Biofoam

[3][4][5] Due to the variable nature of synthesized foams, they can have a variety of characteristics and material properties that make them suitable for packaging, insulation, and other applications.

[6] Fungi are generally composed of mycelium, which is made up of hollow filaments of chitin nanofibers bound to other components.

[7] Animal parts like cancellous bone, horseshoe crab shells, toucan beaks, sponge, coral, feathers, and antlers all contain foam-like structures which decrease overall weight at the expense of other material properties.

[12][13] Honeycomb refers to bioinspired patterns that provide a lightweight design for energy absorbing structures.

Honeycomb design can be found in different structural biological components such as spongy bone and plant vasculature.

These variations on the biological design have yielded significantly improved energy absorption results in comparison to traditional hexagonal honeycomb biofoam.

[14] Due to these increased energy absorption performances, honeycomb inspired structures are being researched for use inside vehicle crumple zones.

Aerogels are also being engineered to mirror the internal foam structures of animal hairs (see Figure 3).

[4] In relation to packaging, starches and biopolyesters make up these biofoams as they are adequate replacements to expanded polystyrene.

[22] Polylactic acids (PLAs) are a common form of the basis of these biofoams since they offer a substitute for polyolefin-based foams that are commonly used in automotive parts, pharmaceutical products, and short life-time disposable packaging industries due to their bio-based and biodegradable properties.

[23] PLA comes from the formation of lactide produced from lactic acid due to bacterial fermentation through ring-opening polymerization, in which the process is shown through Figure 4.

[21] PLA does not have the most desirable traits for biodegradability in the packaging industry as it contains a low heat distortion temperature and has unfavorable water barrier characteristics.

[25] As shown, PGA contains a strong stereochemistry structure which in turn causes it to have high barrier and mechanical properties making it desirable for the packaging industry.

[21] In recent studies, PLA has been specifically combined with hydroxyapatite (HA) in order to make the modulus of the sample more favorable for its application in repairing bone failure.

[26] Specifically in tissue engineering, HA has also been shown to generate osteogenesis by triggering osteoblasts and pre-osteoblastic cells.

This research has evolved to include the creation of biodegradable biofoams, with the intention to replace other foams that may be environmentally harmful or whose production may be unsustainable.

Following this vein, Gunawan et al.[28] conducted research to developed “commercially-relevant polyurethane products that can biodegrade in the natural environment”.

RPO is recovered from the waste of palm oil mill and is a byproduct of that manufacturing process.

Research efforts have been put into using natural components in the creation of potentially biodegradable foam products.

[7][34][35][18] The wheat gluten example was used in combination with graphene to attempt to make a conductive biofoam.

[35] The mycelium-based, chitosan-based, and cellulose-based biofoam examples are intended to become cost effective and low density material options.

Figure 2: Depiction of various honeycomb patterns [ 14 ]
Figure 3: Bioinspired Macroscopic Carbon Tube Aerogel (CTA) compared with polar bear fur at high magnification [ 16 ]
Figure 4. PLA being produced through ring-opening polymerization of lactide. [ 21 ]
Figure 5: The FFF-based 3D printed PLA undergoing compression testing and its shape after heating the sample greater than its glass transition temperature (Tg). [ 21 ]
Figure 7: Biodegradation of PU cubes over 12 weeks. Degradation was analyzed through A) change in appearance, B) cube mass, and C) maximum force at 50% compression force deflection (CFD). Error bars indicate sample standard deviations of the triplicate measurements. For compost and soil mass loss, p < 0.01, and for compost and soil CFD, p < 0.01 (Table S2). [ 28 ]
Figure 6: A) General polyester polyol and polyurethane (PU) syntheses and structure. B) Algenesis algae-based PU flip-flop prototype [ 28 ]