Biology subjects

Alsberg, E.

Publications and source records attributed to Alsberg, E..

21 records · Page 2Linked to original sources

bioRxiv2019

Combinatorial morphogenetic and mechanical cues to mimic bone development for defect repair

Endochondral ossification during long bone development and natural fracture healing initiates by mesenchymal cell condensation and is directed by local morphogen signals and mechanical cues. Here, we aimed to mimic these developmental conditions for regeneration of large bone defects. We hypothesized that engineered human mesenchymal stem cell (hMSC) condensations with in situ presentation of transforming growth factor-{beta}1 (TGF-{beta}1) and/or bone morphogenetic protein-2 (BMP-2) from encapsulated microparticles would promote endochondral regeneration of critical-sized rat femoral bone defects in a manner dependent on the in vivo mechanical environment. Mesenchymal condensations induced bone formation dependent on morphogen presentation, with dual BMP-2 + TGF-{beta}1 fully restoring mechanical bone function by week 12. In vivo ambulatory mechanical loading, initiated at week 4 by delayed unlocking of compliant fixation plates, significantly enhanced the bone formation rate in the four weeks after load initiation in the dual morphogen group. In vitro, local presentation of either BMP-2 alone or BMP-2 + TGF-{beta}1 initiated endochondral lineage commitment of mesenchymal condensations, inducing both chondrogenic and osteogenic gene expression through SMAD3 and SMAD5 signaling. In vivo, however, endochondral cartilage formation was evident only in the BMP-2 + TGF-{beta}1 group and was enhanced by mechanical loading. The degree of bone formation was comparable to BMP-2 soaked on collagen but without the ectopic bone formation that limits the clinical efficacy of BMP-2/collagen. In contrast, mechanical loading had no effect on autograft-mediated repair. Together, this study demonstrates a biomimetic template for recapitulating developmental morphogenic and mechanical cues in vivo for tissue engineering. One Sentence SummaryMimicking aspects of the cellular, biochemical, and mechanical environment during early limb development, chondrogenically-primed human mesenchymal stem cell condensations promoted functional healing of critical-sized femoral defects via endochondral ossification, and healing rate and extent was a function of the in vivo mechanical environment.

bioengineering↗

bioRxiv2018

Non-adhesive alginate hydrogels support growth of pluripotent stem cell-derived intestinal organoids

Human intestinal organoids (HIOs) represent a powerful system to study human development and are promising candidates for clinical translation as drug-screening tools or engineered tissue. Experimental control and clinical use of HIOs is limited by growth in expensive and poorly defined tumor-cell-derived extracellular matrices, prompting investigation of synthetic ECM-mimetics for HIO culture. Since HIOs possess an inner epithelium and outer mesenchyme, we hypothesized that adhesive cues provided by the matrix may be dispensable for HIO culture. Here, we demonstrate that alginate, a minimally supportive hydrogel with no inherent cell adhesion properties, supports HIO growth in vitro and leads to HIO epithelial differentiation that is virtually indistinguishable from Matrigel-grown HIOs. Additionally, alginate-grown HIOs mature to a similar degree as Matrigel-grown HIOs when transplanted in vivo, both resembling human fetal intestine. This work demonstrates that purely mechanical support from a simple-to-use and inexpensive hydrogel is sufficient to promote HIO survival and development.

developmental biology↗

bioRxiv2017

Recapitulating bone development for tissue regeneration through engineered mesenchymal condensations and mechanical cues

Large bone defects cannot heal without intervention and have high complication rates even with the best treatments available. In contrast, bone fractures naturally healing with high success rates by recapitulating the process of bone development through endochondral ossification.1 Endochondral tissue engineering may represent a promising paradigm, but large bone defects are unable to naturally form a callus. We engineered mesenchymal condensations featuring local morphogen presentation (TGF-{beta}1) to mimic the cellular organization and lineage progression of the early limb bud. As mechanical forces are 2,3 critical for proper endochondral ossification during bone morphogenesis2,3 and fracture healing, we hypothesized that mechanical cues would be important for endochondral regeneration.4,5 Here, using fixation plates that modulate ambulatory load transfer through dynamic tuning of axial compliance, we found that in vivo mechanical loading was necessary to restore bone function to large bone defects through endochondral ossification. Endochondral regeneration produced zonal cartilage and primary spongiosa mimetic of the native growth plate. Live human chondrocytes contributed to endochondral regeneration in vivo, while cell devitalization prior to condensation transplantation abrogated bone formation. Mechanical loading induced regeneration comparable to high-dose BMP-2 delivery, but without heterotopic bone formation and with order-of-magnitude greater mechanosensitivity.6-8 In vitro, mechanical loading promoted chondrogenesis, and upregulated pericellular collagen 6 deposition and angiogenic gene expression. Consistently, in vivo mechanical loading regulated cartilage formation and neovascular invasion dependent on load timing. Together, this study represents the first demonstration of the effects of mechanical loading on transplanted cell-mediated bone defect regeneration, and provides a new template for recapitulating developmental programs for tissue engineering.

bioengineering↗