Biology subjects

Heiskanen, A.

Publications and source records attributed to Heiskanen, A..

4 recordsLinked to original sources

bioRxiv2026

Real-Time Neurotransmitter Sensing in Midbrain Organoids Using 3D Carbon Cup Electrodes

Real time, chemically selective detection of neurotransmitter release in brain organoids remains a challenge due to their complex three dimensional architecture and limited optical accessibility. We introduce 3D printed carbon cup electrodes (CCEs) -pyrolyzed, multi level pillar structures - designed to confine a single organoid, increase electroactive surface area, and enable amperometric recordings of oxidizable neurotransmitters. The CCEs exhibit excellent electrochemical performance and reproducibility, supporting diffusion controlled dopamine redox behavior without interference from culture medium. Using ventral midbrain (vMB) organoids at two maturation stages (Day 30 and Day 90), we demonstrate real time detection of potassium evoked dopamine release directly from organoids. Mature organoids exhibit higher peak currents, correlating with increased tyrosine hydroxylase (TH) expression confirmed by immunocytochemistry. Embedding organoids in Matrigel significantly attenuates dopamine signals, indicating a diffusion barrier that limits stimulant access and/or dopamine transport to the electrode. Repetitive stimulations reveal progressive depletion of dopamine stores, consistent with diminished vesicular release. Chemical perturbations using 6 hydroxydopamine and verapamil further validate the platform by producing substantial reductions in dopamine release accompanied by loss of TH neurons. These results establish CCEs as a powerful tool for label free, real-time monitoring of neurotransmission in human organoids, with potential for multiplexed sensing and integration of enzymatic detection strategies for non electroactive neurotransmitters.

neuroscience↗

bioRxiv2026

Embedded Printing-Derived Pyrolytic Carbon Electrodes with Graphene-like Features for Neural Stem Cell Differentiation and Dopamine Sensing

Carbon is a versatile electrode material that is used in applications ranging from electrical energy storage and electrosynthesis to CO2 conversion, H2 production, and biosensing. The development of pyrolytic carbon electrodes derived from lithographically patterned photoresist structures has expanded the possibilities for creating diverse 2D and 3D electrode designs. In this paper, we present disc-shaped SU-8-derived pyrolytic carbon scaffold electrodes with an open hexagonal honeycomb lattice. The scaffolds were fabricated, using embedded 3D printing within a shear-thinning support bath composed of fused silica nanoparticles (7% w/v) in mineral oil. The rheological properties of the support bath were optimized to enable the printing of low-viscosity materials like SU-8, which would otherwise lack structural integrity in standard extrusion-based 3D printing. The SU-8 scaffolds were then pyrolyzed and characterized using SEM, Raman spectroscopy, Energy Dispersive X-ray, X-ray Photoelectron Spectrometry, and Transmission Electron Microscopy, which revealed graphene-like 'microflowers' on its surface. Electrochemical analysis demonstrated excellent electrochemical properties. The functionality of the scaffold electrodes was validated by differentiation of human neural stem cells into dopaminergic neurons on the scaffold surface, followed by real-time detection of dopamine exocytosis upon cell depolarization.

bioengineering↗

bioRxiv2025

Reconstruction of the human nigrostriatal pathway in vitro reveals target-dependent dopamine neuron maturation

The human nigrostriatal pathway, comprising dopaminergic neurons in the ventral midbrain (vMB) projecting to the dorsolateral striatum, is essential for motor control and selectively vulnerable in Parkinsons disease (PD). How this circuit assembles during development and how it degenerates under pathological conditions remains poorly understood in a human context and in vitro models capturing its long-range connectivity and spatial organization have been lacking. Here, we introduce the connectoid, a compartmentalized, human stem cell-based model of the nigrostriatal pathway that integrates vMB and striatal organoids within a custom-engineered microfluidic device, confining cell bodies while guiding axonal growth, mimicking the in vivo topography. Functional connectivity was confirmed by retrograde rabies tracing, and optogenetic and pharmacological stimulation, while 6-hydroxydopamine-induced selective degeneration of dopamine neurons, recapitulating a key feature of PD. Additionally, single-cell transcriptomics revealed that interaction with striatal targets enhances dopaminergic neuron maturation and activates transcriptional programs linked to synaptic signaling. Thus, connectoids uniquely allow spatial segregation of regionalized organoids while preserving long-range communication, providing a scalable and physiologically relevant platform for studying human circuit assembly, selective vulnerability, and therapeutic interventions in PD.

neuroscience↗

bioRxiv2021

Embedded 3D printing in self-healing annealable composites for functional patterning of human neural constructs

Human in vitro models of neural tissue with controllable cellular identity, tunable microenvironment, and defined spatial arrangement are needed to facilitate studies of brain development and disease. Towards this end, embedded printing in jammed microgel supports (i.e., granular gels) holds great promise as it allows precise and programmable patterning of extremely soft and compliant tissue constructs. However, in contrast to the vast material landscape available for bulk hydrogels, granular printing support formulations are restricted to a handful of materials without the ability for facile adjustment of biofunctional properties of the cellular microenvironment. Therefore, there has been a need for novel materials that take advantage of versatile biomimicry of bulk hydrogels while providing high-fidelity support for embedded printing akin to granular gels. To address this need, we present a modular platform for bioengineering of neuronal networks via direct embedded 3D printing of human stem cells inside Self-Healing Annealable Particle-Extracellular matrix (SHAPE) composites. SHAPE composites consist of soft microgels immersed in viscous extracellular-matrix solution to enable precise freeform patterning of human stem cells and consequent generation and long-term maintenance of mature subtype-specific neurons that extend projections within the volume of the annealed support. The developed approach further allows multi-ink deposition, live spatial and temporal monitoring of oxygen levels, as well as creation of vascular channels. Due to its modularity, SHAPE biomanufacturing toolbox not only offers a solution for functional modeling of mechanically sensitive neural constructs, but also has potential to be applied to a wide range of biomaterials with different crosslinking mechanisms to model tissues and diseases where recapitulation of complex architectural features and topological cues is essential.

bioengineering↗