Desirable features of exosomes have made them a suitable manipulative platform for biomedical applications, including targeted drug delivery, gene therapy, cancer diagnosis and therapy, development of vaccines, and tissue regeneration. Although natural exosomes have various potentials, their clinical application is associated with some inherent limitations. Recently, these limitations inspired various attempts to engineer exosomes and develop designer exosomes. Mostly, designer exosomes are being developed to overcome the natural limitations of exosomes for targeted delivery of drugs and functional molecules to wounds, neurons, and the cardiovascular system for healing of damage. In this review, we summarize the possible improvements of natural exosomes by means of two main approaches: parental cell-based or pre-isolation exosome engineering and direct or post-isolation exosome engineering. Parental cell-based engineering methods use genetic engineering for loading of therapeutic molecules into the lumen or displaying them on the surface of exosomes. On the other hand, the post-isolation exosome engineering approach uses several chemical and mechanical methods including click chemistry, cloaking, bio-conjugation, sonication, extrusion, and electroporation. This review focuses on the latest research, mostly aimed at the development of designer exosomes using parental cell-based engineering and their application in cancer treatment and regenerative medicine. Graphic Abstract

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Embryonic stem (ES) cell pluripotency is being investigated increasingly to obtain specific cell lineages for tissue engineering. However, the possibility that ES cells can give rise to lung tissue has not been tested. We hypothesized that lung epithelial cells (type II pneumocytes) can be derived in vitro from murine ES cells. After withdrawal of leukemia inhibitory factor (LIF) and formation of embryoid bodies in maintenance medium for 10, 20, and 30 days, differentiating ES cells were kept in the same medium or transferred to serum-free small airway growth medium (SAGM) for a further 3 or 14 days of culture. The presence of type II pneumocytes in the resulting mixed cultures was demonstrated by reverse transcriptase-polymerase chain reaction (RT-PCR) of surfactant protein C (SPC) mRNA, immunostaining of SPC, and electron microscopy of osmiophilic lamellar bodies only at 30 days sampling time. SAGM appeared to be more favorable for type II cell formation than ES medium. No SPC transcripts were found in differentiating cells grown under the same conditions without formation of embryoid bodies. These findings could form the basis for the enrichment of ES cell-derived cultures with type II pneumocytes, and provide an in vitro system for investigating mechanisms of lung repair and regeneration.

Burn injuries have been reported to be an important cause of morbidity and mortality and they are still considered as unmet clinical need. Although there is a myriad of effective stem cells that have been suggested for skin regeneration, there is no one ideal scaffold. The aim of this study was to develop a three-dimensional (3D) bi-layer scaffold made of biological decellularized human amniotic membrane (AM) with viscoelastic electrospun nanofibrous silk fibroin (ESF) spun on top. The fabricated 3D bi-layer AM/ESF scaffold was submerged in ethanol to induce β-sheet transformation as well as to get a tightly coated and inseparable bi-layer. The biomechanical and biological properties of the 3D bi-layer AM/ESF scaffold were investigated. The results indicate significantly improved mechanical properties of the AM/ESF compared with the AM alone. Both the AM and AM/ESF possess a variety of suitable adhesion cells without detectable cytotoxicity against adipose tissue-derived mesenchymal stem cells (AT-MSCs). The AT-MSCs show increased expression of two main pro-angiogenesis factors, vascular endothelial growth factor and basic fibroblast growth factor, when cultured on the AM/ESF for 7 days, when comparing with AM alone. The results suggest that the AM/ESF scaffold with autologous AT-MSCs has excellent cell adhesion and proliferation along with production of growth factors which serves as a possible application in a clinical setting for skin regeneration.

The aim of this study is to develop a simple and cost-effective method for decellularization and preservation of human amniotic membrane (HAM) as a soft tissue replacement and a delivery system for stem cells. The HAM is decellularized (D) using new chemical and mechanical techniques. The decellularization scaffold is evaluated histologically and fully characterized. The cell adhesion and proliferation on the scaffold are also investigated and the biocompatibility of D tissues is evaluated in vivo. The histological studies reveal that the cells are successfully removed from the D tissue. The DNA extraction shows more than 95% cell removal (p = 0.001). The in vitro results indicate that the decellularisation process does not deteriorate the mechanical properties of the tissue, whereas it increases the in vitro biodegradation value (p < 0.05). In the D samples, there is no significant cytotoxicity, and no changes are found in the rate of cell proliferation (p > 0.05). Immunohistochemistry staining indicates that all the tested components remain unchanged within the D tissues. The count of inflammatory cells show that the decellularization process slightly increases the biocompatibility of the tissue after 7 days post-surgery. The results indicate that scaffold proves to be reproducible, rapid, and cost-effective, with a potential role for clinical application.