HTGAA: 3D Bio Printing and Biofabrication

Class Material

Introduction

Given that the same factors that determine cell fate and function in vivo also determine the progression of cell differentiation in vitro, our ability to grow a 3-dimensional tissue in the laboratory is therefore directly related to our ability, as engineers, to recapitulate the natural microenvironment. This principle is referred to as the biomimetic paradigm (i.e. “copying nature”).

Hence, for tissue engineering applications, major efforts have been invested into characterizing native tissue environments, and describing these environments by parameters that may be recapitulated experimentally (e.g. the convection of blood through perfusion, the stiffness/porosity of scaffolds, the exposure of cells to a mechanical loading or electrical field stimulation, etc). Below are some exercises that allow us to explore what some of these design considerations look like in practice.

Problem 1: Design considerations for electrical stimulation systems

Below appears an oscilloscope reading for a stimulus waveform from commercial stimulator (refer to: 2009 Tandon et al. Nature Protocols). When a bioreactor is attached (pink), the stimulus waveform (blue) is no longer faithfully applied.

Problem 2: Morphological changes associated with electrical stimulation

Below appears Human adipose derived stem cells (hASCs) which were exposed to direct-current electrical stimulation for a period of 4 hours (refer to: 2009 Tandon et al. Conf Proc IEEE Eng Med Biol Soc.).

Problem 3: design considerations for perfusion bioreactors

Hands-on activity: DIY decellularized scaffolds!

EpiBone uses decellularized bovine bone as a scaffold for engineering living bone. There are many benefits to decellularized scaffolds, including their high porosity, and high degree of interconnected pores, which are difficult to achieve with current additive manufacturing technology (i.e. 3D printing).

Furthermore, from the perspective of regenerative medicine, decellularized scaffolds, since they lack cellular components and maintain extracellular matrices, may be able to act as an inductive template for recellularization, resulting in a construct that lacks risk for rejection (refer to: Badylak et al 2011).

Decellularization is a process that may be accomplished with a number of different modalities, including physical, enzymatic, and/or chemical. In this hands-on exercise, you will try a combination of physical (i.e. freezing) and chemical (i.e. detergent) processes to a selection of fruits/veggies/meats you may have on hand. PLEASE don’t go out to procure any ingredients for the sake of this exercise. But DO feel free to think creatively.

This exercise is based on the work of Andrew Pelling, who famously talked about his approach to “make ears out of apples” in his TED talk. Read the home version of this exercise here and watch the accompanying video about decellularizing fruits/veggies (don’t worry about not having a pump). And see here for an example of this process being applied to bacon towards making some pretty interesting looking lamps/vases. I’ll be truthful, I haven’t tried this yet myself, but figured it was low-hanging fruit (pun intended) and could be fun. I’ll plan to try this at home alongside you guys if my husband and baby cooperate.

Instructions:

Related Readings & References