Mesenchymal Stromal Cell-Derived Extracellular Vesicles in Wound Healing.

The well-orchestrated process of wound healing may be negatively impacted from interrupted or incomplete tissue regenerative processes. The healing potential is further compromised in patients with diabetes mellitus, chronic venous insufficiency, critical limb ischemia, and immunocompromised conditions, with a high health care burden and expenditure. Stem cell-based therapy has shown promising results in clinical studies. Mesenchymal stem cell-derived exosomes (MSC Exos) may favorably impact intercellular signaling and immunomodulation, promoting neoangiogenesis, collagen synthesis, and neoepithelization. This article gives an outline of the biogenesis and mechanism of extracellular vesicles (EVs), particularly exosomes, in the process of tissue regeneration and discusses the use of preconditioned exosomes, platelet-rich plasma-derived exosomes, and engineered exosomes in three-dimensional bioscaffolds such as hydrogels (collagen and chitosan) to prolong the contact time of exosomes at the recipient site within the target tissue. An appropriate antibiotic therapy based on culture-specific guidance coupled with the knowledge of biopolymers helps to fabricate nanotherapeutic materials loaded with MSC Exos to effectively deliver drugs locally and promote novel approaches for the management of chronic wounds.

Allogenic perinatal tissue for musculoskeletal regenerative medicine applications: a systematic review protocol.

BACKGROUND: Musculoskeletal ailments impact the lives of millions of people, and at times necessitate surgery followed by physiotherapy, drug treatments, or immobilization. Regenerative musculoskeletal medicine has undergone enormous progress over the last few decades. Sources of tissues used for regenerative medicine purposes can be grouped into autologous or allogenic. Although autologous sources are promising, there is a wide range of limitations with the treatment, including the lack of randomized controlled studies for orthopaedic conditions, donor site morbidity, and highly variable outcomes for patients. Allogenic sources bypass some of these shortcomings and are a promising source for orthopaedic regenerative medicine applications. METHODS: A systematic search will be performed using PubMed, Elsevier, ScienceDirect, and Google Scholar databases for articles published in English before May 2022. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement and guidelines will be used. Studies will be eligible if they apply to acute and chronic orthopaedic musculoskeletal complications or animal or human disease models. Publications must include the use of MSCs and/or tissue obtained from amniotic/chorionic membrane, amniotic fluid, umbilical cord, and/or umbilical cord-derived Wharton's jelly as an intervention. Placebos, noninjury models, acute injury models, non-injury models, and gold standard treatments will be compared. The study selection will be performed by two independent reviewers using a dedicated reference management software. Data synthesis and meta-analysis will be performed separately for preclinical and clinical studies. DISCUSSION: The results will be published in relevant peer-reviewed scientific journals. Investigators will present results at national or international conferences. TRIAL REGISTRATION: The Protocol will be registered on PROSPERO international prospective register of systematic reviews prior to commencement.

Coracoid Impingement and Morphology Is Associated with Fatty Infiltration and Rotator Cuff Tears.

This study describes measurements between the coracoid, glenoid, and humerus; characterizes coracoid shape, rotator cuff fatty infiltration, and quantitatively evaluates coracoid impingement and its association with anterosuperior rotator cuff tears (ASCT). 193 shoulder magnetic resonance imaging (MRI) scans demonstrating: rotator cuff tear; isolated tear of the supraspinatus; tear of supraspinatus and subscapularis, were included. MRI measurements included coracohumeral interval (CHI), coracoid overlap (CO), coracoid recess (CR), coracoglenoid angle (CGA), and coracoglenoid interval (CGI) on axial slices; acromiohumeral interval (AHI) on coronal slices; and coracohumeral interval (CHI) and coracoacromial ligament (CAL) thickness on sagittal slices. The coracoid shape was classified as flat, curved, or hooked. An Independent T-test was used to compare the MRI measurements and the different rotator cuff tear groups. In 79% of the patients with ASCT tears, the coracoid was curved. Axial CHI, CGA, sagittal CHI, and AHI were decreased in ASCT when compared to no tears and isolated supraspinatus tears (p < 0.05). CO was increased in ASCT compared to no tears and isolated supraspinatus tears (p < 0.05). Patients with an ASCT had a significantly increased subscapularis and supraspinatus Goutallier fatty infiltration score when compared to no tear and isolated supraspinatus tears (p < 0.05). These quantitative measurements may be useful in identifying patients at risk for ASCT. Level of Evidence III.

Umbilical Cord-Derived Wharton's Jelly for Regenerative Medicine Applications: A Systematic Review.

Musculoskeletal ailments affect millions of people around the world and place a high burden on healthcare. Traditional treatment modalities are limited and do not address underlying pathologies. Mesenchymal stem cells (MSCs) have emerged as an exciting therapeutic alternative and Wharton's jelly-derived mesenchymal stem cells (WJSCs) are some of these. This review reports the clinical and functional outcomes of the applications of WJSCs in orthopedic surgery. A systematic review was conducted utilizing the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. The studies that used culture-expanded, mesenchymal stem or stromal cells, MSCs and/or connective tissues procured from Wharton's jelly (WJ), from January 2010 to October 2021, were included. Conventional non-operative therapies and placebos were used as comparisons. Six studies that directly discussed WJSCs use in an animal model or the basic scientific testing using an injury model were identified. Five publications studied cartilage injury, three studied degenerative disc disease, one was related to osteoarthritis, and one was related to osteochondral defects. The results of these studies suggested the benefits of WJSCs in the management of these orthopedic pathologies. To adequately assess the safety and efficacy of WJSCs in orthopedic surgery, further randomized controlled clinical studies are necessary.

Evaluation of immediate and short-term efficacy of DualStim therapy with and without intracavernosal umbilical cord-derived Wharton's jelly in patients with erectile dysfunction: Study protocol for a randomized controlled trial.

INTRODUCTION: Erectile dysfunction (ED) affects a significant portion of the United States population and causes negative psychological burdens that affects men and their partner's quality of life and satisfaction. Extracorporeal shock therapy (ESWT) utilizing focused ESWT and radial ESWT in Low-intensity shock wave therapy has been used to treat ED with some success. Wharton's Jelly (WJ) is a biologic substance with large amounts of stem cells, growth factors, cytokines and extracellular components. The use of combined focused and radial ESWT (DualStim therapy) with injected WJ have potential uses in ED that may have advantages over current treatments. MATERIALS: A randomized, single-blinded, controlled clinical trial will be conducted to evaluate the efficacy and safety of DualStim therapy and intracavernosal injection of WJ in moderate to severe ED. A total of 60 patients with moderate to severe ED will be enrolled and treated with DualStim therapy with intracavernosal injection of WJ or saline for a period of 7 weeks. The International Index of Erectile Function - Erectile Function score will be used to gauge the treatment related changes in relation to the subject's baseline. The scores will be recorded at baseline and compared to follow-ups 1,3 and 6 months post-treatment. Any adverse events or severe adverse events will be recorded in the corresponding case report forms. Sexual Encounter Profile, as well as the Global Assessment Questionnaire and the Erection Hardness Score will be used to determine the sexual activity improvement from baseline leading to optimal penetration at follow-ups 1,3 and 6 months post-treatment. DISCUSSION: This clinical trial is one of the first studies to determine the immediate and short-term efficacy of DualStim therapy, with and without intracavernosal injection of formulated umbilical cord-derived WJ to improve and/or restore erectile function in patients with moderate to severe ED. This study will also provide insight into the safety and efficacy of WJ. We anticipate clinically significant improvement in patients suffering from moderate and severe ED treated with DualStim therapy with WJ compared to their baseline and DualStim with saline.

Safety and efficacy of umbilical cord-derived Wharton's jelly compared to hyaluronic acid and saline for knee osteoarthritis: study protocol for a randomized, controlled, single-blind, multi-center trial.

BACKGROUND: Osteoarthritis (OA) is the most common joint disorder in the United States of America (USA) with a fast-rising prevalence. Current treatment modalities are limited, and total knee replacement surgeries have shown disadvantages, especially for grade II/III OA. The interest in the use of biologics, including umbilical cord (UC)-derived Wharton's jelly (WJ), has grown in recent years. The results from a preliminary study demonstrated the presence of essential components of regenerative medicine, namely growth factors, cytokines, hyaluronic acid (HA), and extracellular vesicles, including exosomes, in WJ. The proposed study aims to evaluate the safety and efficacy of intra-articular injection of UC-derived WJ for the treatment of knee OA symptoms. METHODS: A randomized, controlled, single-blind, multi-center, prospective study will be conducted in which the safety and efficacy of intra-articular administration of UC-derived WJ are compared to HA (control) and saline (placebo control) in patients suffering from grade II/III knee OA. A total of 168 participants with grade II or III knee OA on the KL scale will be recruited across 53 sites in the USA with 56 participants in each arm and followed for 1 year post-injection. Patient satisfaction, Numeric Pain Rating Scale, Knee Injury and Osteoarthritis Outcome Score, 36-Item Short Form Survey (SF-36), and 7-point Likert Scale will be used to assess the participants. Physical exams, X-rays, and MRI with Magnetic Resonance Observation of Cartilage Repair Tissue score will be used to assess improvement in associated anatomy. DISCUSSION: The study results will provide valuable information into the safety and efficacy of intra-articular administration of Wharton's jelly for grade II/III knee osteoarthritis. The results of this study will also add to the treatment options available for grade II/III OA as well as help facilitate the development of a more focused treatment strategy for patients. TRIAL REGISTRATION: ClinicalTrials.gov, NCT04711304 . Registered on January 15, 2021.

Immunomodulatory extracellular vesicles: an alternative to cell therapy for COVID-19.

Introduction: SARS-CoV-2 induces a cytokine storm and can cause inflammation, fibrosis and apoptosis in the lungs, leading to acute respiratory distress syndrome (ARDS). ARDS is the leading cause of mortality and morbidity the associated to COVID-19, and the cytokine storm is a prominent etiological factor. Mesenchymal stem cell-derived extracellular vesicles are an alternative therapy for the management of inflammatory and autoimmune conditions due to their immunosuppressive properties. The immunomodulatory and tissue regeneration capabilities of extracellular vesicles may support their application as a prospective therapy for COVID-19.Areas Covered: We explored the clinical evidence on extracellular vesicles as antiviral agents and in mitigating ARDS, and their therapeutic potential in COVID-19.Expert Opinion: Clinical trials using extracellular vesicles are registered against COVID-19 associated complications, with some evidence of safety and efficacy. Extracellular vesicles present an alternative potential for cell therapy for COVID-19 management, but further preclinical and clinical investigations are needed.

Umbilical cord-derived Wharton's jelly for treatment of knee osteoarthritis: study protocol for a non-randomized, open-label, multi-center trial.

BACKGROUND: Osteoarthritis (OA) is the most common joint disorder in the USA, and knee OA has the highest prevalence. Inflammation and decrease in vascularization are key factors in the degeneration of articular cartilage and the associated pain and decrease in function. To combat this process, the use of biologics including umbilical cord-derived Wharton's Jelly (UC-derived WJ) has grown. UC-derived WJ contains large quantities of regenerative factors, including growth factors (GFs), cytokines (CKs), hyaluronic acid (HA), and extracellular vesicles (EVs). The proposed study evaluates the safety and efficacy of intraarticular injection of UC-derived WJ for treatment of knee OA symptoms. METHODS AND ANALYSIS: This is a non-randomized, open-label, multi-center, prospective study in which the safety and efficacy of intraarticular UC-derived WJ in patients suffering from grade II/III OA will be assessed. Twelve patients with grade II/III OA who meet the inclusion and exclusion criteria will be recruited for this study which will be conducted at up to two sites within the USA. The participants will be followed for 1 s. Participants will be assessed using the Numeric Pain Rating Scale (NPRS), Knee Injury and Osteoarthritis Outcome Score (KOOS), 36-item short form survey (SF-36), Single Assessment Numeric Evaluation (SANE), physical exams, plain radiography, and Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) score for improvements in pain, satisfaction, function, and cartilage regeneration. DISCUSSION: This prospective study will contribute to the limited amount of data on UC-derived WJ, particularly with regard to its safety and efficacy. The outcomes from this study will also lay the groundwork for a large placebo-controlled trial of intraarticular UC-derived WJ for symptomatic knee OA. TRIAL REGISTRATION: ClinicalTrials.gov NCT04719793 . Registered on 22 January 2021.

Umbilical cord: an allogenic tissue for potential treatment of COVID-19.

The COVID-19 pandemic has placed an unprecedented burden on health care systems and economies around the globe. Clinical evidences demonstrate that SARS-CoV-2 infection produces detrimental levels of pro-inflammatory cytokines and chemokines that can lead to acute respiratory distress syndrome (ARDS) and significant systemic organ damage. Currently, there is no definitive therapy for COVID-19 or associated complications, and with the hope of a safe and effective vaccine in the distant future, the search for an answer is paramount. Mesenchymal stem cells (MSCs) provide a viable option due to their immunomodulatory effects and tissue repair and regeneration abilities. Studies have demonstrated that compassionate use of MSCs can reduce symptoms associated with SARS-CoV-2 infection, eliminate fluid buildup, and act as a regenerative technique for alveolar damage; all in a safe and effective way. With multiple autologous sources available for MSCs, each with their own respective limitations, allogenic umbilical cord (UC) and/or UC-derived Wharton's jelly (WJ) seem to be best positioned source to harvest MSCs to treat COVID-19 and associated symptoms. As an allogenic source, UC is readily available, easily obtainable, and is rich in immunomodulatory and regenerative factors. In this manuscript, we reviewed the current evidences and explored the potential therapeutic use of allogenic UC and/or WJ-derived MSCs for the treatment of COVID-19. Although, preliminary preclinical and clinical studies indicate that their use is safe and potentially effective, more multi-center, randomized, controlled trials are needed to adequately assess the safety and efficacy of UC and/or WJ-derived MSCs for the treatment of COVID-19.

Umbilical cord-derived Wharton's jelly for regenerative medicine applications in orthopedic surgery: a systematic review protocol.

BACKGROUND: Musculoskeletal injuries and conditions affect millions of individuals. These ailments are typically managed by immobilization, physiotherapy, or activity modification. Regenerative medicine has experienced tremendous growth in the past decades, especially in musculoskeletal medicine. Umbilical cord-derived Wharton's jelly is an exciting new option for such therapies. Wharton's jelly is a connective tissue located within the umbilical cord largely composed of mesenchymal stem cells and extracellular matrix components, including collagen, chondroitin sulfate, hyaluronic acid, and sulfated proteoglycans. Wharton's jelly is a promising and applicable biologic source for orthopedic regenerative application. METHODS: A systematic search will be conducted in PubMed, ScienceDirect, and Google Scholar databases of English, Italian, French, Spanish, and Portuguese language articles published to date. References will be screened and assessed for eligibility by two independent reviewers as per PRISMA guidelines. Articles will be considered without exclusion to sex, activity, or age. Studies will be included if they used culture-expanded, mesenchymal stem/stromal cells of mesenchymal stem cells and/or connective tissue obtained from Wharton's jelly. Studies will be excluded if Wharton's jelly is not the sole experimental examined cell type. Placebos, conventional non-operative therapies including steroid injections, exercise, and NSAIDs will be compared. The study selection process will be performed independently by two reviewers using a reference software. Data synthesis and meta-analysis will be performed separately for clinical and pre-clinical studies. DISCUSSION: The results will be published in relevant peer-reviewed scientific journals. Investigators will present results at national or international conferences. TRIAL REGISTRATION: The protocol was registered on PROSPERO international prospective register of systematic reviews prior to commencement, CRD42020182487 .

Umbilical cord-derived Wharton's jelly for regenerative medicine applications.

BACKGROUND: The last decade has seen an explosion in the interest in using biologics for regenerative medicine applications, including umbilical cord-derived Wharton's Jelly. There is insufficient literature assessing the amount of growth factors, cytokines, hyaluronic acid, and extracellular vesicles including exosomes in these products. The present study reports the development of a novel Wharton's jelly formulation and evaluates the presence of growth factors, cytokines, hyaluronic acid, and extracellular vesicles including exosomes. METHODS: Human umbilical cords were obtained from consenting caesarian section donors. The Wharton's jelly was then isolated from the procured umbilical cord and formulated into an injectable form. Randomly selected samples from different batches were analyzed for sterility testing and to quantify the presence of growth factors, cytokines, hyaluronic acid, and extracellular vesicles. RESULTS: All samples passed the sterility test. Growth factors including IGFBP 1, 2, 3, 4, and 6, TGF-α, and PDGF-AA were detected. Several immunomodulatory cytokines, such as RANTES, IL-6R, and IL-16, were also detected. Pro-inflammatory cytokines MCSFR, MIP-1a; anti-inflammatory cytokines TNF-RI, TNF-RII, and IL-1RA; and homeostatic cytokines TIMP-1 and TIMP-2 were observed. Cytokines associated with wound healing, ICAM-1, G-CSF, GDF-15, and regenerative properties, GH, were also expressed. High concentrations of hyaluronic acid were observed. Particles in the extracellular vesicle size range were also detected and were enclosed by the membrane, indicative of true extracellular vesicles. CONCLUSION: There are numerous growth factors, cytokines, hyaluronic acid, and extracellular vesicles present in the Wharton's jelly formulation analyzed. The amount of these factors in Wharton's jelly is higher compared with other biologics and may play a role in reducing inflammation and pain and augment healing of musculoskeletal injuries.

Surgical retrieval, isolation and in vitro expansion of human anterior cruciate ligament-derived cells for tissue engineering applications.

Injury to the ACL is a commonly encountered problem in active individuals. Even partial tears of this intra-articular knee ligament lead to biomechanical deficiencies that impair function and stability. Current options for the treatment of partial ACL tears range from nonoperative, conservative management to multiple surgical options, such as: thermal modification, single-bundle repair, complete reconstruction, and reconstruction of the damaged portion of the native ligament. Few studies, if any, have demonstrated any single method for management to be consistently superior, and in many cases patients continue to demonstrate persistent instability and other comorbidities. The goal of this study is to identify a potential cell source for utilization in the development of a tissue engineered patch that could be implemented in the repair of a partially torn ACL. A novel protocol was developed for the expansion of cells derived from patients undergoing ACL reconstruction. To isolate the cells, minced hACL tissue obtained during ACL reconstruction was digested in a Collagenase solution. Expansion was performed using DMEM/F12 medium supplemented with 10% fetal bovine serum (FBS) and 1% penicillin/streptomycin (P/S). The cells were then stored at -80 ºC or in liquid nitrogen in a freezing medium consisting of DMSO, FBS and the expansion medium. After thawing, the hACL derived cells were then seeded onto a tissue engineered scaffold, PLAGA (Poly lactic-co-glycolic acid) and control Tissue culture polystyrene (TCPS). After 7 days, SEM was performed to compare cellular adhesion to the PLAGA versus the control TCPS. Cellular morphology was evaluated using immunofluorescence staining. SEM (Scanning Electron Microscope) micrographs demonstrated that cells grew and adhered on both PLAGA and TCPS surfaces and were confluent over the entire surfaces by day 7. Immunofluorescence staining showed normal, non-stressed morphological patterns on both surfaces. This technique is promising for applications in ACL regeneration and reconstruction.

In vitro evaluation of three-dimensional single-walled carbon nanotube composites for bone tissue engineering.

The purpose of this study was to develop three-dimensional single-walled carbon nanotube composites (SWCNT/PLAGA) using 10-mg single-walled carbon nanotubes (SWCNT) for bone regeneration and to determine the mechanical strength of the composites, and to evaluate the interaction of MC3T3-E1 cells via cell adhesion, growth, survival, proliferation, and gene expression. PLAGA (polylactic-co-glycolic acid) and SWCNT/PLAGA microspheres and composites were fabricated, characterized, and mechanical testing was performed. MC3T3-E1 cells were seeded and cell adhesion/morphology, growth/survival, proliferation, and gene expression analysis were performed to evaluate biocompatibility. Imaging studies demonstrated microspheres with uniform shape and smooth surfaces, and uniform incorporation of SWCNT into PLAGA matrix. The microspheres bonded in a random packing manner while maintaining spacing, thus resembling trabeculae of cancellous bone. Addition of SWCNT led to greater compressive modulus and ultimate compressive strength. Imaging studies revealed that MC3T3-E1 cells adhered, grew/survived, and exhibited normal, nonstressed morphology on the composites. SWCNT/PLAGA composites exhibited higher cell proliferation rate and gene expression compared with PLAGA. These results demonstrate the potential of SWCNT/PLAGA composites for musculoskeletal regeneration, for bone tissue engineering, and are promising for orthopedic applications as they possess the combined effect of increased mechanical strength, cell proliferation, and gene expression.

Single walled carbon nanotube composites for bone tissue engineering.

The purpose of this study was to develop single walled carbon nanotubes (SWCNT) and poly lactic-co-glycolic acid (PLAGA) composites for orthopedic applications and to evaluate the interaction of human stem cells (hBMSCs) and osteoblasts (MC3T3-E1 cells) via cell growth, proliferation, gene expression, extracellular matrix production and mineralization. PLAGA and SWCNT/PLAGA composites were fabricated with various amounts of SWCNT (5, 10, 20, 40, and 100 mg), characterized and degradation studies were performed. Cells were seeded and cell adhesion/morphology, growth/survival, proliferation and gene expression analysis were performed to evaluate biocompatibility. Imaging studies demonstrated uniform incorporation of SWCNT into the PLAGA matrix and addition of SWCNT did not affect the degradation rate. Imaging studies revealed that MC3T3-E1 and hBMSCs cells exhibited normal, non-stressed morphology on the composites and all were biocompatible. Composites with 10 mg SWCNT resulted in highest rate of cell proliferation (p < 0.05) among all composites. Gene expression of alkaline phosphatase, collagen I, osteocalcin, osteopontin, Runx-2, and Bone Sialoprotein was observed on all composites. In conclusion, SWCNT/PLAGA composites imparted beneficial cellular growth capabilities and gene expression, and mineralization abilities were well established. These results demonstrate the potential of SWCNT/PLAGA composites for musculoskeletal regeneration and bone tissue engineering (BTE) and are promising for orthopedic applications.

The indications and use of bone morphogenetic proteins in foot, ankle, and tibia surgery.

Tissue engineering is an area of rapid growth. Tissue engineering in orthopedic surgery involves the use of growth factors, mesenchymal stem cells, and scaffolds, individually or in combination, toward the growth and restoration of various musculoskeletal tissues, such as ligaments, tendons, muscles, nerves, and bone. These advances are constantly evolving in foot and ankle surgery as well. Bone morphogenetic proteins (BMPs) have played an integral role in the advancement of tissue engineering strategies across multiple orthopedic subspecialities and have proved to play a role in the development of bone and musculoskeletal tissues. BMPs have recently been applied in several areas of foot and ankle surgery, including acute fracture augmentation, nonunions, and arthrodesis, with promising results. This article reviews the key aspects of clinical translation of strategies in tissue engineering as well as current applications and results of BMP use in tibia, foot, and ankle surgery. Future applications of BMP and novel materials in foot and ankle surgery are also reviewed.

Xenotransplantation in orthopaedic surgery.

We define xenotransplantation as including any procedure that involves the transplantation, implantation, or infusion into a human recipient of cells, tissues, or organs from a nonhuman animal source or of human body fluids, cells, tissues, or organs that have had ex vivo contact with nonhuman animal cells, tissues, or organs. The current FDA definition of xenotransplantation relates to procedures involving live, nonhuman materials. The proposed use of xenotransplanted tissues for treatment of a wide variety of human diseases is increasing. In orthopaedic surgery, a number of xeno-based products for treatment of musculoskeletal conditions have been cleared by the FDA. Commercially available products include those used as alternatives for bone, cartilage, and soft-tissue repair. Most xenografts are from bovine- or porcine-derived sources. Studies internationally have demonstrated a low relative risk of disease transmission, although there is concern regarding the potential for transmission into humans of agents not considered pathogenic or not detected in animals.

Human osteoblast cells: isolation, characterization, and growth on polymers for musculoskeletal tissue engineering.

We performed a detailed examination of the isolation, characterization, and growth of human osteoblast cells derived from trabecular bone. We further examined the morphology, phenotypic gene expression, mineralization,and growth of these human osteoblasts on polyester polymers used for musculoskeletal tissue engineering. Polylactic-co-glycolic acid [PLAGA (85:15, 50:50, 75:25)], and poly-lactic acid (L-PLA, D,L-PLA) were examined. The osteoblastic expression of key phenotypic markers osteocalcin, alkaline phosphatase, collagen, and bone sialoprotein at 4 and 8 weeks was examined. Reverse transcription-polymerase chain reaction studies revealed that trabecular-derived osteoblasts were positive for all markers evaluated with higher levels expressed over long-term culture. These cells also revealed mineralization and maturation as evidenced by energy dispersive X-ray analysis and scanning electron microscopy. Growth studies on PLAGA at 50:50,75:25, and 85:15 ratios and PLA in the L and DL isoforms revealed that human osteoblasts actively grew, with significantly higher cell numbers attached to scaffolds composed of PLAGA 50:50 in the short term and PLAGA 85:15 in the long term compared with PLA (p < 0.05). We believe human cell adhesion among these polymeric materials may be dependent on differences in cellular integrin expression and extracellular matrix protein elaboration.

Bone graft substitutes.

The current gold standard of bone grafts is the autograft since it possesses all the characteristics necessary for new bone growth, namely osteoconductivity, osteogenicity and osteoinductivity. However, the autograft has its limitations, including donor-site morbidity and supply limitations, hindering this as an option for bone repair. An extensive list of currently available alternatives to bone grafts is provided, along with a classification scheme that divides these bone graft substitutes into five groups depending on the primary material composition: allograft, cell, factor, ceramic and polymer. Of the bone graft substitutes listed, several are discussed in detail. Beyond the current state of the art, attention is paid to what lies ahead in the field of bone graft substitutes. Biodegradable composite structures and various new architectures are discussed, as are newly developed polymeric materials, with tissue engineering providing the platform for future directions within this discipline.

Molecular regulation of osteoblasts for tissue engineered bone repair.

The use of biodegradable polymers in medicine and biomedical research is increasing. A key growth area has been the use of these materials in tissue engineering, especially for guided regeneration of bone and cartilage. Our interest has been in determining the mechanisms by which cellular attachment and growth occurs on these materials. In the current study, we examined human osteoblast cell adhesion, growth, and morphologic changes on polymeric scaffolds composed of polylactic-co-glycolic acid and polylactic acid materials. We examined these characteristics in association with measurements of levels of key adhesion integrin receptors in the presence and absence of antibodies against alpha2, alpha3, alpha4, alpha5, alpha6, and beta1 subunits, and the adhesion ligand peptides RGD (Arg-Gly-Asp) and RGE (Arg-Gly-Ser). At 2 hours, results showed initial cell adhesion was considerably decreased on polylactic-co-glycolic acid and polylactic acid in the presence of the alpha2 and beta1, antibodies with a 70% adhesion rate difference observed among the groups evaluated. Higher levels of inhibition were observed on polylactic-co-glycolic acid relative to polylactic acid, which may be correlated to a higher number of cells being able to interact with the surface initially. The presence of known competitive peptide (RGD) at 2 hours, revealed its ability to block cellular adhesion to these matrices relative to the control and noncompetitive peptide RGE on polylactic-co-glycolic acid matrices. Overall adhesion rate was affected by the presence of the integrin antibodies to the alpha2, alpha3, alpha4, alpha5, alpha6, and beta1 subunits with highest differences among polylactic-co-glycolic acid relative to its control, therefore suggesting that initial osteoblastic cell adhesion to commonly used biomaterials is regulated through integrin binding.