptide nanofibers on RSF surfaces significantly improved cellular attachment, cellular density, as well as morphology of PC12 cells. The live / dead assay confirmed that RSF and I3K have negligible cytotoxicity against PC12 cells. Atomic force microscopy (AFM) was used to image the topography and neurite formation of PC12 cells, where results revealed that self-assembled I3K nanofibers can support the formation of PC12 cell neurites. Immunolabelling also demonstrated that coating of I3K nanofibers onto the RSF surfaces not only increased the percentage of cells bearing neurites but also increased the average maximum neurite length. Therefore, the peptide I3K could be used as an alternative to poly-l-lysine for cell culture and tissue engineering applications. As micro-patterning of neural cells to guide neurite growth is important for developing nerve tissue engineering scaffolds, inkjet printing was used to pattern self-assembled I3K peptide nanofibers on RSF surfaces for directional control of PC12 cell growth. The results demonstrated that inkjet-printed peptide micro-patterns can effectively guide the cell alignment and organization on RSF scaffold surfaces, providing great potential for nerve regeneration applications

Recent advances in microfluidics for the preparation of drug and gene delivery systems

Drug delivery systems (DDSs) have great potential for improving the treatment of several diseases, especially microbial infections and cancers. However, the formulation procedures of DDSs remain challenging, especially at the nanoscale. Reducing batch-to-batch variation and enhancing production rate are some of the essential requirements for accelerating the translation of DDSs from a small scale to an industrial level. Microfluidic technologies have emerged as an alternative to the conventional bench methods to address these issues. By providing precise control over the fluid flows and rapid mixing, microfluidic systems can be used to fabricate and engineer different types of DDSs with specific properties for efficient delivery of a wide range of drugs and genetic materials. This review discusses the principles of controlled rapid mixing that have been employed in different microfluidic strategies for producing DDSs. Moreover, the impact of the microfluidic device design and parameters on the type and properties of DDS formulations was assessed, and recent applications in drug and gene delivery were also considered

Peptide-functionalised magnetic silk nanoparticles produced by a swirl mixer for enhanced anticancer activity of ASC-J9

Silk fibroin is an FDA approved biopolymer for clinical applications with great potential in nanomedicine. However, silk-based nanoformulations are still facing several challenges in processing and drug delivery efficiency (such as reproducibility and targetability), especially in cancer therapy. To address these challenges, robust and controllable production methods are required for generating nanocarriers with desired properties. This study aimed to develop a novel method for the production of peptide-functionalized magnetic silk nanoparticles with higher selectivity for cancer cells for targeted delivery of the hydrophobic anticancer agent ASC-J9. A new microfluidic device with a swirl mixer was designed to fabricate magnetic silk nanoparticles (MSNP) with desired size and narrow size distribution. The surface of MSNPs was functionalized with a cationic amphiphilic anticancer peptide, G(IIKK)3I-NH2 (G3), to enhance their selectivity towards cancer cells. The G3-MSNPs increased the cellular uptake and anticancer activity of G3 in HCT 116 colorectal cancer cells compared to free G3. Moreover, the G3-MSNPs exhibited considerably higher cellular uptake and cytotoxicity in HCT 116 colorectal cancer cells compared to normal cells (HDFs). Encapsulating ASC-J9 in G3-MSNPs resulted in augmented anticancer activity compared to free ASC-J9 and non-functionalized ASC-J9 loaded MSNPs within its biological half-life. Hence, functionalizing MSNPs with G3 enabled targeted delivery of ASC-J9 to cancer cells and enhanced its anticancer effect. Functionalization of nanoparticles with anticancer peptides could be regarded as a new strategy for targeted delivery and enhanced efficiency of anticancer drugs. Furthermore, the microfluidic device introduced in this paper offers a robust and reproducible method for fabrication of small sized homogenous nanoparticles

Correlation between the secondary structure and surface activity of β-sheet forming cationic amphiphilic peptides and their anticancer activity

Cancer is one of the main causes of death worldwide. The current cancer treatment strategies often lack selectivity for cancer cells resulting in dose-limiting adverse effects and reduced quality of life. Recently, anticancer peptides (ACPs) have emerged as an alternative treatment with higher selectivity, less adverse effects, and lower propensity for drug resistance. However, most of the current studies on the ACPs are focused on α-helical ACPs and there is lack of systematic studies on β-sheet forming ACPs. Herein we report the development of a new series of rationally designed short cationic amphiphilic β-sheet forming ACPs and their structure activity relationship. The peptides had the general formula (XY1XY2)3, with X representing hydrophobic amino acids (isoleucine (I) or leucine (L)), Y1 and Y2 representing cationic amino acids (arginine (R) or lysine (K)). The cytotoxicity of the designed ACPs in HCT 116 colorectal cancer, HeLa cervical cancer and human dermal fibroblast (HDF) cells was assessed by MTT test. The physicochemical properties of the peptides were characterized by various techniques including RP-HPLC, LC-MS, and Circular Dichroism (CD) spectroscopy. The surface activity of the peptides at the air-water interface and their interaction with the lipid monolayers as models for cell membranes were studied by Langmuir trough. The peptides consisting of I with R and K had selective anticancer activity while the combination of L and R diminished the anticancer activity of the peptides but rendered them more toxic to HDFs. The anticancer activity of the peptides was directed by their surface activity (amphiphilicity) and their secondary structure in hydrophobic surfaces including cancer cell membranes. The selectivity of the peptides for cancer cells was a result of their higher penetration into cancer cell membranes compared to normal cell membranes. The peptides exerted their anticancer activity by disrupting the mitochondrial membranes and eventually apoptosis. The results presented in this study provide an insight into the structure-activity relationship of this class of ACPs which can be employed as guidance to design new ACPs with improved anticancer activity and lower toxicity against normal cells