Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. In order to fit functional demand, materials with desired physical, chemical, biological, biomechanical and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications.

/pdf/biomedical-applications-of-biodegradable-polymers-2db9gcyzxw.pdf

Biomedical Applications of Biodegradable Polymers

Biopolymer-based hydrogels as scaffolds for tissue engineering applications: a review

Polymer surface modification for the attachment of bioactive compounds

Injectable hydrogels with biodegradability have in situ formability which in vitro/in vivo allows an effective and homogeneous encapsulation of drugs/cells, and convenient in vivo surgical operation in a minimally invasive way, causing smaller scar size and less pain for patients. Therefore, they have found a variety of biomedical applications, such as drug delivery, cell encapsulation, and tissue engineering. This critical review systematically summarizes the recent progresses on biodegradable and injectable hydrogels fabricated from natural polymers (chitosan, hyaluronic acid, alginates, gelatin, heparin, chondroitin sulfate, etc.) and biodegradable synthetic polymers (polypeptides, polyesters, polyphosphazenes, etc.). The review includes the novel naturally based hydrogels with high potential for biomedical applications developed in the past five years which integrate the excellent biocompatibility of natural polymers/synthetic polypeptides with structural controllability via chemical modification. The gelation and biodegradation which are two key factors to affect the cell fate or drug delivery are highlighted. A brief outlook on the future of injectable and biodegradable hydrogels is also presented (326 references).

Injectable and biodegradable hydrogels: gelation, biodegradation and biomedical applications

Organ printing can be defined as layer-by-layer additive robotic biofabrication of three-dimensional functional living macrotissues and organ constructs using tissue spheroids as building blocks. The microtissues and tissue spheroids are living materials with certain measurable, evolving and potentially controllable composition, material and biological properties. Closely placed tissue spheroids undergo tissue fusion - a process that represents a fundamental biological and biophysical principle of developmental biology-inspired directed tissue self-assembly. It is possible to engineer small segments of an intraorgan branched vascular tree by using solid and lumenized vascular tissue spheroids. Organ printing could dramatically enhance and transform the field of tissue engineering by enabling large-scale industrial robotic biofabrication of living human organ constructs with "built-in" perfusable intraorgan branched vascular tree. Thus, organ printing is a new emerging enabling technology paradigm which represents a developmental biology-inspired alternative to classic biodegradable solid scaffold-based approaches in tissue engineering.

Organ Printing: Tissue Spheroids as Building Blocks

Porous nano-HA/collagen/PLLA scaffold containing chitosan microspheres for controlled delivery of synthetic peptide derived from BMP-2.

The use of carbon nanotubes to induce osteogenic differentiation of human adipose-derived MSCs in vitro and ectopic bone formation in vivo

Bone tissue engineering is an exciting approach to directly repair bone defects or engineer bone tissue for transplantation. Biomaterials play a pivotal role in providing a template and extracellular environment to support regenerative cells and promote tissue regeneration. A variety of signaling cues have been identified to regulate cellular activity, tissue development, and the healing process. Numerous studies and trials have shown the promise of tissue engineering, but successful translations of bone tissue engineering research into clinical applications have been limited, due in part to a lack of optimal delivery systems for these signals. Biomedical engineers are therefore highly motivated to develop biomimetic drug delivery systems, which benefit from mimicking signaling molecule release or presentation by the native extracellular matrix during development or the natural healing process. Engineered biomimetic drug delivery systems aim to provide control over the location, timing, and release kinetics of the signal molecules according to the drug’s physiochemical properties and specific biological mechanisms. This article reviews biomimetic strategies in signaling delivery for bone tissue engineering, with a focus on delivery systems rather than specific molecules. Both fundamental considerations and specific design strategies are discussed with examples of recent research progress, demonstrating the significance and potential of biomimetic delivery systems for bone tissue engineering. Bone tissue engineering offers exciting possibilities for repairing bone defects or regenerating bone tissue for transplantation, and biomimetic drug delivery systems (DDSs) hold promise in providing an environment to support the tissue regeneration. Biomimetic DDSs mimic the release of signaling molecules during development or in the natural healing process, and a team headed by Peter Ma at the University of Michigan in the United States conducted a review of the biomimetic strategies that have been adopted for bone tissue engineering. Various DDSs have been developed that mimic the natural healing or development processes, and they provide controlled drug release. The authors conclude that integrating DDSs with bone implants or scaffolds (which stimulate the growth of bone cells on their surface) could lead to advanced tissue engineering therapy for repairing bone defects.

Biomimetic delivery of signals for bone tissue engineering

Bioinspired mineralized collagen scaffolds for bone tissue engineering.

Regenerative medicine consisting of cells and materials provides a new way for the repair and regeneration of tissues and organs. Nano-biomaterials are highlighted due to their advantageous features compared with conventional micro-materials. The aim of this study is to investigate the effects of micro-/nano- sized hydroxyapatite (μ/n-HA) on the osteogenic differentiation of rat bone marrow derived mesenchymal stem cells (rBMSCs). μ/n-HA were prepared by a microwave synthesizer and precipitation method, respectively. Different sizes of μ/n-HA were characterized by IR, XRD, SEM, TEM and co-cultured with rBMSCs. It was shown that rBMSCs expressed higher levels of osteoblast-related markers by n-HA than μ-HA stimulation. The size of HA is an important factor for affecting the osteogenic differentiation of rBMSCs. This provides a new avenue for mechanistic studies of stem cell differentiation and a new approach to obtain more committed differentiated cells.

Xufeng Niu

Papers

Porous nano-HA/collagen/PLLA scaffold containing chitosan microspheres for controlled delivery of synthetic peptide derived from BMP-2.

The use of carbon nanotubes to induce osteogenic differentiation of human adipose-derived MSCs in vitro and ectopic bone formation in vivo

Biomimetic delivery of signals for bone tissue engineering

Bioinspired mineralized collagen scaffolds for bone tissue engineering.

Micro-/Nano- sized hydroxyapatite directs differentiation of rat bone marrow derived mesenchymal stem cells towards an osteoblast lineage