Cell mediated reactions create TGF-β delivery limitations in engineered cartilage.

Area of Science:

• Biomaterials Science
• Tissue Engineering
• Cellular Biology

Background:

• Endogenous transforming growth factor-beta (TGF-β) activity in cartilage development is precisely controlled by cell-mediated reactions.
• These natural regulatory mechanisms contrast with the requirements for exogenous TGF-β delivery in tissue engineering (TE), which often demands sustained or long-range distribution.
• The impact of cell-mediated reactions on exogenous TGF-β distribution in cartilage TE remains poorly understood.

Purpose of the Study:

• To investigate how cell-mediated reactions influence the spatiotemporal distribution of administered TGF-β within cartilage TE constructs.
• To characterize the binding and internalization rates of TGF-β by cells and the extracellular matrix (ECM) in engineered cartilage.
• To develop computational models predicting TGF-β delivery profiles under the influence of these cellular reactions.

Main Methods:

• Experimental characterization of TGF-β binding to ECM and internalization by cell receptors in bovine chondrocyte-seeded constructs.
• Analysis of TGF-β binding using Brunauer-Emmett-Teller (BET) adsorption isotherms.
• Determination of TGF-β internalization kinetics via Michaelis-Menten and power-law models.
• Development of computational models to simulate TGF-β spatiotemporal distribution.

Main Results:

• TGF-β binding to the ECM exhibited non-linear BET adsorption, with up to seven TGF-β molecules potentially aggregating per binding site.
• Cell-mediated TGF-β internalization followed Michaelis-Menten kinetics at low doses (≤130 ng/mL) but showed an unexpected non-saturating power trend at higher doses (≥130 ng/mL).
• Computational models revealed significant TGF-β spatial gradients with media supplementation, with concentration decaying by ~90% within 500 micrometers.
• Cellular internalization drastically reduced TGF-β retention time on heparin-conjugated scaffolds (160-360-fold decrease) compared to acellular controls.

Conclusions:

• Cell-mediated chemical reactions impose significant limitations on the effective delivery of TGF-β in cartilage tissue engineering.
• These reactions lead to restricted penetration when delivering TGF-β via media and drastically reduce retention when using affinity scaffolds.
• Novel TGF-β delivery platforms must explicitly account for these cell-mediated reactions to achieve optimal exposure profiles for cartilage regeneration.