Recent advancements in 3D bioprinting have led to the fabrication of more complex, more precise, and larger printed tissue constructs. As the field continues to advance, it is critical to develop quantitative benchmarks to compare different bio-inks for key cell-biomaterial interactions, including (1) cell sedimentation within the ink cartridge, (2) cell viability during extrusion, and (3) cell viability after ink curing. Here we develop three simple protocols for quantitative analysis of bio-ink performance. These methods are used to benchmark the performance of two commonly used bio-inks, poly(ethylene glycol) diacrylate (PEGDA) and gelatin methacrylate (GelMA), against three formulations of a novel bio-ink, Recombinant-protein Alginate Platform for Injectable Dual-crosslinked ink (RAPID ink). RAPID inks undergo peptide-self-assembly to form weak, shear-thinning gels in the ink cartridge and undergo electrostatic crosslinking with divalent cations during curing. In the one-hour cell sedimentation assay, GelMA, the RAPID inks, and PEGDA with xanthan gum prevented appreciable cell sedimentation, while PEGDA alone or PEGDA with alginate experienced significant cell settling. To quantify cell viability during printing, 3T3 fibroblasts were printed at a constant flowrate of 75 μl/min and immediately tested for cell membrane integrity. Less than 10% of cells were damaged using the PEGDA and GelMA bio-inks, while less than 4% of cells were damaged using the RAPID inks. Finally, to evaluate cell viability after curing, cells were exposed to ink-specific curing conditions for five minutes and tested for membrane integrity. After exposure to light with photo-initiator at ambient conditions, over 50% of cells near the edges of printed PEGDA and GelMA droplets were damaged. In contrast, fewer than 20% of cells found near the edges of RAPID inks were damaged after a 5-minute exposure to curing in a 10 mM CaCl2 solution. As new bio-inks continue to be developed, these protocols offer a convenient means to quantitatively benchmark their performance against existing inks.

NATure BIoMedIcAl eNgINeerINgdeveloped an approach for in-cell site-specific protein phosphorylation to synthesize bioactive proteins fused with a phosphorylated alum-binding peptide (ABP) tag. We used this approach to produce a series of ABP-labelled cytokines, which rapidly adsorbed to alum after simple mixing, and upon i.t. injection were retained in tumours for more than a week. Applied to the cytokine IL-12, this approach dramatically increased i.t. retention of the cytokine and eliminated systemic toxicities seen upon i.t. injection of the free drug, while also increasing anti-tumour efficacy. Moreover, a single i.t. dose of alum-anchored IL-12 elicited strong IFN-γ-dependent collaboration between innate and adaptive immune cells, producing robust systemic anti-tumour responses in multiple poorly immunogenic preclinical models when combined with systemic checkpoint blockade therapy. ResultsTargeted phosphorylation via an in-cell approach is robust. A single kinase, Fam20C, is responsible for phosphorylation of

Direct injection of therapies into tumors has emerged as an administration route capable of achieving high local drug exposure and strong anti-tumor response. A diverse array of immune agonists ranging in size and target are under development as local immunotherapies. However, due to the relatively recent adoption of intratumoral administration, the pharmacokinetics of locally-injected biologics remains poorly defined, limiting rational design of tumor-localized immunotherapies. Here we define a pharmacokinetic framework for biologics injected intratumorally that can predict tumor exposure and effectiveness. We find empirically and computationally that extending the tumor exposure of locally-injected interleukin-2 by increasing molecular size and/or improving matrix-targeting affinity improves therapeutic efficacy in mice. By tracking the distribution of intratumorally-injected proteins using positron emission tomography, we observe size-dependent enhancement in tumor exposure occurs by slowing the rate of diffusive escape from the tumor and by increasing partitioning to an apparent viscous region of the tumor. In elucidating how molecular weight and matrix binding interplay to determine tumor exposure, our model can aid in the design of intratumoral therapies to exert maximal therapeutic effect.

Fiber drawing enables scalable fabrication of multifunctional flexible fibers that integrate electrical, optical, and microfluidic modalities to record and modulate neural activity. Constraints on thermomechanical properties of materials, however, have prevented integrated drawing of metal electrodes with low‐loss polymer waveguides for concurrent electrical recording and optical neuromodulation. Here, two fabrication approaches are introduced: 1) an iterative thermal drawing with a soft, low melting temperature (Tm) metal indium, and 2) a metal convergence drawing with traditionally non‐drawable high Tm metal tungsten. Both approaches deliver multifunctional flexible neural interfaces with low‐impedance metallic electrodes and low‐loss waveguides, capable of recording optically‐evoked and spontaneous neural activity in mice over several weeks. These fibers are coupled with a light‐weight mechanical microdrive (1 g) that enables depth‐specific interrogation of neural circuits in mice following chronic implantation. Finally, the compatibility of these fibers with magnetic resonance imaging is demonstrated and they are applied to visualize the delivery of chemical payloads through the integrated channels in real time. Together, these advances expand the domains of application of the fiber‐based neural probes in neuroscience and neuroengineering.