Advancement in "Garbage In Biomaterials Out (GIBO)" concept to develop biomaterials from agricultural waste for tissue engineering and biomedical applications

Presently on a global scale, one of the major concerns is to find effective strategies to manage the agricultural waste to protect the environment. One strategy that has been drawing attention among the researchers is the development of biocompatible materials from agricultural waste. This strategy implies successful conversion of agricultural waste products (e.g.: cellulose, eggshell etc.) into building blocks for biomaterial development. Some of these wastes contain even bioactive compounds having biomedical applications. The replacement and augmentation of human tissue with biomaterials as alternative to traditional method not only bypasses immune-rejection, donor scarcity, and maintenance; but also provides long term solution to damaged or malfunctioning organs. Biomaterials development as one of the key challenges in tissue engineering approach, resourced from natural origin imparts better biocompatibility due to closely mimicking composition with cellular microenvironment. The "Garbage In, Biomaterials Out (GIBO)" concept, not only recycles the agricultural wastes, but also adds to biomaterial raw products for further product development in tissue regeneration. This paper reviews the conversion of garbage agricultural by-products to the biocompatible materials for various biomedical applications.

GRAPHICAL ABSTRACT

The agro-waste biomass processed, purified, modified, and further utilized for the fabrication of biomaterials-based support system for tissue engineering applications to grow living body parts in vitro or in vivo.

Influence of Different ECM-Like Hydrogels on Neurite Outgrowth Induced by Adipose Tissue-Derived Stem Cells

Mesenchymal stem cells (MSCs) have been proposed for spinal cord injury (SCI) applications due to their capacity to secrete growth factors and vesicles—secretome—that impacts important phenomena in SCI regeneration. To improve MSC survival into SCI sites, hydrogels have been used as transplantation vehicles. Herein, we hypothesized if different hydrogels could interact differently with adipose tissue-derived MSCs (ASCs). The efficacy of three natural hydrogels, gellan gum (functionalized with a fibronectin peptide), collagen, and a hydrogel rich in laminin epitopes (NVR-gel) in promoting neuritogenesis (alone and cocultured with ASCs), was evaluated in the present study. Their impact on ASC survival, metabolic activity, and gene expression was also evaluated. Our results indicated that all hydrogels supported ASC survival and viability, being this more evident for the functionalized GG hydrogels. Moreover, the presence of different ECM-derived biological cues within the hydrogels appears to differently affect the mRNA levels of growth factors involved in neuronal survival, differentiation, and axonal outgrowth. All the hydrogel-based systems supported axonal growth mediated by ASCs, but this effect was more robust in functionalized GG. The data herein presented highlights the importance of biological cues within hydrogel-based biomaterials as possible modulators of ASC secretome and its effects for SCI applications.

Cytotoxic effect of 4-hydroxytamoxifen conjugate material on human Schwann cells: Synthesis and characterization

In this study, the toxicity of 4-hydroxytamoxifen (4-OHT) on human Schwann cells (HSCs) was evaluated. Substantial alterations in the cell morphology and viability were observed at 4-OHT concentrations higher than 3 µg/mL. Therefore, we designed and synthesized a drug–polymer conjugate, based on N-(2-hydroxypropyl)methacrylamide (HPMA) and ethyl acrylate (EA) for delivering 4-OHT to the target tissue without the detrimental consequences of the systemic therapy currently used. The macromer carrier of 4-OHT (MATX), with a functionalization degree of 80%, was synthesized in two steps and verified by 1H-NMR and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy. MATX was conjugated to the poly(HPMA-co-EA) copolymer network via radical polymerization. The influence of MATX on the physical, chemical, and mechanical properties of poly(HPMA-co-EA-co-MATX) with a ratio of 69/29/2 wt% was compared to those of poly(HPMA-co-EA) networks with a similar feed mixture. The in vitro release of 4-OHT within 1 month was 6 wt% of the total amount of drug linked to the copolymer backbone.

Microstructure, degradation and in vitro MG63 cells interactions of a new poly(ε-caprolactone), zein, and hydroxyapatite composite for bone tissue engineering

Novel biodegradable biomaterials were investigated for potential application in bone tissue engineering. The biomaterials were prepared by blending poly(ε-caprolactone) and thermoplastic zein, a corn protein, with or without the incorporation of hydroxyapatite particles. The biomaterials were characterized in vitro to assess the degradation in phosphate buffer saline for 56 days by monitoring weight change, morphology, wettability, and tensile properties. The interaction between the biomaterials and MG63 was evaluated by proliferation, morphological characterization, and osteogenic differentiation assays up to 28 days in in vitro cultures. The incorporation of thermoplastic zein within poly(ε-caprolactone) enhanced the hydrophilicity and degradability, while minor effects were observed after the inclusion of the hydroxyapatite particles. Compared to the neat poly(ε-caprolactone), the multiphase poly(ε-caprolactone)/thermoplastic zein–hydroxyapatite composite improved the osteogenic differentiation of MG63 cells and is being considered a candidate material for bone tissue engineering applications.

Hot melt poly-ε-caprolactone/poloxamine implantable matrices for sustained delivery of ciprofloxacin

It has been suggested that prevention and treatment of osteomyelitis could be achieved through local drug delivery using implantable devices, which provide therapeutic levels at the infection site with minimum side-effects. Physical blends of polycaprolactone (PCL) and poloxamine (Tetronic®) were prepared by applying a solvent-free hot melting approach to obtain cytocompatible implants with a tunable bioerosion rate, ciprofloxacin release profile and osteoconductive features. Differential scanning calorimetry and X-ray analysis indicate that the hydrophilic poloxamine varieties T908, T1107, and T1307 are miscible with PCL, while the hydrophobic block copolymer T1301 is immiscible. Incorporation of the block copolymer at weight ratios ranging from 25 to 75 wt.% led to matrices with viscoelastic parameters in the range of those of fresh cortical bone. Once immersed in buffer the matrices underwent a similar weight loss in the first week to the content of poloxamine, followed by a slower erosion rate due to PCL. The initial rapid erosion and the increase in porosity partially explain the observed burst of ciprofloxacin release, which is more intense in the PCL:T1301 formulation due to drug/T1301 repulsion due to polarity. The matrices sustained ciprofloxacin release for several months (<50% released after 3 months) and showed in vitro efficacy against Staphylococcus aureus, eradicating the bacteria in less than 48 h. PCL:poloxamine was cytocompatible with osteoblasts and the matrices prepared with low proportions of T908 were also compatible with mesenchymal stem cell differentiation to osteoblasts. The influence of the nature and proportion of temperature-responsive poloxamine on the performance of PCL implantable systems was determined.

Effects of different extracellular matrices and growth factor immobilization on biodegradability and biocompatibility of macroporous bacterial cellulose

To improve the biocompatibility of bacterial cellulose hydrogel (BCHG), different extracellular matrices (ECMs; collagen, elastin, and hyaluronan) and growth factors (B-FGF, H-EGF, and KGF) were immobilized onto macroporous BCHG. The microstructure of BCHG had inter-connective channels that were well-integrated with the alginate gel. The alginate gel formed a semi-penetrate hydrogel that allowed the ECM and growth factor to diffuse under physiological conditions. The H-EGF and collagen-modified BCHG supported the growth of human skin fibroblast. The improved BCHG was biocompatible and exhibited desirable skin substitute characteristics that could be used as a deliver vehicle for therapeutic compounds during wound healing.

Carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles in central nervous systems-regenerative medicine: effects on neuron/glial cell viability and internalization efficiency

The applicability of CMCht/PAMAM dendrimer nanoparticles for CNS applications was investigated. AFM and TEM observations revealed that the nanoparticles possessed a nanosphere-like shape with a size from 22.0 to 30.7 nm. The nanoparticles could be bound to fluorescent-probe FITC for tracing purposes. Post-natal hippocampal neurons and cortical glial cells were both able to internalize the FITC-labeled CMCht/PAMAM dendrimer nanoparticles with high efficiency. The percentage of positive cells internalizing the nanoparticles varied, reaching a peak after 48 h of incubation. Further experiments for periods up to 7 d revealed that the periodical addition of FITC-labelled CMCht/PAMAM dendrimer nanoparticles was needed to maintain the overall percentage of cells internalizing them. Finally, it was also observed that cell viability was not significantly affected by the incubation of dendrimer nanoparticles.