Optimization of diamine bridges in glutaraldehyde treated bioprosthetic aortic wall tissue

Dexamethasone- loaded polymeric porous sponge as a direct pulp capping agent

This study aims to achieve the principles of tissue engineering using biopolymers to be applied in the field of vital endodontic treatment to stimulate stem cells and engineering and regeneration of dentin tissue. the polymer blend was loaded with the steroidal anti-inflammatory drug, dexamethasone, and the porous drug-loaded bio-sponge was produced by lyophilization. Bio-sponge, as a direct pulp capping agent, was histologically studied compared to calcium hydroxide Ca(OH)₂ in an animal experiment. The results indicated the effectiveness of the bio-sponge as a direct pulp capping agent where the dentin bridge was formed faster than Ca(OH)₂ treated samples. There was no inflammatory response in the pulp tissue throughout the follow-up period. The porous bio-sponge loaded with dexamethasone with a neutral pH resulted in enhancement of the odontoblast differentiation from stem cells, resulting in the formation of a renewed dentin bridge without the slightest inflammatory response in the pulp.

Surface-bound collagen 4 is significantly more stable than collagen 1

Collagen 1 (C1) is commonly used to improve biological responses to implant surfaces. Here, the stability of C1 was compared with collagen 4 (C4) on a mixed macrodiol polyurethane, both adsorbed and covalently bound via acetaldehyde glow discharge polymerization and reductive amination. Substrate specimens were incubated in solutions of C1 and C4. The strength of conjugation was tested by incubation in 8 M urea followed by enzyme linked immunosorbent assays to measure residual C1 and C4. The basal lamina protein, laminin-332 (L332) was superimposed via adsorption on C4-treated specimens. Keratinocytes were grown on untreated, C1-treated, C4-treated, and C4 + L332-treated specimens, followed by measurement of cell area, proliferation, and focal adhesion density. Adsorbed C4 was shown to be significantly more stable than C1 and covalent conjugation conferred even greater stability, with no degradation of C4 over twenty days in 8 M urea. Cell growth was similar for C1 and C4, with no additional benefit conferred by superimposition of L332. The greater resistance of C4 to degradation may be consequent to cysteine residues and disulphide bonds in its non-collagenous domains. The use of C4 on implants, rather than C1, may improve their long-term stability in tissues. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1364-1373, 2017.

l-Arginine intercedes bio-crosslinking of a collagen–chitosan 3D-hybrid scaffold for tissue engineering and regeneration: in silico, in vitro, and in vivo studies

Development ofl-arginine crosslinked three-dimensional collagen/chitosan hybrid scaffold for tissue engineering/regeneration.

Three-dimensional scaffold of type II collagen promote the differentiation of adipose-derived stem cells into a nucleus pulposus-like phenotype

Type II collagen is reported to have the capability of guiding adipose-derived stem cells (ADSCs) to differentiate towards a nucleus pulposus (NP)-like phenotype. So this study aimed to establish a three-dimensional (3D) collagen scaffold using N,N-(3-dimethylaminopropyl)-N'-ethyl carbodiimide and N-hydroxysuccinimide (EDAC/NHS) to increase the efficiency of ADSC differentiation into NP-like cells. Physical properties, such as porosity, biodegradation, and microstructure, and biological characteristics such as cytotoxicity, cell proliferation, and expression of relevant genes and proteins were measured to evaluate the efficacy of different scaffolds. Collagen scaffolds cross-linked with EDAC/NHS exhibited higher biological stability, better spatial structure, and higher gene and protein expression of functional markers such as aggrecan, SOX9 and COL2 than those of other groups. Based on the results, freeze-dried type II collagen cross-linked with EDAC/NHS formed the best 3D scaffold, for inducing ADSC proliferation and differentiation toward a NP-like phenotype. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1687-1693, 2016.

Mechanical and biocompatible characterization of a cross-linked collagen-hyaluronic acid wound dressing

Collagen scaffolds have been widely employed as a dermal equivalent to induce fibroblast infiltrations and dermal regeneration in the treatment of chronic wounds and diabetic foot ulcers. Cross-linking methods have been developed to address the disadvantages of the rapid degradation associated with collagen-based scaffolds. To eliminate the potential drawbacks associated with glutaraldehyde cross-linking, methods using a water soluble carbodiimide have been developed. In the present study, the glycosaminoglycan (GAG) hyaluronic acid (HA), was covalently attached to an equine tendon derived collagen scaffold using 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) to create ntSPONGE™. The HA was shown to be homogeneously distributed throughout the collagen matrix. In vitro analyses of the scaffold indicated that the cross-linking enhanced the biological stability by decreasing the enzymatic degradation and increasing the thermal denaturation temperature. The material was shown to support the attachment and proliferation of mouse L929 fibroblast cells. In addition, the cross-linking decreased the resorption rate of the collagen as measured in an intramuscular implant model in rabbits. The material was also shown to be biocompatible in a variety of in vitro and in vivo assays. These results indicate that this cross-linked collagen-HA scaffold, ntSPONGE™, has the potential for use in chronic wound healing.

Inflammation in cardiovascular tissue engineering: the challenge to a promise: a minireview

Tissue engineering employs scaffolds, cells, and stimuli brought together in such a way as to mimic the functional architecture of the target tissue or organ. Exhilarating advances in tissue engineering and regenerative medicine allow us to envision in vitro creation or in vivo regeneration of cardiovascular tissues. Such accomplishments have the potential to revolutionize medicine and greatly improve our standard of life. However, enthusiasm has been hampered in recent years because of abnormal reactions at the implant-host interface, including cell proliferation, fibrosis, calcification and degeneration, as compared to the highly desired healing and remodeling. Animal and clinical studies have highlighted uncontrolled chronic inflammation as the main cause of these processes. In this minireview, we present three case studies highlighting the importance of inflammation in tissue engineering heart valves, vascular grafts, and myocardium and propose to focus on the endothelial barrier, the “final frontier” endowed with the natural potential and ability to regulate inflammatory signals.

Detoxification of Glutaraldehyde Treated Porcine Pericardium Using L-arginine & NABH(4)

Background

Calcification is the most frequent cause of clinical failure of bioprosthetic tissues fabricated from GA-fixed porcine valves or bovine pericardium. A multi-factorial approach using different mechanisms was recently developed to reduce the calcification of bioprosthetic tissues. The purpose of the present study was to evaluate the synchronized synergism of using L-arginine and NaBH₄, compared with ethanol and L-lysine, in glutaraldehyde treated porcine pericardium from the standpoint of calcification and tissue elasticity.

Materials and Methods

Porcine pericardium was fixed at 0.625% GA (7 days at room temperature after 2 days at 4℃). An interim step of ethanol (80%; 1 day at room temperature) or L-lysine (0.1 M; 2 days at 37℃) or L-arginine (0.1 M; 2 days at 37℃) was followed by completion of the GA fixation. A final step of NaBH₄ (0.1 M; 2 days at room temperature) was followed. Their tensile strength, thickness, and thermal stability were measured. Treated pericardia were implanted subcutaneously into three-week-old Sprague-Dawley rats for 8 weeks. Calcium content was assessed by atomic absorption spectroscopy and histology.

Results

L-arginine and NaBH₄ pretreatment (1.81±0.39 kgf/5 mm p=0.001, 0.30±0.08 mm p<0.001) significantly increased tensile strength and thickness compared with the control (0.53±0.34 kgf/5 mm, 0.10±0.02 mm). In a thermal stability test, L-arginine and NaBH₄ pretreatment (84.25±1.12℃, p=0.023) caused a significant difference from the control (86.25±0.00℃). L-lysine and NaBH₄ pretreatment (183.8±42.6 ug/mg, p=0.804), and L-arginine and NaBH₄ pretreatment (163.3±27.5 ug/mg, p=0.621) did not significantly inhibit calcification compared to the control (175.5±45.3 ug/mg), but ethanol and NaBH₄ pretreatment did (38.5±37.3 ug/mg, p=0.003).

Conclusion

The combined pretreatment using L-arginine and NaBH₄ after GA fixation seemed to increase the tensile strength and thickness of porcine pericardium, fixed with GA. Additionally, it seemed to keep thermal stability. However it could not decrease the calcification of porcine pericardium fixed with GA. NaBH₄ pretreatment seemed to decrease the calcification of porcine pericardium fixed with GA, but only with ethanol.

Initial investigation of novel human-like collagen/chitosan scaffold for vascular tissue engineering

With the increasing occurrence of vascular diseases and poor long-term patency rates of current small diameter vascular grafts, it becomes urgent to pursuit biomaterial as scaffold to mimic blood vessel morphologically and mechanically. In this study, novel human-like collagen (HLC, produced by recombinant E. coli)/chitosan tubular scaffolds were fabricated by cross-linking and freeze-drying process. The scaffolds were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and tensile test, respectively. Human venous fibroblasts were expanded and seeded onto the scaffolds in the density of 1 x 10(5) cells/cm(2). After a 15-day culture under static conditions, the cell-polymer constructs were observed using SEM, confocal laser scanning microscopy (CLSM), histological examination, and biochemical assays for cell proliferation and extracellular matrix production (collagen and glycosaminoglycans). Furthermore, the scaffolds were implanted into rabbits' livers to evaluate their biocompatibility. The results indicated that HLC/chitosan tubular scaffolds (1) exhibited interconnected porous structure; (2) achieved the desirable levels of pliability (elastic up to 30% strain) and stress of 300 +/- 16 kPa; (3) were capable of enhancing cell adhesion and proliferation and ECM secretion; (4) showed superior biocompatibility. This study suggested the feasibility of HLC/chitosan composite as a promising candidate scaffold for blood vessel tissue engineering.

Biodegradability and cell-mediated contraction of porous collagen scaffolds: the effect of lysine as a novel crosslinking bridge

A novel crosslinking method was adopted to modify the porous collagen scaffolds by using a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDAC) and N-hydroxysuccinimide (NHS) in the presence of lysine, which functions as a crosslinking bridge. In vitro biodegradation tests proved that in the presence of lysine the biostability of the EDAC crosslinked scaffolds was greatly enhanced. The biostability of the resultant scaffolds was also elucidated as a function of the concentrations of lysine and EDAC/NHS. Compared to the Col-DHT, the ability of the Col-EDAC and the Col/Lys to resist cell-mediated contraction (CMC) was greatly enhanced. Yet no obvious difference between the Col-EDAC and the Col/Lys was found with respect to CMC. SEM observations showed that the microstructure of the crosslinked scaffolds could be largely preserved after fibroblast seeding. As a result, MTT assays proved that the fibroblasts in the Col/Lys scaffolds proliferated faster compared to the DHT-treated one on the assumption that the cell viability was preserved to a similar level. Histological section results indicated that the Col/Lys scaffolds had the ability to accelerate the cell infiltration and proliferation. All these results demonstrated that this novel crosslinking method is an effective way to achieve a collagen scaffold with improved biostability and a more stable structure, which can resist cell-mediated contraction. (c) 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 334-342, 2004.

Calcification of Tissue Heart Valve Substitutes: Progress Toward Understanding and Prevention

Calcification plays a major role in the failure of bioprosthetic and other tissue heart valve substitutes. Tissue valve calcification is initiated primarily within residual cells that have been devitalized, usually by glutaraldehyde pretreatment. The mechanism involves reaction of calcium-containing extracellular fluid with membrane-associated phosphorus to yield calcium phosphate mineral deposits. Calcification is accelerated by young recipient age, valve factors such as glutaraldehyde fixation, and increased mechanical stress. Recent studies have suggested that pathologic calcification is regulated by inductive and inhibitory factors, similar to the physiologic mineralization of bone. The most promising preventive strategies have included binding of calcification inhibitors to glutaraldehyde fixed tissue, removal or modification of calcifiable components, modification of glutaraldehyde fixation, and use of tissue cross linking agents other than glutaraldehyde. This review summarizes current concepts in the pathophysiology of tissue valve calcification, including emerging concepts of endogenous regulation, progress toward prevention of calcification, and issues related to calcification of the aortic wall of stentless bioprosthetic valves.

Prevention of calcification in bioprosthetic heart valves: challenges and perspectives

Surgical replacement with artificial devices has revolutionised the care of patients with severe valvular diseases. Mechanical valves are very durable, but require long-term anticoagulation. Bioprosthetic heart valves (BHVs), devices manufactured from glutaraldehyde-fixed animal tissues, do not need long-term anticoagulation, but their long-term durability is limited to 15 - 20 years, mainly because of mechanical failure and tissue calcification. Although mechanisms of BHV calcification are not fully understood, major determinants are glutaraldehyde fixation, presence of devitalised cells and alteration of specific extracellular matrix components. Treatments targeted at the prevention of calcification include those that target neutralisation of the effects of glutaraldehyde, removal of cells, and modifications of matrix components. Several existing calcification-prevention treatments are in clinical use at present, and there are excellent mid-term clinical follow-up reports available. The purpose of this review is to appraise basic knowledge acquired in the field of prevention of BHV calcification, and to provide directions for future research and development.

Enhanced biological stability of collagen porous scaffolds by using amino acids as novel cross-linking bridges

Collagen porous scaffolds have been widely employed as a dermal equivalent to induce fibroblasts infiltration and dermal regeneration. To eliminate the disadvantageous drawback of the fast degradation speed, a cross-linking method was adopted by using a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDAC) and N-hydroxysuccinimide (NHS) in the presence of amino acids (glycin, glutamic acid or lysine), which function as cross-linking bridge between collagen molecular chains. In vitro assessment of the biological stability of the cross-linked collagen scaffolds found that the collagenase biodegradation degree was greatly decreased when lysine was added, resulting in a more biological stable scaffold. On the other hand, the biodegradation degree was accelerated compared with the purely cross-linked when glutamic acid was added, while less influenced by glycin addition. By comparing the biodegradation degree of the scaffolds added with amino acids and their model compounds, i.e. adipic acid and hexane diamine, the key factor influencing the biological stability was further investigated. The results indicated that the crucial factor is dependent on the ratio of amino groups to carboxyl groups in the cross-linking system. At optimal ratio the lowest biodegradation degree is achieved. Scanning electron microscopy measurements prove that the three-dimensional structure of the scaffolds was largely preserved. Preliminary in vitro culture of fibroblasts in the collagen scaffold cross-linked with EDAC/NHS in the presence of lysine has shown that the original good cytocompatibility of collagen was retained.

Effects of periodate and chondroitin 4-sulfate on proteoglycan stabilization of ostrich pericardium. Inhibition of calcification in subcutaneous implants in rats

Chemical modification of biological materials used in the manufacture of cardiac valves tends to reduce the relatively high degree of biodegradation and calcification of the implanted bioprostheses. The most widely used treatment to reduce biodegradability of the valves is glutaraldehyde fixation. However, this treatment is potentially toxic and induces tissue calcification. In order to minimize these undesirable effects, we have analyzed the effect of a pre-fixation of endogenous proteoglycans and exogenous glycosaminoglycans, as well as the borohydride reduction influence on the different modified ostrich pericardium implants after subcutaneous implantation in rats. The presence of calcific deposits was detected in all implanted GA-fixed samples; however, calcification was highly reduced in both groups of periodate-prefixed materials, which showed also a very low Ca/P molar ratio. Borohydride post-treatment of these biomaterials resulted in a significant increase in calcium phosphate precipitation, with the appearance of calcium deposits mainly in an amorphous form even though X-ray diffraction allowed the detection of brushite- and apatite-like crystals. Regarding tissue stability, no significant differences were found among the borohydride-untreated implants but higher levels of matrix metalloproteinases were observed by gelatin zymography in the periodate pre-fixed materials. This increase was partially reduced by pre-fixation of exogenous chondroitin 4-sulfate. On the other hand, borohydride post-treatment not only increased calcification, but also reduced tissue stability and increased the presence of matrix-degrading activities.