Difficulties in the translation of functionalized biomaterials into regenerative medicine clinical products

Enhanced bone regeneration in rat calvarial defects through BMP2 release from engineered poly(ethylene glycol) hydrogels

The clinical standard therapy for large bone defects, typically addressed through autograft or allograft donor tissue, faces significant limitations. Tissue engineering offers a promising alternative strategy for the regeneration of substantial bone lesions. In this study, we harnessed poly(ethylene glycol) (PEG)-based hydrogels, optimizing critical parameters including stiffness, incorporation of arginine-glycine-aspartic acid (RGD) cell adhesion motifs, degradability, and the release of BMP2 to promote bone formation. In vitro we demonstrated that human bone marrow derived stromal cell (hBMSC) proliferation and spreading strongly correlates with hydrogel stiffness and adhesion to RGD peptide motifs. Moreover, the incorporation of the osteogenic growth factor BMP2 into the hydrogels enabled sustained release, effectively inducing bone regeneration in encapsulated progenitor cells. When used in vivo to treat calvarial defects in rats, we showed that hydrogels of low and intermediate stiffness optimally facilitated cell migration, proliferation, and differentiation promoting the efficient repair of bone defects. Our comprehensive in vitro and in vivo findings collectively suggest that the developed hydrogels hold significant promise for clinical translation for bone repair and regeneration by delivering sustained and controlled stimuli from active signaling molecules.

Regenerative bioelectronics: A strategic roadmap for precision medicine

In the past few decades, stem cell-based regenerative engineering has demonstrated its significant potential to repair damaged tissues and to restore their functionalities. Despite such advancement in regenerative engineering, the clinical translation remains a major challenge. In the stance of personalized treatment, the recent progress in bioelectronic medicine likewise evolved as another important research domain of larger significance for human healthcare. Over the last several years, our research group has adopted biomaterials-based regenerative engineering strategies using innovative bioelectronic stimulation protocols based on either electric or magnetic stimuli to direct cellular differentiation on engineered biomaterials with a range of elastic stiffness or functional properties (electroactivity/magnetoactivity). In this article, the role of bioelectronics in stem cell-based regenerative engineering has been critically analyzed to stimulate futuristic research in the treatment of degenerative diseases as well as to address some fundamental questions in stem cell biology. Built on the concepts from two independent biomedical research domains (regenerative engineering and bioelectronic medicine), we propose a converging research theme, 'Regenerative Bioelectronics'. Further, a series of recommendations have been put forward to address the current challenges in bridging the gap in stem cell therapy and bioelectronic medicine. Enacting the strategic blueprint of bioelectronic-based regenerative engineering can potentially deliver the unmet clinical needs for treating incurable degenerative diseases.

Additive Biomanufacturing with Collagen Inks

Collagen is a natural polymer found abundantly in the extracellular matrix (ECM). It is easily extracted from a variety of sources and exhibits excellent biological properties such as biocompatibility and weak antigenicity. Additionally, different processes allow control of physical and chemical properties such as mechanical stiffness, viscosity and biodegradability. Moreover, various additive biomanufacturing technology has enabled layer-by-layer construction of complex structures to support biological function. Additive biomanufacturing has expanded the use of collagen biomaterial in various regenerative medicine and disease modelling application (e.g., skin, bone and cornea). Currently, regulatory hurdles in translating collagen biomaterials still remain. Additive biomanufacturing may help to overcome such hurdles commercializing collagen biomaterials and fulfill its potential for biomedicine.

A new approach to the production of a biovital skin graft based on human acellular dermal matrix produced in-house, in vitro revitalized internally by human fibroblasts and keratinocytes on the surface

Patients with extensive and deep burns who do not have enough donor sites for autologous skin grafts require alternative treatment methods. Tissue engineering is a useful tool to solve this problem. The aim of this study was to find the optimal method for the production of a biovital skin substitute based on acellular dermal matrix (ADM) and in vitro cultured fibroblasts and keratinocytes. In this work, nine methods of ADM production were assessed. The proposed methods are based on the use of the following enzymes: Dispase II, collagenase I/ethylenediaminetetraacetic acid (EDTA), collagenase II/EDTA, and mechanical perforation using DermaRoller and mesh dermatome. The obtained ADMs were examined (both on the side of the basement membrane and on the "cut-off" side) by means of scanning electron microscopy, immunohistochemistry tests and strength tests. ADM was revitalized with human fibroblasts and keratinocytes. The ability of in-depth revitalization of cultured fibroblasts and their ability to secrete collagen IV was examined. The obtained results indicate that the optimal method of production of live skin substitutes is the colonization of autologous fibroblasts and keratinocytes on the scaffold obtained using two-step incubation method: Trypsin/EDTA and dispase II.

Functionalization of phosphocalcic bioceramics for bone repair applications

This work is devoted to the processing of bone morphogenetic protein (BMP-2) functionalized silicate substituted hydroxyapatite (SiHA) ceramic spheres. The motivation behind it is to develop injectable hydrogel/bioceramic composites for bone reconstruction applications. SiHA microspheres were shaped by spray drying and thoroughly characterized. The silicate substitution was used to provide preferred chemical sites at the ceramic surface for the covalent immobilization of BMP-2. In order to control the density and the release of the immobilized BMP-2, its grafting was performed via ethoxysilanes and polyethylene glycols. A method based on Kaiser's test was used to quantify the free amino groups of grafted organosilanes available at the ceramic surface for BMP-2 immobilization. The SiHA surface modification was investigated by means of X-ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy and thermogravimetry coupled with mass spectrometry. The BMP-2 bioactivity was assessed, in vitro, by measuring the luciferase expression of a stably transfected C3H10 cell line (C3H10-BRE/Luc cells). The results provided evidence that the BMP-2 grafted onto SiHA spheres remained bioactive.

Leveraging advances in biology to design biomaterials

Biomaterials have dramatically increased in functionality and complexity, allowing unprecedented control over the cells that interact with them. From these engineering advances arises the prospect of improved biomaterial-based therapies, yet practical constraints favour simplicity. Tools from the biology community are enabling high-resolution and high-throughput bioassays that, if incorporated into a biomaterial design framework, could help achieve unprecedented functionality while minimizing the complexity of designs by identifying the most important material parameters and biological outputs. However, to avoid data explosions and to effectively match the information content of an assay with the goal of the experiment, material screens and bioassays must be arranged in specific ways. By borrowing methods to design experiments and workflows from the bioprocess engineering community, we outline a framework for the incorporation of next-generation bioassays into biomaterials design to effectively optimize function while minimizing complexity. This framework can inspire biomaterials designs that maximize functionality and translatability.

Atomic force microscopy in the production of a biovital skin graft based on human acellular dermal matrix produced in-house and in vitro cultured human fibroblasts

The most efficient method in III° burn treatment is the use of the autologous split thickness skin grafts that were donated from undamaged body area. The main limitation of this method is lack of suitable donor sites. Tissue engineering is a useful tool to solve this problem. The goal of this study was to find the most efficient way of producing biovital skin substitute based on in house produced acellular dermal matrix ADM and in vitro cultured fibroblasts. Sixty samples of sterilized human allogeneic skin (that came from 10 different donors) were used to examine the influence of decellularizing substances on extracellular matrix and clinical usefulness of the test samples of allogeneic human dermis. Six groups of acellular dermal matrix were studied: ADM-1 control group, ADM-2 research group (24 h incubation in 0.05% trypsin/EDTA solution), ADM-3 research group (24 h incubation in 0.025% trypsin/EDTA solution), ADM-4 research group (24 h incubation in 0.05% trypsin/EDTA solution and 4 h incubation in 0,1% SDS), ADM-5 research group (24 h incubation in 0.025% trypsin/EDTA solution and 4 h incubation in 0,1% SDS), and ADM-6 research group (24 h incubation in 0,1% SDS). Obtained ADMs were examined histochemically and by atomic force microscopy (AFM). ADMs were settled by human fibroblasts. The number of cultured cells and their vitality were measured. The obtained results indicated that the optimal method for production of living skin substitutes is colonization of autologous fibroblasts on the scaffold prepared by the incubation of human allogeneic dermis in 0.05% trypsin/EDTA. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 726-733, 2018.

Biomimetic approaches with smart interfaces for bone regeneration

A 'smart tissue interface' is a host tissue-biomaterial interface capable of triggering favourable biochemical events inspired by stimuli responsive mechanisms. In other words, biomaterial surface is instrumental in dictating the interface functionality. This review aims to investigate the fundamental and favourable requirements of a 'smart tissue interface' that can positively influence the degree of healing and promote bone tissue regeneration. A biomaterial surface when interacts synergistically with the dynamic extracellular matrix, the healing process become accelerated through development of a smart interface. The interface functionality relies equally on bound functional groups and conjugated molecules belonging to the biomaterial and the biological milieu it interacts with. The essential conditions for such a special biomimetic environment are discussed. We highlight the impending prospects of smart interfaces and trying to relate the design approaches as well as critical factors that determine species-specific functionality with special reference to bone tissue regeneration.

Biomimetic L-aspartic acid-derived functional poly(ester amide)s for vascular tissue engineering

Functionalization of polymeric biomaterials permits the conjugation of cell signaling molecules capable of directing cell function. In this study, l-phenylalanine and l-aspartic acid were used to synthesize poly(ester amide)s (PEAs) with pendant carboxylic acid groups through an interfacial polycondensation approach. Human coronary artery smooth muscle cell (HCASMC) attachment, spreading and proliferation was observed on all PEA films. Vinculin expression at the cell periphery suggested that HCASMCs formed focal adhesions on the functional PEAs, while the absence of smooth muscle α-actin (SMαA) expression implied the cells adopted a proliferative phenotype. The PEAs were also electrospun to yield nanoscale three-dimensional (3-D) scaffolds with average fiber diameters ranging from 130 to 294nm. Immunoblotting studies suggested a potential increase in SMαA and calponin expression from HCASMCs cultured on 3-D fibrous scaffolds when compared to 2-D films. X-ray photoelectron spectroscopy and immunofluorescence demonstrated the conjugation of transforming growth factor-β1 to the surface of the functional PEA through the pendant carboxylic acid groups. Taken together, this study demonstrates that PEAs containing aspartic acid are viable biomaterials for further investigation in vascular tissue engineering.

Interactions between inorganic and organic phases in bone tissue as a source of inspiration for design of novel nanocomposites

Mimicking the nanostructure of bone and understanding the interactions between the nanoscale inorganic and organic components of the extracellular bone matrix are crucial for the design of biomaterials with structural properties and a functionality similar to the natural bone tissue. Generally, these interactions involve anionic and/or cationic functional groups as present in the organic matrix, which exhibit a strong affinity for either calcium or phosphate ions from the mineral phase of bone. This study reviews the interactions between the mineral and organic extracellular matrix components in bone tissue as a source of inspiration for the design of novel nanocomposites. After providing a brief description of the various structural levels of bone and its main constituents, a concise overview is presented on the process of bone mineralization as well as the interactions between calcium phosphate (CaP) nanocrystals and the organic matrix of bone tissue. Bioinspired synthetic approaches for obtaining nanocomposites are subsequently addressed, with specific focus on chemical groups that have affinity for CaPs or are involved in stimulating and controlling mineral formation, that is, anionic functional groups, including carboxyl, phosphate, sulfate, hydroxyl, and catechol groups.

Using extracellular matrix for regenerative medicine in the spinal cord

Regeneration within the mammalian central nervous system (CNS) is limited, and traumatic injury often leads to permanent functional motor and sensory loss. The lack of regeneration following spinal cord injury (SCI) is mainly caused by the presence of glial scarring, cystic cavitation and a hostile environment to axonal growth at the lesion site. The more prominent experimental treatment strategies focus mainly on drug and cell therapies, however recent interest in biomaterial-based strategies are increasing in number and breadth. Outside the spinal cord, approaches that utilize the extracellular matrix (ECM) to promote tissue repair show tremendous potential for various application including vascular, skin, bone, cartilage, liver, lung, heart and peripheral nerve tissue engineering (TE). Experimentally, it is unknown if these approaches can be successfully translated to the CNS, either alone or in combination with synthetic biomaterial scaffolds. In this review we outline the first attempts to apply the potential of ECM-based biomaterials and combining cell-derived ECM with synthetic scaffolds.

Perspectives on the interface of drug delivery and tissue engineering

Controlled drug delivery of bioactive molecules continues to be an essential component of engineering strategies for tissue defect repair. This article surveys the current challenges associated with trying to regenerate complex tissues utilizing drug delivery and gives perspectives on the development of translational tissue engineering therapies which promote spatiotemporal cell-signaling cascades to maximize the rate and quality of repair.

Thinking inside the box: keeping tissue-engineered constructs in vitro for use as preclinical models

Tissue engineers have made great strides toward the creation of living tissue replacements for a wide range of tissue types and applications, with eventual patient implantation as the primary goal. However, an alternate use of tissue-engineered constructs exists: as in vitro preclinical models for purposes such as drug screening and device testing. Tissue-engineered preclinical models have numerous potential advantages over existing models, including cultivation in three-dimensional geometries, decreased cost, increased reproducibility, precise control over cultivation conditions, and the incorporation of human cells. Over the past decade, a number of researchers have developed and used tissue-engineered constructs as preclinical models for testing pharmaceuticals, gene therapies, stents, and other technologies, with examples including blood vessels, skeletal muscle, bone, cartilage, skin, cardiac muscle, liver, cornea, reproductive tissues, adipose, small intestine, neural tissue, and kidney. The focus of this article is to review accomplishments toward the creation and use of tissue-engineered preclinical models of each of these different tissue types.