Tissue engineering

Topological structure of electrospun membrane regulates immune response, angiogenesis and bone regeneration

The fate of biomaterials is orchestrated by biocompatibility and bioregulation characteristics, reported to be closely related to topographical structures. For the purpose to investigate the topography of fibrous membranes on the guided bone regeneration performance, we successfully fabricated poly (lactate-co-glycolate)/fish collagen/nano-hydroxyapatite (PFCH) fibrous membranes with random, aligned and latticed topography by electrospinning. The physical, chemical and biological properties of the three topographical PFCH membranes were systematically investigated by in vitro and in vivo experiments. The subcutaneous implantation of C57BL6 mice showed an acceptable mild foreign body reaction of all three topological membranes. Interestingly, the latticed PFCH membrane exhibited superior abilities to recruit macrophage/monocyte and induce angiogenesis. We further investigated the osteogenesis of the three topographical PFCH membranes via the critical-size calvarial bone defect model of rats and mice and the results suggested that latticed PFCH membrane manifested promising performance to promote angiogenesis through upregulation of the HIF-1α signaling pathway; thereby enhancing bone regeneration. Our research illustrated that the topological structure of fibrous membranes, as one of the characteristics of biomaterials, could regulate its biological functions, and the fibrous structure of latticed topography could serve as a favorable surface design of biomaterials for bone regeneration. STATEMENT OF SIGNIFICANCE: In material-mediated regeneration medicine, the interaction between the biomaterial and the host is key to successful tissue regeneration. The micro-and nano-structure becomes one of the most critical physical clues for designing biomaterials. In this study, we fabricated three topological electrospun membranes (Random, Aligned and Latticed) to understand how topological structural clues mediate bone tissue regeneration. Interestingly, we found that the Latticed topographical PFCH membrane promotes macrophage recruitment, angiogenesis, and osteogenesis in vivo, indicating the fibrous structure of latticed topography could serve as a favorable surface design of biomaterials for bone regeneration.

The Emerging Potential of Extracellular Vesicles in Cell-Free Tissue Engineering and Regenerative Medicine

Extracellular vesicles (Evs) are membrane-enclosed vesicles secreted by all cell types that mediate cell-cell communication via their protein, lipid, carbohydrate, and nucleic acid (RNA, DNA) cargo. EVs are involved in a multitude of physiological processes, including development, cell differentiation, and angiogenesis, and have been implicated in tissue repair. Thus, they have been suggested to offer opportunities for the development of novel cell-free tissue engineering (TE) approaches. In this review, we provide an overview of current understanding and emerging applications of EVs in TE and address opportunities and challenges for clinical translation. In addition, we discuss systemic and local routes of delivery of EVs and the advantages and disadvantages of different biomaterials in providing a substrate for the sustained release of EVs in vivo. Impact statement Extracellular vesicles (EVs) are nanoscale, membrane-bound vesicles released by most, if not all, cells in the body. They are implicated in a wide range of physiological processes and diseases ranging from cancer to neurodegeneration, and hold huge potential as mediators of tissue regeneration. This has led to an explosion of interest in using EVs in a variety of tissue engineering applications. In this review, we provide an overview of current progress in the field and highlight the opportunities and challenges of harnessing the potential of EVs in regenerative medicine.

Polycaprolactone nanofibrous mesh reduces foreign body reaction and induces adipose flap expansion in tissue engineering chamber

Tissue engineering chamber technique can be used to generate engineered adipose tissue, showing the potential for the reconstruction of soft tissue defects. However, the consequent foreign body reaction induced by the exogenous chamber implantation causes thick capsule formation on the surface of the adipose flap following capsule contracture, which may limit the internal tissue expansion. The nanotopographical property and architecture of nanofibrous scaffold may serve as a promising method for minimizing the foreign body reaction. Accordingly, electrospinning porous polycaprolactone (PCL) nanofibrous mesh, a biocompatible synthetic polymer, was attached to the internal surface of the chamber for the reducing local foreign body reaction. Adipose flap volume, level of inflammation, collagen quantification, capsule thickness, and adipose tissue-specific gene expression in chamber after implantation were evaluated at different time points. The in vivo study revealed that the engineered adipose flaps in the PCL group had a structure similar to that in the controls and normal adipose tissue structure but with a larger flap volume. Interleukin (IL)-1β, IL-6, and transforming growth factor-β expression decreased significantly in the PCL group compared with the control. Moreover, the control group had much more collagen deposition and thicker capsule than that observed in the PCL group. These results indicate that the unique nanotopographical effect of electrospinning PCL nanofiber can reduce foreign body reaction in a tissue engineering chamber, which maybe a promising new method for generating a larger volume of mature, vascularized, and stable adipose tissue.

Analysis of intellectual properties on animal-derived regenerative, implantable medical devices

This article analyses and summarizes issues of intellectual property involved in animal-derived regenerative, implantable medical devices (ADRIMD) in order to better understand global trends in patent applications and disclosures, the legal status of patent families (i.e. sets of patents filed in various countries to protect a single invention), and International Patent Classification topics such as main assignee and core expertise. Analysis of research trends will enhance and inform the decision-making capacity of researchers, investors, government regulators and other stake-holders as they undertake to develop, deploy, invest in or regulate ADRIMD.

A novel strategy for engineering vascularized grafts in vitro

Tissue engineering is an interdisciplinary field promising new therapeutic means for replacing lost or severely damaged tissues or organs. However, the fabrication of complex engineered tissues has been hampered due to the lack of vascularization to provide sufficient blood supply after implantation. In this article, we propose using rapid prototyping technology to prefabricate a scaffold with an inside hollowed vascular system including an arterial end, a venous end and capillary networks between them. The scaffold will be ''printed'' layer by layer. When printing every layer, a ''low-melting point'' material will be used to form a blood vessel network and a tissue-specific material will be used outside it. Hereafter the 'low-melting point' material will be evacuated by vaporization to ensure a hollowed vessel network. Then the inside hollowed capillary network can be endothelialized by using autologous endothelial cells in a cycling bioreactor while the outside material can be embedded with tissue-special cells. In the end, the new vascularized autologous grafts could be transferred to the defect site by using microsurgical techniques to connect the grafts with the host artery and vein. The strategy would facilitate construction of complex tissue engineering if the hypothesis proved to be practical.

Bioengineering strategies to generate vascularized soft tissue grafts with sustained shape

Tissue engineering offers the possibility for soft tissue reconstruction and augmentation without autologous grafting or conventional synthetic materials. Two critical challenges have been addressed in a number of recent studies: a biology challenge of angiogenesis and an engineering challenge of shape maintenance. These two challenges are inter-related and are effectively addressed by integrated bioengineering strategies. Recently, several integrated bioengineering strategies have been applied to improve bioengineered adipose tissue grafts, including internalized microchannels, delivery of angiogenic growth factors, tailored biomaterials and transplantation of precursor cells with continuing differentiation potential. Bioengineered soft tissue grafts are only clinically meaningful if they are vascularized, maintain shape and dimensions, and remodel with the host. Ongoing studies have begun to demonstrate the feasibility towards an ultimate goal to generate vascularized soft tissue grafts that maintain anatomically desirable shape and dimensions.

Host rather than graft origin of Matrigel-induced adipose tissue in the murine tissue-engineering chamber

We have recently shown that Matrigel-filled chambers containing fibroblast growth factor-2 (FGF2) and placed around an epigastric pedicle in the mouse were highly adipogenic. Contact of this construct with pre-existing tissue or a free adipose graft was required. To further investigate the mechanisms underpinning formation of new adipose tissue, we seeded these chambers with human adipose biopsies and human adipose-derived cell populations in severe combined immunodeficient mice and assessed the origin of the resultant adipose tissue after 6 weeks using species-specific probes. The tissues were negative for human-specific vimentin labeling, suggesting that the fat originates from the murine host rather than the human graft. This was supported by the strong presence of mouse-specific Cot-1 deoxyribonucleic acid labeling, and the absence of human Cot-1 labeling in the new fat. Even chambers seeded with FGF2/Matrigel containing cultured human stromal-vascular fraction (SVF) labeled strongly only for human vimentin in cells that did not have a mature adipocyte phenotype; the newly formed fat tissue was negative for human vimentin. These findings indicate that grafts placed in the chamber have an inductive function for neo-adipogenesis, rather than supplying adipocyte-precursor cells to generate the new fat tissue, and preliminary observations implicate the SVF in producing inductive factors. This surprising finding opens the door for refinement of current adipose tissue-engineering approaches.

Adipose tissue engineering from human adult stem cells: clinical implications in plastic and reconstructive surgery

BACKGROUND

Despite certain levels of clinical efficacy, current autografts and synthetic materials for soft-tissue reconstruction and/or augmentation suffer from donor-site morbidity, rupture, dislocation, and volume reduction. Human adult stem cells can self-replicate and differentiate into adipogenic cells in response to appropriate signaling cues. This study investigated the shape and dimension maintenance of engineered adipose tissue from adult human mesenchymal stem cells.

METHODS

Human mesenchymal stem cells were isolated from bone marrow of a healthy donor and differentiated into adipogenic cells. Adipocytes derived from these cells were encapsulated in a poly(ethylene glycol)-based hydrogel shaped into a generic cylinder (n = 6 implants), with hydrogel encapsulating human mesenchymal stem cells (n = 6) and cell-free hydrogel (n = 6) as controls. Porous collagen sponges were also used to seed human mesenchymal stem cell-derived adipocytes (n = 6), human mesenchymal stem cells (n = 4), or without cells (n = 4). All poly(ethylene glycol) and collagen constructs were implanted subcutaneously in athymic mice for 4 weeks.

RESULTS

In vivo grafts demonstrated the formation of substantial adipose tissue encapsulating human mesenchymal stem cell-derived adipogenic cells in either poly(ethylene glycol)-based hydrogel or collagen sponge and a lack of adipose tissue formation in cell-free or human mesenchymal stem cell-derived grafts. Engineered adipose tissue in poly(ethylene glycol)-based hydrogel maintained approximately 100 percent of the original dimensions after 4-week in vivo implantation, significantly higher than the approximately 35 to 65 percent volume retention by collagen sponge.

CONCLUSIONS

These findings demonstrate that the predefined shape and dimensions of adipose tissue engineered from human mesenchymal stem cells can be maintained after in vivo implantation. These data further indicate the potential for autologous applications in reconstructive and plastic surgery procedures.

Human preterm amnion cells cultured in 3-dimensional collagen I and fibrin matrices for tissue engineering purposes

OBJECTIVE

In this study, human preterm amnion cells were investigated in 3-dimensional (3D) cell-matrix culture systems in an attempt to design therapeutic strategies for preterm premature rupture of the membranes.

STUDY DESIGN

Three-dimensional collagen I and fibrin cell-containing biomatrices were created to mimic the architecture of native amnion. Amnion mesenchymal cells were embedded in 3D matrices, and epithelial cells were placed on top of these matrices. Cell viability and morphology were visualized by DiI-ac-LDL, F-actin, and nuclear staining. Proteolytic activity of matrix metalloproteinases (MMPs) was investigated using gelatine zymography.

RESULTS

Preterm amnion epithelial and mesenchymal cells cultured in collagen I and fibrin matrices assume cell morphologies similar to those observed in vivo. Mesenchymal cells were capable of remodelling collagen I, as seen by extensive volume contraction, by 40% at day 1 and 80% at day 5. Matrix contraction was independent of the presence of epithelial cells, and could not be inhibited by GM6001 and/or aprotinin. No contraction was observed in fibrin matrices over 8 days. The migratory response of mesenchymal cells cultured in 3D fibrin matrices supplemented with fibronectin was associated with specific activated MMP-9.

CONCLUSION

Three-dimensional fibrin matrices might be useful in amnion cell tissue engineering, including cell-matrix transplantation.

Regulatory and microbiological safety issues surrounding cell and tissue-engineering products

Cell therapies and tissue‐engineered products that contain living cells are potentially some of the most exciting of the novel therapeutic products currently under development. These products, however, present a number of important safety issues, particularly with respect to the transmission of human viruses. In addition, the short shelf life of these products precludes the normally extensive characterization performed on other biotherapeutic products. Careful examination of the risks and extensive testing of the raw materials have been used in place of product testing to ensure safety.

Tissue-engineering approaches for axonal guidance

Owing to the profound impact of nervous system damage, extensive studies have been carried out aimed at facilitating axonal regeneration following injury. Tissue engineering, as an emerging and rapidly growing field, has received extensive attention for nervous system axonal guidance. Numerous engineered substrates containing oriented extracellular matrix molecules, cells or channels have displayed potential of supporting axonal regeneration and functional recovery. Most attempts are focused on seeking new biomaterials, new cell sources, as well as novel designs of tissue-engineered neuronal bridging devices, to generate safer and more efficacious neuronal tissue repairs.

Surgical reconstruction in patients with cancer of the head and neck

Reconstructive surgical techniques have greatly changed the treatment approach for patients with cancer of the head and neck. These techniques provide head and neck surgeons the flexibility of performing tumor resection without concerns about the repair of the final defect and significantly increase the quality of life in patients who have undergone ablative surgery by providing better cosmetic and functional outcome after cancer resection. Reconstruction of the defects after ablative surgery for head and neck cancer includes various options, and each option has its own advantages and disadvantages. Techniques for head and neck reconstruction are summarized in this article along with recent advances in their application.

Periosteal cells in bone tissue engineering

In 1742, H.L. Duhamel published a report in which the osteogenic function of periosteum was described. In 1932 H.B. Fell was the first to successfully culture periosteum; Fell concluded that this tissue might have the capability to form mineralized tissue in vitro. In the 1990s the research group of A.L. Caplan pioneered work exploring the osteogenic potential of periosteal cells in the field of bone engineering. On the basis of these studies a number of research groups have developed hard tissue generation concepts that aim to repeat the clinical success of bone autografts by culturing cells from periosteum and seeding a sufficient quantity of those cells into scaffolds made of biomaterials of natural and synthetic origin. The highly porous matrices support the induction of bone regeneration by creating and maintaining a space that facilitates progenitor cell migration, proliferation, and differentiation as well as graft revascularization. In this way, a host tissue-scaffold cell interphase might be created that allows reproduction of the intrinsic properties of autogenous bone, including the ability to be incorporated into the surrounding host bone and to continue normal bone-remodeling processes. This review discusses the history and state of the art of bone tissue engineering from a periosteum and periosteal cell source point of view and attempts to indicate future research directions.