Modification of layered atelocollagen: enzymatic degradation and cytotoxicity evaluation

Mesenchymal stem cell-based nanoparticles and scaffolds in regenerative medicine

Mesenchymal stem cells (MSCs) are adult stem cells owing to their regenerative potential and multilineage potency. MSCs have wide-scale applications either in their native cellular form or in conjugation with specific biomaterials as nanocomposites. Majorly, these natural or synthetic biomaterials are being used in the form of metallic and non-metallic nanoparticles (NPs) to encapsulate MSCs within hydrogels like alginate or chitosan or drug cargo loading into MSCs. In contrast, nanofibers of polymer scaffolds such as polycaprolactone (PCL), poly-lactic-co-glycolic acid (PLGA), poly-L-lactic acid (PLLA), silk fibroin, collagen, chitosan, alginate, hyaluronic acid (HA), and cellulose are used to support or grow MSCs directly on it. These MSCs based nanotherapies have application in multiple domains of biomedicine including wound healing, bone and cartilage engineering, cardiac disorders, and neurological disorders. This study focused on current approaches of MSCs-based therapies and has been divided into two major sections. The first section elaborates on MSC-based nano-therapies and their plausible applications including exosome engineering and NPs encapsulation. The following section focuses on the various MSC-based scaffold approaches in tissue engineering. Conclusively, this review mainly focused on MSC-based nanocomposite's current approaches and compared their advantages and limitations for building effective regenerative medicines.

Evaluation of 1-Ethyl-3-(3-Dimethylaminopropyl) Carbodiimide Cross-Linked Collagen Membranes for Guided Bone Regeneration in Beagle Dogs

The purpose of this study was to evaluate the bone regeneration efficacy of an 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-cross-linked collagen membrane for guided bone regeneration (GBR). A non-cross-linked collagen membrane (Control group), and an EDC-cross-linked collagen membrane (Test group) were used in this study. In vitro, mechanical, and degradation testing and cell studies were performed. In the animal study, 36 artificial bone defects were formed in the mandibles of six beagles. Implants were inserted at the time of bone grafting, and membranes were assigned randomly. Eight weeks later, animals were sacrificed, micro-computed tomography was performed, and hematoxylin-eosin stained specimens were prepared. Physical properties (tensile strength and enzymatic degradation rate) were better in the Test group than in the Control group. No inflammation or membrane collapse was observed in either group, and bone volumes (%) in defects around implants were similar in the two groups (p > 0.05). The results of new bone areas (%) analysis also showed similar values in the two groups (p > 0.05). Therefore, it can be concluded that cross-linking the collagen membranes with EDC is the method of enhancing the physical properties (tensile strength and enzymatic degradation) of the collagen membranes without risk of toxicity.

The effect of different cross-linking conditions of EDC/NHS on type II collagen scaffolds: an in vitro evaluation

The purpose of this paper is to analyze the properties of porcine cartilage type II collagen scaffolds crosslinked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxy-succinamide (EDC/NHS) under different conditions. The porous EDC/NHS-crosslinked scaffolds were obtained through a two-step freeze-drying process. To determine the optimal crosslinking condition, we used different solvents and various crosslinking temperatures to prepare the scaffolds. Three crosslinking solutions were prepared with different solvents, photographs were taken with a flash in the darkroom, and light transmission was observed. Type II collagen was crosslinked on a horizontal shaker at a speed of 60 r/min according to the above grouping conditions, and then the structural change of the scaffold in each group was observed. To investigate the swelling ratio and the in vitro degradation of the collagen scaffold, tests were also carried out by immersion of the scaffolds in a PBS solution and digestion in type II collagenase, respectively. The influence of the scaffolds on the proliferation of chondrocytes was assessed by the methyl thiazolyl tetrazolium colorimetric assay. The morphology of the crosslinked scaffolds cocultured with chondrocytes was characterized by a scanning electron microscope. The results proved that 75% alcohol and a crosslinking temperature of 37 °C are recommended. Collagen fibrils are more densely packed after crosslinking with EDC/NHS and have a more uniform structure than that of noncrosslinked ones. The EDC-crosslinked scaffolds possessed excellent mechanical property and biocompatibility.

Fabrication and characterization of Chinese giant salamander skin composite collagen sponge as a high-strength rapid hemostatic material

Chinese giant salamander (CGS) has high medicinal value and long history of clinical use in ancient China. In this study, CGS skin (CGSS) collagen was extracted and purified to prepare collagen sponge by freeze-drying. TEMPO oxidized microfibrillated cellulose (TEMPO-MFC) and genipin were adopted to improve the mechanical properties of collagen sponge. The hygroscopicity, porosity, mechanical properties, hemostatic performance, morphology, and biodegradability of the resultant sponges were investigated in detail. The results indicated that CGSS collagen was type I collagen with intact triple-helical structure, and the prepared sponge had porous structure and excellent hemostatic performance with procoagulant ratio of 53.28%. However, the CGSS collagen sponge showed low tensile strength (TS) of 98.80 KPa, compression strength (CS) of 1.48 KPa, and elongation at break (E) of 4.72%. Incorporating 2.5% TEMPO-MFC into the native CGSS collagen sponge resulted in an increase of 188.26% in TS to 284.80 KPa, 166.89% in CS to 3.95 KPa, and 73.52% in E to 8.19%. The improvements were attributed to the physical filling of TEMPO-MFC in cavity and cavity wall of collagen sponge and the stable chemical linkage between carboxyl of TEMPO-MFC and amino group of collagen which effectively improved the toughening of sponge and formed good interface bonding, respectively. Subsequent 0.3% genipin treatment further improved the TS to 605.00 KPa and the CS to 8.66 KPa as a result of crosslinking reaction. Moreover, the composite reinforcing also improved the anti-degradation ability and procoagulant ratio of collagen sponge. All results suggested that the TEMPO-MFC toughened and genipin crosslinked CGSS composite collagen sponge is a promising rapid hemostatic material with high-strength and can be applicated in biomedical field.

In Vitro Enzymatic Degradation of Tissue Grafts and Collagen Biomaterials by Matrix Metalloproteinases: Improving the Collagenase Assay

Matrix metalloproteinase-1 and -8 are active during the wound healing and remodelling processes, degrading native extracellular matrix and implantable devices. However, traditional in vitro assays utilize primarily matrix metalloproteinase-1 to mimic the in vivo degradation microenvironment. Herein, we assessed the influence of various concentrations of matrix metalloproteinase- 1 and 8 (50, 100, and 200 U/mL) as a function of pH (5.5 and 7.4) and time (3, 6, 9, 12, and 24 h) on the degradation profile of three tissue grafts (chemically cross-linked Permacol, nonchemically cross-linked Permacol and nonchemically cross-linked Strattice) and a collagen biomaterial (nonchemically cross-linked collagen sponge). Chemically cross-linked and nonchemically cross-linked Permacol samples exhibited the highest resistance to enzymatic degradation, while nonchemically cross-linked collagen sponges exhibited the least resistance to enzymatic degradation. Qualitative and quantitative degradation analysis of all samples revealed a similar degradation profile over time, independently of the matrix metalloproteinase used and its respective concentration and pH. These data indicate that matrix metalloproteinase-1 and matrix metalloproteinase-8 exhibit similar degradation profile in vitro, suggesting that matrix metalloproteinase-8 should be used for collagenase assay.

Porous, Ventricular Extracellular Matrix-Derived Foams as a Platform for Cardiac Cell Culture

To more closely mimic the native cellular microenvironment, 3D scaffolds derived from the extracellular matrix (ECM) are being developed as alternatives to conventional 2D culture systems. In the present study, we established methods to fabricate nonchemically cross-linked 3D porous foams derived entirely from decellularized porcine left ventricle (DLV) for use as an in vitro cardiac cell culture platform. Furthermore, we explored the effects of physically preprocessing the DLV through mechanical mincing versus cryomilling, as well as varying the ECM concentration on the structure, composition, and physical properties of the foams. Our results indicate that the less highly processed minced foams had a more cohesive and complex network of ECM components, enhanced mechanical properties, and improved stability under simulated culturing conditions. To validate the DLV foams, a proof-of-concept study was conducted to explore the early cardiomyogenic differentiation of pericardial fat adipose-derived stem/stromal cells (pfASCs) on the minced DLV foams relative to purified collagen I gel controls. Differentiation was induced using a modified cardiomyogenic medium (MCM) or through stimulation with 5-azacytidine (5-aza), and cardiomyocyte marker expression was characterized by immunohistochemistry and real-time reverse transcriptase-polymerase chain reaction. Our results indicate that early markers of cardiomyogenic differentiation were significantly enhanced on the DLV foams cultured in MCM, suggesting a synergistic effect of the cardiac ECM-derived scaffolds and the culture medium on the induction of pfASC differentiation. Furthermore, in analyzing the response in the noninduced control groups, the foams were observed to provide a mildly inductive microenvironment for pfASC cardiomyogenesis, supporting the rationale for using tissue-specific ECM as a substrate for cardiac cell culture applications.

Collagen cryogel cross-linked by naturally derived dialdehyde carboxymethyl cellulose

We present the use of a natural derivative, dialdehyde carboxymethyl cellulose (DCMC) as the cross-linker for the preparation of spongy collagen cryogels by freezing-thawing method. The DCMC has been characterized by laser light scattering (LLS), showing the molecular weight of 2.38 × 10(5)g/mol. FT-IR studies demonstrate that the cross-linking reaction and the cryogenic treatment do not destroy the triple helix of collagen. SEM images indicate that the cryogel has a heterophase structure with interconnecting macropores. DSC measurements reveal that the incorporation of a very small amount of DCMC can significantly improve the thermal stability of collagen. Moreover, the cryogels exhibit fast swelling rate, and their equilibrium swelling ratio is related to DCMC content and pH-dependent. The in vitro blood-compatibility tests prove that the introduction of DCMC does not cause the reducing performance in hemolysis and blood clotting compared with pure collagen. Hence, the low-cost and non-toxic nature of DCMC confers the cryogel great potential in tissue engineering and other biomedical applications.

The effects of different crossing-linking conditions of genipin on type I collagen scaffolds: an in vitro evaluation

The purpose of this paper is to analyze the properties of fabricating rat tail type I collagen scaffolds cross-linked with genipin under different conditions. The porous genipin cross-linked scaffolds are obtained through a two step freeze-drying process. To find out the optimal cross-link condition, we used different genipin concentrations and various cross-linked temperatures to prepare the scaffolds in this study. The morphologies of the scaffolds were characterized by scanning electron microscope, and the mechanical properties of the scaffolds were evaluated under dynamic compression. Additionally, the cross-linking degree was assessed by ninhydrin assay. To investigate the swelling ratio and the in vitro degradation of the collagen scaffold, the tests were also carried out by immersion of the scaffolds in a PBS solution or digestion in a type I collagenase respectively. The morphologies of the non-cross-linked scaffolds presented a lattice-like structure while the cross-linked ones displayed a sheet-like framework. The morphology of the genipin cross-linked scaffolds could be significantly changed by either increasing genipin concentration or the temperature. The swelling ratio of each cross-linked scaffold was much lower than that of the control (non-cross-linked).The ninhydrin assay demonstrated that the higher temperature and genipin concentration could obviously increase the cross-linking efficiency. The in vitro degradation studies indicated that genipin cross-linking can effectively elevate the biostability of the scaffolds. The biocompatibility and cytotoxicity of the scaffolds was evaluated by culturing rat chondrocytes on the scaffold in vitro and by MTT. The results of MTT and the fact that the chondrocytes adhered well to the scaffolds demonstrated that genipin cross-linked scaffolds possessed an excellent biocompatibility and low cytotoxicity. Based on these results, 0.3 % genipin concentrations and 37 °C cross-linked temperatures are recommended.

Effects of different cross-linking conditions on the properties of genipin-cross-linked chitosan/collagen scaffolds for cartilage tissue engineering

A cross-linking reagent is required to improve mechanical strength and degradation properties of biopolymers for tissue engineering. To find the optimal preparative method, we prepared diverse genipin-cross-linked chitosan/collagen scaffolds using different genipin concentrations and various cross-linking temperatures and cross-linking times. The compressive strength increased with the increasing of genipin concentration from 0.1 to 1.0%, but when concentration exceeded 1.0%, the compressive strength decreased. Similarly, the compressive strength increased with the increasing of temperature from 4 to 20°C, but when temperature reached 37°C, the compressive strength decreased. Showing a different trend from the above two factors, the effect of cross-linking time on the compressive strength had a single increasing tendency. The other results also demonstrated that the pore size, degradation rate and swelling ratio changed significantly with different cross-linking conditions. Based on our study, 1.0% genipin concentration, 20°C cross-linking temperature and longer cross-linking time are recommended.

Tissue Engineering Bone Formation in Novel Recombinant Human Bone Morphogenic Protein 2–Atelocollagen Composite Scaffolds

BACKGROUND

Bone morphogenic proteins (BMPs) are important bone-induction factors, and the development of a suitable carrier for BMPs is a critical step to achieve osteoinductive function. The aims of the present study were to evaluate, at the cellular and molecular levels, the feasibility of recombinant human BMP-2 (rhBMP-2)-collagen composite scaffold and its efficiency for carrying BMP-2 in ectopic bone formation in rats.

METHODS

Scaffolds with (test) or without rhBMP-2 (control) were made and implanted into the calf muscle of 16 5-week-old rats. The tissue responses to the scaffolds were examined by histology. Masson's trichrome and von Kossa stainings were performed to examine collagen matrix deposition and calcification at 3, 7, 10, and 14 days. Expressions of bone phenotypic markers, alkaline phosphatase, osteocalcin, osteopontin, and bone sialoprotein were detected by reverse transcription-polymerase chain reaction and immunohistochemistry.

RESULTS

No detectable adverse responses were noted around the implanted scaffolds, and the area of the resorbed scaffold had been replaced by young connective tissue by 3 to 7 days in both groups. In the rhBMP-2 composite scaffold, collagen matrix deposition was found in the implanted site on day 7 and initial signs of endochondral differentiation also appeared. Mineralization and the expressions of key bone proteins were demonstrated in chondroblasts and osteoblasts at 7 to 14 days. Molecular cascades of bone induction were not shown in control specimens.

CONCLUSION

The rhBMP-2-atelocollagen scaffold showed excellent biocompatibility and possessed a bone-inducing capacity in rat within 2 weeks, and, thus, may provide a potential application in tissue engineering of bone tissue.

Preparation and characterization of cross-linked collagen–phospholipid polymer hybrid gels

2-methacryloyloxyethyl phosphorylcholine (MPC)-immobilized collagen gel was developed. Using 1-ethyl-3-(3-dimethyl aminopropyl)-1-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), we cross-linked a collagen film in 2-morpholinoethane sulfonic acid (MES) buffer (EN gel). EN gel was prepared under both pH 4.5 and pH 9.0 in order to observe changes in cross-linking ability. To cross-link MPC to collagen gel, poly(MPC-co-methacrylic acid) (PMA) having a carboxyl group side chain was chosen. E/N gel was added to the MES buffer having pre-NHS activated PMA to make MPC-immobilized collagen gel (MiC gel). MiC gel was prepared under both acidic and alkaline conditions to observe the changes in the cross-linking ability of PMA. X-ray photoelectron spectroscopy showed that the PMA was cross-linked with collagen under both acidic and alkaline conditions. Differential scanning calorimetry (DSC) results showed that the shrinkage temperature increased for the MiC gels and that the increase would be greater for the MiC gel prepared under alkaline conditions. The data showed that swelling would be less when the MiC gel was prepared under alkaline conditions. The biodegradation caused by collagenase was suppressed for the MiC gel prepared under alkaline conditions due to stable inter- and intrahelical networks.

Characterization of collagen matrices crosslinked using microbial transglutaminase

In search of a new approach for crosslinking collagen-based biomaterials, we examined the effect of microbial transglutaminase (MTGases) as a crosslinking reagent on collagenous matrices made from porcine type I collagen. As the results revealed, MTGase exhibited a crosslinking action that raised the viscosity of the collagen solution. Matrices crosslinked with MTGase at the low pH values of pH 3 and 4 exhibited higher tensile strengths than those at high pH values. In comparison with untreated matrices, the denaturation temperatures of the corresponding matrices shifted toward higher temperatures. These enzyme-catalyzed crosslinked matrices were proven by MTT assay to be non-cytotoxic. In conclusion, this enzymatic method of using MTGase provides an alternative potential way for crosslinking collagen-based matrices.

Effects of the controlled-released TGF-beta 1 from chitosan microspheres on chondrocytes cultured in a collagen/chitosan/glycosaminoglycan scaffold

The objectives of this study were (1) to develop a three-dimensional collagen/chitosan/glycosaminoglycan (GAG) scaffold in combination with transforming growth factor-beta1 (TGF-beta 1)-loaded chitosan microspheres, and (2) to evaluate the effect of released TGF-beta 1 on the chondrogenic potential of rabbit chondrocytes in such scaffolds. TGF-beta 1 was loaded into chitosan microspheres using an emulsion-crosslinking method. The controlled release of TGF-beta 1, as measured by enzyme-linked immunosorbent assay (ELISA), was monitored for 7 days. The porous scaffolds containing collagen and chitosan were fabricated by using a freeze drying technique and crosslinked using 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide (EDC) in the presence of chondroitin sulfate (CS), as a GAG component. The TGF-beta 1 microspheres were encapsulated into the scaffold at a concentration of 10 ng TGF-beta 1/scaffold and then chondrocytes were seeded in the scaffold and incubated in vitro for 3 weeks. Both proliferation rate and glycosaminoglycan (GAG) production were significantly higher in the TGF-beta 1 microsphere-incorporated scaffolds than in the control scaffolds without microspheres. Extracellular matrix staining by Safranin O and immunohistochemistry for type II collagen were elevated in the scaffold with TGF-beta 1 microspheres. These results suggest that TGF-beta 1 microspheres when incorporated into a scaffold have the potential to enhance cartilage formation.

Influence of the concentrations of hyaluronic acid on the properties and biocompatibility of Cs–Gel–HA membranes

The object of this study was to investigate the relationship between the concentrations of HA solutions and the physicochemical properties and the biocompatibility of Cs-Gel-HA membranes. The addition of different concentrations of HA not only improved the wettability significantly and extended the degradation time of Cs-Gel-HA membranes, but also changed their mechanical properties. The concentration of HA had a significant influence on the biocompatibility of Cs-Gel-HA membranes. Results demonstrated that it was only the concentrations of HA in a certain range (0.01-0.1%), that could promote the cell adhesion, migration and proliferation, while the concentration of HA was above 0.1% it would either reduce or even inhibit these behaviors.

Characterization of porous collagen/hyaluronic acid scaffold modified by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide cross-linking

In order to develop a scaffolding material for tissue regeneration, porous matrices containing collagen and hyaluronic acid were fabricated by freeze drying at -20 degrees C, -70 degrees C or -196 degrees C. The fabricated porous membranes were cross-linked using 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) in a range of 1-100 mM concentrations for enhancing mechanical stability of the composite matrix. Scanning electron microscope (SEM) views of the matrices demonstrated that the matrices obtained before cross-linking process had interconnected pores with mean diameters of 40, 90 or 230 microm and porosity of 58-66% according to the freezing temperature, and also the porous structures after cross-linking process were retained. The swelling test and IR spectroscopic measurement of different cross-linked membranes were carried out as a measure of the extent of cross-linking. The swelling behavior of cross-linked membranes showed no significant differences as cross-linking degree increased. FT-IR spectra showed the increase of the intensity of the absorbencies at amide bonds (1655, 1546, 1458 cm(-1)) compared to that of CH bond (2930 cm(-1)). In enzymatic degradation test, EDC treated membranes showed significant enhancement of the resistance to collagenase activity in comparison with 0.625% glutaraldehyde treated membranes. In cytotoxicity test using L929 fibroblastic cells, the EDC-cross-linked membranes demonstrated no significant toxicity.