Extreme Tissue Engineering

Preface: Extreme Tissue Engineering - a User's Guide xi 1 Which Tissue Engineering Tribe Are You From? 1 1.1 Why do we need to engineer tissues at all? 1 1.1.1 Will the real tissue engineering and regenerative medicine please stand up? 2 1.1.2 Other people's definitions 3 1.1.3 Defining our tissue engineering: fixing where we are on the scale-hierarchy 4 1.2 Bio-integration as a fundamental component of engineering tissues 7 1.2.1 Bio-scientists and physical scientists/engineers: understanding diversity in TERM 8 1.3 What are the 'tribes' of tissue engineering? 10 1.3.1 Special needs for special characteristics: why is networking essential for TERM? 13 1.4 Surprises from tissue engineering (Veselius to Vacanti) 16 1.5 So really is there any difference between tissue engineering and regenerative medicine? 20 1.5.1 Questions never really asked: repair versus regeneration? 20 1.5.2 Understanding the full spectrum: tissue replacement repair and regeneration 23 1.6 Conclusions 27 1.7 Summarizing definitions 28 Annex 1 Other people's definitions of tissue engineering 29 Annex 2 Other people's definitions of regenerative medicine 30 Further reading 30 2 Checking Out the Tissue Groupings and the Small Print 33 2.1 Checking the small print: what did we agree to engineer? 33 2.2 Identifying special tissue needs problems and opportunities 37 2.3 When is 'aiming high' just 'over the top'? 39 2.4 Opportunities risks and problems 41 2.4.1 Experimental model tissues (as distinct from spare-parts and fully regenerated tissues) 41 2.4.2 The pressing need for 3D model tissues 42 2.4.3 Tissue models can be useful spin-offs on the way to implants 42 2.5 Special needs for model tissues 44 2.5.1 Cell selection: constancy versus correctness 44 2.5.2 Support matrices - can synthetics fake it? 45 2.5.3 Tissue dimensions: when size does matter! 46 2.6 Opportunities and sub-divisions for engineering clinical implant tissues 46 2.6.1 Making physiological implants: spare parts or complete replacement? 47 2.6.2 Making pathological and aphysiological constructs: inventing new parts and new uses 47 2.6.3 Learning to use the plethora of tissue requirements as an opportunity 48 2.7 Overall summary 49 Further reading 49 3 What Cells 'Hear' When We Say '3D' 51 3.1 Sensing your environment in three dimensions: seeing the cues 51 3.2 What is this 3D cell culture thing? 54 3.3 Is 3D for cells more than a stack of 2Ds? 55 3.4 On in and between tissues: what is it like to be a cell? 58 3.5 Different forms of cell-space: 2D 3D pseudo-3D and 4D cell culture 62 3.5.1 What has '3D' ever done for me? 62 3.5.2 Introducing extracellular matrix 63 3.5.3 Diffusion and mass transport 65 3.5.4 Oxygen mass transport and gradients in 3D engineered tissues: scaling Mount Doom 66 3.6 Matrix-rich cell-rich and pseudo-3D cell cultures 69 3.7 4D cultures - or cultures with a 4th dimension? 71 3.8 Building our own personal understanding of cell position in its 3D space 73 3.9 Conclusion 75 Further reading 75 4 Making Support-Scaffolds Containing Living Cells 77 4.1 Two in one: maintaining a synergy means keeping a good duet together 77 4.2 Choosing cells and support-scaffolds is like matching carriers with cargo 78 4.3 How like the 'real thing' must a scaffold be to fool its resident cells? 80 4.4 Tissue prosthetics and cell prosthetics - what does it matter? 83 4.5 Types of cell support material for tissue engineering - composition or architecture? 85 4.5.1 Surface or bulk - what does it mean to the cells? 85 4.5.2 Bulk material breakdown and the local 'cell economy' 85 4.6 Three generic types of bulk composition for support materials 86 4.6.1 Synthetic materials for cell supports 88 4.6.2 Natural native polymer materials for cell supports 90 4.6.3 Hybrids: composite cell support materials having synthetic and natural components 98 4.7 Conclusions 100 Further reading 101 5 Making the Shapes for Cells in Support-Scaffolds 103 5.1 3D shape and the size hierarchy of support materials 104 5.2 What do we think 'substrate shape' might control? 106 5.3 How we fabricate tissue structures affects what we get out in the end: bottom up or top down? 107 5.4 What shall we seed into our cell-support materials? 110 5.4.1 Cell loading: guiding the willing bribing the reluctant or trapping the unwary? 111 5.4.2 Getting cells onto/into pre-fabricated constructs (the willing and the reluctant) 114 5.4.3 Trapping the unwary: Seeding cells into self-assembling gel-forming materials 115 5.5 Acquiring our cells: recruiting the enthusiastic or press-ganging the resistant 118 5.5.1 From cell expansion to selection and differentiation 121 5.6 Cargo crew or stowaway? 124 5.6.1 Crew-type cells: helping with the journey 124 5.6.2 Cargo-type cells: building the bulk tissue 125 5.6.3 Stowaway or ballast-type cells 128 5.7 Chapter summary 128 Further reading 129 6 Asymmetry: 3D Complexity and Layer Engineering - Worth the Hassle? 131 6.1 Degrees of tissue asymmetry 133 6.2 Making simple anisotropic/asymmetrical structures 134 6.3 Thinking asymmetrically 137 6.4 How do we know which scale to engineer first? 140 6.5 Making a virtue of hierarchical complexity: because we have to 144 6.6 Cell-layering and matrix-layering 147 6.7 No such thing as too many layers: theory and practice of tissue layer engineering 151 6.7.1 Examples of layer engineering 153 6.8 Other forms of tissue fabrication in layers and zones 158 6.8.1 Section summary 158 6.9 Familiar asymmetrical construction components: everyday 'layer engineering' 159 6.10 Summary 160 7 Other Ways to Grow Tissues? 163 7.1 General philosophies for repair replacement and regeneration 163 7.1.1 What does reconstructive surgery have to teach us? 165 7.1.2 Clues from the natural growth of tissues 166 7.2 What part of grow do we not understand? 167 7.2.1 Childhood growth of soft connective tissues: a good focus? 169 7.2.2 Mechanically induced 'growth' of tissues in children 170 7.2.3 Mechanically induced 'growth' of adult tissue 171 7.2.4 Growth has a mirror image - 'ungrowth' or shrinkage-remodelling 172 7.3 If growth and ungrowth maintain a tensional homeostasis what are its controls? 173 7.3.1 Tension-driven growth and tensional homeostasis - the cell's perspective? 174 7.3.2 Mechanically reactive collagen remodelling - the 'constant tailor' theory 177 7.4 Can we already generate tension-driven growth in in vivo tissue engineering? 178 7.4.1 Mechanical loading of existing tissues 178 7.5 Conclusions: what can we learn from engineered growth? 179 Appendix to Chapter 7 179 Further reading 182 8 Bioreactors and All That Bio-Engineering Jazz 185 8.1 What are 'tissue bioreactors' and why do we need them? 186 8.1.1 Rumblings of unease in the smaller communities 186 8.1.2 Hunting for special cells or special cues 187 8.1.3 Farming - culture or engineered fabrication 188 8.2 Bioreactors: origins of tissue bioreactor logic and its problems 190 8.2.1 What have tissue engineers ever done for bioreactor technology? 190 8.2.2 The 3D caveat 191 8.2.3 Fundamental difference between biochemical and tissue bioreactors: 3D solid material fabrication 193 8.2.4 Why should a little thing like 'matrix' change so much? 194 8.2.5 The place of tissue bioreactors in tissue engineering logic: what happened to all the good analogies? 195 8.3 Current strategies for tissue bioreactor process control: views of Christmas past and present 199 8.3.1 Bioreactor enabling factors 200 8.3.2 Cell and architecture control 203 8.4 Extreme tissue engineering solutions to the tissue bioreactor paradox: a view of Christmas future? 209 8.4.1 In vivo versus in vitro tissue bioreactors: the new 'nature versus nurture' question? 209 8.4.2 Do we need tissue bioreactors at all? 210 8.5 Overall summary - how can bioreactors help us in the future? 212 Further reading 214 9 Towards 4D Fabrication: Time Monitoring Function and Process Dynamics 217 9.1 Controlling the dynamics of what we make: what can we control? 218 9.2 Can we make tissue bioreactor processes work - another way forward? 222 9.2.1 Blending the process systems: balancing the Yin and the Yang 224 9.2.2 Making the most of hybrid strategies: refining the timing and sequence 226 9.2.3 A real example of making tissues directly 230 9.3 The 4th dimension applied to bioreactor design 232 9.3.1 Change change change! 232 9.3.2 For bioreactor monitoring what are we really talking about? 233 9.3.3 Monitoring and processes - chickens and eggs: which come first? 234 9.4 What sort of monitoring: how do we do it? 238 9.4.1 Selecting parameters to be monitored 238 9.4.2 What is so special about our particular 'glass slipper'? 241 9.5 The take-home message 245 Further reading 246 10 Epilogue: Where Can Extreme Tissue Engineering Go Next? 247 10.1 So where can extreme tissue engineering go next? 247 Index 249