Hydrogels are used in a wide range of biomedical applications, including three-dimensional (3D) cell culture, cell therapy and bioprinting. To enable processing using advanced additive fabrication techniques and to mimic the dynamic nature of the extracellular matrix (ECM), the properties of the hydrogels must be possible to tailor and change over time with high precision. The design of hydrogels that are both structurally and functionally dynamic, while providing necessary mechanical support is challenging using conventional synthesis techniques. Here, we show a modular and 3D printable hydrogel system that combines a robust but tunable covalent bioorthogonal cross-linking strategy with specific peptide-folding mediated interactions for dynamic modulation of cross-linking and functionalization. The hyaluronan-based hydrogels were covalently cross-linked by strain-promoted alkyne-azide cycloaddition using multi-arm poly(ethylene glycol). In addition, a de novo designed helix-loop-helix peptide was conjugated to the hyaluronan backbone to enable specific peptide-folding modulation of cross-linking density and kinetics, and hydrogel functionality. An array of complementary peptides with different functionalities was developed and used as a toolbox for supramolecular tuning of cell-hydrogel interactions and for controlling enzyme-mediated biomineralization processes. The modular peptide system enabled dynamic modifications of the properties of 3D printed structures, demonstrating a novel route for design of more sophisticated bioinks for four-dimensional bioprinting.

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Thiolated polymers are widely used in hydrogels for drug delivery, tissue engineering, and biofabrication. The oxidation of thiols is spontaneous, resulting in the formation of disulfide bridges and cross-linking of polymers. The cross-linking process is, however, difficult to control and is initiated directly when the thiolated components are exposed to ambient conditions, which significantly complicates handling of the materials. Here, we show a fully bioorthogonal enzyme-mediated thiol-based chemistry for dynamic covalent cross-linking of carbohydrate-based hydrogels that circumvents the problems with uncontrolled thiol oxidation. Alginate was modified with cysteine residues, protected by an enzyme-labile thiol-protecting group (Phacm). Releasing the Phacm group by penicillin G acylase generates free thiols that oxidize under physiological conditions, resulting in a reversible cross-linking and formation of hydrogels with tunable stiffness. Prior to deprotection, the components can be exposed to ambient conditions. The enzyme-triggered deprotection and subsequent gelation allows for encapsulation of cells and 3D bioprinting of cell-laden hydrogel structures. Remaining deprotected thiols enabled postprinting modifications and hydrogel self-healing. The proposed hydrogel synthesis strategy significantly increases the versatility of thiol-based cross-linking chemistries and provides new possibilities to generate dynamic covalent hydrogels for a broad range of biomedical applications.

Bioprinting of hydrogel-based bioinks can allow for the fabrication of elaborate, cell-laden 3D structures. In addition to providing an adequate extracellular matrix mimetic environment and high cell viability, the hydrogels must offer facile extrusion through the printing nozzle and retain the shape of the printed structure. We demonstrate a strategy to incorporate cellulose oxalate nanofibrils in hyaluronan-based hydrogels to generate shear thinning bioinks that allowed for printing of free-standing multilayer structures, covalently cross-linked after bioprinting, yielding longterm stability. The storage modulus of the hydrogels was tunable between 0.5 and 1.5 kPa. The nanocellulose containing hydrogels showed good biocompatibility, with viability of primary human dermal fibroblasts above 80% at day 7 after seeding. The cells were also shown to tolerate the printing process well, with viability above 80% 24 h after printing. We anticipate that this hydrogel system can find broad use as a bioink to produce complex geometries that can support cell growth.

Longitudinal serum samples and nasopharyngeal/nasal swab samples were collected from forty-eight individuals (median age 66yrs) with Covid-19 PCR-positive test results at Linköping University Hospital. Samples were collected from initial visit and for 6 months follow up. Presence of serum IgG and IgA against SARS-CoV-2 antigens (S1-spike, nucleocapsid and NSP3) were analyzed. Nasal swabs were tested for presence of IgA against the outer envelope S1 spike protein. Ninety-two percent of participants were seropositive against SARS-CoV-2 recombinant proteins at day 28 from study entry and all (100%) were seropositive from samples collected at 2 months or later. The most common antibody responses (both serum IgG, mainly IgG1 and IgA) were detected against the S1-spike protein and the nucleoprotein. In samples collected from nasal tissues considerably lower frequencies of IgA-positive reactivities were detected. Sixteen to 18 percent of study participants showed detectable IgA levels in nasal samples, except at day 60 when 36% of tested individuals showed presence of IgA against the S1-spike protein. The study suggests that the absolute majority of studied naturally infected Covid-19 patient in the Linkoping, Ostergotland health region develop over 6 months lasting detectable levels of serum IgG and IgA responses towards the SARS-CoV-2 S1-spike protein as well as against the nucleoprotein, but not against the non-structural protein 3.

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Longitudinal serum samples, nasopharyngeal/nasal swabs and rectal swab samples were collected from eighty-nine individuals (median age 66 y) with SARS-CoV-2 PCR-positive test results at Linköping University Hospital. Samples were collected from the initial visit and thereafter for up to 2 years of follow-up. The presence of serum IgG and IgA against SARS-CoV-2 antigens (S1-spike, nucleocapsid, and NSP3) was analysed. Nasal and rectal swabs were tested for the presence of mucosal IgA against the outer envelope S1 spike and the nucleocapsid protein. Ninety percent of the participants were seropositive for SARS-CoV-2 recombinant proteins on Day 28 after study entry, and all (100%) were seropositive based on samples collected 2 months or later. Almost all (95%) developed serum SARS-CoV-2-neutralizing antibodies that were measurable from 6 to 24 months. The most common antibody responses (both serum IgG, mainly IgG1, and in nasal mucosa IgA) reacted with the S1-spike protein and the nucleoprotein. In samples collected from nasal tissues, IgA anti-S1 spike protein was mainly observed during 2 months of follow-up. In a subpopulation (18% of tested individuals), rectal IgA swabs showed the presence of anti-S1 spike IgA for 1 month of follow-up among the participants studied. .

In native tissue, remodeling of the pericellular space is essential for cellular activities and is mediated by tightly regulated proteases. Protease activity is dysregulated in many diseases, including many forms of cancer. Increased proteolytic activity is directly linked to tumor invasion into stroma, metastasis, and angiogenesis as well as all other hallmarks of cancer. Here we show how integrated 3D bioprinted structures with distinctly different responses to proteolytic activity can be utilized for systematic investigation of proteolytic remodeling of the extra cellular matrix and the impact of stromal cells on protease driven processes. Bioprinted structures combining non-degradable and degradable hydrogels were designed and demonstrated to be selectively degraded by proteases allowing for protease-mediated material reorganization with high spatial resolution. Bioprinting of tumor microenvironments combining bioinks with different susceptibilities to proteolytic degradation shows that breast cancer cell proliferation, migration into stromal compartments, and spheroid size are significantly increased in protease degradable hydrogels, but only in the presence of fibroblasts. Proteolytic remodeling of the tumor microenvironment has a significant effect on tumor progression and is drastically influenced by the intimate crosstalk between fibroblast and breast cancer cells.