Cell-biomaterial Interface Research Articles

Magnetoactive Nanotopography on Hydrogels for Stimulated Cell Adhesion and Differentiation

Advanced cell culture platforms that vary the biophysical microenvironment are useful tools for mechanobiology studies and for directing the differentiation of adherent cells to therapeutically relevant phenotypes. Herein, the fabrication of magnetoactive nanofiber mats for integration with hydrogels as a platform for dynamic stimulation at the cell–biomaterial interface is demonstrated. Electrospinning is used to form iron oxide‐loaded gelatin‐based nanofibers that are stabilized and cross‐linked to the surface of gelatin methacryloyl hydrogels. The presence of a magnetic field stimulates focal adhesion formation and maturation in adherent adipose‐derived stromal cells, with concurrent changes in cell and nuclear morphology. Adding lineage guiding supplements has been shown to complement biophysical cues, providing optimal conditions for differentiation into osteogenic and adipogenic lineages. The presence of nanofibers at the interface is beneficial to both lineages, but stiffening through an applied magnetic field encourages further osteogenesis while inhibiting adipogenesis. The system is further demonstrated with skeletal myoblasts, where nanotopography and stiffening promote the formation of mature multinucleated muscle cells. This magnetoactive nanofiber platform could prove useful in a wide array of mechanically sensitive cell systems for fundamental studies and for cell production, with flexibility for use with virtually any hydrogel cell culture system.

Biomaterials for Cell Manufacturing.

Cell therapies, potent populations of cells used to treat disease and injury, can be strategically manufactured with biomaterial intervention to improve clinical translation. In this viewpoint, we discuss biomaterial design and integration into cell manufacturing steps to achieve three main goals: scale-up, phenotype control, and selection of potent cells. Material properties can be engineered to influence the cell-biomaterial interface and, therefore, impart desirable cell behavior such as growth, secretory activity, and differentiation. Future directions for the field should capitalize on the combinatorial design of biomaterial properties to yield highly specific and potent cell populations. Furthermore, future biomaterials could contribute to novel high-throughput cell separation technologies that can individually select the most therapeutically relevant cells within a produced batch.

Unraveling and Harnessing the Immune Response at the Cell-Biomaterial Interface for Tissue Engineering Purposes.

Biomaterials are defined as "engineered materials" and include a range of natural and synthetic products, designed for their introduction into and interaction with living tissues. Biomaterials are considered prominent tools in regenerative medicine that support the restoration of tissue defects and retain physiologic functionality. Although commonly used in the medical field, these constructs are inherently foreign toward the host and induce an immune response at the material-tissue interface, defined as the foreign body response (FBR). A strong connection between the foreign body response and tissue regeneration is suggested, in which an appropriate amount of immune response and macrophage polarization is necessary to trigger autologous tissue formation. Recent developments in this field have led to the characterization of immunomodulatory traits that optimizes bioactivity, the integration of biomaterials and determines the fate of tissue regeneration. This review addresses a variety of aspects that are involved in steering the inflammatory response, including immune cell interactions, physical characteristics, biochemical cues, and metabolomics. Harnessing the advancing knowledge of the FBR allows for the optimization of biomaterial-based implants, aiming to prevent damage of the implant, improve natural regeneration, and provide the tools for an efficient and successful in vivo implantation.

Complex effects of Mg-biomaterials on the osteoblast cell machinery: A proteomic study.

The cell-biomaterial interface is highly complex; thousands of molecules and many processes participate in its formation. Growing demand for improved biomaterials has highlighted the need to understand the structure and functions of this interface. Proteomic methods offer a viable alternative to the traditional in vitro techniques for analyzing such systems. Magnesium is a promoter of cell adhesion and osteogenesis. Here, we used the LC-MS/MS to compare the protein expression profiles of human osteoblasts (HOb) exposed to sol-gel coatings without (MT) and with Mg (MT1.5Mg) for 1, 3, and 7days. PANTHER, DAVID, and IPA databases were employed for protein identification and data analysis. Confocal microscopy and gene expression analysis were used for further characterization. Exposure to MT1.5Mg increased the HOb cell area and the expression of SP7, RUNX2, IBP3, COL3A1, MXRA8, and FBN1 genes. Proteomic analysis showed that MT1.5Mg affected the early osteoblast maturation (PI3/AKT, mTOR, ERK/MAPK), insulin metabolism, cell adhesion (integrin, FAK, actin cytoskeleton regulation) and oxidative stress pathways. Thus, the effects of Mg on cell adhesion and osteogenesis are rather complex, affecting several pathways rather than single processes. Our analysis also confirms the potential of proteomics in biomaterial characterization, showing a good correlation with in vitro results.

Automatic Actin Filament Quantification and Cell Shape Modeling of Osteoblasts on Charged Ti Surfaces

Surface charges at the cell–biomaterial interface are known to determine cellular functions. Previous findings on cell signaling indicate that osteoblastic cells favor certain moderately positive surface charges, whereas highly positive charges are not tolerated. In this study, we aimed to gain deeper insights into the influence exerted by surface charges on the actin cytoskeleton and the cell shape. We analyzed surfaces with a negative, moderately positive, and highly positive zeta (ζ) potential: titanium (Ti), Ti with plasma polymerized allylamine (PPAAm), and Ti with a polydiallyldimethylammonium chloride (PDADMA) multilayer, respectively. We used the software FilaQuant for automatic actin filament quantification of osteoblastic MG-63s, analyzed the cell edge height with scanning ion conductance microscopy (SICM), and described the cellular shape via a mathematical vertex model. A significant enhancement of actin filament formation was achieved on moderately positive (+7 mV) compared with negative ζ-potentials (−87 mV). A hampered cell spreading was reflected in a diminished actin filament number and length on highly positively charged surfaces (+50 mV). Mathematical simulations suggested that in these cells, cortical tension forces dominate the cell–substrate adhesion forces. Our findings present new insights into the impact of surface charges on the overall cell shape and even intracellular structures.

Natural Architectures for Tissue Engineering and Regenerative Medicine.

The ability to control the interactions between functional biomaterials and biological systems is of great importance for tissue engineering and regenerative medicine. However, the underlying mechanisms defining the interplay between biomaterial properties and the human body are complex. Therefore, a key challenge is to design biomaterials that mimic the in vivo microenvironment. Over millions of years, nature has produced a wide variety of biological materials optimised for distinct functions, ranging from the extracellular matrix (ECM) for structural and biochemical support of cells to the holy lotus with special wettability for self-cleaning effects. Many of these systems found in biology possess unique surface properties recognised to regulate cell behaviour. Integration of such natural surface properties in biomaterials can bring about novel cell responses in vitro and provide greater insights into the processes occurring at the cell-biomaterial interface. Using natural surfaces as templates for bioinspired design can stimulate progress in the field of regenerative medicine, tissue engineering and biomaterials science. This literature review aims to combine the state-of-the-art knowledge in natural and nature-inspired surfaces, with an emphasis on material properties known to affect cell behaviour.

Functionalized Graphene Oxide Thin Films for Anti-tumor Drug Delivery to Melanoma Cells.

Since Graphene discovery, their associated derivate nanomaterials, Graphene Oxide (GO) and reduced-GO were in the forefront of continuous developments in bio-nano-technology due to unique physical-chemical properties. Although GO nano-colloids (GON) were proposed as drug release matrix for targeting cancer cells, there is still a concern regarding its cytotoxicity issues. In this study, we report on the fabrication of functional GON bio-coatings by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) to be used as drug carriers for targeting melanoma cells. We first performed a thorough in vitro cytotoxicity assay for comparison between GON and protein functionalized GON coatings. As functionalization protein, Bovine Serum Albumin (BSA) was non-covalently conjugated to GO surface. Safe concentration windows were identified in cytotoxicity tests by live/dead staining and MTS assays for five different human melanoma cell lines as well as for non-transformed melanocytes and human dermal fibroblasts. Hybrid GON-BSA nano-scaled thin coatings incorporating Dabrafenib (DAB) and Trichostatin A (TSA) inhibitors for cells bearing BRAFV600E pathway activating mutation were assembled on solid substrates by MAPLE technique. We further demonstrated the successful immobilization for each drug-containing GON-BSA assembling systems by evaluating cellular BRAF activity inhibition and histone deacetylases activity blocking, respectively. DAB activity was proven by the decreased ERK phosphorylation in primary melanoma cells (SKmel28 BRAFV600E cell line), while TSA effect was evidenced by acetylated histones accumulation in cell's nuclei (SKmel23 BRAF WT cell line). In addition, melanoma cells exposed to GON-BSA coatings with compositional gradient of inhibitors evidenced a dose-dependent effect on target activity. Such functional bio-platforms could present high potential for cell-biomaterial interface engineering to be applied in personalized cancer therapy studies.

Chondroinduction of Mesenchymal Stem Cells on Cellulose-Silk Composite Nanofibrous Substrates: The Role of Substrate Elasticity.

Smart biomaterials with an inherent capacity to elicit specific behaviors in lieu of biological prompts would be advantageous for regenerative medicine applications. In this work, we employ an electrospinning technique to model the in vivo nanofibrous extracellular matrix (ECM) of cartilage using a chondroinductive cellulose and silk polymer blend (75:25 ratio). This natural polymer composite is directly electrospun for the first time, into nanofibers without post-spun treatment, using a trifluoroacetic acid and acetic acid cosolvent system. Biocompatibility of the composite nanofibres with human mesenchymal stem cells (hMSCs) is demonstrated and its inherent capacity to direct chondrogenic stem cell differentiation, in the absence of stimulating growth factors, is confirmed. This chondrogenic stimulation could be countered biochemically using fibroblast growth factor-2, a growth factor used to enhance the proliferation of hMSCs. Furthermore, the potential mechanisms driving this chondroinduction at the cell-biomaterial interface is investigated. Composite substrates are fabricated as two-dimensional film surfaces and cultured with hMSCs in the presence of chemicals that interfere with their biochemical and mechanical signaling pathways. Preventing substrate surface elasticity transmission resulted in a significant downregulation of chondrogenic gene expression. Interference with the classical chondrogenic Smad2/3 phosphorylation pathway did not impact chondrogenesis. The results highlight the importance of substrate mechanical elasticity on hMSCs chondroinduction and its independence to known chondrogenic biochemical pathways. The newly fabricated scaffolds provide the foundation for designing a robust, self-inductive, and cost-effective biomimetic biomaterial for cartilage tissue engineering.

Screening a chemically defined extracellular matrix mimetic substrate library to identify substrates that enhance substrate-mediated transfection.

Nonviral gene delivery, though limited by inefficiency, has extensive utility in cell therapy, tissue engineering, and diagnostics. Substrate-mediated gene delivery (SMD) increases efficiency and allows transfection at a cell-biomaterial interface, by immobilizing and concentrating nucleic acid complexes on a surface. Efficient SMD generally requires substrates to be coated with serum or other protein coatings to mediate nucleic acid complex immobilization, as well as cell adhesion and growth; however, this strategy limits reproducibility and may be difficult to translate for clinical applications. As an alternative, we screened a chemically defined combinatorial library of 20 different extracellular matrix mimetic substrates containing combinations of (1) different sulfated polysaccharides that are essential extracellular matrix glycosaminoglycans (GAGs), with (2) mimetic peptides derived from adhesion proteins, growth factors, and cell-penetrating domains, for use as SMD coatings. We identified optimal substrates for DNA lipoplex and polyplex SMD transfection of fibroblasts and human mesenchymal stem cells. Optimal extracellular matrix mimetic substrates varied between cell type, donor source, and transfection reagent, but typically contained Heparin GAG and an adhesion peptide. Multiple substrates significantly increased transgene expression (i.e. 2- to 20-fold) over standard protein coatings. Considering previous research of similar ligands, we hypothesize extracellular matrix mimetic substrates modulate cell adhesion, proliferation, and survival, as well as plasmid internalization and trafficking. Our results demonstrate the utility of screening combinatorial extracellular matrix mimetic substrates for optimal SMD transfection towards application- and patient-specific technologies.Impact statementSubstrate-mediated gene delivery (SMD) approaches have potential for modification of cells in applications where a cell-material interface exists. Conventional SMD uses ill-defined serum or protein coatings to facilitate immobilization of nucleic acid complexes, cell attachment, and subsequent transfection, which limits reproducibility and clinical utility. As an alternative, we screened a defined library of extracellular matrix mimetic substrates containing combinations of different glycosaminoglycans and bioactive peptides to identify optimal substrates for SMD transfection of fibroblasts and human mesenchymal stem cells. This strategy could be utilized to develop substrates for specific SMD applications in which variability exists between different cell types and patient samples.

Electrophoretic Deposition of Magnesium Oxide Nanoparticles on Magnesium: Processing Parameters, Microstructures, Degradation, and Cytocompatibility.

Magnesium (Mg) and its alloys are a class of promising materials for biodegradable orthopedic and craniomaxillofacial implants; however, rapid release of hydrogen gas remains a key challenge for clinical translation. This study reported the optimal parameters of electrophoretic deposition (EPD), at which magnesium oxide nanoparticles (nMgO) could be deposited onto Mg substrates with homogeneous surface morphology and elemental distribution. The results showed that the distribution and uniformity of the nMgO coatings on Mg improved when the nMgO concentration in ethanol increased and the time of applied voltage decreased. The nMgO-coated Mg showed a homogeneous surface and distinct degradation mode during the 9-day immersion studies in revised simulated body fluid (r-SBF) and Dulbecco's modified Eagle's medium (DMEM), when compared with the noncoated Mg controls. The nMgO coating initially mitigated hydrogen gas formation. The degradation layer on nMgO-coated Mg was thicker than the noncoated Mg and enriched with Ca and P that are favorable for skeletal implant applications. In the direct culture study with bone marrow derived mesenchymal stem cells (BMSCs) in vitro, the cell adhesion density and morphology were not affected by the solubilized degradation products released by the nMgO-coated Mg under indirect contact. However, at the cell-biomaterial interface, the cell spreading decreased under direct contact, possibly because of the continuous dynamic degradation of the samples. The electrophoretically deposited nMgO coatings on Mg-based medical implants should be further studied to improve the coating-substrate and cell-material interfaces for clinical applications.

TiO2 Nanorod Arrays with Mesoscopic Micro-Nano Interfaces for in Situ Regulation of Cell Morphology and Nucleus Deformation.

Cell morphology and nucleus deformation are important when circulating tumor cells break away from the primary tumor and migrate to a distant organ. Cells are sensitive to the microenvironment and respond to the cell-material interfaces. We fabricated TiO2 nanorod arrays with mesoscopic micro-nano interfaces through a two-step hydrothermal reaction method to induce severe changes in cell morphology and nucleus deformation. The average size of the microscale voids was increased from 5.1 to 10.5 μm when the hydrothermal etching time was increased from 3 to 10 h, whereas the average distances between voids were decreased from 0.88 to 0.40 μm. The nucleus of the MCF-7 cells on the TiO2 nanorod substrate that was etched for 10 h exhibited a significant deformation, because of the large size of the voids and the small distance between voids. Nucleus defromation was reversible during the cells proliferate process when the cells were cultured on the mesoscopic micro-nano interface.This reversible process was regulated by combining of the uniform pressure applied by the actin cap and the localized pressure applied by the actin underneath the nucleus. Cell morphology and nucleus shape interacted with each other to adapt to the microenvironment. This mesoscopic micro-nano interface provided a new insight into the cell-biomaterial interface to investigate cell behaviors.

A Comparison Study on the Degradation and Cytocompatibility of Mg-4Zn-xSr Alloys in Direct Culture.

This article reports the behaviors of bone-marrow-derived mesenchymal stem cells (BMSCs) in the direct culture with four Mg-4Zn-xSr alloys (x = 0.15, 0.5, 1.0, 1.5 wt %), designated as ZSr41A, B, C, and D, respectively; and a systematic comparison on the degradation of the ZSr41 alloys and their biological impact in the direct culture with different cell types in their respective media. The direct culture method, in which cells are seeded directly onto the surface of the sample, was used to investigate cellular responses at the cell-biomaterial interface in vitro. The results showed that BMSCs adhered and remained viable on the surfaces of all ZSr41 alloys, but the faster degrading ZSr41A and ZSr41B alloys showed a significantly lower amount of viable BMSCs adhered to their surfaces. Moreover, BMSCs adhered to the culture plate surrounding the samples were unaffected by the solubilized degradation products from the ZSr41 alloys. The results from the comparison study showed that the in vitro degradation rates of Mg-based biomaterials in different culture systems might be mostly affected by media buffer capacity (i.e., HCO3- concentration), and to a lesser extent, d-glucose concentration. The comparison study also indicated that BMSCs were more robust than H9 human embryonic stem cells and human umbilical vein endothelial cells for screening the cytocompatibility of Mg-based biomaterials. In general, the adhesion and viability of BMSCs at the cell-material interface were inversely proportional to the alloy degradation rates. This study presented a clinically relevant in vitro culture system for screening bioresorbable alloys in direct culture, and provided valuable guidelines for determining the degradation rates of Mg-based biomaterials.

Dynamic Reorganization and Enzymatic Remodeling of Type IV Collagen at Cell-Biomaterial Interface.

Vascular basement membrane remodeling involves assembly and degradation of its main constituents, type IV collagen (Col IV) and laminin, which is critical during development, angiogenesis, and tissue repair. Remodeling can also occur at cell-biomaterials interface altering significantly the biocompatibility of implants. Here we describe the fate of adsorbed Col IV in contact with endothelial cells adhering on positively charged NH2 or hydrophobic CH3 substrata, both based on self-assembly monolayers (SAMs) and studied alone or mixed in different proportions. AFM studies revealed distinct pattern of adsorbed Col IV, varying from single molecular deposition on pure NH2 to network-like assembly on mixed SAMs, turning to big globular aggregates on bare CH3. Human umbilical endothelial cells (HUVECs) interact better with Col IV adsorbed as single molecules on NH2 surface and readily rearrange it in fibril-like pattern that coincide with secreted fibronectin fibrils. The cells show flattened morphology and well-developed focal adhesion complexes that are rich on phosphorylated FAK while expressing markedly low pericellular proteolytic activity. Conversely, on hydrophobic CH3 substrata HUVECs showed abrogated spreading and FAK phosphorylation, combined with less reorganization of the aggregated Col IV and significantly increased proteolytic activity. The later involves both MMP-2 and MMP-9, as measured by zymography and FITC-Col IV release. The mixed SAMs support intermediate remodeling activity. Taken together these results show that chemical functionalization combined with Col IV preadsorption provides a tool for guiding the endothelial cells behavior and pericellular proteolytic activity, events that strongly affect the fate of cardiovascular implants.

Evaluation of BMSC viability at the cell-biomaterial interface with Mg-xSr and Mg-1Ca-xSr alloys

Evaluation of BMSC viability at the cell-biomaterial interface with Mg-xSr and Mg-1Ca-xSr alloys

Dynamic Behavior of Vitronectin at the Cell-Material Interface.

Considering that vitronectin (VN) can promote both cell adhesion and matrix degradation, it is likely to play a dual role at the cell-biomaterial interface. In this paper we therefore describe details of the dynamic interplay between matrix adhesion and pericellular proteolysis in endothelial cells adhered to glass model substratum. Initially we show that coating concentration determines protein organization at the surface. When the protein coating density approached saturation (63 ng cm-2), VN spontaneously organized itself in multimeric aggregates at the surface (30-50 nm in diameter). At subsaturation protein density (17 ng cm-2) VN molecules were present predominantly as single entities, indicating that a minimum coating density was required for VN multimerization. By fluorescent visualization of surface-associated VN in different ways, we provide the first evidence of significant proteolytic remodelling of VN by endothelial cells (HUVECs) at the sites of αv integrin clusters. The degree of proteolysis was estimated using a novel approach relying on dequenching of FITC-labeled VN upon proteolytic activity, showing that about one-third of the surface-associated VN was proteolytically altered by adhering HUVECs. In addition, we demonstrate that HUVECs can internalize surface-associated VN and deposit it in a linear pattern along longitudinal actin filaments. Deposited VN was partly colocalized with urokinase receptors. Taken altogether, we elucidate the complex and dynamic behavior of VN during initial cell-biomaterials interactions, the equilibrium if which could have a significant impact on the biocompatibility of any blood contacting implants.

Dielectric barrier discharge plasma treatment of ultrahigh molecular weight polyethylene in different discharge atmospheres at medium pressure: A cell-biomaterial interface study

Nonthermal plasma activation of ultrahigh molecular weight polyethylene (UHMWPE) is performed in different discharge atmospheres (helium, nitrogen, argon, and air) using a parallel-plate dielectric barrier discharge reactor at medium pressure. Obtained samples are characterized via water contact angle, x-ray photoelectron spectroscopy (XPS), and atomic force microscopy. Plasma treatments were found to significantly alter the samples' surface chemical and physical characteristics. Before conducting a biocompatibility study, the influence of postplasma sterilization processes (ethanol rinsing/UV exposure) on the plasma treatment effects were studied. XPS studies showed that samples' surface chemical composition is least affected by UV exposure, thus making this process the most adequate for sterilization. In-vitro evaluation of biocompatibility was carried out by studying human foreskin fibroblast interaction with untreated and plasma treated surfaces. Cell attachment and viability on all plasma treated UHM...

Cell-scaffold adhesion dynamics measured in first seconds predicts cell growth on days scale – optical tweezers study.

Understanding the cell-biomaterial interface from the very first contact is of crucial importance for their successful implementation and function in damaged tissues. However, the lack of bio- and mechano-analytical methods to investigate and probe the initial processes on the interface, especially in 3D, raises the need for applying new experimental techniques. In our study, optical tweezers combined with confocal fluorescence microscopy were optimized to investigate the initial cell-scaffold contact and to investigate its correlation with the material-dependent cell growth. By the optical tweezers-induced cell manipulation accompanied by force detection up to 100 pN and position detection by fluorescence microscopy, accurate adhesion dynamics and strength analysis was implemented, where several attachment sites were formed on the interface in the first few seconds. More importantly, we have shown that dynamics of cell adhesion on scaffold surfaces correlates with cell growth on the days scale, which indicates that the first seconds of the contact could markedly direct further cell response. Such a contact dynamics analysis on 3D scaffold surfaces, applied for the first time, can thus serve to predict scaffold biocompatibility.

Single-Cell Force Spectroscopy, an Emerging Tool to Quantify Cell Adhesion to Biomaterials

Cell adhesion receptors play a central role in sensing and integrating signals provided by the cellular environment. Thus, understanding adhesive interactions at the cell-biomaterial interface is essential to improve the design of implants that should emulate certain characteristics of the cell's natural environment. Numerous cell adhesion assays have been developed; among these, atomic force microscopy-based single-cell force spectroscopy (AFM-SCFS) provides a versatile tool to quantify cell adhesion at physiological conditions. Here we discuss how AFM-SCFS can be used to quantify the adhesion of living cells to biomaterials and give examples of using AFM-SCFS in tissue engineering and regenerative medicine. We anticipate that in the near future, AFM-SCFS will be established in the biomaterial field as an important technique to quantify cell-biomaterial interactions and thereby will contribute to the optimization of implants, scaffolds, and medical devices.

Fibroblasts remodeling of type IV collagen at a biomaterials interface.

This paper describes the fate of adsorbed type IV collagen (Col IV) in contact with fibroblasts on model biomaterial surfaces, varying in wettability, chemistry and charge. We found that fibroblasts not only interact but also tend to remodel differently adsorbed Col IV employing two distinct mechanisms: mechanical reorganization and proteolytic degradation. Apart from the trend of adsorption -NH2 > CH3 > COOH > OH- the cells interact better with NH2 and OH surfaces -i.e. independently of the amount of adsorbed Col IV - evident from the quantitative measurements of cell adhesion and spreading and the improved recruitment of alpha 1 and alpha 2 integrins as well as p-FAK in focal adhesions. The linearly arranged Col IV co-localize with FN fibrils formed from either secreted, or exogenously added protein, which confirms their interdependence during a reorganization process. We further found that this reorganization is better pronounced on hydrophilic OH and positively charged NH2 surfaces correlating with the improved cellular interaction. Conversely, the fibroblasts tend to round on COOH and CH3 surfaces in compliance with the altered integrin signaling and also the increased pericellular proteolysis activity quantified by the increased de-quenching of adsorbed FITC-Col IV and zymography. Taken together, these results show that remodeling of Col IV at a cell-biomaterial interface depends strongly on the surface properties of a material and affects significantly its biological performance.

Protein–Hydrogel Interactions in Tissue Engineering: Mechanisms and Applications

Recent advances in our understanding of the sophistication of the cellular microenvironment and the dynamics of tissue remodeling during development, disease, and regeneration have increased our appreciation of the current challenges facing tissue engineering. As this appreciation advances, we are better equipped to approach problems in the biology and therapeutics of even more complex fields, such as stem cells and cancer. To aid in these studies, as well as the established areas of tissue engineering, including cardiovascular, musculoskeletal, and neural applications, biomaterials scientists have developed an extensive array of materials with specifically designed chemical, mechanical, and biological properties. Herein, we highlight an important topic within this area of biomaterials research, protein-hydrogel interactions. Due to inherent advantages of hydrated scaffolds for soft tissue engineering as well as specialized bioactivity of proteins and peptides, this field is well-posed to tackle major needs within emerging areas of tissue engineering. We provide an overview of the major modes of interactions between hydrogels and proteins (e.g., weak forces, covalent binding, affinity binding), examples of applications within growth factor delivery and three-dimensional scaffolds, and finally future directions within the area of hydrogel-protein interactions that will advance our ability to control the cell-biomaterial interface.