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The delivery of hydrophilic drugs from hydrophobic polymers is a long-standing challenge in the biomaterials field due to the limited solubility of the therapeutic agent within the polymer matrix. In this work, we develop a drug delivery mechanism that enables the impregnation and subsequent elution of hydrophilic drugs from a hydrophobic polymer material. This was achieved by synthesizing core cross-linked star polymer amphiphiles with hydrophilic cores and hydrophobic coronas. While significant work has been done to create nanocarriers for hydrophilic drugs, this work is distinct from previous work in that it designs amphiphilic and core cross-linked particles for controlled release from hydrophobic matrices. Ultraviolet-mediated atom transfer radical polymerization was used to synthesize the poly(ethylene glycol) (PEG)-based hydrophilic cores of the star polymers, and hydrophobic coronas of poly(caprolactone) (PCL) were then built onto the stars using ring-opening polymerization. We illustrated the cytocompatibility of PCL loaded with these star polymers through human endothelial cell adhesion and proliferation for up to 7 days, with star loadings of up to 40 wt %. We demonstrated successful loading of the hydrophilic drug heparin into the star polymer core, achieving a loading efficiency and content of 50 and 5%, respectively. Finally, the heparin-loaded star polymers were incorporated into a PCL matrix and sustained release of heparin was illustrated for over 40 days. These results support the use of core cross-linked star polymer amphiphiles for the delivery of hydrophilic drugs from hydrophobic polymer matrices. These materials were developed for application as drug-eluting and biodegradable coronary artery stents, but this flexible drug delivery platform could have impact in a broad range of medical applications.

Antibiotic-resistant bacteria are a severe threat to human health. The World Health Organization's Global Antimicrobial Surveillance System has revealed widespread occurrence of antibiotic resistance among half a million patients across 22 countries, with Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae being the most common resistant species. Antimicrobial nanoparticles are emerging as a promising alternative to antibiotics in the fight against antimicrobial resistance. In this work, selenium nanoparticles coated with the antimicrobial polypeptide, e-poly-l-lysine, (Se NP-e-PL) were synthesized and their antibacterial activity and cytotoxicity were investigated. Se NP-e-PL exhibited significantly greater antibacterial activity against all eight bacterial species tested, including Gram-positive, Gram-negative, and drug-resistant strains, than their individual components, Se NP and e-PL. The nanoparticles showed no toxicity toward human dermal fibroblasts at the minimum inhibitory concentrations, demonstrating a therapeutic window. Furthermore, unlike the conventional antibiotic kanamycin, Se NP-e-PL did not readily induce resistance in E. coli or S. aureus. Specifically, S. aureus began to develop resistance to kanamycin from ∼44 generations, whereas it took ∼132 generations for resistance to develop to Se NP-e-PL. Startlingly, E. coli was not able to develop resistance to the nanoparticles over ∼300 generations. These results indicate that the multifunctional approach of combining Se NP with e-PL to form Se NP-e-PL is a highly efficacious new strategy with wide-spectrum antibacterial activity, low cytotoxicity, and significant delays in development of resistance.

We have engineered biomaterials that display nanoclusters of ligands that bind both integrin and syndecan-4 cell receptors. These surfaces regulate cell behaviors under static conditions including adhesion, spreading, actin stress fiber formation, and migration. The syndecan-4 receptors are also critical mediators of cellular mechanotransduction. In this contribution we assess whether this novel class of materials can regulate the response of cells to applied mechanical stimulation, using the shear stress imparted by laminar fluid flow as a model stimulus. Specifically, we assess endothelial cell detachment due to flow, cell alignment due to flow, and cell adhesion from the flowing fluid. A high degree of cell retention was observed on surfaces containing integrin-binding ligands or a mixed population of integrin- and syndecan-binding ligands. However, the presence of both ligand types was necessary for the cells to align in the direction of flow. These results imply that integrin engagement is necessary for adhesion strength, but engagement of both receptor types aids in appropriate mechanotransduction. Additionally, it was found that surfaces functionalized with both ligand types were able to scavenge a larger number of cells from flow, and to do so at a faster rate, compared to surfaces functionalized with only integrin- or syndecan-binding ligands. These results show that interfaces functionalized with both integrin- and syndecan-binding ligands regulate a significant range of biophysical cell behaviors in response to shear stress.

Purpose: Selenium nanoparticles (Se NPs) are promising antibacterial agents to tackle the growing problem of antimicrobial resistance. The aim of this study was to fabricate Se NPs with a net positive charge to enhance their antibacterial efficacy. Methods: Se NPs were coated with a positively charged protein--recombinant spider silk protein eADF4([kappa] 16)--to give them a net positive surface charge. Their cytotoxicity and antibacterial activity were investigated, with negatively charged polyvinyl alcohol coated Se NPs as a control. Besides, these eADF4([kappa] 16)-coated Se NPs were immobilized on the spider silk films, and the antibacterial activity of these films was investigated. Results: Compared to the negatively charged polyvinyl alcohol coated Se NPs, the positively charged eADF4([kappa] 16)-coated Se NPs demonstrated a much higher bactericidal efficacy against the Gram-negative bacteria E. coli, with a minimum bactericidal concentration (MBC) approximately 50 times lower than that of negatively charged Se NPs. Cytotoxicity testing showed that the eADF4([kappa] 16)-coated Se NPs are safe to both Balb/3T3 mouse embryo fibroblasts and HaCaT human skin keratinocytes up to 31 [micro]g/mL, which is much higher than the MBC of these particles against E. coli (8 [+ or -] 1 [micro]g/mL). In addition, antibacterial coatings were created by immobilising the eADF4([kappa] 16)-coated Se NPs on positively charged spider silk films and these were shown to retain good bactericidal efficacy and overcome the issue of low particle stability in culture broth. It was found that these Se NPs needed to be released from the film surface in order to exert their antibacterial effects and this release can be regulated by the surface charge of the film, such as the change of the spider silk protein used. Conclusion: Overall, eADF4([kappa] 16)-coated Se NPs are promising new antibacterial agents against life-threatening bacteria.

Decellularized extracellular matrix (dECM) deposited by mesenchymal stromal cells (MSCs) has emerged as a promising substrate for improved expansion of MSCs. To date, essentially all studies that have produced dECM for MSC expansion have done so on tissue culture plastic or glass. However, substrate surface chemistry has a profound impact on the adsorption of proteins that mediate cell-material interactions, and different surface chemistries can cause changes in cell behavior, ECM deposition, and the

Biomaterials are a cornerstone technology of the biomedical device, tissue engineering, and regenerative medicine industries. While traditional biomaterials are fully defined synthetics, growing evidence supports the use of extracellular matrix-based biomaterials produced through the decellularization of organs, tissues, or cell cultures. These materials are particularly advantageous as they largely retain the structure and the biochemical nature of the original tissue, properties that are often difficult to reproduce with synthetics. Indeed, there are many FDA-approved and clinically used extracellular matrix-based materials that are generated through decellularization processes. In this review, we first describe methods of decellularization used to produce these materials and their associated advantages and limitations, discuss the current use of extracellular matrix-based materials in regenerative engineering applications, describe the areas where current research is occurring, and forecast areas where impactful research may appear. The regeneration of tissues often requires a scaffold material to support and guide the cells that are performing the repair. Often, these materials are manmade and lack many of the key features present in native tissue. However, a tissue can be processed to remove its cells (a process called decellularization), leaving behind a scaffold of proteins and polysaccharides known as the extracellular matrix. These decellularized matrices are attractive scaffolds for use in regenerative medicine applications, and they are the subject of this review.

Decellularized extracellular matrixes (dECM) derived from mesenchymal stem cell (MSC) cultures have recently emerged as cell culture substrates that improve the proliferation, differentiation, and maintenance of MSC phenotype during ex vivo expansion. These biomaterials have considerable potential in the fields of stem cell biology, tissue engineering, and regenerative medicine. Processing the dECMs into concentrated solutions of biomolecules that enable the useful properties of the native dECM to be transferred to a new surface via a simple adsorption step would greatly increase the usefulness and impact of this technology. The development of such solutions, hereafter referred to as transferable matrixes, is the focus of this article. In this work, we produced transferable matrixes from dECM derived from two human placental MSC cell lines (DMSC23 and CMSC29) using pepsin digestion (P-ECM), urea extraction (U-ECM), and mechanical homogenization in acetic acid (AA-ECM). Native dECMs improved primary DMSC proliferation as well as osteogenic and adipogenic differentiation, compared with traditional expansion procedures. Interestingly, tissue culture plastic coated with P-ECM was able to replicate the proliferative effects of native dECM, while U-ECM was able to replicate osteogenic differentiation. These data illustrate the feasibility of producing dECM-derived transferable matrixes that replicate key features of the native matrixes and show that different processing techniques produce transferable matrixes with varying bioactivities. Additionally, these transferable matrixes are able to coat 1.3-5.2 times the surface area covered by the native dECM, facilitating scale-up of this technology.

Microbial colonization, infection, and biofilm formation are major complications in the use of implants and are the predominant risk factors in implant failure. Although aseptic surgery and the administration of antimicrobial drugs may reduce the risk of infection, the systemic use of antibiotics can lead to a lack of efficacy, an increase in the risk of tissue toxicity, and the development of drug-resistant infections. To reduce implant-related infections, antimicrobial materials are increasingly being investigated and applied to implant surfaces using various methods depending on the agents and their microbicidal mechanisms. Through the development of biomaterials and nanotechnology, antimicrobial nanoparticles are becoming promising candidates for implant coatings, as their multifactorial antimicrobial mechanisms combat microbial adherence, viability, and biofilm formation. Despite their antimicrobial promise, the application of nanoparticles onto implant surfaces while retaining their antimicrobial potency faces many challenges. Herein, we review the potential and challenges associated with the design and implementation of antimicrobial nanoparticle coatings for the medical implant industry, particularly focusing on manufacturing considerations, sterilization, long-term stability, protein fouling, regulation, and safety, with a view to providing researchers the necessary tools to aid the translation of materials from the bench to the clinic.

Electrospun poly(vinylidene fluoride-co-hexafluoro propylene) (PVDF-HFP) nanofibre membranes are developed for CO2 stripping within a membrane contactor. The porous and hydrophobic nature of the membranes is ideal for membrane CO2 stripping applications, providing fast gas transport, high CO2 recovery and mechanical strength. Three different morphologies of the PVDF-HFP membranes are assessed: nanofibre membranes (NFM), bead-on-string membranes (NFM-BS) and microparticles on nanofibre membranes (NFM-MP). We illustrate that both the bead-on-string and microparticles on nanofibre membranes are more hydrophobic compared to nanofibre constructs and a traditional asymmetric control membrane. The NFM-BS and NFM-MP membranes both exhibit significantly improved CO2 stripping flux over short times, while the NFM-BS membranes provides significantly improved stripping flux over longer times (240 h) compared to all other treatments, including conventional asymmetric phase inversion membranes. The structures may also show promise for membrane distillation applications.

Tissue engineering and regenerative medicine (TERM) is a field that applies biology and engineering principles to "restore, maintain or repair a tissue after injury". Besides the potential to treat various diseases, these endeavours increase our understanding of fundamental cell biology. Although TERM has progressed rapidly, engineering a whole organ is still beyond our skills, primarily due to the complexity of tissues. Material science and current manufacturing methods are not capable of mimicking this complexity. Therefore, many researchers explore the use of naturally derived materials that maintain important biochemical, structural and mechanical properties of tissues. Consequently, employing non-cellular components of tissues, particularly the extracellular matrix, has emerged as an alternative to synthetic materials. Because of their complexity, decellularized tissues are not as well defined as synthetic materials but they provide cells with a microenvironment that resembles their natural niche. Decellularized tissues are produced from a variety of sources, among which the fetal membranes are excellent candidates since their supply is virtually unlimited, they are readily accessible with minimum ethical concerns and are often discarded as a biological waste. In this review, we will discuss various applications of decellularized fetal membranes as substrates for the expansion of stem cells, their use as two and three-dimensional scaffolds for tissue regeneration, and their use as cell delivery systems. We conclude that fetal membranes have great potential for use in TERM.

A dual-responsive, cell capture and release surface was prepared through the incorporation of phenylboronic acid (PBA) groups into an oxime-based polyethylene glycol (PEG) hydrogel. Owing to its PEG-like properties, the unfunctionalized hydrogel was nonfouling. The use of highly efficient oxime chemistry allows the incorporation of commercially available 3,5-diformylphenyl boronic acid into the hydrogel matrix. Thus, the surface properties of the hydrogel were modified to enable reversible cell capture and release. Boronic ester formation between PBA groups and cell surface carbohydrates enabled efficient cell capture at pH 6.8. An increase to pH 7.8 resulted in cell detachment. This capture-and-release procedure was performed on MCF-7 human breast cancer cells, NIH-3T3 fibroblast cells, and primary human umbilical vein endothelial cells (HUVECs) and could be cycled with negligible loss in activity. The facile preparation of PBA-functionalized surfaces presented here has applications in biomedical fields such as cell diagnostics and cell culture.

The overuse of antibiotics has induced the rapid development of antibiotic resistance in bacteria. As a result, antibiotic efficacy has become limited, and infection with multidrug-resistant bacteria is considered to be one of the largest global human health threats. Consequently, new, effective and safe antimicrobial agents need to be developed urgently. One promising candidate to address this requirement is selenium nanoparticles (Se NPs), which are made from the essential dietary trace element Se and have antimicrobial activity against Gram-positive bacteria. The size of nanomaterials can strongly affect their biophysical properties and functions; however, the effects of the size of Se NPs on their antibacterial efficacy has not been systematically investigated. Therefore, in this work, spherical Se NPs ranging from 43 to 205 nm in diameter were fabricated, and their mammalian cytotoxicity and antibacterial activity as a function of their size were systematically studied. The antibacterial activity of the Se NPs was shown to be strongly size dependent, with 81 nm Se NPs showing the maximal growth inhibition and killing effect of methicillin-sensitive and methicillin-resistant Staphylococcus aureus (MSSA and MRSA). The Se NPs were shown to have multi-modal mechanisms of action that depended on their size, including depleting internal ATP, inducing ROS production, and disrupting membrane potential. All the Se NPs were non-toxic towards mammalian cells up to 25 μg mL−1. Furthermore, the MIC value for the 81 nm particles produced in this research is 16 ± 7 μg mL−1, significantly lower than previously reported MIC values for Se NPs. This data illustrates that Se NP size is a facile yet critical and previously underappreciated parameter that can be tailored for maximal antimicrobial efficacy. We have identified that using Se NPs with a size of 81 nm and concentration of 10 μg mL−1 shows promise as a safe and efficient way to kill S. aureus without damaging mammalian cells.

Biofabrication is a fast-evolving and multi-disciplinary field, harnessing the benefits and capabilities of additive manufacturing and complementary bioassembly techniques at the intersection of biology and engineering. Biofabrication is promising for printing of transplantable tissues, though near-term applications in practice include biomimetically engineered models for drug discovery, cosmetics testing, tissue regeneration and medical devices. Recapitulating the structure and complexity of native tissues, however, remains a significant challenge. To address this, recent biofabrication work has demonstrated improvements in the scale, rate and intricacy at which tissues can be fabricated, with examples including work in volumetric bioprinting, scaffold-free bioassembly, and hybrid biofabrication strategies. These and other emerging techniques have the potential for the strategic arrangement of multiple materials, cells and extracellular matrix components at length scales down to the level of single cells. This review evaluates emerging biofabrication techniques and highlights their recent application and future potential in producing complex heterogeneous tissues.

Membrane gas–liquid contactors have been developed to reduce the capital cost and energy consumption of conventional CO2 absorption and stripping columns. As a hybrid technology of membrane separation and amine absorption, these units can improve the gas absorption process by generating 400–1500% greater mass transfer area per unit volume leading to smaller equipment sizes. Regeneration of CO2 can occur within a membrane contactor below the boiling point of the solvent, leading to lower energy consumption. Over recent years, a vast array of polymeric and ceramic materials have been considered for membrane gas–liquid contactors and an array of solvents have been used including amines, potassium carbonate, ammonia and amino acids. The major technical challenge with membrane contactors is the wetting of the membrane pores with solvent, which reduces the mass transfer coefficient. However, other factors such as the choice of solvent, the placement of the solvent on the shell or lumen side and the operational temperature are also critical to success. This review describes the recent progress in membrane gas–liquid contactor technology for CO2 separation in terms of the materials, solvents, modules and processes and provides direction on where research can best be directed in the future to enhance the feasibility of the technology’s industrial application.

Blood contacting devices are commonly used in today's medical landscape. However, such devices (including small diameter vascular grafts) are limited by poor blood compatibility and may fail due to thrombosis. An attractive strategy for improving the blood compatibility of such devices is to generate biomaterials that foster a confluent and functioning endothelial cell layer. Synthesizing materials that display integrin-binding peptide ligands is a common way to promote endothelialization. However, in addition to integrin-ligand binding, integrin clustering is necessary to achieve intracellular signaling events that influence cellular phenotype. In this study, we explored the impact of nano-scale clustering of integrin-binding ligands on endothelial cell functions by designing novel materials that promote the clustering of integrin receptors. RGD-functionalized copolymers were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization and used for the preparation of random and nano-clustered surfaces spanning a range of global and local RGD densities (global densities 0.4-1.9 μg of peptide per mg of polymer and local densities of 1-2.4 ligands per nano-cluster). The adhesion and migration of endothelial cells was improved on nano-clustered surfaces compared to random surfaces. The highest adhesion and migration speed of endothelial cells and the rapid development of the endothelial monolayer were observed on surfaces with the highest local and global peptide density. These results indicate that the nano-clustering of peptide ligands is a promising strategy for next generation cardiovascular biomaterials, especially for small diameter vascular graft applications where the development of a confluent and functioning endothelium holds the potential to prevent device failure due to thrombosis.

Decellularized cell secreted matrices (dECMs) are an emerging class of materials with unique and beneficial biological properties, and have found wide-ranging applications in the fields of tissue engineering and regenerative medicine. These materials are obtained through the decellularization of cell cultures, resulting in the isolation of an extracellular matrix that is believed to be a more biologically accurate representation of the in vivo cell niche compared with conventional cell culture substrates. In this chapter, we discuss the methods used to produce and characterize the dECMs, as well as the beneficial biological properties that have made them promising materials in cell expansion and tissue engineering applications.

Coatings produced from extracellular matrixes (ECMs) have emerged as promising surfaces for the improved ex vivo expansion of mesenchymal stem cells (MSCs). However, identifying a readily available source of ECM to generate these coatings is currently the bottleneck of this technology. In this study, we assessed if ECM coatings derived from decellularized fetal membranes were a suitable substrate for MSC expansion. We separated and decellularized the two main components of the fetal membranes, the amnion and the chorion. Characterization of the decellularized membranes revealed that each membrane component has a distinct composition, implying that coatings produced from these materials would have unique biological properties. The membranes were processed further to produce solubilized forms of the decellularized amniotic membrane (s-dAM) and decellularized chorionic membrane (s-dCM). On s-dAM coatings decidual MSCs (DMSC) were more proliferative than those cultured on tissue culture plastic alone or on Matrigel coatings; were smaller in size (a measure of MSC potency); exhibited greater adipogenic differentiation capacity; and improved osteogenic capacity. Additionally, long term culture studies showed late passage DMSCs (passage 8) cultured on s-dAM showed a decrease in cell diameter over three passages. These data support the use of s-dAM as a substrate for improved MSC expansion. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 232-242, 2019.

Biomaterials are a powerful platform for directing cellular behaviour. Herein, we employed a biomimetic strategy to synthesize a low-fouling polymer functionalized with nano-scale clusters of ligands that bind both integrin and syndecan-4 receptors, as both receptor types are critical in focal adhesion signalling and mechanotransduction. Our results demonstrate that the presence of both ligand types synergistically increases the adhesion of human umbilical vein endothelial cells (more than a two fold increase after 4 h) and increases the rate of surface endothelialization compared to surfaces functionalized with only one ligand type. Additionally, we observe that the mixed population of ligands regulates endothelial cell migration, likely due to improved focal adhesion formation as observed through confocal microscopy. Furthermore, we illustrate that only endothelial cells cultured on these mixed ligand surfaces exhibit the appropriate morphological changes - elongation and alignment in the direction of flow - when exposed to laminar shear flow, and neither of the individual ligands alone is sufficient. These results illustrate that both receptor types must be engaged for optimum cell-material interactions and are mandatory for appropriate mechanotransduction. The results presented in this manuscript will be critical for the development of next generation biomedical devices and tissue engineering scaffolds.

Material systems that exhibit tailored interactions with cells are a cornerstone of biomaterial and tissue engineering technologies. One method of achieving these tailored interactions is to biofunctionalize materials with peptide ligands that bind integrin receptors present on the cell surface. However, cell biology research has illustrated that both integrin binding and integrin clustering are required to achieve a full adhesion response. This biophysical knowledge has motivated researchers to develop material systems biofunctionalized with nanoscale clusters of ligands that promote both integrin occupancy and clustering of the receptors. These materials have improved a wide variety of biological interactions in vitro including cell adhesion, proliferation, migration speed, gene expression, and stem cell differentiation; and improved in vivo outcomes including increased angiogenesis, tissue healing, and biomedical device integration. This review first introduces the techniques that enable the fabrication of these nanopatterned materials, describes the improved biological effects that have been achieved, and lastly discusses the current limitations of the technology and where future advances may occur. Although this technology is still in its nascency, it will undoubtedly play an important role in the future development of biomaterials and tissue engineering scaffolds for both in vitro and in vivo applications.

International audience; Hydrogen sulfide (H2 S) has been identified as an important cell-signaling mediator and has a number of biological functions, such as vascular smooth muscle relaxation, neurotransmission, and regulation of inflammation. A facile and versatile approach for H2 S production initiated by light irradiation and controlled by reaction with an amine or an amino acid was developed. The donor was synthesized in a one-pot reaction, and simple crystallization led to a yield of approximately 90 %. The synthetic strategy is scalable and versatile, and the H2 S donors can be expressed ina number of different molecular and macromolecular forms, including crystalline small-molecule compounds, water-soluble polymers, polystyrene films, and hydrogels. The H2 S donors based on polystyrene film and hydrogel were used as cell-culture scaffolds. The H2 S donor based on water-soluble polymer was applied in photocontrolled inhibition of P-selectin expression on human platelets and subsequent regulation of platelet aggregation. This study provides the simplest controllable H2 S source to study its biological functions. The developed materials are also new therapeutic platforms to deliver H2 S, as there is no accumulation of toxic byproducts, and the donor materials from polystyrene films and hydrogels can be readily removed after releasing H2 S.

The field of biomaterials science has exhibited astounding growth during the last half century. This growth can be attributed to a more thorough understanding of cellular behaviours, new mechanistic insights into cell-materials interactions, advances in polymer synthesis, and the development of innovative fabrication techniques. This progress has enabled biomaterials to transition from materials that fill in for damaged or diseased tissues to implants that actively work with biology to aid in the healing process. In this review, we will discuss several of these advances including emerging knowledge on mechanotransduction, the use of substrate topography in modulating cellular behaviour, and the incorporation of bioactive molecules to foster specific cellular adhesion, promote tissue morphogenesis, and enable biologically driven degradation. We will then consider future challenges and directions in the field.

Transparent, high water content (>65%), and cytocompatible hydrogels, which also possess super high refractive indices (RI > 1.5), are needed for ophthalmological applications. Most hydrogels can achieve either high RI or high water content but not both in the same system because water is a low RI material. Here, high water content/high RI hydrogels fabricated through elevated-temperature UV polymerization of an aqueous solution of acrylamide (AM) and methacrylamide (MAM) with tri(ethylene glycol) dimethacrylate (TEDA) crosslinker are reported. By varying the AM:MAM ratios (2:8 to 8:2) and crosslinker density (5 to 11 mol %), it is discovered that high water content (66%) AM:MAM copolymer hydrogels exhibiting anomalously high refractive indices (1.53); they are also colorless, transparent (99.4%), and cytocompatible with human keratinocytes.

A family of methacrylic terpolymer biomaterials was electrospun into three-dimensional scaffolds. The glass transition temperature of the polymer correlates with the morphology of the resulting scaffold. Glassy materials produce scaffolds with discrete fibers and large pore areas (1531±1365 μm(2)), while rubbery materials produce scaffolds with fused fibers and smaller pore areas (154±110 μm(2)). Three different endothelial-like cell populations were seeded onto these scaffolds under static conditions: human umbilical vein endothelial cells (HUVECs), adult human peripheral blood-derived outgrowth endothelial cells, and umbilical cord blood-derived human blood outgrowth endothelial cells. Cellular behavior depended on both cell type and scaffold topography. Specifically, cord blood-derived outgrowth endothelial cells showed more robust adhesion and growth on all scaffolds in comparison to other cell types as measured by the density of adherent cells, the number of proliferative cells, and the enzymatic activity of the adherent cells. Peripheral blood-derived outgrowth cells exhibited less ability to inhabit the terpolymer interfaces in comparison to their cord blood-derived counterparts. HUVECs also exhibited less of a capacity to colonize the terpolymer interfaces in comparison to the cord blood-derived cells. However, the mature endothelial cells did show scaffold-dependent behavior. Specifically, we observed an increase in their ability to populate the low-porosity scaffolds. All cells maintained an endothelial phenotype after 1 week of culture on the electrospun scaffolds.

Capturing the promise of mesenchymal stem cell (MSC)-based treatments is currently limited by inefficient production of cells needed for clinical therapies. During conventional ex vivo expansion, a large portion of MSCs lose the properties that make them attractive for use in cell therapies. Decellularized extracellular matrix (dECM) has recently emerged as a promising substrate for the improved expansion of MSCs. MSCs cultured on these surfaces exhibit improved proliferation capacity, maintenance of phenotype, and increased differentiation potential. Additionally, these dECMs can be solubilized and used to coat new cell culture surfaces, imparting key biological properties of the native matrices to other surfaces such as tissue engineering scaffolds. Although this technology is still developing, there is potential for an impact in the fields of MSC biology, biomaterials, tissue engineering, and therapeutics. In this article, we review the role of dECM in MSC expansion by first detailing the decellularization methods that have been used to produce the dECM substrates; discussing the shortcomings of current decellularization methods; describing the improved MSC characteristics obtained when the cells are cultured on these surfaces; and considering the effect of the passage number, age of donor, and dECM preparation method on the quality of the dECM. Finally we describe the critical roadblocks that must be addressed before this technology can fulfil its potential, including elucidating the mechanism by which the dECMs improve the expansion of primary MSCs and the identification of a readily available source of dECM. Statement of Significance Current mesenchymal stem cell (MSC) culture methods result in premature cellular senescence or loss of differentiation potential. This creates a major bottleneck in their clinical application, as prolonged expansion is necessary to achieve clinically relevant numbers of cells. Recently, decellularized extracellular matrix (dECM) produced by primary MSC has emerged as an attractive substrate for the improved expansion of MSC; cells cultured on these surfaces retain their desired stem cell characteristics for prolonged times during culture. This review article describes the inception and development of this dECM-based technology, points out existing challenges that must be addressed, and suggests future directions of research. To our knowledge, this is the first review written on the use of dECM for improved mesenchymal stem cell expansion.

Mesenchymal stem/stromal cells (MSCs) exhibit undesired phenotypic changes during ex vivo expansion, limiting production of the large quantities of high quality primary MSCs needed for both basic research and cell therapies. Primary MSCs retain many desired MSC properties including proliferative capacity and differentiation potential when expanded on decellularized extracellular matrix (dECM) prepared from primary MSCs. However, the need to use low passage number primary MSCs (passage 3 or lower) to produce the dECM drastically limits the utility and impact of this technology. Here, we report that primary MSCs expanded on dECM prepared from high passage number (passage 25) human telomerase reverse transcriptase (hTERT) transduced immortal MSC cell lines also exhibit increased proliferation and osteogenic differentiation. Two hTERT-transduced placenta-derived MSC cell lines, CMSC29 and DMSC23 [derived from placental chorionic villi (CMSCs) and decidua basalis (DMSCs), respectively], were used to prepare dECM-coated substrates. These dECM substrates showed structural and biochemical differences. Primary DMSCs cultured on dECM-DMSC23 showed a three-fold increase in cell number after 14 days expansion in culture and increased osteogenic differentiation compared with controls. Primary CMSCs cultured on the dECM-DMSC23 exhibited a two-fold increase in cell number and increased osteogenic differentiation. We conclude that immortal MSC cell lines derived from different parts of the placenta produce dECM with varying abilities for supporting increased primary MSC expansion while maintaining important primary MSC properties. Additionally, this is the first demonstration of using high passage number cells to produce dECM that can promote primary MSC expansion, and this advancement greatly increases the feasibility and applicability of dECM-based technologies.

Synthetic polypeptides are a class of bioinspired polymers with well demonstrated biocompatibility, enzyme biodegradability, and cell adhesive properties, making them promising materials for the preparation of macroporous hydrogels as 3D cellular scaffolds. Three-dimensional macroporous hydrogels composed entirely of biocompatible and enzyme biodegradable synthetic polypeptides have thus been prepared. Under cryoconditions, macroporous hydrogels in the form of macroporous cryogels were prepared using a single copolymer component through direct EDC/sulfo-NHS zero-length cross-linking between poly(l-glutamic acid) (PLG) and poly(l-lysine) (PLL) residues on a PLG-r-PLL random copolypeptide chain. The resulting macroporous cryogels were found to contain large interconnected pores (≥100 μm) highly suitable for tissue engineering applications. Tuning the relative ratios of the amino acid components could result in cryogels with very different pore structures, swelling, and mechanical properties, suitable for developing gels for a range of possible soft tissue engineering applications. These cryogels were shown to be enzymatically biodegradable and demonstrated excellent biocompatibility, cell attachment and cell proliferation profiles with mammalian fibroblast (NIH-3T3) cells, demonstrating the appeal of these novel cryogels as highly suitable cellular scaffolds.

The medial layer of small diameter blood vessels contains circumferentially aligned vascular smooth muscle cells (vSMC) that possess contractile phenotype. In tissue-engineered constructs, these cellular characteristics are usually achieved by seeding planar scaffolds with vSMC, rolling the cell-laden scaffold into a tubular structure, and maturing the construct in a pulsatile bioreactor, a lengthy process that can take up to two months. During the maturation phase, the cells circumferentially orient, their contractile protein expression increases, and they obtain a contractile phenotype. Generating cell culture platforms that enable the rapid production of directionally oriented vSMC with increased contractile protein expression would be a major step forward for blood vessel tissue engineering and would greatly facilitate the in vitro study of vSMC biology. Previously, we developed a micropatterned cell culture surface that promotes orientation and contractile protein expression of vSMC. Herein, we explore two potential applications of this technology. First, we fabricate tubular and biodegradable scaffolds that possess the micropatterning on their exterior surface. When vSMC are seeded on these scaffolds, they initially proliferate in order to fill the microchannels and as confluence is reached the cells align in the direction of the micropatterning resulting in a biodegradable scaffold that is inhabited by circumferentially aligned vSMC within a week. Second, we illustrate that we can generate biostable cell culture surfaces that allow the in vitro study of the cells in a more contractile state. Specifically, we explore contractile protein expression of cells cultured on the micropatterned surfaces with the addition of soluble transforming growth factor beta one (TGFβ1).

A methacrylic terpolymer system with non-fouling interfacial properties was synthesized by the random copolymerization of hexyl methacrylate, methyl methacrylate and sulfobetaine methacrylate (a monomer bearing a zwitterionic pendant group). Polymers were synthesized from feeds containing 0-15 mol.% of the zwitterion-containing methacrylate. Proton nuclear magnetic resonance verified the incorporation of sulfobetaine methacrylate into the polymer structure. Water absorption studies illustrate that the hydrophilicity of the material increases with increasing zwitterion concentration. The biological properties of the polymer were probed by fibrinogen adsorption, human umbilical vein endothelial cell adhesion and growth, and platelet adhesion. Strong resistance to protein adsorption and cell and platelet attachment was observed on materials synthesized from 15 mol.% sulfobetaine methacrylate. Results were compared to the non-fouling behavior of a PEGylated terpolymer formulation and it was observed that the poly(ethylene glycol)-containing materials were slightly more effective at resisting human umbilical vein endothelial cell adhesion and growth over a 7 day incubation period, but the zwitterion-containing materials were equally effective at resisting fibrinogen adsorption and platelet adhesion. The zwitterion-containing materials were electrospun into three-dimensional random fiber scaffolds. Materials synthesized from 15 mol.% of the zwitterion-containing monomer retained their non-fouling character after fabrication into scaffolds.

A nonfouling peptide grafted polymer was synthesized that can promote endothelial cell (EC) binding. The polymer was composed of hexyl methacrylate, methyl methacrylate, poly(ethylene glycol) methacrylate, and CGRGDS peptide. The peptide was incorporated into the polymer system either by a chain transfer reaction or by coupling to an acrylate-PEG-N-hydroxysuccinimide (NHS) comonomer. The introduction of PEG chains minimizes protein adsorption. Human umbilical vein ECs and endothelial colony forming cells were cultured on these surfaces in short term and long-term studies. A difference in number and morphology of ECs was observed depending on the method of peptide incorporation. Both cell types adhered better to polymer films containing NHS coupled RGD peptide after 2 h even in the presence of albumin but significant cell detachment occurred after 4 days. Polymer solutions were electrospun into fibrous scaffolds. Both nonfouling and peptide binding characteristics were retained after processing.

Polydimethylsiloxane stamp materials used during soft lithography undermine the non-fouling behaviour of bio-inert PEG-based hydrogels, resulting in increased protein adsorption and cell adhesion and migration on the gel. This previously unreported phenomenon undermines the function of lab-on-a-chip devices that require the device to be bio-inert, and slows the implementation of promising micromolding and imprinting methods for 3D culture and commercial cell culture systems. We illustrate that the degree of cell adhesion and protein adsorption to the gels correlates with the amount of residual stamp material remaining at the hydrogel interface after fabrication. After identifying this previously unreported phenomenon, we screened multiple polymer cleaning/fabrication techniques in order to maintain/restore the non-fouling properties of the gels including PDMS curing and extraction, use of other common soft lithography stamp materials, post-fabrication cleaning of the hydrogels, and changing the composition of the hydrogel. The optimal solution was determined to be incorporation of reactive sites into the hydrogel during micromolding followed by grafting of PEG macromers to these sites post-fabrication. This treatment resulted in micromolded hydrogels with robust cell resistant properties. Broadly, this work identifies and solves a previously unreported problem in hydrogel micromolding, and specifically reports the development of a cell culture platform that when combined with video microscopy enables high-resolution in situ study of single cell behaviour during in vitro culture.

Herein we combine cell sheet technology and electrospun scaffolding to rapidly generate circumferentially aligned tubular constructs of human aortic smooth muscles cells with contractile gene expression for use as tissue engineered blood vessel media. Smooth muscle cells cultured on micropatterned and N-isopropylacrylamide-grafted (pNIPAm) polydimethylsiloxane (PDMS), a small portion of which was covered by aligned electrospun scaffolding, resulted in a single sheet of unidirectionally aligned cells. Upon cooling to room temperature, the scaffold, its adherent cells, and the remaining cell sheet detached and were collected on a mandrel to generating tubular constructs with circumferentially aligned smooth muscle cells which possess contractile gene expression and a single layer of electrospun scaffold as an analogue to a small diameter blood vessel's internal elastic lamina (IEL). This method improves cell sheet handling, results in rapid circumferential alignment of smooth muscle cells which immediately express contractile genes, and introduction of an analogue to small diameter blood vessel IEL.

Transparent, high water content (65%), and cytocompatible hydrogels, which also possess super high refractive indices (RI 1.5), are needed for ophthalmological applications. Most hydrogels can achieve either high RI or high water content but not both in the same system because water is a low RI material. Here, high water content/high RI hydrogels fabricated through elevated-temperature UV polymerization of an aqueous solution of acrylamide (AM) and methacrylamide (MAM) with tri(ethylene glycol) dimethacrylate (TEDA) crosslinker are reported. By varying the AM:MAM ratios (2:8 to 8:2) and crosslinker density (5 to 11 mol %), it is discovered that high water content (66%) AM:MAM copolymer hydrogels exhibiting anomalously high refractive indices (1.53); they are also colorless, transparent (99.4%), and cytocompatible with human keratinocytes.

The lack of a blood compatible synthetic interface is one of the largest unaddressed challenges in the field of biomaterials science. This technological shortcoming hinders the successful clinical application of small diameter vascular grafts and other cardiovascular devices such as stents and artificial heart valves. Therefore, intensive research activities are ongoing to develop polymer materials with improved blood compatibility. One attractive strategy to improve the blood compatibility of an interface is to design surfaces that promote the development of an endothelium, the monolayer of endothelial cells that line our native vasculature and is responsible for blood compatibility. This article describes the recent strategies that have been used to generate polymeric materials that promote the development of an endothelium, discusses shortcomings in the field, and proposes future directions of research that can be undertaken to design next generation polymeric biomaterial that promote endothelialization. (Figure presented.).

Polymers represent the largest class of materials used in medicine. They have a range of unique properties making them useful in biomaterial applications, including orthopedics, dental, hard and soft tissue replacements, drug delivery, and cardiovascular devices. This chapter explains the basic principles of polymer science, illustrates how polymer materials can be specifically designed to fill needs in the biomaterials field, and provides examples of how this class of materials is currently used in medical applications. Structure–property relationships, including molecular architecture, molecular mass, and chemical composition related to the physical and chemical properties of the macroscopic material, are included. A biomaterials scientist aware of structure–property relationships can engineer a polymer system for a specific need.

A family of methacrylic terpolymer biomaterials was electrospun into three-dimensional fibrous scaffolds. The glass transition temperature of the polymer correlates with the morphology of the resulting scaffold. Glassy materials produce scaffolds with discrete fibers and a high percent void space (84%) while the rubbery materials produced scaffolds with fused fibers and a much lower percent void space (18%). By electrospinning onto a rotating mandrel, aligned fiber scaffolds were fabricated, and it was shown that controlling the rotation speed of the collector allowed for control over the degree of fiber alignment. The electrospinning was shown to not degrade the number average molecular weight of the polymer chains. Human umbilical vein endothelial cells (HUVECs) were seeded onto the electrospun scaffolds under static conditions and it was found that the morphology of the scaffold controlled the cellular proliferation, the metabolic activity, and the morphology of adherent cells. In particular, HUVECs seeded onto low void space scaffolds exhibited enhanced cellular spreading, enzymatic activity, and proliferation. HUVECs seeded onto aligned fiber scaffolds did not demonstrate increased proliferation; however, the cells did organize themselves in the direction of fiber alignment resulting in cells with elongated morphology.