Peptide-Functionalized Hydrogels Modulate Integrin Expression and Stemness in Adult Human Epidermal Keratinocytes

Engineered hydrogel biomaterials facilitate lung progenitor cell differentiation from induced pluripotent stem cells

Lung progenitor (LP) cells identified by the expression of transcription factor NK2 homeobox 1 (NKX2.1) are essential for the development of all lung epithelial cell types and hold tremendous potential for pulmonary research and translational regenerative medicine applications. Here, we present engineered hydrogels as a promising alternative to the naturally derived materials that are often used to differentiate human-induced pluripotent stem cells (iPSCs) into LP cells. Poly(ethylene glycol) norbornene (PEGNB) hydrogels with defined composition were used to systematically investigate the role of microenvironmental stiffness, cell origin, and splitting during the differentiation process. Results demonstrated that each factor impacted LP differentiation efficiency and that the soft hydrogels replicating healthy lung stiffness [elastic modulus (E) = 4.00 ± 0.25 kPa] produced the highest proportion of LP cells based on flow cytometric analysis results (54%) relative to the stiff hydrogels (48%) and Matrigel controls (32%) at the end of the nonsplit differentiation protocol. Collectively, these results showed that engineered hydrogels provide a well-defined microenvironment for iPSC-to-LP differentiation and perform as effectively as the current gold standard Matrigel-coated tissue culture plastic. Adopting engineered biomaterials in cell culture protocols may enable greater control over differentiation parameters and has the potential to enhance the clinical translation of iPSC-derived LP cells.NEW & NOTEWORTHY Standard iPSC differentiation protocols rely on Matrigel, a basement membrane extract from mouse sarcoma cells that is poorly defined and exhibits significant batch-to-batch variation. Due to these limitations, Matrigel-derived products have never been approved by the Food and Drug Administration. This study introduces a novel method for differentiating iPSCs into lung progenitor cells using well-defined hydrogel substrates. These biomaterials not only enhance differentiation efficiency but also streamline the regulatory pathway, facilitating their potential therapeutic application.

3D-bioprinted, phototunable hydrogel models for studying adventitial fibroblast activation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease of the lung vasculature, characterized by elevated pulmonary blood pressure, remodeling of the pulmonary arteries, and ultimately right ventricular failure. Therapeutic interventions for PAH are limited in part by the lack ofin vitroscreening platforms that accurately reproduce dynamic arterial wall mechanical properties. Here we present a 3D-bioprinted model of the pulmonary arterial adventitia comprised of a phototunable poly(ethylene glycol) alpha methacrylate (PEG-αMA)-based hydrogel and primary human pulmonary artery adventitia fibroblasts (HPAAFs). This unique biomaterial emulates PAH pathogenesisin vitrothrough a two-step polymerization reaction. First, PEG-αMA macromer was crosslinked off-stoichiometry by 3D bioprinting an acidic bioink solution into a basic gelatin support bath initiating a base-catalyzed thiol-ene reaction with synthetic and biodegradable crosslinkers. Then, matrix stiffening was induced by photoinitiated homopolymerization of unreacted αMA end groups. A design of experiments approach produced a hydrogel platform that exhibited an initial elastic modulus (E) within the range of healthy pulmonary arterial tissue (E= 4.7 ± 0.09 kPa) that was stiffened to the pathologic range of hypertensive tissue (E= 12.8 ± 0.47 kPa) and supported cellular proliferation over time. A higher percentage of HPAAFs cultured in stiffened hydrogels expressed the fibrotic marker alpha-smooth muscle actin than cells in soft hydrogels (88 ± 2% versus 65 ± 4%). Likewise, a greater percentage of HPAAFs were positive for the proliferation marker 5-ethynyl-2'-deoxyuridine (EdU) in stiffened models (66 ± 6%) compared to soft (39 ± 6%). These results demonstrate that 3D-bioprinted, phototunable models of pulmonary artery adventitia are a tool that enable investigation of fibrotic pathogenesisin vitro.

Pulmonary fibrosis distal airway epithelia are dynamically and structurally dysfunctional

The airway epithelium serves as the interface between the host and external environment. In many chronic lung diseases, the airway is the site of substantial remodeling after injury. While, idiopathic pulmonary fibrosis (IPF) has traditionally been considered a disease of the alveolus and lung matrix, the dominant environmental (cigarette smoking) and genetic (gain of function MUC5B promoter variant) risk factor primarily affect the distal airway epithelium. Moreover, airway-specific pathogenic features of IPF include bronchiolization of the distal airspace with abnormal airway cell-types and honeycomb cystic terminal airway-like structures with concurrent loss of terminal bronchioles in regions of minimal fibrosis. However, the pathogenic role of the airway epithelium in IPF is unknown. Combining biophysical, genetic, and signaling analyses of primary airway epithelial cells, we demonstrate that healthy and IPF airway epithelia are biophysically distinct, identifying pathologic activation of the ERBB-YAP axis as a specific and modifiable driver of prolongation of the unjammed-to-jammed transition in IPF epithelia. Furthermore, we demonstrate that this biophysical state and signaling axis correlates with epithelial-driven activation of the underlying mesenchyme. Our data illustrate the active mechanisms regulating airway epithelial-driven fibrosis and identify targets to modulate disease progression.

Engineering Tissue-Informed Biomaterials to Advance Pulmonary Regenerative Medicine

Biomaterials intentionally designed to support the expansion, differentiation, and three-dimensional (3D) culture of induced-pluripotent stem cells (iPSCs) may pave the way to cell-based therapies for chronic respiratory diseases. These conditions are endured by millions of people worldwide and represent a significant cause of morbidity and mortality. Currently, there are no effective treatments for the majority of advanced lung diseases and lung transplantation remains the only hope for many chronically ill patients. Key opinion leaders speculate that the novel coronavirus, COVID-19, may lead to long-term lung damage, further exacerbating the need for regenerative therapies. New strategies for regenerative cell-based therapies harness the differentiation capability of human iPSCs for studying pulmonary disease pathogenesis and treatment. Excitingly, biomaterials are a cell culture platform that can be precisely designed to direct stem cell differentiation. Here, we present a closer look at the state-of-the-art of iPSC differentiation for pulmonary engineering, offer evidence supporting the power of biomaterials to improve stem cell differentiation, and discuss our perspective on the potential for tissue-informed biomaterials to transform pulmonary regenerative medicine.

Keratinocyte-Specific Peptide-Based Surfaces for Hemidesmosome Upregulation and Prevention of Bacterial Colonization

Percutaneous devices like orthopedic prosthetic implants for amputees, catheters, and dental implants suffer from high infection rates. A critical aspect mediating peri-implant infection of dental implants is the lack of a structural barrier between the soft tissue and the implant surface which could impede bacteria access and colonization of exposed implant surfaces. Parafunctional soft tissue regeneration around dental implants is marked by a lack of hemidesmosome formation and thereby weakened mechanical attachment. In response to this healthcare burden, a simultaneously hemidesmosome-inducing, antimicrobial, multifunctional implant surface was engineered. A designer antimicrobial peptide, GL13K, and a laminin-derived peptide, LamLG3, were coimmobilized with two different surface fractional areas. The coimmobilized peptide surfaces showed antibiofilm activity against Streptococcus gordonii while enhancing proliferation, hemidesmosome formation, and mechanical attachment of orally derived keratinocytes. Notably, the coatings demonstrated specific activation of keratinocytes: the coatings showed no effects on gingival fibroblasts which are known to impede the quality of soft tissue attachment to dental implants. These coatings demonstrated stability and retained activity against mechanical and thermochemical challenges, suggesting their intraoral durability. Overall, these multifunctional surfaces may be able to reduce peri-implantitis rates and enhance the success rates of all percutaneous devices via strong antimicrobial activity and enhanced soft tissue attachment to implants.

Clickable decellularized extracellular matrix as a new tool for building hybrid-hydrogels to model chronic fibrotic diseases in vitro

Fibrotic disorders account for over one third of mortalities worldwide. Despite great efforts to study the cellular and molecular processes underlying fibrosis, there are currently few effective therapies. Dual-stage polymerization reactions are an innovative tool for recreating heterogeneous increases in extracellular matrix (ECM) modulus, a hallmark of fibrotic diseases in vivo. Here, we present a clickable decellularized ECM (dECM) crosslinker incorporated into a dynamically responsive poly(ethylene glycol)-α-methacrylate (PEGαMA) hybrid-hydrogel to recreate ECM remodeling in vitro. An off-stoichiometry thiol-ene Michael addition between PEGαMA (8-arm, 10 kg mol-1) and the clickable dECM resulted in hydrogels with an elastic modulus of E = 3.6 ± 0.24 kPa, approximating healthy lung tissue (1-5 kPa). Next, residual αMA groups were reacted via a photo-initiated homopolymerization to increase modulus values to fibrotic levels (E = 13.4 ± 0.82 kPa) in situ. Hydrogels with increased elastic moduli, mimicking fibrotic ECM, induced a significant increase in the expression of myofibroblast transgenes. The proportion of primary fibroblasts from dual-reporter mouse lungs expressing collagen 1a1 and alpha-smooth muscle actin increased by approximately 60% when cultured on stiff and dynamically stiffened hybrid-hydrogels compared to soft. Likewise, fibroblasts expressed significantly increased levels of the collagen 1a1 transgene on stiff regions of spatially patterned hybrid-hydrogels compared to the soft areas. Collectively, these results indicate that hybrid-hydrogels are a new tool that can be implemented to spatiotemporally induce a phenotypic transition in primary murine fibroblasts in vitro.

Embedding of Precision-Cut Lung Slices in Engineered Hydrogel Biomaterials Supports Extended Ex Vivo Culture

Maintaining the three-dimensional architecture and cellular complexity of lung tissue ex vivo can enable elucidation of the cellular and molecular pathways underlying chronic pulmonary diseases. Precision-cut lung slices (PCLS) are one human-lung model with the potential to support critical mechanistic studies and early drug discovery. However, many studies report short culture times of 7-10 days. Here, we systematically evaluated poly(ethylene glycol)-based hydrogel platforms for the encapsulation of PCLS. We demonstrated the ability to support ex vivo culture of embedded PCLS for at least 21 days compared with control PCLS floating in media. These customized hydrogels maintained PCLS architecture (no difference), viability (4.7-fold increase, P < 0.0001), and cellular phenotype as measured by SFTPC (1.8-fold increase, P < 0.0001) and vimentin expression (no change) compared with nonencapsulated controls. Collectively, these results demonstrate that hydrogel biomaterials support the extended culture times required to study chronic pulmonary diseases ex vivo using PCLS technology.