Biological matrices and bionanotechnology

Tissue Regeneration on Rise: Dental Hard Tissue Regeneration and Challenges-A Narrative Review

Background

As people live longer, there is an increasing need for hard tissue regeneration and whole-tooth regeneration. Despite the advancements in the field of medicine, the field of regenerative dentistry is still challenging due to the complexity of dental hard tissues. Cross-disciplinary collaboration among material scientists, cellular biologists, and odontologists aimed at developing strategies and uncovering solutions related to dental tissue regeneration. Methodology. A search of the literature was done for pertinent research. Consistent with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) 2020 Statement, the electronic databases looked at were PubMed, Science Direct, Scopus, and Google Scholar, with the keyword search "hard dental tissue regeneration."

Results

Database analysis yielded a total of 476 articles. 222 duplicate articles have been removed in total. Articles that have no connection to the directed regeneration of hard dental tissue were disregarded. The review concluded with the inclusion of four studies that were relevant to our research objective.

Conclusion

Current molecular signaling network investigations and novel viewpoints on cellular heterogeneity have made advancements in understanding of the kinetics of dental hard tissue regeneration possible. Here, we outline the fundamentals of stem hard dental tissue maintenance, regeneration, and repair, as well as recent advancements in the field of hard tissue regeneration. These intriguing findings help establish a framework that will eventually enable basic research findings to be utilized towards oral health-improving medicines.

Multiscale computational modeling of aortic valve calcification

Calcific aortic valve disease (CAVD) is a common cardiovascular disease that affects millions of people worldwide. The disease is characterized by the formation of calcium nodules on the aortic valve leaflets, which can lead to stenosis and heart failure if left untreated. The pathogenesis of CAVD is still not well understood, but involves several signaling pathways, including the transforming growth factor beta (TGF β ) pathway. In this study, we developed a multiscale computational model for TGF β -stimulated CAVD. The model framework comprises cellular behavior dynamics, subcellular signaling pathways, and tissue-level diffusion fields of pertinent chemical species, where information is shared among different scales. Processes such as endothelial to mesenchymal transition (EndMT), fibrosis, and calcification are incorporated. The results indicate that the majority of myofibroblasts and osteoblast-like cells ultimately die due to lack of nutrients as they become trapped in areas with higher levels of fibrosis or calcification, and they subsequently act as sources for calcium nodules, which contribute to a polydispersed nodule size distribution. Additionally, fibrosis and calcification processes occur more frequently in regions closer to the endothelial layer where the cell activity is higher. Our results provide insights into the mechanisms of CAVD and TGF β signaling and could aid in the development of novel therapeutic approaches for CAVD and other related diseases such as cancer. More broadly, this type of modeling framework can pave the way for unraveling the complexity of biological systems by incorporating several signaling pathways in subcellular models to simulate tissue remodeling in diseases involving cellular mechanobiology.

Shear and endothelial induced late-stage calcific aortic valve disease-on-a-chip develops calcium phosphate mineralizations

Calcific aortic valve disease (CAVD) is an active pathobiological process leading to severe aortic stenosis, where the only treatment is valve replacement. Late-stage CAVD is characterized by calcification, disorganization of collagen, and deposition of glycosaminoglycans, such as chondroitin sulfate (CS), in the fibrosa. We developed a three-dimensional microfluidic device of the aortic valve fibrosa to study the effects of shear stress (1 or 20 dyne per cm²), CS (1 or 20 mg mL^-1), and endothelial cell presence on calcification. CAVD chips consisted of a collagen I hydrogel, where porcine aortic valve interstitial cells were embedded within and porcine aortic valve endothelial cells were seeded on top of the matrix for up to 21 days. Here, we show that this CAVD-on-a-chip is the first to develop human-like calcified nodules varying in calcium phosphate mineralization maturity resulting from high shear and endothelial cells, specifically di- and octa-calcium phosphates. Long-term co-culture microfluidic studies confirmed cell viability and calcium phosphate formations throughout 21 days. Given that CAVD has no targeted therapies, the creation of a physiologically relevant test-bed of the aortic valve could lead to advances in preclinical studies.

Evaluation of ethylene oxide, gamma radiation, dry heat and autoclave sterilization processes on extracellular matrix of biomaterial dental scaffolds

Scaffolds used to receive stem cells are a promising perspective of tissue regeneration research, and one of the most effective solutions to rebuild organs. In the near future will be possible to reconstruct a natural tooth using stems cells, but to avoid an immune-defensive response, sterilize the scaffold is not only desired, but also essential to be successful. A study confirmed stem cells extracted from rat's natural teeth, and implanted into the alveolar bone, could differentiate themselves in dental cells, but the scaffold's chemistry, geometry, density, morphology, adherence, biocompatibility and mechanical properties remained an issue. This study intended to produce a completely sterilized dental scaffold with preserved extracellular matrix. Fifty-one samples were collected, kept in formaldehyde, submitted to partial demineralization and decellularization processes and sterilized using four different methods: dry heating; autoclave; ethylene-oxide and gamma-radiation. They were characterized through optical images, micro-hardness, XRD, EDS, XRF, SEM, histology and sterility test. The results evidenced the four sterilization methods were fully effective with preservation of ECM molecular arrangements, variation on chemical composition (proportion of Ca/P) was compatible with Ca/P proportional variation between enamel and dentine regions. Gamma irradiation and ethylene oxide presents excellent results, but their viability are compromised by the costs and technology's accessibility (requires very expensive equipment and/or consumables). Excepted gamma irradiation, all the sterilization methods more than sterilizing also reduced the remaining pulp. Autoclave presents easy equipment accessibility, lower cost consumables, higher reduction of remaining pulp and complete sterilization, reason why was considered the most promising technique.

3D Tissue-Engineered Vascular Drug Screening Platforms: Promise and Considerations

Despite the efforts devoted to drug discovery and development, the number of new drug approvals have been decreasing. Specifically, cardiovascular developments have been showing amongst the lowest levels of approvals. In addition, concerns over the adverse effects of drugs to the cardiovascular system have been increasing and resulting in failure at the preclinical level as well as withdrawal of drugs post-marketing. Besides factors such as the increased cost of clinical trials and increases in the requirements and the complexity of the regulatory processes, there is also a gap between the currently existing pre-clinical screening methods and the clinical studies in humans. This gap is mainly caused by the lack of complexity in the currently used 2D cell culture-based screening systems, which do not accurately reflect human physiological conditions. Cell-based drug screening is widely accepted and extensively used and can provide an initial indication of the drugs' therapeutic efficacy and potential cytotoxicity. However, in vitro cell-based evaluation could in many instances provide contradictory findings to the in vivo testing in animal models and clinical trials. This drawback is related to the failure of these 2D cell culture systems to recapitulate the human physiological microenvironment in which the cells reside. In the body, cells reside within a complex physiological setting, where they interact with and respond to neighboring cells, extracellular matrix, mechanical stress, blood shear stress, and many other factors. These factors in sum affect the cellular response and the specific pathways that regulate variable vital functions such as proliferation, apoptosis, and differentiation. Although pre-clinical in vivo animal models provide this level of complexity, cross species differences can also cause contradictory results from that seen when the drug enters clinical trials. Thus, there is a need to better mimic human physiological conditions in pre-clinical studies to improve the efficiency of drug screening. A novel approach is to develop 3D tissue engineered miniaturized constructs in vitro that are based on human cells. In this review, we discuss the factors that should be considered to produce a successful vascular construct that is derived from human cells and is both reliable and reproducible.

The effects and potential applications of concentrated growth factor in dentin-pulp complex regeneration

The dentin-pulp complex is essential for the long-term integrity and viability of teeth but it is susceptible to damage caused by external factors. Because traditional approaches for preserving the dentin-pulp complex have various limitations, there is a need for novel methods for dentin-pulp complex reconstruction. The development of stem cell-based tissue engineering has given rise to the possibility of combining dental stem cells with a tissue-reparative microenvironment to promote dentin-pulp complex regeneration. Concentrated growth factor, a platelet concentrate, is a promising scaffold for the treatment of dentin-pulp complex disorders. Given its characteristics of autogenesis, convenience, usability, and biodegradability, concentrated growth factor has gained popularity in medical and dental fields for repairing bone defects and promoting soft-tissue healing. Numerous in vitro studies have demonstrated that concentrated growth factor can promote the proliferation and migration of dental stem cells. Here, we review the current state of knowledge on the effects of concentrated growth factor on stem cells and its potential applications in dentin-pulp complex regeneration.

Dissecting Calcific Aortic Valve Disease-The Role, Etiology, and Drivers of Valvular Fibrosis

Calcific aortic valve disease (CAVD) is a highly prevalent and progressive disorder that ultimately causes gradual narrowing of the left ventricular outflow orifice with ensuing devastating hemodynamic effects on the heart. Calcific mineral accumulation is the hallmark pathology defining this process; however, fibrotic extracellular matrix (ECM) remodeling that leads to extensive deposition of fibrous connective tissue and distortion of the valvular microarchitecture similarly has major biomechanical and functional consequences for heart valve function. Significant advances have been made to unravel the complex mechanisms that govern these active, cell-mediated processes, yet the interplay between fibrosis and calcification and the individual contribution to progressive extracellular matrix stiffening require further clarification. Specifically, we discuss (1) the valvular biomechanics and layered ECM composition, (2) patterns in the cellular contribution, temporal onset, and risk factors for valvular fibrosis, (3) imaging valvular fibrosis, (4) biomechanical implications of valvular fibrosis, and (5) molecular mechanisms promoting fibrotic tissue remodeling and the possibility of reverse remodeling. This review explores our current understanding of the cellular and molecular drivers of fibrogenesis and the pathophysiological role of fibrosis in CAVD.

Collagen networks within 3D PEG hydrogels support valvular interstitial cell matrix mineralization

Enzymatically degradable hydrogels were designed for the 3D culture of valvular interstitial cells (VICs), and through the incorporation of various functionalities, we aimed to investigate the role of the tissue microenvironment in promoting the osteogenic properties of VICs and matrix mineralization. Specifically, porcine VICs were encapsulated in a poly(ethylene glycol) hydrogel crosslinked with a matrix metalloproteinase (MMP)-degradable crosslinker (KCGPQG↓IWGQCK) and formed via a thiol-ene photoclick reaction in the presence or absence of collagen type I to promote matrix mineralization. VIC-laden hydrogels were treated with osteogenic medium for up to 15 days, and the osteogenic response was characterized by the expression of RUNX2 as an early marker of an osteoblast-like phenotype, osteocalcin (OCN) as a marker of a mature osteoblast-like phenotype, and vimentin (VIM) as a marker of the fibroblast phenotype. In addition, matrix mineralization was characterized histologically with Von Kossa stain for calcium phosphate. Osteogenic response was further characterized biochemically with calcium assays, and physically via optical density measurements. When the osteogenic medium was supplemented with calcium chloride, OCN expression was upregulated and mineralization was discernable at 12 days of culture. Finally, this platform was used to screen various drug therapeutics that were assessed for their efficacy in preventing mineralization using optical density as a higher throughput readout. Collectively, these results suggest that matrix composition has a key role in supporting mineralization deposition within diseased valve tissue.

Tissue Engineering Approaches for Enamel, Dentin, and Pulp Regeneration: An Update

Stem/progenitor cells are undifferentiated cells characterized by their exclusive ability for self-renewal and multilineage differentiation potential. In recent years, researchers and investigations explored the prospect of employing stem/progenitor cell therapy in regenerative medicine, especially stem/progenitor cells originating from the oral tissues. In this context, the regeneration of the lost dental tissues including enamel, dentin, and the dental pulp are pivotal targets for stem/progenitor cell therapy. The present review elaborates on the different sources of stem/progenitor cells and their potential clinical applications to regenerate enamel, dentin, and the dental pulpal tissues.

A human pericardium biopolymeric scaffold for autologous heart valve tissue engineering: cellular and extracellular matrix structure and biomechanical properties in comparison with a normal aortic heart valve

The objective of our study was to compare the cellular and extracellular matrix (ECM) structure and the biomechanical properties of human pericardium (HP) with the normal human aortic heart valve (NAV). HP tissues (from 12 patients) and NAV samples (from 5 patients) were harvested during heart surgery. The main cells in HP were pericardial interstitial cells, which are fibroblast-like cells of mesenchymal origin similar to the valvular interstitial cells in NAV tissue. The ECM of HP had a statistically significantly (p < 0.001) higher collagen I content, a lower collagen III and elastin content, and a similar glycosaminoglycans (GAGs) content, in comparison with the NAV, as measured by ECM integrated density. However, the relative thickness of the main load-bearing structures of the two tissues, the dense part of fibrous HP (49 ± 2%) and the lamina fibrosa of NAV (47 ± 4%), was similar. In both tissues, the secant elastic modulus (Es) was significantly lower in the transversal direction (p < 0.05) than in the longitudinal direction. This proved that both tissues were anisotropic. No statistically significant differences in UTS (ultimate tensile strength) values and in calculated bending stiffness values in the longitudinal or transversal direction were found between HP and NAV. Our study confirms that HP has an advantageous ECM biopolymeric structure and has the biomechanical properties required for a tissue from which an autologous heart valve replacement may be constructed.

Tissue engineering: Dentin - pulp complex regeneration approaches (A review)

Dental pulp is a highly specialized tissue that preserves teeth. It is important to maintain the capabilities of dental pulp before a pulpectomy by creating a local restoration of the dentin-pulp complex from residual dental pulp. The articles identified were selected by two reviewers based on entry and exit criteria. All relevant articles indexed in PubMed, Springer, Science Direct, and Scopus with no limitations from 1961 to 2016 were searched. Factors investigated in the selected articles included the following key words: Dentin-Pulp Complex, Regeneration, Tissue Engineering, Scaffold, Stem Cell, and Growth Factors. Of the 233 abstracts retrieved, the papers which were selected had evaluated the clinical aspects of the application of dentin-pulp regeneration. Generally, this study has introduced a new approach to provoke the regeneration of the dentin-pulp complex after a pulpectomy, so that exogenous growth factors and the scaffold are able to induce cells and blood vessels from the residual dental pulp in the tooth root canal. This study further presents a new strategy for local regeneration therapy of the dentin-pulp complex. This review summarizes the current knowledge of the potential beneficial effects derived from the interaction of dental materials with the dentin-pulp complex as well as potential future developments in this exciting field.

Application of hydrogels in heart valve tissue engineering

With an increasing number of patients requiring valve replacements, there is heightened interest in advancing heart valve tissue engineering (HVTE) to provide solutions to the many limitations of current surgical treatments. A variety of materials have been developed as scaffolds for HVTE including natural polymers, synthetic polymers, and decellularized valvular matrices. Among them, biocompatible hydrogels are generating growing interest. Natural hydrogels, such as collagen and fibrin, generally show good bioactivity but poor mechanical durability. Synthetic hydrogels, on the other hand, have tunable mechanical properties; however, appropriate cell-matrix interactions are difficult to obtain. Moreover, hydrogels can be used as cell carriers when the cellular component is seeded into the polymer meshes or decellularized valve scaffolds. In this review, we discuss current research strategies for HVTE with an emphasis on hydrogel applications. The physicochemical properties and fabrication methods of these hydrogels, as well as their mechanical properties and bioactivities are described. Performance of some hydrogels including in vitro evaluation using bioreactors and in vivo tests in different animal models are also discussed. For future HVTE, it will be compelling to examine how hydrogels can be constructed from composite materials to replicate mechanical properties and mimic biological functions of the native heart valve.

Heart valve regeneration: the need for systems approaches

Tissue-engineered heart valves are promising alternatives to address the limitations of current valve replacements, particularly for growing children. Current heart valve tissue engineering strategies involve the selection of biomaterial scaffolds, cell types, and often in vitro culture conditions aimed at regenerating a valve for implantation and subsequent maturation in vivo. However, identifying optimal combinations of cell sources, biomaterials, and/or bioreactor conditions to produce functional, durable valve tissue remains a challenge. Despite some short-term success in animal models, attempts to recapitulate aspects of the native heart valve environment based on 'best guesses' of a limited number of regulatory factors have not proven effective. Better outcomes for valve tissue regeneration will likely require a systems-level understanding of the relationships between multiple interacting regulatory factors and their effects on cell function and tissue formation. Until recently, conventional culture methods have not allowed for multiple design parameters to be considered at once. Emerging microtechnologies are well suited to systematically probe multiple inputs, in combination, in high throughput and with great precision. When combined with statistical and network systems analyses, these microtechnologies have excellent potential to define multivariate signal-response relationships and reveal key regulatory pathways for robust functional tissue regeneration.

Evaluation of bioprosthetic heart valve failure using a matrix-fibril shear stress transfer approach

A matrix-fibril shear stress transfer approach is devised and developed in this paper to analyse the primary biomechanical factors which initiate the structural degeneration of the bioprosthetic heart valves (BHVs). Using this approach, the critical length of the collagen fibrils l c and the interface shear acting on the fibrils in both BHV and natural aortic valve (AV) tissues under physiological loading conditions are calculated and presented. It is shown that the required critical fibril length to provide effective reinforcement to the natural AV and the BHV tissue is l c  = 25.36 µm and l c  = 66.81 µm, respectively. Furthermore, the magnitude of the required shear force acting on fibril interface to break a cross-linked fibril in the BHV tissue is shown to be 38 µN, while the required interfacial force to break the bonds between the fibril and the surrounding extracellular matrix is 31 µN. Direct correlations are underpinned between these values and the ultimate failure strength and the failure mode of the BHV tissue compared with the natural AV, and are verified against the existing experimental data. The analyses presented in this paper explain the role of fibril interface shear and critical length in regulating the biomechanics of the structural failure of the BHVs, for the first time. This insight facilitates further understanding into the underlying causes of the structural degeneration of the BHVs in vivo.

Manipulation of valve composition to elucidate the role of collagen in aortic valve calcification

Background

Extracellular matrix (ECM) disarray is found in calcific aortic valvular disease (CAVD), yet much remains to be learned about the role of individual ECM components in valvular interstitial cell (VIC) function and dysfunction. Previous clinical analyses have shown that calcification is associated with decreased collagen content, while previous in vitro work has suggested that the presence of collagen attenuates the responsiveness of VICs to pro-calcific stimuli. The current study uses whole leaflet cultures to examine the contributions of endogenous collagen in regulating the phenotype and calcification of VICs.

Methods

A “top-down” approach was used to characterize changes in VIC phenotype in response to collagen alterations in the native 3D environment. Collagen-deficient leaflets were created via enzymatic treatment and cultured statically for six days in vitro. After culture, leaflets were harvested for analysis of DNA, proliferation, apoptosis, ECM composition, calcification, and gene/protein expression.

Results

In general, disruption of collagen was associated with increased expression of disease markers by VICs in whole organ leaflet culture. Compared to intact control leaflets, collagen-deficient leaflets demonstrated increased VIC proliferation and apoptosis, increased expression of disease-related markers such as alpha-smooth muscle actin, alkaline phosphatase, and osteocalcin, and an increase in calcification as evidenced by positive von Kossa staining.

Conclusions

These results indicate that disruption of the endogenous collagen structure in aortic valves is sufficient to stimulate pathological consequences in valve leaflet cultures, thereby highlighting the importance of collagen and the valve extracellular matrix in general in maintaining homeostasis of the valve phenotype.

Sequential use of human-derived medium supplements favours cardiovascular tissue engineering

For clinical application of tissue engineering strategies, the use of animal-derived serum in culture medium is not recommended, because it can evoke immune responses in patients. We previously observed that human platelet-lysate (PL) is favourable for cell expansion, but generates weaker tissue as compared to culture in foetal bovine serum (FBS). We investigated if human serum (HS) is a better human supplement to increase tissue strength. Cells were isolated from venous grafts of 10 patients and expanded in media supplemented with PL or HS, to determine proliferation rates and expression of genes related to collagen production and maturation. Zymography was used to assess protease expression. Collagen contraction assays were used as a two-dimensional (2D) model for matrix contraction. As a prove of principle, 3D tissue culture and tensile testing was performed for two patients, to determine tissue strength. Cell proliferation was lower in HS-supplemented medium than in PL medium. The HS cells produced less active matrix metallo-proteinase 2 (MMP2) and showed increased matrix contraction as indicated by gel contraction assays and 3D-tissue culture. Tensile testing showed increased strength for tissues cultured in HS when compared to PL. This effect was more pronounced if cells were sequentially cultured in PL, followed by tissue culture in HS. These data suggest that sequential use of PL and HS as substitutes for FBS in culture medium for cardiovascular tissue engineering results in improved cell proliferation and tissue mechanical properties, as compared to use of PL or HS apart.

Decreased mechanical properties of heart valve tissue constructs cultured in platelet lysate as compared to fetal bovine serum

In autologous heart valve tissue engineering, there is an ongoing search for alternatives of fetal bovine serum (FBS). Human platelet-lysate (PL) might be a promising substitute. In the present article, we aimed to examine the tissue formation, functionality, and mechanical properties of engineered three-dimensional tissue constructs cultured in PL as a substitute for FBS. Our results show that tissue constructs that were cultured in PL and FBS produce similar amounts of collagen, glycosoaminoglycans, and collagen crosslinks, and that the cellular phenotype remains unchanged. Nevertheless, mechanical testing showed that the ultimate tensile strength in PL constructs was on average approximately three times lower as compared to FBS (0.25 vs. 0.74 MPa, respectively, p<0.01), and also the elastic modulus was almost three times lower (1.33 MPa of PL constructs vs. 3.94 MPa of FBS constructs, p<0.01). Additional tests indicated that this difference might be explained by different collagen fiber architecture possibly due to increased production of matrix-degrading proteases by cells cultured in PL. In summary, our results indicate that PL is not preferred for the culture of strong heart valve tissue constructs.

Nanotechnology, bionanotechnology and microbial cell factories

Nanotechnology is increasingly using both materials and nano-objects synthesized by living beings, most of them produced by microbial cells. Emerging technologies and highly integrative approaches (such as 'omics and systems biology), that have been largely proven successful for the production of proteins and secondary metabolites are now expected to become fully adapted for the improved biological production of nanostructured materials with tailored properties. The so far underestimated potential of microbial cell factories in nanotechnology and nanomedicine is expected to emerge, in the next years, in the context of novel needs envisaged in the nanoscience universe. This should prompt a careful revisiting of the microbial cell factories as the most versatile biological platforms to supply functional materials for nanotechnological applications.

Platelet-lysate as an autologous alternative for fetal bovine serum in cardiovascular tissue engineering

There is an ongoing search for alternative tissue culture sera to engineer autologous tissues, since use of fetal bovine serum (FBS) is limited under Good Tissue Practice guidelines. We compared FBS with human platelet-lysate (PL) in media for in vitro cell culture. A threefold increase in duplication rate was found when human, saphenous vein-derived myofibroblasts were cultured in PL, whereas expression of marker proteins (alpha-smooth muscle actin, vimentin, desmin, and nonmuscle myosin heavy chain) was similar. Heat shock protein 47 mRNA expression was increased in PL cells, and type III collagen fibers were seen on PL-cell monolayers but not on cells cultured in FBS. These results imply a more efficient collagen fiber production. We also found higher levels of proteins involved in tissue repair and collagen remodeling, which could explain increased production of proteases and protease inhibitors by PL cells. Our findings indicate that PL is beneficial due to the increased duplication rate, in addition to the increased matrix production and remodeling. This could lead to production of strong tissue with properly organized collagen fibers, which is important for heart valve tissue engineering.

On the multiscale modeling of heart valve biomechanics in health and disease

Theoretical models of the human heart valves are useful tools for understanding and characterizing the dynamics of healthy and diseased valves. Enabled by advances in numerical modeling and in a range of disciplines within experimental biomechanics, recent models of the heart valves have become increasingly comprehensive and accurate. In this paper, we first review the fundamentals of native heart valve physiology, composition and mechanics in health and disease. We will then furnish an overview of the development of theoretical and experimental methods in modeling heart valve biomechanics over the past three decades. Next, we will emphasize the necessity of using multiscale modeling approaches in order to provide a comprehensive description of heart valve biomechanics able to capture general heart valve behavior. Finally, we will offer an outlook for the future of valve multiscale modeling, the potential directions for further developments and the challenges involved.

Transforming growth factor beta 1 and hyaluronan oligomers synergistically enhance elastin matrix regeneration by vascular smooth muscle cells

Elastin is a vital structural and regulatory matrix protein that plays an important role in conferring elasticity to blood vessel wall. Previous tissue engineering approaches to regenerate elastin in situ or within tissue engineering constructs are curtailed by innate poor elastin synthesis potential by adult vascular smooth muscle cells (SMCs). Currently, we seek to develop cellular cues to enhance tropoelastin synthesis and improve elastin matrix yield, stability, and ultrastructure. Our earlier studies attest to the elastogenic utility of hyaluronan (HA)-based cellular cues, though their effects are fragment size dependent and dose dependent, with HA oligomers deemed most elastogenic. We presently show transforming growth factor beta 1 (TGF-beta1) and HA oligomers, when provided concurrently, to synergistically and dramatically improve elastin matrix regeneration by adult vascular SMCs. Together, these cues suppress SMC proliferation, enhance synthesis of tropoelastin (8-fold) and matrix elastin protein (5.5-fold), and also improve matrix elastin yield (45% of total elastin vs. 10% for nonadditive controls), possibly by more efficient recruitment of tropoelastin for crosslinking. The density of desmosine crosslinks within the elastin matrix was itself attenuated, although the cues together modestly increased production and activity of the elastin crosslinking enzyme, lysyl oxidase. TGF-beta1 and HA oligomers together induced much greater assembly of mature elastin fibers than they did separately, and did not induce matrix calcification. The present outcomes might be great utility to therapeutic regeneration of elastin matrix networks in situ within elastin-compromised vessels, and within tissue-engineered vascular graft replacements.

Benefits of concurrent delivery of hyaluronan and IGF-1 cues to regeneration of crosslinked elastin matrices by adult rat vascular cells

Elastin, a major component of vascular matrices, critically determines vascular mechanics and maintains the quiescence of smooth muscle cells (SMCs). Attempts to regenerate elastin in elastin-compromised blood vessels using tissue-engineering approaches is limited by the unavailability of elastogenic cues to upregulate poor elastin output and matrix assembly by adult vascular cells. We previously showed that hyaluronan (HA) elastogenically stimulates aortic SMCs, although these effects are highly specific to HA fragment size. The elastogenic response of SMCs can also be modulated with growth factors such as insulin-like growth factor (IGF-1). Here, we evaluate the benefits of concurrent delivery of HA fragments (0.76-2000 kDa) and IGF-1 (500 ng/ml) to elastin synthesis, organization and crosslinking. The study outcomes show that, relative to supplement-free cultures, IGF-1 and long-chain HA/large HA fragments, but not HA oligomers, together induce multifold increases in the synthesis of elastin precursors, structural elastin matrix yields and crosslink densities within cell layers, and encourage elastic fibre formation. These outcomes are not all obtained when either of the cues is provided separately. IGF-1 and large HA fragments (>20 kDa) also together inhibit cell proliferation, a concern in elastin-compromised vessels, where SMC hyperproliferation is common. The results will benefit efforts to provide exogenous or scaffold-based elastogenic cues (IGF-1 + HMW HA/large HA fragments) to enable robust and faithful regeneration of elastin matrix structures in vivo or in vitro. The present outcomes may be used to restore elastin matrix homeostasis in de-elasticized vessels and tissue-engineered constructs that may be grafted as a substitute.

Immunoproteomic identification of bovine pericardium xenoantigens

Bovine pericardium is an important biomaterial with current application in glutaraldehyde-fixed bioprosthetic heart valves and possible future application as an unfixed biological scaffold for tissue engineering. The importance of both humoral and cell-mediated rejection responses toward fixed and unfixed xenogeneic tissues has become increasingly apparent. However, the full scope and specific identities of bovine pericardium proteins that can elicit an immune response remain largely unknown. In this study, an immunoproteomic approach was used to survey bovine pericardium proteins for their ability to elicit a humoral immune response in rabbits. A two-stage protein extraction protocol was used to separate bovine pericardium proteins into water- and lipid-soluble fractions. Two-dimensional (2-D) gel electrophoresis was performed to separate the proteins from each fraction. Western blots were generated from 2-D gels of both bovine pericardium protein fractions. These blots were probed with serum from rabbits immunized with bovine pericardium and a secondary antibody was used to assess for IgG positivity. Western blots were compared to duplicate 2-D gels and proteins in matched spots were identified by tandem mass spectrometry. Thirty-one putative protein antigens were identified, eight of which are known to be antigenic from previous studies. All of the putative antigens demonstrated progressive staining intensity with increasing days of post-exposure serum. Identified antigenic proteins represented a variety of functional and structural protein types, and included both cellular and matrix proteins. The results of this study have implications for the use of bovine pericardium as a biomaterial in bioprostheses and tissue engineering applications, as well as xenotransplantation in general.