An Effective Method ofAtelocollagenType 1/3 Isolation from Human Placenta and ItsIn VitroCharacterization in Two-Dimensional and Three-Dimensional Cell Culture Applications

Extraction and Characterization of Human Adipose Tissue-Derived Collagen: Toward Xeno-Free Tissue Engineering

BACKGROUND

Collagen is a key component of connective tissue and has been frequently used in the fabrication of medical devices for tissue regeneration. Human-originated collagen is particularly appealing due to its low immune response as an allograft biomaterial compared to xenografts and its ability to accelerate the regeneration process. Ethically and economically, adipose tissues available from liposuction clinics are a good resource to obtain human collagen. However, studies are still scarce on the extraction and characterization of human collagen, which originates from adipose tissue. The aim of this study is to establish a novel and simple method to extract collagen from human adipose tissue, characterize the collagen, and compare it with commercial-grade porcine collagen for tissue engineering applications.

METHODS

We developed a method to extract the collagen from human adipose tissue under quasi-Good Manufacturing Practice (GMP) conditions, including freezing the tissue, blood removal, and ethanol-based purification. Various techniques, including protein quantification, decellularization assessment, SDS-PAGE, FTIR, and CD spectroscopy analysis, were used for characterization. Amino acid composition was compared with commercial collagen. Biocompatibility and cell proliferation tests were performed, and in vitro tests using collagen sponge scaffolds were conducted with statistical analysis.

RESULTS

Our results showed that this human adipose-derived collagen was equivalent in quality to commercially available porcine collagen. In vitro testing demonstrated high cell attachment and the promotion of cell proliferation.

CONCLUSION

In conclusion, we developed a simple and novel method to extract and characterize collagen and extracellular matrix from human adipose tissue, offering a potential alternative to animal-derived collagen for xeno-free tissue engineering applications.

Designing highly customizable human based platforms for cell culture using proteins from the amniotic membrane

In the past few years researchers have witnessed a paradigm shift in the development of biomaterials for drug discovery, tissue engineering, and regenerative medicine. After the great advances resulting from the transition of the 2D to the 3D, the new focus has been to increase the clinical relevance of such systems, as well as avoid the use of animals, by developing platforms that better replicate the human physiology in vitro. In this sense, we envisage the use of human matrices extracted from ethically sourced and readily available tissues as an optimal and promising alternative to currently used approaches. Hereupon, we report for the first time the chemical modification of human ECM proteins from the amniotic membrane (AM) with photoresponsive groups to produce bioinks and hydrogel precursors to engineer customizable platforms that are representative of native tissues and capable of supporting long-term cell culture. Our results demonstrated an efficient decellularization, liquefaction and functionalization of AM-derived ECM with methacryloyl domains (AMMA), with production of stable and versatile hydrogels. Mechanical characterization evidenced an increased compression strength as a function of methacrylation degree and decellularized ECM concentration. Three-dimensional (3D) stem cell culture in the AMMA hydrogels resulted in viable and proliferative cells up to 7 days; moreover, the mouldable character of the hydrogel precursors permits the processing of patterned hydrogel constructs allowing the control over cellular alignment and elongation, or microgels with highly tunable shape.

Frequently used strategies to isolate ECM proteins from human placenta and adipose tissue

BACKGROUND

The natural extracellular matrix (ECM) provides the optimal environment for cells. Many enzymatic or non-enzymatic based strategies to extract ECM proteins from tissues were published over the last years. However, every single isolation strategy reported so far is associated with specific bottlenecks. Experiment: In this study, frequently used strategies to isolate extracellular matrix (ECM) from human placenta or adipose tissue using Tris-, serum, or pepsin-based buffers were compared. The resulting ECM proteins were biochemically characterized by analysis of cellular remnants using HOECHST DNA staining, glycosaminoglycan (GAG) content by dimethylemethylene blue (DMMB), visualization of protein bands using SDS PAGE analysis combined with amino acid quantification and assessment of the pro-angiogenic profile using an angiogenesis array.

RESULTS

Tris-NaCl extracted ECM proteins showed a high heterogenic degree of extracted proteins, bioactive growth factors and GAGS, but no collagen-I. Active serum extracted ECM showed significant lower DNA remnants when compared to the Tris-NaCl isolation strategy. Pepsin-extracted ECM was rich in collagen-I and low amounts of remaining bioactive growth factors. This strategy was most effective to reduce DNA amounts when compared to the other isolation strategies. Pepsin-extracted ECM from both tissues easily gelled at 37°C, whereas the other extracted ECM strategies did not gel at 37°C (Tris-NaCl: liquid; serum: sponge).

CONCLUSIONS

All relevant characteristics (DNA residues, ECM diversity and bioactivity, shape) of the extracted ECM proteins highly depend on its isolation strategy and could still be optimized.

Novel Human Placenta-Based Extract for Vascularization Strategies in Tissue Engineering

There is critical unmet need for new vascularized tissues to support or replace injured tissues and organs. Various synthetic and natural materials were already established for use of two-dimensional (2D) and three-dimensional (3D) in vitro neovascularization assays, however, they still cannot mimic the complex functions of the sum of the extracellular matrix (ECM) in native intact tissue. Currently, this issue is only addressed by artificial products such as Matrigel^™, which comprises a complex mixture of ECM proteins, extracted from animal tumor tissue. Despite its outstanding bioactivity, the isolation from tumor tissue hinders its translation into clinical applications. Since nonhuman ECM proteins may cause immune reactions, as are frequently observed in clinical trials, human ECM proteins represent the best option when aiming for clinical applications. Here, we describe an effective method of isolating a human placenta substrate (hpS) that induces the spontaneous formation of an interconnected network of green fluorescence-labeled human umbilical vein endothelial cells (gfpHUVECs) in vitro. The substrate was biochemically characterized by using a combination of bicinchoninic acid (BCA) assay, DNA, and glycosaminoglycan (GAG) content assays, sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) analysis and Western blot, angiogenesis arrays, chromatographic thrombin detection, high performance liquid chromatography (HPLC)-based amino acid quantification analysis, and assessment of antimicrobial properties. 2D in vitro cell culture experiments have been performed to determine the vasculogenic potential of hpS, which demonstrated that cell networks developed on hpS show a significantly higher degree of complexity (number of tubules/junctions; total/mean tube length) when compared with Matrigel. As 3D cell culture techniques represent a more accurate representation of the in vivo condition, the substrate was 3D solidified using various natural polymers. 3D in vitro vasculogenesis assays have been performed by seeding gfpHUVECs in an hpS-fibrinogen clot. In conclusion, hpS provides a potent human/material-based alternative to xenogenic-material-based biomaterials for vascularization strategies in tissue engineering.

Development of photo-crosslinkable collagen hydrogel building blocks for vascular tissue engineering applications: A superior alternative to methacrylated gelatin?

The present work targets the development of collagen-based hydrogel precursors, functionalized with photo-crosslinkable methacrylamide moieties (COL-MA), for vascular tissue engineering (vTE) applications. The developed materials were physico-chemically characterized in terms of crosslinking kinetics, degree of modification/conversion, swelling behavior, mechanical properties and in vitro cytocompatibility. The collagen derivatives were benchmarked to methacrylamide-modified gelatin (GEL-MA), due to its proven track record in the field of tissue engineering. To the best of our knowledge, this is the first paper in its kind comparing these two methacrylated biopolymers for vTE applications. For both gelatin and collagen, two derivatives with varying degrees of substitutions (DS) were developed by altering the added amount of methacrylic anhydride (MeAnH). This led to photo-crosslinkable derivatives with a DS of 74 and 96% for collagen, and a DS of 73 and 99% for gelatin. The developed derivatives showed high gel fractions (i.e. 74% and 84%, for the gelatin derivatives; 87 and 83%, for the collagen derivatives) and an excellent crosslinking efficiency. Furthermore, the results indicated that the functionalization of collagen led to hydrogels with tunable mechanical properties (i.e. storage moduli of [4.8-9.4 kPa] for the developed COL-MAs versus [3.9-8.4 kPa] for the developed GEL-MAs) along with superior cell-biomaterial interactions when compared to GEL-MA. Moreover, the developed photo-crosslinkable collagens showed superior mechanical properties compared to extracted native collagen. Therefore, the developed photo-crosslinkable collagens demonstrate great potential as biomaterials for vTE applications.

Collagen-based scaffolds: An auspicious tool to support repair, recovery, and regeneration post spinal cord injury

Spinal cord injury (SCI) is a perplexing traumatic disease that habitually gives ride to permanent disability, motor, and sensory impairment. Despite the existence of several therapeutic approaches for the injured motor or sensory neurons, they can't promote axonal regeneration. Whether prepared by conventional or rapid prototyping techniques, scaffolds can be applied to refurbish the continuity of the injured site, by creating a suitable environment for tissue repair, axonal regeneration, and vascularization. Collagen is a multi-sourced protein, found in animals skin, tendons, cartilage, bones, and human placenta, in addition to marine biomass. Collagen is highly abundant in the extracellular matrix and is known for its biocompatibility, biodegradability, porous structure, good permeability, low immunogenicity and thus is extensively applied in the pharmaceutical, cosmetic, and food industries as well as the tissue engineering field. Collagen in scaffolds is usually functionalized with different ligands and factors such as, stem cells, embryonic or human cells to augment its binding specificity and activity. The review summarizes the significance of collagen-based scaffolds and their influence on regeneration, repair and recovery of spinal cord injuries.

Protocols for accelerated production and purification of collagen scaffold and atelocollagen from animal tissues

Traditional purification of atelocollagen involves a harsh extraction process with environment-polluting chemicals and costly and/or time-consuming procedures which include salting-out, alkali, acid and enzymatic treatment and ion-exchange chromatography. The atelocollagen market is growing exponentially, with demand in the skincare industry and for various medical applications. As a result, there is an urgent need for an eco-friendly production process with minimal manipulation. We developed a novel technique involving supercritical carbon dioxide extraction technology to remove the cells and noncollagenous substances from the porcine hide. Subsequent processes allow the production of several products, including decellularized dermal membrane, high-purity collagen particles and atelocollagen. The advantages of our process are its faster speed and lower environmental impact and its generation of multiple products, including high purity atelocollagen with complete removal of telopeptides.

Purinergic P2Y2 receptors modulate endothelial sprouting

Purinergic P2 receptors are critical regulators of several functions within the vascular system, including platelet aggregation, vascular inflammation, and vascular tone. However, a role for ATP release and P2Y receptor signalling in angiogenesis remains poorly defined. Here, we demonstrate that blood vessel growth is controlled by P2Y2 receptors. Endothelial sprouting and vascular tube formation were significantly dependent on P2Y2 expression and inhibition of P2Y2 using a selective antagonist blocked microvascular network generation. Mechanistically, overexpression of P2Y2 in endothelial cells induced the expression of the proangiogenic molecules CXCR4, CD34, and angiopoietin-2, while expression of VEGFR-2 was decreased. Interestingly, elevated P2Y2 expression caused constitutive phosphorylation of ERK1/2 and VEGFR-2. However, stimulation of cells with the P2Y2 agonist UTP did not influence sprouting unless P2Y2 was constitutively expressed. Finally, inhibition of VEGFR-2 impaired spontaneous vascular network formation induced by P2Y2 overexpression. Our data suggest that P2Y2 receptors have an essential function in angiogenesis, and that P2Y2 receptors present a therapeutic target to regulate blood vessel growth.

Microfibrous scaffolds from poly(l-lactide-co-ε-caprolactone) blended with xeno-free collagen/hyaluronic acid for improvement of vascularization in tissue engineering applications

Success of 3D tissue substitutes in clinical applications depends on the presence of vascular networks in their structure. Accordingly, research in tissue engineering is focused on the stimulation of angiogenesis or generation of a vascular network in the scaffolds prior to implantation. A novel, xeno-free, collagen/hyaluronic acid-based poly(l-lactide-co-ε-caprolactone) (PLC/COL/HA) (20/9.5/0.5 w/w/w) microfibrous scaffold was produced by electrospinning. Collagen types I and III, and hyaluronic acid were isolated from human umbilical cords and blended with the GMP grade PLC. When compared with PLC scaffolds the PLC/COL/HA had higher water uptake capacity (103% vs 66%) which may have contributed to the decrease in its Young's Modulus (from 1.31 to 0.89 MPa). The PLC/COL/HA better supported adipose tissue-derived mesenchymal stem cell (AT MSC) adhesion; within 24 h the cell number on the PLC/COL/HA scaffolds was 3 fold higher. Co-culture of human umbilical vein endothelial cells and AT MSCs induced capillary formation on both scaffold types, but the PLC/COL/HA led to formation of interconnected vessels whose total length was 1.6 fold of the total vessel length on PLC. Clinical use of this scaffold would eliminate the immune response triggered by xenogeneic collagen and transmission of animal-borne diseases while promoting a better vascular network formation.

Human Placenta Laminin-111 as a Multifunctional Protein for Tissue Engineering and Regenerative Medicine

Laminins are major components of all basement membranes surrounding nerve or vascular tissues. In particular laminin-111, the prototype of the family, facilitates a large spectrum of fundamental cellular responses in all eukaryotic cells. Laminin-111 is a biomaterial frequently used in research, however it is primarily isolated from non-human origin or produced with time-intensive recombinant techniques at low yield.Here, we describe an effective method for isolating laminin-111 from human placenta, a clinical waste material, for various tissue engineering applications. By extraction with Tris-NaCl buffer combined with non-protein-denaturation ammonium sulfate precipitation and rapid tangential flow filtration steps, we could effectively isolate native laminin-111 within only 4 days. The resulting material was biochemically characterized using a combination of dot blot, SDS-PAGE, Western blot and HPLC-based amino acid analysis. Cytocompatibility studies demonstrated that the isolated laminin-111 promotes rapid and efficient adhesion of primary Schwann cells. In addition, the bioactivity of the isolated laminin-111 was demonstrated by (a) using the material as a substrate for outgrowth of NG 108-15 neuronal cell lines and (b) promoting the formation of interconnected vascular networks by GFP-expressing human umbilical vein endothelial cells.In summary, the isolation procedure of laminin-111 as described here from human placenta tissue, fulfills many demands for various tissue engineering and regenerative medicine approaches and therefore may represent a human alternative to various classically used xenogenic standard materials.