Stages of Cell Development and Stem Cell Applications

3 stages of development in cells

Division, Determination, Differentiation

Division stage

Cells replicate, leading to growth

Determination stage

Internal mechanisms fix the identity a stem cell will become

Differentiation stage

Cell becomes a specialised type with new morphology and function

Stem cells

Cells that can divide indefinitely and differentiate into other cell types

Roles of stem cells

Growth & development; Replacement & repair

Continuous growth example

Fish & crustaceans

Determinate growth example

Birds and mammals (growth stops in adulthood)

Permanent cells

Cells that cannot be replaced once damaged (e.g. lens, auditory hair cells)

Simple duplication in cell replacement

Differentiated cells like endothelial cells divide to replace or grow vessels

Unipotent stem cell

Stem cell that can become one type of cell (e.g., olfactory basal cells)

Multipotent stem cell

Can become several types of cells (e.g., gut epithelium cells)

Gut epithelium cell types

Absorptive, Goblet, Enteroendocrine, Paneth

Absorptive cell function

Absorbs via microvilli

Goblet cell function

Secretes mucus

Enteroendocrine cell function

Secretes hormones

Paneth cell function

Provides immune defense

Pluripotent stem cell

Can become many types (e.g., blood cells from bone marrow)

Totipotent stem cell

Can become all cell types (e.g., early embryo)

Haematopoiesis

Process of blood cell formation from pluripotent stem cells

Haematopoiesis stages

Pluripotent → Progenitor (myeloid/lymphoid) → Progenitor cells → Blood cells

Methods of stem cell therapy

1. Embryonic culture, 2. Adult stem cell collection, 3. Reprogram adult cells

Pros of adult stem cell therapy

Ethically preferred and reduced immune rejection

Cons of adult stem cell therapy

Not available for all tissue types, limited numbers

iPSCs

Adult cells reprogrammed to a totipotent state

3D bioprinting

Precise placement of cells/materials to create tissue/organs

Approaches to 3D bioprinting

Biomimicry, Autonomous self-assembly, Mini-tissue building blocks

Autologous stem cells in bioprinting

Reduce immune rejection and improve compatibility

Scaffold in tissue engineering

Structure that mimics tissue properties and guides cell growth

Key features of a good scaffold

Tissue-specific signals, strength, cytokine release, degradability

Challenges in scaffold design

Immune response, mechanical mismatch, poor cell distribution

Spinach leaf scaffold example

Plant veins mimic blood vessels for growing heart tissue

Mini-tissues

Small structural/functional tissue units (e.g., nephron) used to build larger organs

Organ-on-a-Chip

Microfluidic 3D model of an organ for drug testing and disease modeling

Liver-on-a-chip models

Accurate, cost-effective drug screening before clinical trials

Liver-on-a-chip model description

HepG2/C3A spheroids in GelMA hydrogel, 7×7 array, 10× growth in 30 days

iPSCs in organ chips

Allow patient-specific testing and drug response modeling